KSynth

Beginnings of a dual tone synthesizer for the Apple II

All the code is in this README, since it's small enough to copy and paste into an emulator for now. There is also a Merlin32 compatible source file, ksynth.s, with comments and equivalents to make it more relocatable.

The included DSK file contains the following files:

KSYNTH: The core sound generation routine KSYNTH.PLAYER: Basic player routine. Assumes SONG bytes starting at $1000 BFLATSCALE.SONG: B-Flat scale VICTORY.SONG: "Victory" tune from Karateka
DAISYBELL.SONG: "Bicylce Built for Two" AKA "Daisy Bell"
DAISYBELL.MIDI: "Bicylce Built for Two" AKA "Daisy Bell" in MIDI-like format for KSYNTH.MIDI KSYNTH.MIDI: MIDI-style KSYNTH player routine. Looks up notes from MIDI.LOOKUP instead of raw cycle counts.
MIDI.LOOKUP: Lookup table of notes to cycle counts for MIDI style player.
RANDOMNOTES: A routine to play random tones with the KSYNTH routine. MIDI.LOOKUP2: Alternate MIDI lookup table that covers larger range of tones TWOTONE.PLAYER: Slightly different MIDI-style player. Plays arbitrary two-note combinations.

To do: Add more MIDI example songs.

The synth code itself

##Two Tone Generator##

0300-   A5 FD       LDA   $FD	;	load second oscillator value into $FE
0302-   85 FE       STA   $FE	;
0304-   A9 FF       LDA   #$FF	;	load duration multiplier into $FC
0306-   85 FC       STA   $FC	;
0308-   A4 FA       LDY   $FA	;	load duration into Y
030A-   A6 FB       LDX   $FB	;	load oscillator into X
030C-   CA          DEX			;	start countdown first oscillator, X
030D-   EA          NOP			;	wait...
030E-   EA          NOP			;
030F-   D0 05       BNE   $0316	;	if X = 0, click. otherwise, skip
0311-   2C 30 C0    BIT   $C030	;	click
0314-   A6 FB       LDX   $FB	;	reset X to beginning of countdown
0316-   C6 FE       DEC   $FE	;	countdown second oscillator, $FE
0318-   EA          NOP			;	wait...
0319-   EA          NOP			;
031A-   D0 07       BNE   $0323	;	if $FE = 0, click. otherwise, skip
031C-   2C 30 C0    BIT   $C030	;	click
031F-   A5 FD       LDA   $FD	;	reset $FE to beginning of countdown
0321-   85 FE       STA   $FE	;
0323-   88          DEY			;	countdown duration
0324-   D0 E6       BNE   $030C	;	if duration hasn't expired, return and count down oscillators
0326-   A4 FA       LDY   $FA	;	if duration has expired, reset duration 
0328-   C6 FC       DEC   $FC	;	decrement duration multiplier
032A-   D0 E0       BNE   $030C	;	if multiplier hasn't expired, return and count down oscillators
032C-   60          RTS			;	all done

300: A5 FD 85 FE A9 FF 85 FC A4 FA A6 FB CA EA EA D0 05 8D 30 C0 A6 FB C6 FE EA EA D0 07 8D 30 C0 A5 FD 85 FE 88 D0 E6 A4 FA C6 FC D0 E0 60       

##Player##

0330-   A9 00       LDA   #$00		;	start at zero
0332-   AA          TAX				;	X = 0; LOOP
0333-   BD 00 10    LDA   $1000,X	;	load note duration
0336-   F0 31       BEQ   $0369		;	if note is 0 duration, end the song
0338-   85 FA       STA   $FA		;	store duration at $FA
033A-   E8          INX				;	increment to note value
033B-   BD 00 10    LDA   $1000,X	;	load note value
033E-   85 FB       STA   $FB		;	store note value at $FB
0340-   85 FD       STA   $FD		; 	store note value at $FD
0342-   C9 FF       CMP   #$FF		;	if note value is FF, rest
0344-   D0 06       BNE   $034C		;	skip over if !=FF
0346-   8D 1E 03    STA   $031E		;	change the $C030 click to $$FF30	
0349-   8D 13 03    STA   $0313		;	change the $C030 click to $$FF30	
034C-   C6 FD       DEC   $FD		;	decrement $FD for That Karateka Sound™
034E-   8A          TXA				;	put current note address in Accumulator
034F-   85 FF       STA   $FF		;	store that in $FF						
0351-   20 00 03    JSR   $0300		;	play the actual note
0354-   AD 13 03    LDA   $0313		;	did we mess with the C030 click?
0357-   C9 FF       CMP   #$FF		;	if it's FF, we did. change it back.
0359-   D0 08       BNE   $0363		;	skip if !=FF
035B-   A9 C0       LDA   #$C0		;	set click points back to $c030
035D-   8D 1E 03    STA   $031E		;
0360-   8D 13 03    STA   $0313		;	
0363-   E6 FF       INC   $FF		;	increment to next note address
0365-   A5 FF       LDA   $FF		;	load Accumulator with next note address
0367-   D0 C9       BNE   $0332		;	branch to LOOP
0369-   60          RTS				;

