Game 1 Unit 3 of 64 1 hr learning time

Making It Your Own

Customise the SID voices and visual style. Learn the internals by changing them.

5% of SID Symphony

Mark as complete Completed!

The game works. Now make it yours.

This unit teaches the SID chip and colour system by having you change them. You won’t just read about waveforms and ADSR - you’ll modify them and hear the results. By the end, you’ll understand exactly how the C64’s sound chip works because you’ll have bent it to your will.

Run It

Assemble and run:

acme -f cbm -o symphony.prg symphony.asm

Unit 3 Screenshot

This doesn’t look or sound like the previous versions. The border is blue. The track lines are dark grey. The bottom says “CUSTOMISE ME!” And when you press Z, X, or C - the sounds have their own character. Sawtooth, pulse, triangle.

Customised colours and waveforms — same mechanics, different feel

Same game, completely different feel.

The Customisation Section

All the changes come from one section at the top of the code:

; ============================================================================
; CUSTOMISATION SECTION - Change these values and reassemble!
; ============================================================================

; --- SID Voice Settings ---
; Waveforms: $11=triangle, $21=sawtooth, $41=pulse, $81=noise
VOICE1_WAVE = $21               ; Sawtooth - bright, buzzy
VOICE2_WAVE = $41               ; Pulse - hollow, reedy
VOICE3_WAVE = $11               ; Triangle - soft, mellow

; Frequencies (higher = higher pitch)
; Common notes: $07=C3, $0E=C4, $1C=C5, $38=C6
VOICE1_FREQ = $1C               ; High pitch (C5)
VOICE2_FREQ = $0E               ; Mid pitch (C4)
VOICE3_FREQ = $07               ; Low pitch (C3)

; ADSR - Attack/Decay/Sustain/Release
; Attack: 0-15 (0=2ms, 15=8s)   Decay: 0-15 (0=6ms, 15=24s)
; Sustain: 0-15 (volume level)  Release: 0-15 (0=6ms, 15=24s)
VOICE_AD    = $09               ; Attack=0 (instant), Decay=9 (medium)
VOICE_SR    = $00               ; Sustain=0 (none), Release=0 (instant)

; Pulse width (only affects pulse wave, $41)
PULSE_WIDTH = $08               ; $08 = 50% duty cycle (square wave)

; --- Visual Settings ---
; Colours: 0=black, 1=white, 2=red, 3=cyan, 4=purple, 5=green
;          6=blue, 7=yellow, 8=orange, 9=brown, 10=light red
;          11=dark grey, 12=grey, 13=light green, 14=light blue, 15=light grey

BORDER_COL  = 6                 ; Blue border
BG_COL      = 0                 ; Black background

TRACK1_NOTE_COL = 10            ; Light red notes on track 1
TRACK2_NOTE_COL = 13            ; Light green notes on track 2
TRACK3_NOTE_COL = 14            ; Light blue notes on track 3

TRACK_LINE_COL = 11             ; Dark grey track lines
HIT_ZONE_COL = 7                ; Yellow hit zone

; ============================================================================
; END OF CUSTOMISATION - Code below uses the settings above
; ============================================================================

This is your control panel. Change these values, reassemble, and hear/see the difference immediately.

Understanding Waveforms

The SID has four waveform types. Each has a distinct sound:

; SID Waveforms - Each has a distinct character
;
; $11 = Triangle - Pure, soft, flute-like
;       Smooth wave with no harsh harmonics
;       Good for bass and mellow leads
;
; $21 = Sawtooth - Bright, buzzy, aggressive
;       Rich in harmonics, sounds "sharp"
;       Good for leads and brass-like sounds
;
; $41 = Pulse (square) - Hollow, woody, reedy
;       Character changes with pulse width
;       50% = pure square, other widths = more nasal
;
; $81 = Noise - Hiss, crash, explosion
;       Random waveform, no pitch
;       Good for drums, percussion, effects
;
; The waveform value goes in the control register (SID_V1_CTRL etc.)
; Add $01 (gate bit) to trigger the sound: $21 + $01 = $22 won't work!
; Must OR the gate bit: $21 OR $01 = $21 (waveform already has bit 0 clear)

play_voice1:
            lda #VOICE1_WAVE    ; e.g., $21 for sawtooth
            ora #$01            ; Add gate bit to trigger
            sta SID_V1_CTRL
            rts

Try This: All Triangle

Make all three voices use triangle waves:

VOICE1_WAVE = $11               ; Triangle
VOICE2_WAVE = $11               ; Triangle
VOICE3_WAVE = $11               ; Triangle

The game will sound softer, more mellow. Like a flute choir.

Try This: All Noise

For a chaotic, percussive feel:

VOICE1_WAVE = $81               ; Noise
VOICE2_WAVE = $81               ; Noise
VOICE3_WAVE = $81               ; Noise

No pitch - just white noise bursts. Good for drum machines, terrible for melody.

Try This: Mixed Character

Create contrast between voices:

VOICE1_WAVE = $81               ; Noise - percussion hit
VOICE2_WAVE = $21               ; Sawtooth - bright lead
VOICE3_WAVE = $11               ; Triangle - soft bass

Now each track has its own sonic identity.

Understanding ADSR

ADSR shapes how sound evolves over time:

; ADSR Envelope - Shapes how the sound evolves over time
;
; Attack:  How quickly the sound reaches full volume (0=instant, 15=slow)
; Decay:   How quickly it drops to sustain level (0=instant, 15=slow)
; Sustain: Volume level while key is held (0=silent, 15=full)
; Release: How quickly it fades when released (0=instant, 15=slow)
;
; Packed into two bytes:
;   AD register: upper nibble = Attack, lower nibble = Decay
;   SR register: upper nibble = Sustain, lower nibble = Release
;
; Examples:
;
; $09, $00 = Instant attack, medium decay, no sustain, instant release
;            Good for: Plucked strings, percussion hits
;
; $00, $F0 = Instant everything, but sustain at max while gate is on
;            Good for: Organ, held notes
;
; $50, $90 = Slow attack, instant decay, high sustain, medium release
;            Good for: Pads, strings, atmospheric sounds
;
; $0C, $00 = Instant attack, long decay, no sustain
;            Good for: Piano-like decay

VOICE_AD    = $09               ; Attack=0, Decay=9
VOICE_SR    = $00               ; Sustain=0, Release=0

Try This: Slow Attack

VOICE_AD    = $59               ; Attack=5 (slow rise), Decay=9
VOICE_SR    = $00               ; Sustain=0, Release=0

Notes now “swell in” instead of hitting instantly. Like a violin bow.

Try This: Long Sustain

VOICE_AD    = $00               ; Attack=0 (instant), Decay=0 (instant)
VOICE_SR    = $F0               ; Sustain=15 (max), Release=0

Notes hold at full volume as long as you’d hold the key (in a real game). With our trigger-and-release approach, you’ll hear the maximum sustain level briefly.

Try This: Piano-Style Decay

VOICE_AD    = $0C               ; Attack=0, Decay=12 (long)
VOICE_SR    = $00               ; Sustain=0, Release=0

Notes ring out with a natural decay, like piano strings.

