Re: [Jack-Devel] Why does jack change the sampling rate?

On 06/28/2012 05:13 AM, Eric Renrut wrote:
> is there anything I can do to get jack to
> capture at a sample rate of 8khz, mono and using 16 or 8 bit samples?

Hi Eric,

I don't think there is.

If you need the live signal in some other jack-app or output it again in
real-time: you can use two plugins: a low-pass filter at 4Hz and a
bit-decimator.

Steve Harris has written LADSPA plugins for that [1] (they have been
ported to LV2 plugins, too). Just fire-up jack-rack or your favorite
JACK-plugin-host..

If you need 8Hz, 8bit files you can resample them after recording; there
are lots of tools and GUIs that can do that (basically every audio-file
editor) and a commandline utils like `sndfile-resample` or `sox`. The
latter can actually do both at the same time: resample & decimate.

If you want to record them in one step (no intermediate file,
post-processing), you can use pipe the live-audio from jack into `sox`:

jack-stdout system:capture_1 \
| sox -b 16 -r 44100 -t raw -e signed -c 1 - \
      -b 8 -r 8k /tmp/recording_8bit_8kHz.wav

Above command-pipe records channel 1, re-samples and decimate before
writing to disk. Note: jack is assumed to run at 44.1kHz. By default
jack-stdout writes 16bit signed integer raw audio.

HTH,
robin

[1] http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html#tth_sEc2.26

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