330: A9 00 AA BD 00 10 F0 31 85 FA E8 BD 00 10 85 FB 85 FD C9 FF D0 06 8D 1E 03 8D 13 03 C6 FD 8A 85 FF 20 00 03 AD 13 03 C9 FF D0 08 A9 C0 8D 1E 03 8D 13 03 E6 FF A5 FF D0 C9 60       

##Creating Music##

Music is stored in the following format, beginning (by default) at $1000.

Starting address = A ($1000)

A+0 = duration

e.g. FF = 1.63 seconds

A+1 = note

e.g. 59 = 440Hz A

per chart at [https://www.seventhstring.com/resources/notefrequencies.html]

NOTE	C	C#	D	Eb	E	F	F#	G	G#	A	Bb	B
FREQ				155.6	164.8	174.6	185.0	196.0	207.7	220.0	233.1	246.9
BYTE				FC	EF	E1	D5	C9	BD	B3	A9	9F
FREQ	261.6	277.2	293.7	311.1	329.6	349.2	370.0	392.0	415.3	440.0	466.2	493.9
BYTE	96	8E	86	7E	77	71	6A	64	5E	59	54	4F
FREQ	523.3	554.4	587.3	622.3	659.3	698.5	740.0	784.0	830.6	880.0	932.3	987.8
BYTE	4B	47	43	3F	3C	38	35	32	2F	2D	2A	27
FREQ	1047	1109	1175	1245	1319	1397	1480	1568	1661	1760	1865	1976
BYTE	25	23	21	1F	1E	1C	1A	19	17	16	15	13

##Bb scale:##

1000: 20 A9 20 96 20 86 20 7E 20 71 20 64 20 59 20 54 20 59 20 64 20 71 20 7E 20 86 20 96 FF A9 FF FF 10 A9 10 86 10 71 10 54 10 71 10 86 FF A9 00

##Karateka victory:##

1000: 10 a8 20 FF 8 c7 5 FF 10 a8 15 FF 25 7e 20 FF 10 63 08 FF 80 63 00 00

and, of course, the requisite

##Daisy Bell (Bicycle Built For Two)##

1000: 30 71 30 86 30 A9 30 e1 10 C9 10 B3 10 A9 20 C9 10 A9 60 e1 30 96 30 71 30 86 30 A9 10 C9 10 B3 10 A9 20 96 10 86 40 96 10 FF 10 86 10 77 10 86
1030: 10 96 20 71 10 86 10 96 40 A9 10 96 20 86 10 A9 20 C9 10 A9 10 C9 40 e1 10 E1 20 A9 10 86 10 96 20 FF 20 A9 10 86 10 96 10 FF 5 86 5 77 10 71 10 86 10 A9 20 96 10 e1 40 A9 00 00

##MIDI Translation##

Using the above table as a starting point, a MIDI lookup table can be created. MIDI addresses up to 127 notes, from a C three octaves below Bass Clef, up to a G 9 octaves above. [http://www.midikits.net/midi_analyser/midi_note_numbers_for_octaves.htm]

440hz A is note 69 in MIDI, so byte 69 (0x45) of the KSYNTH lookup table.