Understanding Colours

The C64 has 16 colours:

; C64 Colour Palette (16 colours)
;
; Value  Colour       Notes
; -----  -----------  ---------------------------------
;   0    Black        Background, shadows
;   1    White        Highlights, text
;   2    Red          Danger, track 1
;   3    Cyan         Cool, water
;   4    Purple       Rich, royal
;   5    Green        Nature, track 2, success
;   6    Blue         Sky, calm, track 3
;   7    Yellow       Warning, attention, hit zone
;   8    Orange       Warm, energy
;   9    Brown        Earth, wood
;  10    Light Red    Pink, softer danger
;  11    Dark Grey    Subtle, inactive
;  12    Grey         Neutral, disabled
;  13    Light Green  Bright nature, success
;  14    Light Blue   Sky, highlight
;  15    Light Grey   Soft neutral
;
; Use colour for meaning:
; - Hit zone in yellow (attention, "hit here!")
; - Track lines in dark grey (background, don't distract)
; - Notes in bright colours (important, focus here)
; - Flash colours matching note colours

TRACK1_NOTE_COL = 10            ; Light red - danger zone
TRACK2_NOTE_COL = 13            ; Light green - go zone
TRACK3_NOTE_COL = 14            ; Light blue - cool zone

Try This: Warm Theme

BORDER_COL  = 8                 ; Orange border
BG_COL      = 0                 ; Black background
TRACK1_NOTE_COL = 2             ; Red
TRACK2_NOTE_COL = 8             ; Orange
TRACK3_NOTE_COL = 7             ; Yellow
TRACK_LINE_COL = 9              ; Brown

Try This: Cool Theme

BORDER_COL  = 14                ; Light blue border
BG_COL      = 6                 ; Blue background
TRACK1_NOTE_COL = 3             ; Cyan
TRACK2_NOTE_COL = 14            ; Light blue
TRACK3_NOTE_COL = 1             ; White
TRACK_LINE_COL = 6              ; Blue (subtle on blue bg)

Try This: High Contrast

BORDER_COL  = 1                 ; White border
BG_COL      = 0                 ; Black background
TRACK1_NOTE_COL = 1             ; White
TRACK2_NOTE_COL = 1             ; White
TRACK3_NOTE_COL = 1             ; White
TRACK_LINE_COL = 12             ; Grey

The Complete Code

; ============================================================================
; SID SYMPHONY - Unit 3: Making It Your Own
; ============================================================================
; Customise the game to make it yours. Change the SID voices, pick your own
; colours, experiment with waveforms and ADSR. Learn the internals by
; modifying them and hearing/seeing the results.
;
; Controls: Z = Track 1 (high), X = Track 2 (mid), C = Track 3 (low)
; ============================================================================

; ============================================================================
; CUSTOMISATION SECTION - Change these values and reassemble!
; ============================================================================

; --- SID Voice Settings ---
; Waveforms: $11=triangle, $21=sawtooth, $41=pulse, $81=noise
VOICE1_WAVE = $21               ; Sawtooth - bright, buzzy
VOICE2_WAVE = $41               ; Pulse - hollow, reedy
VOICE3_WAVE = $11               ; Triangle - soft, mellow

; Frequencies (higher = higher pitch)
; Common notes: $07=C3, $0E=C4, $1C=C5, $38=C6
VOICE1_FREQ = $1C               ; High pitch (C5)
VOICE2_FREQ = $0E               ; Mid pitch (C4)
VOICE3_FREQ = $07               ; Low pitch (C3)

; ADSR - Attack/Decay/Sustain/Release
; Attack: 0-15 (0=2ms, 15=8s)   Decay: 0-15 (0=6ms, 15=24s)
; Sustain: 0-15 (volume level)  Release: 0-15 (0=6ms, 15=24s)
VOICE_AD    = $09               ; Attack=0 (instant), Decay=9 (medium)
VOICE_SR    = $00               ; Sustain=0 (none), Release=0 (instant)

; Pulse width (only affects pulse wave, $41)
PULSE_WIDTH = $08               ; $08 = 50% duty cycle (square wave)

; --- Visual Settings ---
; Colours: 0=black, 1=white, 2=red, 3=cyan, 4=purple, 5=green
;          6=blue, 7=yellow, 8=orange, 9=brown, 10=light red
;          11=dark grey, 12=grey, 13=light green, 14=light blue, 15=light grey

BORDER_COL  = 6                 ; Blue border
BG_COL      = 0                 ; Black background

TRACK1_NOTE_COL = 10            ; Light red notes on track 1
TRACK2_NOTE_COL = 13            ; Light green notes on track 2
TRACK3_NOTE_COL = 14            ; Light blue notes on track 3

TRACK_LINE_COL = 11             ; Dark grey track lines
HIT_ZONE_COL = 7                ; Yellow hit zone

; Track flash colours (when key pressed)
FLASH1_COL  = 2                 ; Red flash for track 1
FLASH2_COL  = 5                 ; Green flash for track 2
FLASH3_COL  = 6                 ; Blue flash for track 3

; ============================================================================
; END OF CUSTOMISATION - Code below uses the settings above
; ============================================================================

; ----------------------------------------------------------------------------
; Memory Addresses
; ----------------------------------------------------------------------------

SCREEN      = $0400
COLRAM      = $D800
BORDER      = $D020
BGCOL       = $D021

; SID registers
SID         = $D400
SID_V1_FREQ_LO = $D400
SID_V1_FREQ_HI = $D401
SID_V1_PWLO = $D402
SID_V1_PWHI = $D403
SID_V1_CTRL = $D404
SID_V1_AD   = $D405
SID_V1_SR   = $D406

SID_V2_FREQ_LO = $D407
SID_V2_FREQ_HI = $D408
SID_V2_PWLO = $D409
SID_V2_PWHI = $D40A
SID_V2_CTRL = $D40B
SID_V2_AD   = $D40C
SID_V2_SR   = $D40D

SID_V3_FREQ_LO = $D40E
SID_V3_FREQ_HI = $D40F
SID_V3_PWLO = $D410
SID_V3_PWHI = $D411
SID_V3_CTRL = $D412
SID_V3_AD   = $D413
SID_V3_SR   = $D414

SID_VOLUME  = $D418

; CIA keyboard
CIA1_PRA    = $DC00
CIA1_PRB    = $DC01

; Track positions
TRACK1_ROW  = 8
TRACK2_ROW  = 12
TRACK3_ROW  = 16

; Hit zone column
HIT_ZONE_COLUMN = 3

; Note settings
NOTE_CHAR   = $57               ; Filled dot character
TRACK_CHAR  = $2D               ; Minus character
MAX_NOTES   = 8
NOTE_SPAWN_COL = 37

; Timing
FRAMES_PER_BEAT = 25

; Zero page
ZP_PTR      = $FB
ZP_PTR_HI   = $FC

; Variables
frame_count = $02
beat_count  = $03
song_pos    = $04
song_pos_hi = $05
temp_track  = $06

; ----------------------------------------------------------------------------
; BASIC Stub
; ----------------------------------------------------------------------------

            * = $0801

            !byte $0C, $08
            !byte $0A, $00
            !byte $9E
            !text "2064"
            !byte $00
            !byte $00, $00

; ----------------------------------------------------------------------------
; Main Program
; ----------------------------------------------------------------------------

            * = $0810

start:
            jsr init_screen
            jsr init_sid
            jsr init_notes

            lda #<song_data
            sta song_pos
            lda #>song_data
            sta song_pos_hi

            lda #0
            sta frame_count
            sta beat_count

main_loop:
            lda #$FF
wait_raster:
            cmp $D012
            bne wait_raster

            inc frame_count
            lda frame_count
            cmp #FRAMES_PER_BEAT
            bcc no_new_beat

            lda #0
            sta frame_count
            jsr check_spawn_note
            inc beat_count

no_new_beat:
            jsr update_notes
            jsr reset_track_colours
            jsr check_keys

            jmp main_loop

; ----------------------------------------------------------------------------
; Initialize Notes
; ----------------------------------------------------------------------------

init_notes:
            ldx #MAX_NOTES-1
            lda #0
init_notes_loop:
            sta note_track,x
            sta note_col,x
            dex
            bpl init_notes_loop
            rts

