Rolloff in FLAC file frequency response

[Qboy61]

I am trying to figure out what causes VLC to rolloff the uppermost high frequencies in FLAC files. I've captured a noise signal generated with Audacity and saved as a FLAC file with sample rate of 44.1kHz and 24bit depth. The audio is digitally captured via a virtual audio card. When the FLAC file is played with VLC, the high frequencies roll off at 17.8kHz at 3dB down. Playing the same file with Mozilla Firefox results in no rolloff at all. Does anyone know what causes this and/or a way to stop this?

[Lotesdelere]

That is true, I can reproduce it.

But after a quick test with a given pink noise WAV source file it appears that no player that I've tried is giving the expected output and especially over 16 kHz they all have a different cutoff curve.
This needs a deeper investigation from the FFmpeg team and the different players makers.

That said, VLC is resampling audio by default because of the playback speed feature.
You can disable it via the menu Tools -> Preferences (Show settings = ALL) -> Audio -> Audio resampler

[Qboy61]

Thanks Lotesdelere,

I tried disabling the "Audio Resampler" and you are correct. After disabling the audio resampler, the response flattens all the way to 22.05kHz. But something different happened when I returned the audio resampler to "Automatic." The frequency response again rolled off but now at a much higher frequency and a steeper rolloff rate. The -3dB point is now 21.2kHz. I would suspect there's a default configuration for this audio resampler (or the digital filter used) that is misconfigured at installation of VLC and the act of disabling and then returning it to automatic configures the filter more correctly for 44.1kHz sampled data. I've closed VLC and reopened it several times and played some different files and this audio resampling configuration appears to be stuck. On the Mac version of VLC this rolloff seems to be about 19.6kHz and does not move even when disabling the audio resampler nor will playing the FLAC file with Firefox or Audacity change this rolloff. On Windows, Audacity does not filter this way and neither does Mozilla Firefox. But... Having the resampler may make VLC more capatible with many different file formats and hardware and as long as the filter would remain as it's currently functioning at 96% of Nyquist this will work fine. It would be nice to get this function by default though.