The SID chip is easy enough to use that you can easily hardcode sound effects by just creating the parameters in an array and copy that in to the hardware registers for a channel. Unfortunately I don't have a good intuition for sounds so I made a tool I could use for this simple task.
For more details about the SID chip please review https://www.c64-wiki.com/wiki/SID
The tool will export source code of bytes to copy to the SID registers, it will not handle channel allocation or anything else that might interfere with other audio systems. It does add some nice features like timing, looping and sliding (for frequency and pulse).
Each sound is stored as a sequence of events. An event is any time a channel register should change, such as key on and key off.
BDoing is intended to be assembled with the x65 assembler
x65 src\bdoing.s bdoing.prg
The tool runs on a Commodore 64 as a prg file and expects to be loaded from a floppy (d64 or SDIEC). The first screen is a directory listing of the floppy, and using cursor up/down you can select an existing sound file or press '=' to create a new file. If you select a file that is not a sound the directory listing screen will refresh. If you create a new file the tool will ask for a new filename and then a new sound name.
As an example to work with Vice look at run.bat. This file expects to find Vice x64 and c1541 in \Vice\.
- Up / Down (Shift+Down / Down): Navigate Files
- Return: Load the selected file
- =: Create a new file
The sound bank is the list of sounds in a sound file. The sound bank screen lets you test sounds by pressing A-W, and if a sound is looping press 1-3 (based on which channel is playing) to end the loop. Press '=' to create a new sound, followed by typing a name for the sound. Use up/down to navigate and Return to edit a sound.
- A-W: Test sound
- 1-3: Stop loop in channel 1-3
- Up / Down (Shift+Down / Down): Navigate sounds
- Return: Edit the selected sound
- =: Create a new sound
Edit a sound one event at a time in the Edit screen, where each event is made up of registers like frequency, pulse, ADSR, control, frequency slide and pulse slide. In addition to the sound registers there is also loop control and event duration that can be edited. If a sound register is not enabled, it won't be written to hardware when the event happens so events that don't do much, such as key off, end up very small. Exporting extra labels will enable customizing sound events runtime in the code that plays sound effects.
Sound editing is live so anything that is modified while a sound is playing will be reflected even if the sound has already started.
- =: Toggle a sound register for this event (indicated in leftmost column)
- L: Toggle label for this event (indicated in column 2)
- Space: Play a sound, end loop if sound is already playing.
- Up / Down (Shift+Down / Down): Navigate registers in Sound Event
- Left / Right (Shift+Right / Right): Adjust values lesser/greater
- C= + Left/Right: Adjust high byte of 2 byte values (freq. etc.)
- Return: Start typing in a number for a sound register, duration or name
- N: New event (inserted after current event)
- C= + D: Delete event
- @/*: Go back/forward between sound events
- S: Save all sounds in bank
- C= + E: Export source code for all sound data in bank
The exported data is very simple, each event is saved starting with a frame count until the next event, then a mask byte that contains:
- $01 - Frequency
- $02 - Pulse
- $04 - Attack / Decay
- $08 - Sustain / Release
- $10 - Control
- $20 - Frequency Slide
- $40 - Pulse Slide
For each bit in the mask byte the data follows in the same order.
If the frame count is 0 the sound is done, and if it is negative it is a loop point, or -bytes to step back to restart the loop.
Exported data sample
BDoing_SND:
dc.b $03, $1f, $00, $0a, $f8, $07, $12, $c1, $21
dc.b $03, $10, $20
dc.b $0b, $7f, $00, $0c, $00, $08, $23, $89, $41, $00, $02, $a0, $ff
dc.b $0b, $30, $40, $00, $02
dc.b $00
I talked to a number of sound designers (because I'm not really an expert in audio tools) about making a new sound tool. One thing that was mentioned was that if someone was using synthesized sounds rather than premade sounds one major benefit would be the ability to have more procedural sounds, as in having a simple way to modify synth parameters each time a sound is triggered, or while it is playing. To support this in a source format I figured the easiest way would be to somehow bookmark useful event registers in the data so I've added labels. As an example, imagine a looping sound such as the sound of a chopper. By simply adjusting the duration of the loop while the chopper loop is playing you can make it sound as if the blades are slowing down or speeding up.
Labels will be exported as the sound name + occurence within sound + one of:
- Duration: _DUR
- Frequency: _FRQ
- Pulse: _PLS
- Attack / Decay: _AD
- Sustain / Release: _SR
- Control: _CTL
- Frequency Slide: _FDT
- Pulse Slide: _PDT
BDoing_Play.s is provided as a reference implementation to play back sounds. You're encouraged to rewrite it but should work fine as is. See source for further details.
I initially intended to convert frequency and time steps to NTSC automatically but wasn't happy with the automatic conversion result. My conclusion is that the difference is not really noticable, and if it is then it is better to manually create the other version in an emulator.
While working on Pac-Man World 2, Klonoa came out (both are Namco games) and we copied one of the mechanics which was a platform that shoots you up while the camera looks straight down. This was named a BDoing platform.
To iterate on a PC with an emulator I'm using this batch file to move sound assets on and off a d64 and move the exported source files into another folder.
del bdoing.d64
\vice\c1541 -format #bdoing#,8 d64 bdoing.d64 -write BDoing.prg @8:bdoing
for %%i in (example\*.snd) do \vice\c1541 bdoing.d64 -write %%i @8:%%~ni.snd
\vice\x64 -remotemonitor BDoing.d64
IF EXIST tmp rmdir /S /Q tmp
mkdir tmp
cd tmp
dir ..\bdoing.d64
\vice\c1541 ..\bdoing.d64 -extract
cd ..
dir tmp
move /Y tmp\*.snd example
IF EXIST tmp\*.s move /Y tmp\*.s example
rmdir /S /Q tmp