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Diffstat (limited to 'sound.txt')
| -rw-r--r-- | sound.txt | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/sound.txt b/sound.txt new file mode 100644 index 0000000..c9754e9 --- /dev/null +++ b/sound.txt @@ -0,0 +1,56 @@ +Most of the sounds in the game are played by a sound engine that +runs 'in the background' (called every vblank). There are some +exceptions: + +- The descending tones played as the letters materialize, on the + title screen (but, the music after that uses the engine). +- The descending tone you hear as Jumpman materializes, at the + start of a level. +- The sound you hear as the screen crumbles, after you lose your + last life. + +Everything else uses the engine, and is stored as a series of +engine opcodes. I've labelled these sfx_* in the source. + +The engine has 2 entry points: cue_sfx and cue_sfx_lowprior. The +difference is that the _lowprior entry point will abort, if another call +to cue_sfx is in progress. Also the arguments are passed differently. +Also there are _jv (jump vector) versions of both entry points, which +are the ones most of the rest of the code uses. + +Example sound effect: + +sfx_jump: + .byte $01,$A5,$00,$79,$04,$60,$04,$51 ; BFBE 01 A5 00 79 04 60 04 51 ...y.`.Q + .byte $04,$3C,$04,$51,$04,$60,$04,$79 ; BFC6 04 3C 04 51 04 60 04 79 .<.Q.`.y + .byte $04,$00 ; BFCE 04 00 .. + +Sound opcodes: + +00 snd_end end of sound +01 xx yy snd_audc set distortion and volume (AUDCx value) to xx, + play previous freq for yy frames. + yy looks to always be zero in actual use, + except the title screen music where it's $02. +02 xx yy snd_jump jump to address yyxx. this is an unconditional + jump, meaning the sfx plays continuously until + preempted or silenced. +03 xx snd_rest play a rest, xx frames (sets AUDCx to 0) +[04-FF] xx snd_note play [opcode] frequency for xx frames + +so sfx_jump might look like this: + +sfx_jump: + snd_audc $A5,$00 + snd_note $79,$04 + snd_note $60,$04 + snd_note $51,$04 + snd_note $3C,$04 + snd_note $51,$04 + snd_note $60,$04 + snd_note $79,$04 + snd_end + +or in english: distortion $A (pure tone), volume 5. for 4 frames each, +play 3 ascending notes, a higher note, then the same 3 notes in reverse +order. the whole thing takes 28 frames to complete, or about 1/2 sec. |