Re: System audio recording have very low amplitude

[Jeremy Nicoll - ml sox users <jn.ml.sxu.88@wingsandbeaks.org.uk>]

On 2020-07-29 10:39, Ariel Elkin wrote:
> Hello,
> 
> I’m using sox to record the audio produced by the system (i.e. from
> the OS and other running apps), but the recordings sound very quiet.
> 
> I first create a virtual input/output device using Blackhole
> (https://github.com/ExistentialAudio/BlackHole/
> <https://github.com/ExistentialAudio/BlackHole/>) or Loopback
> (https://rogueamoeba.com/loopback/
> <https://rogueamoeba.com/loopback/>). I then start playback of a file
> using iTunes, and start recording thus:
> 
> rec --rate 44100 --channels 2 --no dither test-output.aiff
> 
> (Note that this spits out the following error messages:
> rec WARN formats: can't set sample rate 44100; using 48000
> rec WARN formats: can't set 2 channels; using 16
> 
> However, test-output.aiff ends up being a stereo file at 44.1 kHz)
> 
> test-output.aiff properly records system audio, but the mean amplitude
> is about half the mean amplitude of the original sounds I played back.


What OS are you using?  (I see from those links that the apps are MacOS,
which I know nothing about.  Someone else might do; also what version?)

Does MacOS have an internal audio mixer that determines the levels of 
sound
from various apps and how they go to other devices?  There's certainly 
one
of those in Windows - so eg if I was going to record audio streamed via 
the
BBC's iPlayer and Firefox, I'd start by temporarily turning off the 
other
sources of sound that could get in the way (eg the various tones Windows
error-message boxes will play, eg when it insists on telling me that 
when
I rename a file it may not work properly in future...). I've found out 
that
the hard way, as it's ruined some recordings.


-- 
Jeremy Nicoll - my opinions are my own


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