Update (2010-06-02): And here’s version 4 (which Karl actually put together a while back but somehow it got buried in my inbox – oops, sorry!), with a new Windows GUI… Download WAV2AY v4 (1.5Mb)

url : http://matt.west.co.tt/spectrum/samplepack/

;; Line 3 is automatically added to change the ORGIN setting during compile

org 32768


; sample player
; need 317 tstates per sample

ld hl,33000 ; start address of sample data
ld bc,20007 ; length of sample data, in bytes
push bc

ld a,7 ; set bits 0-5 of AY register 7 so that all channels are fixed at 'high'
ld bc,0xfffd ; output - this way the AY is not generating waveforms of its own, and
out (c),a ; varying the volume (channels 8/9/10) creates our own wave output instead
ld a,63
ld b,0xbf
out (c),a

pop bc
di ; disable interrupts, so that they don't mess with our carefully planned timings

samplelp
push bc ; 11

; get low 4 bits to use as the first volume level
ld a,(hl) ; 7
and 0x0f ; 7

; delay 117ish tstates
ld b,8 ; 7
zzz2 djnz zzz2

; output that volume level to channels 8/9/10
ld bc,0xfffd ; 10
ld d,8 ; 7
out (c),d ; 12
ld b,0xbf ; 7
out (c),a ; 12
inc d ; 4
ld b,0xff ; 7
out (c),d ; 12
ld b,0xbf ; 7
out (c),a ; 12
inc d ; 4
ld b,0xff ; 7
out (c),d ; 12
ld b,0xbf ; 7
out (c),a ; 12

; get the next volume level from the high 4 bits
ld a,(hl) ; 7 ; start tstate count here
srl a ; 8
srl a ; 8
srl a ; 8
srl a ; 8

; delay 152ish tstates
ld b,11 ; 7
zzz1 djnz zzz1
; 8

; output that volume level to channels 8/9/10
ld b,0xff ; 7
ld d,8 ; 7
out (c),d ; 12
ld b,0xbf ; 7
out (c),a ; 12
inc d ; 4
ld b,0xff ; 7
out (c),d ; 12
ld b,0xbf ; 7
out (c),a ; 12
inc d ; 4
ld b,0xff ; 7
out (c),d ; 12
ld b,0xbf ; 4
out (c),a ; 12

; move on to next byte
inc hl ; 6

; loop if we haven't reached the end of the sample
pop bc ; 11
dec bc ; 6
ld a,b ; 4
or c ; 4
jr nz,samplelp ; 12

ei
ret