; ----------------------------------------------------------------------------
; Check Spawn Note
; ----------------------------------------------------------------------------

check_spawn_note:
            ldy #0

spawn_check_loop:
            lda (song_pos),y
            cmp #$FF
            beq spawn_restart_song

            cmp beat_count
            beq spawn_match
            bcs spawn_done

            jmp spawn_advance

spawn_match:
            iny
            lda (song_pos),y
            jsr spawn_note
            dey

spawn_advance:
            lda song_pos
            clc
            adc #2
            sta song_pos
            lda song_pos_hi
            adc #0
            sta song_pos_hi
            jmp spawn_check_loop

spawn_done:
            rts

spawn_restart_song:
            lda #<song_data
            sta song_pos
            lda #>song_data
            sta song_pos_hi
            lda #0
            sta beat_count
            rts

; ----------------------------------------------------------------------------
; Spawn Note
; ----------------------------------------------------------------------------

spawn_note:
            sta temp_track

            ldx #0
spawn_find_slot:
            lda note_track,x
            beq spawn_found_slot
            inx
            cpx #MAX_NOTES
            bne spawn_find_slot
            rts

spawn_found_slot:
            lda temp_track
            sta note_track,x
            lda #NOTE_SPAWN_COL
            sta note_col,x
            jsr draw_note
            rts

; ----------------------------------------------------------------------------
; Update Notes
; ----------------------------------------------------------------------------

update_notes:
            ldx #0

update_loop:
            lda note_track,x
            beq update_next

            jsr erase_note

            dec note_col,x
            lda note_col,x
            cmp #1
            bcc update_deactivate

            jsr draw_note
            jmp update_next

update_deactivate:
            lda #0
            sta note_track,x

update_next:
            inx
            cpx #MAX_NOTES
            bne update_loop
            rts

; ----------------------------------------------------------------------------
; Draw Note
; ----------------------------------------------------------------------------

draw_note:
            lda note_track,x
            cmp #1
            beq draw_note_t1
            cmp #2
            beq draw_note_t2
            cmp #3
            beq draw_note_t3
            rts

draw_note_t1:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK1_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK1_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #NOTE_CHAR
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK1_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK1_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK1_NOTE_COL
            sta (ZP_PTR),y
            rts

draw_note_t2:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK2_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK2_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #NOTE_CHAR
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK2_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK2_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK2_NOTE_COL
            sta (ZP_PTR),y
            rts

draw_note_t3:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK3_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK3_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #NOTE_CHAR
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK3_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK3_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK3_NOTE_COL
            sta (ZP_PTR),y
            rts

; ----------------------------------------------------------------------------
; Erase Note
; ----------------------------------------------------------------------------

erase_note:
            lda note_track,x
            cmp #1
            beq erase_note_t1
            cmp #2
            beq erase_note_t2
            cmp #3
            beq erase_note_t3
            rts

erase_note_t1:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK1_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK1_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #TRACK_CHAR
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK1_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK1_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK_LINE_COL
            sta (ZP_PTR),y
            rts

erase_note_t2:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK2_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK2_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #TRACK_CHAR
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK2_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK2_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK_LINE_COL
            sta (ZP_PTR),y
            rts

erase_note_t3:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK3_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK3_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #TRACK_CHAR
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK3_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK3_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK_LINE_COL
            sta (ZP_PTR),y
            rts

; ----------------------------------------------------------------------------
; Initialize Screen
; ----------------------------------------------------------------------------

init_screen:
            lda #BORDER_COL
            sta BORDER
            lda #BG_COL
            sta BGCOL

            ldx #0
            lda #$20
clr_screen:
            sta SCREEN,x
            sta SCREEN+$100,x
            sta SCREEN+$200,x
            sta SCREEN+$2E8,x
            inx
            bne clr_screen

            ldx #0
            lda #TRACK_LINE_COL
clr_colour:
            sta COLRAM,x
            sta COLRAM+$100,x
            sta COLRAM+$200,x
            sta COLRAM+$2E8,x
            inx
            bne clr_colour

            jsr draw_tracks
            jsr draw_hit_zones
            jsr draw_labels

            rts

; ----------------------------------------------------------------------------
; Draw Tracks
; ----------------------------------------------------------------------------

draw_tracks:
            ldx #0
            lda #TRACK_CHAR
draw_t1:
            sta SCREEN + (TRACK1_ROW * 40),x
            inx
            cpx #38
            bne draw_t1

            ldx #0
draw_t2:
            sta SCREEN + (TRACK2_ROW * 40),x
            inx
            cpx #38
            bne draw_t2

            ldx #0
draw_t3:
            sta SCREEN + (TRACK3_ROW * 40),x
            inx
            cpx #38
            bne draw_t3

            rts

; ----------------------------------------------------------------------------
; Draw Hit Zones
; ----------------------------------------------------------------------------

draw_hit_zones:
            lda #$7D

            sta SCREEN + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN
            sta SCREEN + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta SCREEN + ((TRACK1_ROW+1) * 40) + HIT_ZONE_COLUMN

            sta SCREEN + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN
            sta SCREEN + ((TRACK2_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta SCREEN + ((TRACK2_ROW+1) * 40) + HIT_ZONE_COLUMN

            sta SCREEN + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN
            sta SCREEN + ((TRACK3_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta SCREEN + ((TRACK3_ROW+1) * 40) + HIT_ZONE_COLUMN

            lda #HIT_ZONE_COL
            sta COLRAM + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN
            sta COLRAM + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta COLRAM + ((TRACK1_ROW+1) * 40) + HIT_ZONE_COLUMN

            sta COLRAM + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN
            sta COLRAM + ((TRACK2_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta COLRAM + ((TRACK2_ROW+1) * 40) + HIT_ZONE_COLUMN

            sta COLRAM + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN
            sta COLRAM + ((TRACK3_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta COLRAM + ((TRACK3_ROW+1) * 40) + HIT_ZONE_COLUMN

            rts

; ----------------------------------------------------------------------------
; Draw Labels
; ----------------------------------------------------------------------------

draw_labels:
            ldx #0
draw_title:
            lda title_text,x
            beq draw_title_done
            sta SCREEN + 13,x
            lda #1              ; White
            sta COLRAM + 13,x
            inx
            bne draw_title
draw_title_done:

            lda #$1A            ; Z
            sta SCREEN + (TRACK1_ROW * 40)
            lda #TRACK1_NOTE_COL
            sta COLRAM + (TRACK1_ROW * 40)

            lda #$18            ; X
            sta SCREEN + (TRACK2_ROW * 40)
            lda #TRACK2_NOTE_COL
            sta COLRAM + (TRACK2_ROW * 40)

            lda #$03            ; C
            sta SCREEN + (TRACK3_ROW * 40)
            lda #TRACK3_NOTE_COL
            sta COLRAM + (TRACK3_ROW * 40)

            ldx #0
draw_instr:
            lda instr_text,x
            beq draw_instr_done
            sta SCREEN + (23 * 40) + 8,x
            lda #TRACK_LINE_COL
            sta COLRAM + (23 * 40) + 8,x
            inx
            bne draw_instr
draw_instr_done:

            rts

title_text:
            !scr "sid symphony"
            !byte 0

instr_text:
            !scr "customise me!"
            !byte 0

; ----------------------------------------------------------------------------
; Initialize SID - Uses customisation constants
; ----------------------------------------------------------------------------

init_sid:
            ldx #$18
            lda #0
clear_sid:
            sta SID,x
            dex
            bpl clear_sid

            lda #$0F
            sta SID_VOLUME

            ; Voice 1 - uses VOICE1_* constants
            lda #$00
            sta SID_V1_FREQ_LO
            lda #VOICE1_FREQ
            sta SID_V1_FREQ_HI
            lda #PULSE_WIDTH
            sta SID_V1_PWHI
            lda #VOICE_AD
            sta SID_V1_AD
            lda #VOICE_SR
            sta SID_V1_SR