By shifting 12 bytes up or down (one octave), a song's range can be easily be changed to fit in KSYNTH's limited range.

notes and octaves

  C  C# D  D# E  F  F# G  G# A  A# B
0 00 00 00 00 00 00 00 00 00 00 00 00 
1 00 00 00 00 00 00 00 00 00 00 00 00 
2 00 00 00 00 00 00 00 00 00 00 00 00 
3 00 00 00 00 00 00 00 00 00 00 00 00 
4 00 00 00 FC EF E1 D5 C9 BD B3 A9 9F
5 96 8E 86 7E 77 71 6A 64 5E 59 54 4F
6 4B 47 43 3F 3C 38 35 32 2F 2D 2A 27
7 25 23 21 1F 1E 1C 1A 19 17 16 15 13
8 00 00 00 00 00 00 00 00 00 00 00 00 
9 00 00 00 00 00 00 00 00


bytes 

$30	00 00 00 FC EF E1 D5 C9 BD B3 A9 9F 96 8E 86 7E
$40	77 71 6A 64 5E 59 54 4F 4B 47 43 3F 3C 38 35 32
$50	2F 2D 2A 27 25 23 21 1F 1E 1C 1A 19 17 16 15 13


1133: FC EF E1 D5 C9 BD B3 A9 9F 96 8E 86 7E 77 71 6A 64 5E 59 54 4F 4B 47 43 3F 3C 38 35 32 2F 2D 2A 27 25 23 21 1F 1E 1C 1A 19 17 16 15 13

##Daisy Bell (Bicycle Built For Two) MIDI style##

1000: 30 41 30 3E 30 3A 30 35 10 37 10 39 10 3A 20 37 10 3A 60 35 30 3C 30 41 30 3E 30 3A 10 37 10 39 10 3A 20 3C 10 3E 40 3C 10 FF 10 3E 10 40 10 3E 1030: 10 3C 20 41 10 3E 10 3C 40 3A 10 3C 20 3E 10 3A 20 37 10 3A 10 37 40 35 10 35 20 3A 10 3E 10 3C 20 FF 20 3A 10 3E 10 3C 10 FF 5 3E 5 40 10 41 10 3E 10 3A 20 3C 10 35 40 3A 00 00

##KSYNTH.MIDI: MIDI-like Player##

assumes song src at $1000

assumes lookup table src at $1100

0330-   A9 00       LDA   #$00		;	start at zero
0332-   AA          TAX				;	X = 0	; LOOP
0333-   BD 00 10    LDA   $1000,X	;	load note duration
0336-   F0 35       BEQ   $036D		;	if note is 0 duration, end the song
0338-   85 FA       STA   $FA		;	store duration at $FA
033A-   E8          INX				;	increment pointer to note value
033B-   BD 00 10    LDA   $1000,X	;	load note MIDI-style value
033E-   A8          TAY				;	lookup note loop value from lookup table
033F-   B9 00 11    LDA   $1100,Y	;
0342-   85 FB       STA   $FB		;	store note value at $FB
0344-   85 FD       STA   $FD		; 	store note value at $FD
0346-   C9 FF       CMP   #$FF		;	if note value is FF, rest
0348-   D0 06       BNE   $0350		;	skip over if !=FF
034A-   8D 1E 03    STA   $031E		;	change the $C030 click to BIT $FF30	
034D-   8D 13 03    STA   $0313		;	change the $C030 click to BIT $FF30	
0350-   C6 FD       DEC   $FD		;	decrement $FD for That Karateka Sound™
0352-   8A          TXA				;	put current note pointer in Accumulator
0353-   85 FF       STA   $FF		;	store that in $FF						
0355-   20 00 03    JSR   $0300		;	play the actual note
0358-   AD 13 03    LDA   $0313		;	did we mess with the C030 click?
035B-   C9 FF       CMP   #$FF		;	if it's FF, we did. change it back.
035D-   D0 08       BNE   $0367		;	skip if !=FF
035F-   A9 C0       LDA   #$C0		;	set click points back to $c030
0361-   8D 1E 03    STA   $031E		;
0364-   8D 13 03    STA   $0313		;	
0367-   E6 FF       INC   $FF		;	increment to next note address
0369-   A5 FF       LDA   $FF		;	load Accumulator with next note address
036B-   D0 C5       BNE   $0332		;	branch to LOOP
036D-   60          RTS				;

330: A9 00 AA BD 00 10 F0 35 85 FA E8 BD 00 10 A8 B9 00 11 85 FB 85 FD C9 FF D0 06 8D 1E 03 8D 13 03 C6 FD 8A 85 FF 20 00 03 AD 13 03 C9 FF D0 08 A9 C0 8D 1E 03 8D 13 03 E6 FF A5 FF D0 C5 60       





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