Strong aliasing in 24 kHz mode

FMOD Engine
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1

Hi!
I have an unexplained resampling problem. With a system frequency of 24 kHz on iOS and Android, there is irreparable aliasing. The useful signal from 8 to 12 kHz is reflected in frequencies from 12 to 18 kHz. I have tried all the options for bank settings and system interpolation settings (starting with the obvious - building banks at 24 kHz and using higher quality formats and interpolation methods), and have not yet found a way to eliminate this sound defect.
Tell me, is this a known fmod problem, or is there a way to configure the engine at this frequency so that there is no aliasing?

Screenshot 2024-05-05 210839
Screenshot 2024-05-05 210839612×544 224 KB

Screenshot 2024-05-05 210644
Screenshot 2024-05-05 210644918×543 96.8 KB

Screenshot 2024-05-05 210458
Screenshot 2024-05-05 210458461×577 209 KB

2

This isn’t really an FMOD problem as much as it is an inherent issue with data sampling. That said, we could probably add an anti-aliasing filter to deal with this problem on your behalf- I will suggest that to the Dev team.
For now however, you have two options to deal with aliasing:

  1. Use a sample rate of 44.1khz on iOS and Android. This will slightly increase audio latency, but will resolve the aliasing. You can override the iOS and Android sample rate with a call to System::setSoftwareFormat in your game.
  2. Add a 48dB lowpass filter at 12kHz on your master bus. You will lose a little bit of high end energy, but it should eliminate high-frequency aliasing
    image
    If you are targeting more than just mobile, you can also use Platform Exclusion to only include this filter on Mobile platforms.
3

Thank you Jeff

  1. Yes, but i’m looking for a solution for 24 kHz mode. I think 44.1 kHz is not needed, 36 kHz is enough to take these reflections out of the audible range. This is a last resort method in case I don’t find another solution.
  2. I tried to solve the problem this way - the result is on the 3rd screenshot. It looks like it doesn’t help.
4

Thanks! Anti-aliasing filter would be useful. I think that would be the best solution.

5

After some discussion with the Dev team, they have asked me to follow-up on your results with use of the different interpolation methods, which should have given you better results.
Can you please confirm that you called System::setAdvancedSettings with an alternative FMOD_ADVANCEDSETTINGS::resamplerMethod before you called System::init, and not after?
If you are finding that it doesn’t help at all, then can you please also tell me what version of the FMOD Engine you are using?

6

Yes

2.02.22