[LAU] comparing audio recordings on the command-line?

Fons Adriaensen fons at linuxaudio.org
Tue Sep 17 13:43:17 UTC 2013

On Tue, Sep 17, 2013 at 12:46:06PM +0200, Jörn Nettingsmeier wrote:

> On 09/17/2013 04:37 AM, Eric Wong wrote:
> >Hi, I'd like to compare recording quality of portable recorders.
> >I only care about the line-in input of these portable recorders.
> a look at the impulse reponse will reveal distortion, and a look at
> the raw sine sweep will give you a pretty good idea of the amplitude
> response over frequency.
> then there's "jnoisemeter", also by fons, which can give you a
> pretty good measurement of the noise floor.

The primary tools to measure an A/D or D/A (that's what it amounts
to, the rest just be pretty transparent in any recorder) are jaaa
and jnoisemeter. Both were explicitly designed for the job.

> but all these measurements either rely on reference gear to produce
> the test signals, or _very_ careful thinking if the test signals
> might are already laden with their own problems.

I you have a good quality audio card it is perfectly possible to 
use this as a signal source. First measure it separately, so you
have an idea of the limits of what you can do using it. For some
measurements you also need to calibrate it using a true RMS audio
voltmeter which you can beg, steal or borrow.

You may need some simple HW: passive attenuators (three resistors),
and plugs or test cables to short-circuit inputs. For the rest you
need to perfectly understand *what* you try to measure, and have
a very systematic approach to doing it.
> there's an old saying in german which unfortunately doesn't
> translate well: "wer viel misst, misst mist.", literally, "s/he who
> measures a lot, will measure dung" (as in, will obtain false or
> misleading results).

99% percent of false results are due tp lack of understanding, and
failing to verify basic things such as levels.



A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)

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