[LAU] Record levels lower in Alsa than Jack

[Fons Adriaensen]

On Thu, Nov 05, 2020 at 09:06:19PM +0000, John Murphy wrote:

> Wondering if there's a command line (scriptable) recorder for Jack
> which will record for a configurable duration. Because:
> 
> I've been using Jack TimeMachine to record in its default 'w64' format
> and then converting to wav with sox like:
> 
> sox --no-clobber -S tm-2020-10-27T22:00:15.w64 -b 16 /home/john/2710.wav
> 
> It all works well and sox stat shows min and max amplitude -0.9 and 0.9
> 
> I need to make the recordings automatic and arecord seems to fit the bill
> with its ability to record for a number of seconds with -d, but the level
> seems much lower. I used PulseAudio Volume Control to get something like
> a good level with 150% on the input sliders (10.53dB) and I still only
> see around -0.5 and 0.5 using sox stat. They only go up to 11dB.

First advice: get rid of PA and its braindead controls. If you disable
PA when using Jack, do the same when using arecord.

Then recording using arecord or jack with the ALSA backend (using the
same sound card in both cases of course) should give the same result.
In both cases that will depend on the alsamixer settings if there any
for your sound card. 

The difference between +/-0.9 and +/-0.5 is actually quite small (less
than 6 dB). It doesn't tell you anything unless you can ensure you 
recorded exactly the same signal in both cases. Normal audio signals
(speech, music,...) have level variations that are much bigger than 
6 dB.

Ciao,

-- 
FA