            ; Voice 2 - uses VOICE2_* constants
            lda #$00
            sta SID_V2_FREQ_LO
            lda #VOICE2_FREQ
            sta SID_V2_FREQ_HI
            lda #PULSE_WIDTH
            sta SID_V2_PWHI
            lda #VOICE_AD
            sta SID_V2_AD
            lda #VOICE_SR
            sta SID_V2_SR

            ; Voice 3 - uses VOICE3_* constants
            lda #$00
            sta SID_V3_FREQ_LO
            lda #VOICE3_FREQ
            sta SID_V3_FREQ_HI
            lda #PULSE_WIDTH
            sta SID_V3_PWHI
            lda #VOICE_AD
            sta SID_V3_AD
            lda #VOICE_SR
            sta SID_V3_SR

            rts

; ----------------------------------------------------------------------------
; Reset Track Colours
; ----------------------------------------------------------------------------

reset_track_colours:
            ldx #0
            lda #TRACK_LINE_COL
reset_t1:
            sta COLRAM + (TRACK1_ROW * 40),x
            inx
            cpx #38
            bne reset_t1

            ldx #0
reset_t2:
            sta COLRAM + (TRACK2_ROW * 40),x
            inx
            cpx #38
            bne reset_t2

            ldx #0
reset_t3:
            sta COLRAM + (TRACK3_ROW * 40),x
            inx
            cpx #38
            bne reset_t3

            ; Restore key labels
            lda #TRACK1_NOTE_COL
            sta COLRAM + (TRACK1_ROW * 40)
            lda #TRACK2_NOTE_COL
            sta COLRAM + (TRACK2_ROW * 40)
            lda #TRACK3_NOTE_COL
            sta COLRAM + (TRACK3_ROW * 40)

            ; Restore hit zone colours
            lda #HIT_ZONE_COL
            sta COLRAM + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN
            sta COLRAM + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN
            sta COLRAM + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN

            jsr redraw_all_notes

            rts

; ----------------------------------------------------------------------------
; Redraw All Notes
; ----------------------------------------------------------------------------

redraw_all_notes:
            ldx #0
redraw_loop:
            lda note_track,x
            beq redraw_next
            jsr draw_note
redraw_next:
            inx
            cpx #MAX_NOTES
            bne redraw_loop
            rts

; ----------------------------------------------------------------------------
; Check Keys
; ----------------------------------------------------------------------------

check_keys:
            lda #$FD
            sta CIA1_PRA
            lda CIA1_PRB
            and #$10
            bne check_x_key
            jsr play_voice1
            jsr flash_track1

check_x_key:
            lda #$FB
            sta CIA1_PRA
            lda CIA1_PRB
            and #$80
            bne check_c_key
            jsr play_voice2
            jsr flash_track2

check_c_key:
            lda #$FB
            sta CIA1_PRA
            lda CIA1_PRB
            and #$10
            bne check_keys_done
            jsr play_voice3
            jsr flash_track3

check_keys_done:
            lda #$FF
            sta CIA1_PRA
            rts

; ----------------------------------------------------------------------------
; Play Voices - Uses customisation waveforms
; ----------------------------------------------------------------------------

play_voice1:
            lda #VOICE1_WAVE
            ora #$01            ; Add gate bit
            sta SID_V1_CTRL
            rts

play_voice2:
            lda #VOICE2_WAVE
            ora #$01
            sta SID_V2_CTRL
            rts

play_voice3:
            lda #VOICE3_WAVE
            ora #$01
            sta SID_V3_CTRL
            rts

; ----------------------------------------------------------------------------
; Flash Tracks - Uses customisation colours
; ----------------------------------------------------------------------------

flash_track1:
            ldx #0
            lda #FLASH1_COL
flash_t1_loop:
            sta COLRAM + (TRACK1_ROW * 40),x
            inx
            cpx #38
            bne flash_t1_loop
            lda #1              ; White label
            sta COLRAM + (TRACK1_ROW * 40)
            rts

flash_track2:
            ldx #0
            lda #FLASH2_COL
flash_t2_loop:
            sta COLRAM + (TRACK2_ROW * 40),x
            inx
            cpx #38
            bne flash_t2_loop
            lda #1
            sta COLRAM + (TRACK2_ROW * 40)
            rts

flash_track3:
            ldx #0
            lda #FLASH3_COL
flash_t3_loop:
            sta COLRAM + (TRACK3_ROW * 40),x
            inx
            cpx #38
            bne flash_t3_loop
            lda #1
            sta COLRAM + (TRACK3_ROW * 40)
            rts

; ----------------------------------------------------------------------------
; Song Data
; ----------------------------------------------------------------------------

song_data:
            !byte 0, 1
            !byte 2, 2
            !byte 4, 3
            !byte 6, 1

            !byte 8, 2
            !byte 10, 3
            !byte 12, 1
            !byte 14, 2

            !byte 16, 3
            !byte 18, 1
            !byte 20, 2
            !byte 22, 3

            !byte 24, 1
            !byte 25, 2
            !byte 26, 3
            !byte 28, 1
            !byte 29, 2
            !byte 30, 3

            !byte $FF

; ----------------------------------------------------------------------------
; Note Arrays
; ----------------------------------------------------------------------------

note_track:
            !fill MAX_NOTES, 0

note_col:
            !fill MAX_NOTES, 0

Challenge: Create Your Theme

Design a complete audio-visual style:

Pick waveforms that complement each other
Choose ADSR values that fit your waveforms
Select colours that create the right mood
Test by playing - does it feel cohesive?

Document your choices with comments. Share your theme.

What You’ve Learnt

Waveforms - Triangle (soft), sawtooth (bright), pulse (hollow), noise (chaotic)
ADSR envelopes - Attack (rise time), Decay (fall to sustain), Sustain (held level), Release (fade out)
Colour palette - 16 colours from 0-15, each with its own character
Customisation patterns - Constants at the top of code for easy modification
Learning by doing - Understanding comes from changing things and observing results

What’s Next

In Unit 4, we’ll design custom graphics using the C64’s character set. The game will start looking professional.

