[LAU] Record levels lower in Alsa than Jack

Chris Caudle chris at chriscaudle.org
Fri Nov 6 22:19:22 CET 2020

On Fri, November 6, 2020 7:22 am, John Murphy wrote:
> I think I've discovered where my levels were going awry. I was using
> timemachine to record in w64 format and converting to wav. Now, using:
> jack_capture -s --channels 2 --port system:capture* -d 10 -f w64 t1w64.w64
> \
> & jack_capture -s --channels 2 --port system:capture* -d 10 -f wav
> t1wav.wav
> then:
> sox --no-clobber -S t1w64.w64 -b 16 t2wav.wav
> Then sox stat shows min/max amplitude +/- 0.5 for the wav capture and
> +/- 0.9 for the wav converted from w64. The converted file looks good
> in my editor too.

The w64 vs. wav file thing is not relevant unless you are recording for
more than a couple of hours at a time.  The important distinction is that
jack_capture records as single precision floating point values by default,
and the "-b 16" argument to sox converts to 16 bit integer PCM.

What does sndfile-info show about t1w64.w64 and t2wav.wav files?  I tried
using sox to convert a float file I had in an Ardour project directory to
PCM, and sndfile-info reported the exact same maximum value for both.
Using the sox stat effect also displayed the same maximum and minimum for
original and converted file as well, but sndfile-info might give you some
insight into why sox did not seem to show the same value.

Chris Caudle

More information about the Linux-audio-user mailing list