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PC Engine waveform channel updates

Posted: Wed Mar 28, 2018 4:22 am
by za909
I have recently taken interest in programming for the PC Engine/TG16. I've been meaning to do something interesting with the audio, so I tried regularly changing the waveforms to get more realistic instruments. https://www.youtube.com/watch?v=BI6so4w9mu8

Now based on what I read in the documentation, the waveform data can only be updated when the channel is disabled. But there is no mention whether the channel phase gets reset when you do that. If that actually does happen then the song in the video is actually impossible to do in an actual program. Could anyone confirm any of this to me? Thank you!

Re: PC Engine waveform channel updates

Posted: Wed Mar 28, 2018 7:19 am
by FrankenGraphics
Cannot answer the question but this rearrangement wanted me to walk about town with this in my headphones. Great work!

Re: PC Engine waveform channel updates

Posted: Wed Mar 28, 2018 7:39 am
by ccovell
Feel free to sign up to the PCEngine FX forums http://www.pcenginefx.com/forums/
and use the forum's search function for "waveform". There's been a fair amount of research into changing waveforms while channels are "active" and trying to avoid the popping and artifacts that go with it.

Re: PC Engine waveform channel updates

Posted: Thu Mar 29, 2018 1:05 am
by TOUKO
the waveform data can only be updated when the channel is disabled.
You must use timer interrupt for that,and it's definitively not trivial as it rely on the sound frequency .
The channel is off only when you are updating the new waveform, and switched ON after that,but you're limited on the frequency because it takes time to update the entire 32 bytes buffer, 209 cycles with TIN instruction, plus the others for interrupt and channel setting .

But it's doable in a game, it seems All the Fire Pro Wrestling games did it :
https://www.youtube.com/watch?v=V845pHyaePk

I did it for samples playback, and it works well only on the A rev. of the Hu6280.

Re: PC Engine waveform channel updates

Posted: Thu Mar 29, 2018 3:40 am
by za909
Ah, I only intend to update the waveform once per field at the fastest (up to 1254 cycles if all 6 channels had to be updated), so to me the biggest concern is whether the waveform step is reset to 0 when I update the waveform.

Re: PC Engine waveform channel updates

Posted: Thu Mar 29, 2018 5:29 am
by TOUKO
You reset the waveform pointer like that :

Code: Select all

// First you must select the voice number
lda     #%010_00000
sta     $0804		
stz     $0804
When bit 6 goes from 1 to 0 the pointer is reseted and when you feed the buffer with the new waveform it start at 0 up to 31 and not at the current waveform pointer position .

Re: PC Engine waveform channel updates

Posted: Sat Feb 02, 2019 5:16 am
by za909
I have since tried to do the same on the FDS, a system where I know that the channel has to be halted and reset to change the waveform, and the results are oddly clear with very little artifacts added. This is a promising next step.

Re: PC Engine waveform channel updates

Posted: Sun Feb 03, 2019 2:23 am
by TOUKO
BTW your PCE version of Journey to Silius is incredible :D

Re: PC Engine waveform channel updates

Posted: Thu Oct 31, 2019 3:44 am
by turboxray
You can disable the channel without resetting the waveform pointer. Also you don't have to turn off the channel to write updates to it. You can write updates to it while it's playing and the current pointer position will get over written. A few games do this to get a steal-y sounding timbre change.

Also, what you're doing in that song... is what bloody wolf does. It softens the triangle waveform (the trumpet sound) to give a filter like effect. That sound effect "yeeaahhhh" in bloody wolf is also doing the same thing (once per frame waveform update).