What Changed

Unit 2 → Unit 3

+191-186

1	1		`; ============================================================================`
2		-	`; SID SYMPHONY - Unit 2: Notes Appear`
	2	+	`; SID SYMPHONY - Unit 3: Making It Your Own`
3	3		`; ============================================================================`
4		-	`; Notes scroll from right to left across three tracks. When they reach the`
5		-	`; hit zone, press the matching key to play the sound. A simple test pattern`
6		-	`; loops continuously so you can practice timing.`
	4	+	`; Customise the game to make it yours. Change the SID voices, pick your own`
	5	+	`; colours, experiment with waveforms and ADSR. Learn the internals by`
	6	+	`; modifying them and hearing/seeing the results.`
7	7		`;`
8	8		`; Controls: Z = Track 1 (high), X = Track 2 (mid), C = Track 3 (low)`
	9	+	`; ============================================================================`
	10	+
	11	+	`; ============================================================================`
	12	+	`; CUSTOMISATION SECTION - Change these values and reassemble!`
	13	+	`; ============================================================================`
	14	+
	15	+	`; --- SID Voice Settings ---`
	16	+	`; Waveforms: $11=triangle, $21=sawtooth, $41=pulse, $81=noise`
	17	+	`VOICE1_WAVE = $21 ; Sawtooth - bright, buzzy`
	18	+	`VOICE2_WAVE = $41 ; Pulse - hollow, reedy`
	19	+	`VOICE3_WAVE = $11 ; Triangle - soft, mellow`
	20	+
	21	+	`; Frequencies (higher = higher pitch)`
	22	+	`; Common notes: $07=C3, $0E=C4, $1C=C5, $38=C6`
	23	+	`VOICE1_FREQ = $1C ; High pitch (C5)`
	24	+	`VOICE2_FREQ = $0E ; Mid pitch (C4)`
	25	+	`VOICE3_FREQ = $07 ; Low pitch (C3)`
	26	+
	27	+	`; ADSR - Attack/Decay/Sustain/Release`
	28	+	`; Attack: 0-15 (0=2ms, 15=8s) Decay: 0-15 (0=6ms, 15=24s)`
	29	+	`; Sustain: 0-15 (volume level) Release: 0-15 (0=6ms, 15=24s)`
	30	+	`VOICE_AD = $09 ; Attack=0 (instant), Decay=9 (medium)`
	31	+	`VOICE_SR = $00 ; Sustain=0 (none), Release=0 (instant)`
	32	+
	33	+	`; Pulse width (only affects pulse wave, $41)`
	34	+	`PULSE_WIDTH = $08 ; $08 = 50% duty cycle (square wave)`
	35	+
	36	+	`; --- Visual Settings ---`
	37	+	`; Colours: 0=black, 1=white, 2=red, 3=cyan, 4=purple, 5=green`
	38	+	`; 6=blue, 7=yellow, 8=orange, 9=brown, 10=light red`
	39	+	`; 11=dark grey, 12=grey, 13=light green, 14=light blue, 15=light grey`
	40	+
	41	+	`BORDER_COL = 6 ; Blue border`
	42	+	`BG_COL = 0 ; Black background`
	43	+
	44	+	`TRACK1_NOTE_COL = 10 ; Light red notes on track 1`
	45	+	`TRACK2_NOTE_COL = 13 ; Light green notes on track 2`
	46	+	`TRACK3_NOTE_COL = 14 ; Light blue notes on track 3`
	47	+
	48	+	`TRACK_LINE_COL = 11 ; Dark grey track lines`
	49	+	`HIT_ZONE_COL = 7 ; Yellow hit zone`
	50	+
	51	+	`; Track flash colours (when key pressed)`
	52	+	`FLASH1_COL = 2 ; Red flash for track 1`
	53	+	`FLASH2_COL = 5 ; Green flash for track 2`
	54	+	`FLASH3_COL = 6 ; Blue flash for track 3`
	55	+
	56	+	`; ============================================================================`
	57	+	`; END OF CUSTOMISATION - Code below uses the settings above`
9	58		`; ============================================================================`
10	59
11	60		`; ----------------------------------------------------------------------------`
12	61		`; Memory Addresses`
13	62		`; ----------------------------------------------------------------------------`
14	63
15		-	`SCREEN = $0400 ; Screen memory base`
16		-	`COLRAM = $D800 ; Colour RAM base`
17		-	`BORDER = $D020 ; Border colour`
18		-	`BGCOL = $D021 ; Background colour`
	64	+	`SCREEN = $0400`
	65	+	`COLRAM = $D800`
	66	+	`BORDER = $D020`
	67	+	`BGCOL = $D021`
19	68
20	69		`; SID registers`
21		-	`SID = $D400 ; SID base address`
22		-	`SID_V1_FREQ_LO = $D400 ; Voice 1 frequency low`
23		-	`SID_V1_FREQ_HI = $D401 ; Voice 1 frequency high`
24		-	`SID_V1_PWLO = $D402 ; Voice 1 pulse width low`
25		-	`SID_V1_PWHI = $D403 ; Voice 1 pulse width high`
26		-	`SID_V1_CTRL = $D404 ; Voice 1 control register`
27		-	`SID_V1_AD = $D405 ; Voice 1 attack/decay`
28		-	`SID_V1_SR = $D406 ; Voice 1 sustain/release`
	70	+	`SID = $D400`
	71	+	`SID_V1_FREQ_LO = $D400`
	72	+	`SID_V1_FREQ_HI = $D401`
	73	+	`SID_V1_PWLO = $D402`
	74	+	`SID_V1_PWHI = $D403`
	75	+	`SID_V1_CTRL = $D404`
	76	+	`SID_V1_AD = $D405`
	77	+	`SID_V1_SR = $D406`
29	78
30		-	`SID_V2_FREQ_LO = $D407 ; Voice 2 frequency low`
31		-	`SID_V2_FREQ_HI = $D408 ; Voice 2 frequency high`
32		-	`SID_V2_PWLO = $D409 ; Voice 2 pulse width low`
33		-	`SID_V2_PWHI = $D40A ; Voice 2 pulse width high`
34		-	`SID_V2_CTRL = $D40B ; Voice 2 control register`
35		-	`SID_V2_AD = $D40C ; Voice 2 attack/decay`
36		-	`SID_V2_SR = $D40D ; Voice 2 sustain/release`
	79	+	`SID_V2_FREQ_LO = $D407`
	80	+	`SID_V2_FREQ_HI = $D408`
	81	+	`SID_V2_PWLO = $D409`
	82	+	`SID_V2_PWHI = $D40A`
	83	+	`SID_V2_CTRL = $D40B`
	84	+	`SID_V2_AD = $D40C`
	85	+	`SID_V2_SR = $D40D`
37	86
38		-	`SID_V3_FREQ_LO = $D40E ; Voice 3 frequency low`
39		-	`SID_V3_FREQ_HI = $D40F ; Voice 3 frequency high`
40		-	`SID_V3_PWLO = $D410 ; Voice 3 pulse width low`
41		-	`SID_V3_PWHI = $D411 ; Voice 3 pulse width high`
42		-	`SID_V3_CTRL = $D412 ; Voice 3 control register`
43		-	`SID_V3_AD = $D413 ; Voice 3 attack/decay`
44		-	`SID_V3_SR = $D414 ; Voice 3 sustain/release`
	87	+	`SID_V3_FREQ_LO = $D40E`
	88	+	`SID_V3_FREQ_HI = $D40F`
	89	+	`SID_V3_PWLO = $D410`
	90	+	`SID_V3_PWHI = $D411`
	91	+	`SID_V3_CTRL = $D412`
	92	+	`SID_V3_AD = $D413`
	93	+	`SID_V3_SR = $D414`
45	94
46		-	`SID_FLTLO = $D415 ; Filter cutoff low`
47		-	`SID_FLTHI = $D416 ; Filter cutoff high`
48		-	`SID_FLTCTRL = $D417 ; Filter control`
49		-	`SID_VOLUME = $D418 ; Volume and filter mode`
	95	+	`SID_VOLUME = $D418`
50	96
51	97		`; CIA keyboard`
52		-	`CIA1_PRA = $DC00 ; CIA1 Port A (keyboard column)`
53		-	`CIA1_PRB = $DC01 ; CIA1 Port B (keyboard row)`
54		-
55		-	`; Colours`
56		-	`BLACK = 0`
57		-	`WHITE = 1`
