fix: increasing biquad filter frequency on sound with slowed play speed causes crash

[NTayloe]

Description

If you slow the relative play speed of a sound and increase the frequency (within the 10 to 16000 range) of the biquad resonant filter (or vice versa) there is a loud blip and then (usually) soloud crashes.

Expected Behavior

Since we can't extract the sample rate of audio from flutter_soloud (that I know of) it isn't easy to calculate the proper max frequency/play speed ratio on our end without using other packages. It would be nice if these calculations were automatically done when adjusting either the speed or biquad filter frequency to avoid invalid values that cause the blip and crash.

I'm not sure if this type of mistake is flutter_soloud's responsibility to avoid or if its something I should be keeping track of when users adjust these values, but I thought I'd bring it up in case it isn't known about.

[alnitak]

Hi @NTayloe, sorry for the late reply.

I still have to try to see where the crash occurs, but I think it is in the SoLoud C++ lib where I can't do much.

The output samplerate is always the one used when initializing flutter_soloud, regardless of the sound played. Internally, SoLoud resamples the input to the engine samplerate. When you set a new relative play speed of a sound, the lib just increases or decreases its samplerate, but the output is still the one the engine uses. So, when, for example, decreasing the speed and using the filter to do the same, the output samplerate could reach a value that could cause the crash (I think).

I suspect you are attaching the filter to the sound instead of using an engine filter. Maybe this won't happen if you use the filter as a global filter instead of a filter for the sound.

[NTayloe]

@alnitak thanks for the informative response!

I forgot that the same sample rate was used throughout the engine, that might actually make it easy to avoid the crash on my end. I am indeed attaching the filter to the sound (sorry I forgot to put that in the description) as I'm making a soundscape app where each sound can be adjusted independently, so using the global filter isn't an option for me. But I'll see what I can do to prevent the invalid values by using the engine sample rate, speed, and frequency in an equation.