Speex resampler is bad on Raspberry Pi or other ARM boards

[xiongyihui]

The resampler of libspeexdsp1 is used by PulseAudio and ALSA (if libasound2-plugins is installed) by default. It has serious distortion when converting loud audio from 44100 to 48000. There is a bug report at 2015 (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=799176). Now (2018), it is still a unsolved issue. It's a fixed point overflow problem.

Solutions

• fix the libspeexdsp1 library in debian repository. The one in the repository is built from speex source, but now speexdsp is separated from speex source as a standalone library (https://github.com/xiph/speexdsp)

• or just don't use speex's resampler. For ALSA, add defaults.pcm.rate_converter "samplerate" to /etc/asound.conf or ~/.asoundrc. There are other resamplers, use ls /usr/lib/arm-linux-gnueabihf/alsa-lib to find more resamplers. For PulseAudio, set resample-method = ffmpeg in /etc/pulse/daemon.conf, use pulseaudio --dump-resample-methods to find more resampler.

If you wonder which resampler of PulseAudio is fit for you, there is a resampler quality evaluation from Alexander E. Patrakov. See

http://comments.gmane.org/gmane.comp.audio.pulseaudio.general/21051 https://imgur.com/a/jtIEj

It compares resampler of ffmpeg, sox and speex.

[demon36]

thanks a lot, changing pulseaudio sampler to ffmpeg on rpi4 fixed distorted audio for me.