58		-	`RED = 2`
59		-	`CYAN = 3`
60		-	`PURPLE = 4`
61		-	`GREEN = 5`
62		-	`BLUE = 6`
63		-	`YELLOW = 7`
64		-	`ORANGE = 8`
65		-	`BROWN = 9`
66		-	`LIGHT_RED = 10`
67		-	`DARK_GREY = 11`
68		-	`GREY = 12`
69		-	`LIGHT_GREEN = 13`
70		-	`LIGHT_BLUE = 14`
71		-	`LIGHT_GREY = 15`
	98	+	`CIA1_PRA = $DC00`
	99	+	`CIA1_PRB = $DC01`
72	100
73		-	`; Track positions (row on screen)`
74		-	`TRACK1_ROW = 8 ; High voice track`
75		-	`TRACK2_ROW = 12 ; Mid voice track`
76		-	`TRACK3_ROW = 16 ; Low voice track`
	101	+	`; Track positions`
	102	+	`TRACK1_ROW = 8`
	103	+	`TRACK2_ROW = 12`
	104	+	`TRACK3_ROW = 16`
77	105
78	106		`; Hit zone column`
79		-	`HIT_ZONE_COL = 3 ; Where notes need to be hit`
	107	+	`HIT_ZONE_COLUMN = 3`
80	108
81	109		`; Note settings`
82		-	`NOTE_CHAR = $57 ; Character for note (filled dot/ball)`
83		-	`TRACK_CHAR = $2D ; Minus character for track line`
84		-	`MAX_NOTES = 8 ; Maximum notes on screen at once`
85		-	`NOTE_SPAWN_COL = 37 ; Where notes appear (right side)`
	110	+	`NOTE_CHAR = $57 ; Filled dot character`
	111	+	`TRACK_CHAR = $2D ; Minus character`
	112	+	`MAX_NOTES = 8`
	113	+	`NOTE_SPAWN_COL = 37`
86	114
87	115		`; Timing`
88		-	`FRAMES_PER_BEAT = 25 ; ~120 BPM at 50Hz (PAL)`
	116	+	`FRAMES_PER_BEAT = 25`
89	117
90		-	`; Zero page pointers`
91		-	`ZP_PTR = $FB ; General purpose pointer`
	118	+	`; Zero page`
	119	+	`ZP_PTR = $FB`
92	120		`ZP_PTR_HI = $FC`
93		-
94		-	`; ----------------------------------------------------------------------------`
95		-	`; Variables (in low memory)`
96		-	`; ----------------------------------------------------------------------------`
97	121
98		-	`frame_count = $02 ; Frame counter (0-255)`
99		-	`beat_count = $03 ; Current beat in song (0-255)`
100		-	`song_pos = $04 ; Position in song data (word)`
	122	+	`; Variables`
	123	+	`frame_count = $02`
	124	+	`beat_count = $03`
	125	+	`song_pos = $04`
101	126		`song_pos_hi = $05`
102		-	`temp_track = $06 ; Temporary storage for track number`
	127	+	`temp_track = $06`
103	128
104	129		`; ----------------------------------------------------------------------------`
105		-	`; BASIC Stub - SYS 2064`
	130	+	`; BASIC Stub`
106	131		`; ----------------------------------------------------------------------------`
107	132
108	133		`* = $0801`
109	134
110		-	`!byte $0C, $08 ; Pointer to next line`
111		-	`!byte $0A, $00 ; Line number 10`
112		-	`!byte $9E ; SYS token`
113		-	`!text "2064" ; Address`
114		-	`!byte $00 ; End of line`
115		-	`!byte $00, $00 ; End of program`
	135	+	`!byte $0C, $08`
	136	+	`!byte $0A, $00`
	137	+	`!byte $9E`
	138	+	`!text "2064"`
	139	+	`!byte $00`
	140	+	`!byte $00, $00`
116	141
117	142		`; ----------------------------------------------------------------------------`
118	143		`; Main Program`
			...
121	146		`* = $0810`
122	147
123	148		`start:`
124		-	`jsr init_screen ; Set up the display`
125		-	`jsr init_sid ; Configure SID chip`
126		-	`jsr init_notes ; Clear note arrays`
	149	+	`jsr init_screen`
	150	+	`jsr init_sid`
	151	+	`jsr init_notes`
127	152
128		-	`; Initialize song position`
129	153		`lda #<song_data`
130	154		`sta song_pos`
131	155		`lda #>song_data`
132	156		`sta song_pos_hi`
133	157
134		-	`; Initialize counters`
135	158		`lda #0`
136	159		`sta frame_count`
137	160		`sta beat_count`
138	161
139	162		`main_loop:`
140		-	`; Wait for raster (smooth timing)`
141	163		`lda #$FF`
142	164		`wait_raster:`
143	165		`cmp $D012`
144	166		`bne wait_raster`
145	167
146		-	`; Update frame counter`
147	168		`inc frame_count`
148	169		`lda frame_count`
149	170		`cmp #FRAMES_PER_BEAT`
150	171		`bcc no_new_beat`
151	172
152		-	`; New beat!`
153	173		`lda #0`
154	174		`sta frame_count`
155	175		`jsr check_spawn_note`
156	176		`inc beat_count`
157	177
158	178		`no_new_beat:`
159		-	`; Move all notes left`
160	179		`jsr update_notes`
161		-
162		-	`; Reset track colours to default`
163	180		`jsr reset_track_colours`
164		-
165		-	`; Check keyboard and play sounds`
166	181		`jsr check_keys`
167	182
168	183		`jmp main_loop`
			...
184	199		`; ----------------------------------------------------------------------------`
185	200		`; Check Spawn Note`
186	201		`; ----------------------------------------------------------------------------`
187		-	`; Song data is in beat order. Process all entries matching current beat,`
188		-	`; then return. Entries are (beat, track) pairs ending with $FF.`
189	202
190	203		`check_spawn_note:`
191	204		`ldy #0`
192	205
193	206		`spawn_check_loop:`
194		-	`; Read beat number for current entry`
195	207		`lda (song_pos),y`
196	208		`cmp #$FF`
197	209		`beq spawn_restart_song`
198	210
199		-	`; If entry beat > current beat, we're done for this beat`
200	211		`cmp beat_count`
201		-	`beq spawn_match ; Equal - spawn this note`
202		-	`bcs spawn_done ; Greater - done for now (entries are ordered)`
	212	+	`beq spawn_match`
	213	+	`bcs spawn_done`
203	214
204		-	`; Entry beat < current beat - shouldn't happen, but skip it`
205	215		`jmp spawn_advance`
206	216
207	217		`spawn_match:`
208		-	`; Get track number (next byte)`
209	218		`iny`
210	219		`lda (song_pos),y`
211	220		`jsr spawn_note`
212		-	`dey ; Reset Y for next iteration`
	221	+	`dey`
213	222
214	223		`spawn_advance:`
215		-	`; Move song_pos forward by 2 bytes`
216	224		`lda song_pos`
217	225		`clc`
218	226		`adc #2`
			...
237	245		`; ----------------------------------------------------------------------------`
238	246		`; Spawn Note`
239	247		`; ----------------------------------------------------------------------------`
240		-	`; Input: A = track number (1-3)`
241	248
242	249		`spawn_note:`
243	250		`sta temp_track`
			...
249	256		`inx`
250	257		`cpx #MAX_NOTES`
251	258		`bne spawn_find_slot`
252		-	`rts ; No empty slot`
	259	+	`rts`
253	260
254	261		`spawn_found_slot:`
255	262		`lda temp_track`
			...
293	300		`; ----------------------------------------------------------------------------`
