Fix for fixed point overflow in synthio #10288
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I updated the tests as this change breaks most of them. I looked and as far as I could tell it is small rounding differences due to how I fixed this issue. I also listened but would appreciate it if someone else can confirm that things sound right. The rounding changes were about 1 (for ints) or less then 0.0001 for floats so not large for audio. |
Not that it's necessary for this PR, but would |
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Just finished running tests. No more distortion across the board! Now that we can push Q up to much higher values, I'm a bit disappointed that it doesn't appear to want to self-oscillate like you'd expect from an analog filter. After a bit of research, I was able to find some anecdotes about biquads not being able to self-oscillate without the help of additional processing (using an envelope follower controlling gain). For our purposes, I think we can live without it. |
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Todbot has tested this (comment on #10200) and it fixes the issue he was having as well. |
| @@ -250,7 +270,7 @@ static bool synth_note_into_buffer(synthio_synth_t *synth, int chan, int32_t *ou | |||
| accum = accum - lim + offset; | |||
| } | |||
| int16_t idx = accum >> SYNTHIO_FREQUENCY_SHIFT; | |||
| int16_t wi = (ring_waveform[idx] * out_buffer32[i]) / 32768; | |||
| int16_t wi = (ring_waveform[idx] * out_buffer32[i]) / 32768; // consider for synthio_sat16 but had a weird artificat | |||
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| int16_t wi = (ring_waveform[idx] * out_buffer32[i]) / 32768; // consider for synthio_sat16 but had a weird artificat | |
| int16_t wi = (ring_waveform[idx] * out_buffer32[i]) / 32768; // consider for synthio_sat16 but had a weird artifact |
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Thanks I'll catch it my next time. It mostly is a note to remind myself to look at it more in the future anyways.
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thank you! |
Fix for #10286 and #10200.
There may still be more locations where fixed point could be handled better in
synthiobut this fix hits two big ones that I discovered so worth fixing those now.Also refactored
sat16that will shift a fixed point result back into 16 bits out ofaudiofreeverband intosynthioto be used by any audio module that needs it. Potentially worth moving this to a generic "audiohelper" type module in the future in case someone builds without synthio but still wants audio effects.