294	301		`; Draw Note`
295	302		`; ----------------------------------------------------------------------------`
296		-	`; Input: X = note index`
297	303
298	304		`draw_note:`
299	305		`lda note_track,x`
			...
325	331		`lda #>(COLRAM + TRACK1_ROW * 40)`
326	332		`adc #0`
327	333		`sta ZP_PTR_HI`
328		-	`lda #LIGHT_RED`
	334	+	`lda #TRACK1_NOTE_COL`
329	335		`sta (ZP_PTR),y`
330	336		`rts`
331	337
			...
349	355		`lda #>(COLRAM + TRACK2_ROW * 40)`
350	356		`adc #0`
351	357		`sta ZP_PTR_HI`
352		-	`lda #LIGHT_GREEN`
	358	+	`lda #TRACK2_NOTE_COL`
353	359		`sta (ZP_PTR),y`
354	360		`rts`
355	361
			...
373	379		`lda #>(COLRAM + TRACK3_ROW * 40)`
374	380		`adc #0`
375	381		`sta ZP_PTR_HI`
376		-	`lda #LIGHT_BLUE`
	382	+	`lda #TRACK3_NOTE_COL`
377	383		`sta (ZP_PTR),y`
378	384		`rts`
379	385
380	386		`; ----------------------------------------------------------------------------`
381	387		`; Erase Note`
382	388		`; ----------------------------------------------------------------------------`
383		-	`; Input: X = note index`
384	389
385	390		`erase_note:`
386	391		`lda note_track,x`
			...
412	417		`lda #>(COLRAM + TRACK1_ROW * 40)`
413	418		`adc #0`
414	419		`sta ZP_PTR_HI`
415		-	`lda #GREY`
	420	+	`lda #TRACK_LINE_COL`
416	421		`sta (ZP_PTR),y`
417	422		`rts`
418	423
			...
436	441		`lda #>(COLRAM + TRACK2_ROW * 40)`
437	442		`adc #0`
438	443		`sta ZP_PTR_HI`
439		-	`lda #GREY`
	444	+	`lda #TRACK_LINE_COL`
440	445		`sta (ZP_PTR),y`
441	446		`rts`
442	447
			...
460	465		`lda #>(COLRAM + TRACK3_ROW * 40)`
461	466		`adc #0`
462	467		`sta ZP_PTR_HI`
463		-	`lda #GREY`
	468	+	`lda #TRACK_LINE_COL`
464	469		`sta (ZP_PTR),y`
465	470		`rts`
466	471
			...
469	474		`; ----------------------------------------------------------------------------`
470	475
471	476		`init_screen:`
472		-	`lda #BLACK`
	477	+	`lda #BORDER_COL`
473	478		`sta BORDER`
	479	+	`lda #BG_COL`
474	480		`sta BGCOL`
475	481
476	482		`ldx #0`
			...
484	490		`bne clr_screen`
485	491
486	492		`ldx #0`
487		-	`lda #GREY`
	493	+	`lda #TRACK_LINE_COL`
488	494		`clr_colour:`
489	495		`sta COLRAM,x`
490	496		`sta COLRAM+$100,x`
			...
533	539		`; ----------------------------------------------------------------------------`
534	540
535	541		`draw_hit_zones:`
536		-	`lda #$7D ; Pipe character`
	542	+	`lda #$7D`
537	543
538		-	`sta SCREEN + (TRACK1_ROW * 40) + HIT_ZONE_COL`
539		-	`sta SCREEN + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COL`
540		-	`sta SCREEN + ((TRACK1_ROW+1) * 40) + HIT_ZONE_COL`
	544	+	`sta SCREEN + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN`
	545	+	`sta SCREEN + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COLUMN`
	546	+	`sta SCREEN + ((TRACK1_ROW+1) * 40) + HIT_ZONE_COLUMN`
541	547
542		-	`sta SCREEN + (TRACK2_ROW * 40) + HIT_ZONE_COL`
543		-	`sta SCREEN + ((TRACK2_ROW-1) * 40) + HIT_ZONE_COL`
544		-	`sta SCREEN + ((TRACK2_ROW+1) * 40) + HIT_ZONE_COL`
	548	+	`sta SCREEN + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN`
	549	+	`sta SCREEN + ((TRACK2_ROW-1) * 40) + HIT_ZONE_COLUMN`
	550	+	`sta SCREEN + ((TRACK2_ROW+1) * 40) + HIT_ZONE_COLUMN`
545	551
546		-	`sta SCREEN + (TRACK3_ROW * 40) + HIT_ZONE_COL`
547		-	`sta SCREEN + ((TRACK3_ROW-1) * 40) + HIT_ZONE_COL`
548		-	`sta SCREEN + ((TRACK3_ROW+1) * 40) + HIT_ZONE_COL`
	552	+	`sta SCREEN + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN`
	553	+	`sta SCREEN + ((TRACK3_ROW-1) * 40) + HIT_ZONE_COLUMN`
	554	+	`sta SCREEN + ((TRACK3_ROW+1) * 40) + HIT_ZONE_COLUMN`
549	555
550		-	`lda #YELLOW`
551		-	`sta COLRAM + (TRACK1_ROW * 40) + HIT_ZONE_COL`
552		-	`sta COLRAM + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COL`
553		-	`sta COLRAM + ((TRACK1_ROW+1) * 40) + HIT_ZONE_COL`
	556	+	`lda #HIT_ZONE_COL`
	557	+	`sta COLRAM + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN`
	558	+	`sta COLRAM + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COLUMN`
	559	+	`sta COLRAM + ((TRACK1_ROW+1) * 40) + HIT_ZONE_COLUMN`
554	560
555		-	`sta COLRAM + (TRACK2_ROW * 40) + HIT_ZONE_COL`
556		-	`sta COLRAM + ((TRACK2_ROW-1) * 40) + HIT_ZONE_COL`
557		-	`sta COLRAM + ((TRACK2_ROW+1) * 40) + HIT_ZONE_COL`
	561	+	`sta COLRAM + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN`
	562	+	`sta COLRAM + ((TRACK2_ROW-1) * 40) + HIT_ZONE_COLUMN`
	563	+	`sta COLRAM + ((TRACK2_ROW+1) * 40) + HIT_ZONE_COLUMN`
558	564
559		-	`sta COLRAM + (TRACK3_ROW * 40) + HIT_ZONE_COL`
560		-	`sta COLRAM + ((TRACK3_ROW-1) * 40) + HIT_ZONE_COL`
561		-	`sta COLRAM + ((TRACK3_ROW+1) * 40) + HIT_ZONE_COL`
	565	+	`sta COLRAM + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN`
	566	+	`sta COLRAM + ((TRACK3_ROW-1) * 40) + HIT_ZONE_COLUMN`
	567	+	`sta COLRAM + ((TRACK3_ROW+1) * 40) + HIT_ZONE_COLUMN`
562	568
563	569		`rts`
564	570
			...
572	578		`lda title_text,x`
573	579		`beq draw_title_done`
574	580		`sta SCREEN + 13,x`
575		-	`lda #WHITE`
	581	+	`lda #1 ; White`
576	582		`sta COLRAM + 13,x`
577	583		`inx`
578	584		`bne draw_title`
			...
580	586
581	587		`lda #$1A ; Z`
582	588		`sta SCREEN + (TRACK1_ROW * 40)`
583		-	`lda #LIGHT_RED`
	589	+	`lda #TRACK1_NOTE_COL`
584	590		`sta COLRAM + (TRACK1_ROW * 40)`
585	591
586	592		`lda #$18 ; X`
587	593		`sta SCREEN + (TRACK2_ROW * 40)`
588		-	`lda #LIGHT_GREEN`
	594	+	`lda #TRACK2_NOTE_COL`
589	595		`sta COLRAM + (TRACK2_ROW * 40)`
590	596
591	597		`lda #$03 ; C`
592	598		`sta SCREEN + (TRACK3_ROW * 40)`
593		-	`lda #LIGHT_BLUE`
	599	+	`lda #TRACK3_NOTE_COL`
594	600		`sta COLRAM + (TRACK3_ROW * 40)`
595	601
596	602		`ldx #0`
597	603		`draw_instr:`
598	604		`lda instr_text,x`
599	605		`beq draw_instr_done`
600		-	`sta SCREEN + (23 * 40) + 3,x`
601		-	`lda #GREY`
602		-	`sta COLRAM + (23 * 40) + 3,x`
	606	+	`sta SCREEN + (23 * 40) + 8,x`
	607	+	`lda #TRACK_LINE_COL`
	608	+	`sta COLRAM + (23 * 40) + 8,x`
603	609		`inx`
604	610		`bne draw_instr`
605	611		`draw_instr_done:`
			...
611	617		`!byte 0`
612	618
613	619		`instr_text:`
614		-	`!scr "hit notes when they reach \|"`
	620	+	`!scr "customise me!"`
615	621		`!byte 0`
616	622
617	623		`; ----------------------------------------------------------------------------`
618		-	`; Initialize SID`
	624	+	`; Initialize SID - Uses customisation constants`
619	625		`; ----------------------------------------------------------------------------`
620	626
621	627		`init_sid:`
			...
629	635		`lda #$0F`
630	636		`sta SID_VOLUME`
631	637
632		-	`; Voice 1 - High pitch, sawtooth`
	638	+	`; Voice 1 - uses VOICE1_* constants`
633	639		`lda #$00`
634	640		`sta SID_V1_FREQ_LO`
635		-	`lda #$1C`
	641	+	`lda #VOICE1_FREQ`
636	642		`sta SID_V1_FREQ_HI`
637		-	`lda #$09`
	643	+	`lda #PULSE_WIDTH`
	644	+	`sta SID_V1_PWHI`
	645	+	`lda #VOICE_AD`
638	646		`sta SID_V1_AD`
639		-	`lda #$00`
	647	+	`lda #VOICE_SR`
640	648		`sta SID_V1_SR`
641	649
642		-	`; Voice 2 - Mid pitch, pulse`
	650	+	`; Voice 2 - uses VOICE2_* constants`
643	651		`lda #$00`
644	652		`sta SID_V2_FREQ_LO`
645		-	`lda #$0E`
	653	+	`lda #VOICE2_FREQ`
646	654		`sta SID_V2_FREQ_HI`
647		-	`lda #$08`
	655	+	`lda #PULSE_WIDTH`
648	656		`sta SID_V2_PWHI`
649		-	`lda #$09`
	657	+	`lda #VOICE_AD`
650	658		`sta SID_V2_AD`
651		-	`lda #$00`
	659	+	`lda #VOICE_SR`
652	660		`sta SID_V2_SR`
653	661
654		-	`; Voice 3 - Low pitch, triangle`
	662	+	`; Voice 3 - uses VOICE3_* constants`
655	663		`lda #$00`
656	664		`sta SID_V3_FREQ_LO`
657		-	`lda #$07`
	665	+	`lda #VOICE3_FREQ`
658	666		`sta SID_V3_FREQ_HI`
659		-	`lda #$09`
	667	+	`lda #PULSE_WIDTH`
	668	+	`sta SID_V3_PWHI`
	669	+	`lda #VOICE_AD`
660	670		`sta SID_V3_AD`
661		-	`lda #$00`
	671	+	`lda #VOICE_SR`
662	672		`sta SID_V3_SR`
663	673
664	674		`rts`
			...
669	679
670	680		`reset_track_colours:`
671	681		`ldx #0`
672		-	`lda #GREY`
	682	+	`lda #TRACK_LINE_COL`
673	683		`reset_t1:`
674	684		`sta COLRAM + (TRACK1_ROW * 40),x`
675	685		`inx`
			...
691	701		`bne reset_t3`
692	702
693	703		`; Restore key labels`
694		-	`lda #LIGHT_RED`
	704	+	`lda #TRACK1_NOTE_COL`
695	705		`sta COLRAM + (TRACK1_ROW * 40)`
696		-	`lda #LIGHT_GREEN`
	706	+	`lda #TRACK2_NOTE_COL`
697	707		`sta COLRAM + (TRACK2_ROW * 40)`
698		-	`lda #LIGHT_BLUE`
	708	+	`lda #TRACK3_NOTE_COL`
699	709		`sta COLRAM + (TRACK3_ROW * 40)`
700	710
701	711		`; Restore hit zone colours`
702		-	`lda #YELLOW`
703		-	`sta COLRAM + (TRACK1_ROW * 40) + HIT_ZONE_COL`
704		-	`sta COLRAM + (TRACK2_ROW * 40) + HIT_ZONE_COL`
705		-	`sta COLRAM + (TRACK3_ROW * 40) + HIT_ZONE_COL`
	712	+	`lda #HIT_ZONE_COL`
	713	+	`sta COLRAM + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN`
	714	+	`sta COLRAM + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN`
	715	+	`sta COLRAM + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN`
706	716
707		-	`; Redraw note colours`
708	717		`jsr redraw_all_notes`
709	718
710	719		`rts`
			...
762	771		`rts`
763	772
764	773		`; ----------------------------------------------------------------------------`
765		-	`; Play Voices`
	774	+	`; Play Voices - Uses customisation waveforms`
766	775		`; ----------------------------------------------------------------------------`
767	776
768	777		`play_voice1:`
769		-	`lda #$21`
	778	+	`lda #VOICE1_WAVE`
	779	+	`ora #$01 ; Add gate bit`
770	780		`sta SID_V1_CTRL`
771	781		`rts`
772	782
773	783		`play_voice2:`
774		-	`lda #$41`
	784	+	`lda #VOICE2_WAVE`
	785	+	`ora #$01`
775	786		`sta SID_V2_CTRL`
776	787		`rts`
777	788
778	789		`play_voice3:`
779		-	`lda #$11`
	790	+	`lda #VOICE3_WAVE`
	791	+	`ora #$01`
780	792		`sta SID_V3_CTRL`
781	793		`rts`
782	794
783	795		`; ----------------------------------------------------------------------------`
784		-	`; Flash Tracks`
	796	+	`; Flash Tracks - Uses customisation colours`
785	797		`; ----------------------------------------------------------------------------`
786	798
787	799		`flash_track1:`
788	800		`ldx #0`
789		-	`lda #RED`
	801	+	`lda #FLASH1_COL`
790	802		`flash_t1_loop:`
791	803		`sta COLRAM + (TRACK1_ROW * 40),x`
792	804		`inx`
793	805		`cpx #38`
794	806		`bne flash_t1_loop`
795		-	`lda #WHITE`
	807	+	`lda #1 ; White label`
796	808		`sta COLRAM + (TRACK1_ROW * 40)`
797	809		`rts`
798	810
799	811		`flash_track2:`
800	812		`ldx #0`
801		-	`lda #GREEN`
	813	+	`lda #FLASH2_COL`
802	814		`flash_t2_loop:`
803	815		`sta COLRAM + (TRACK2_ROW * 40),x`
804	816		`inx`
805	817		`cpx #38`
806	818		`bne flash_t2_loop`
807		-	`lda #WHITE`
	819	+	`lda #1`
808	820		`sta COLRAM + (TRACK2_ROW * 40)`
809	821		`rts`
810	822
811	823		`flash_track3:`
812	824		`ldx #0`
813		-	`lda #BLUE`
	825	+	`lda #FLASH3_COL`
814	826		`flash_t3_loop:`
815	827		`sta COLRAM + (TRACK3_ROW * 40),x`
816	828		`inx`
817	829		`cpx #38`
818	830		`bne flash_t3_loop`
819		-	`lda #WHITE`
	831	+	`lda #1`
820	832		`sta COLRAM + (TRACK3_ROW * 40)`
821	833		`rts`
822	834
823	835		`; ----------------------------------------------------------------------------`
824	836		`; Song Data`
825	837		`; ----------------------------------------------------------------------------`
826		-	`; Format: beat, track (1-3)`
827		-	`; $FF marks end of song`
828	838
829	839		`song_data:`
830		-	`; Simple test pattern - 4 bars at 120 BPM`
831		-	`; Bar 1`
832	840		`!byte 0, 1`
833	841		`!byte 2, 2`
834	842		`!byte 4, 3`
835	843		`!byte 6, 1`
836	844
837		-	`; Bar 2`
838	845		`!byte 8, 2`
839	846		`!byte 10, 3`
840	847		`!byte 12, 1`
841	848		`!byte 14, 2`
842	849
843		-	`; Bar 3`
844	850		`!byte 16, 3`
845	851		`!byte 18, 1`
846	852		`!byte 20, 2`
847	853		`!byte 22, 3`
848	854
849		-	`; Bar 4 - faster pattern`
850	855		`!byte 24, 1`
851	856		`!byte 25, 2`
852	857		`!byte 26, 3`
			...
854	859		`!byte 29, 2`
855	860		`!byte 30, 3`
856	861
857		-	`!byte $FF ; End marker`
	862	+	`!byte $FF`
858	863
859	864		`; ----------------------------------------------------------------------------`
860	865		`; Note Arrays`