How to use microphone calibration file

[Pander <pander@users.sourceforge.net>]

Hi all,

I have an UMIK-1 (a calibrated USB microphone) and use rec from sox for
recording. I use a Raspberry Pi and try to get the most out of it in
terms of quality. I am using the following commands:

  export AUDIODEV=hw:1,0
  export AUDIODRIVER=alsa
  rec -q -r 48000 -c 1 -b 24 --buffer 16384 test.wav trim 0 300

1) Should I worry about the following message?

  rec WARN formats: can't set 1 channels; using 2

because the recording results in

  file test.wav
  test.wav: RIFF (little-endian) data, WAVE audio, mono 48000 Hz

and Audacity reports

  Mono, 96000Hz
  32-bit float

2) I doubled the buffer size but sometimes I get

  rec WARN alsa: over-run

but that seems to be independent of the doubling of the buffer size and
only occurs on start up. What is smart to do here?

3) How do I use the microphone calibration file? I can download it from

  http://www.minidsp.com/products/acoustic-measurement/umik-1

and looks like

  Sens Factor =.27710dB, SERNO: 7007***
  10.054	-5.3961
  10.179	-5.2292
  10.306	-5.0655
  ...
  19527.604	-0.7159
  19770.697	-0.7462
  20016.816	-0.7772

A simple line plot of the entire files reveals as

  https://i.imgur.com/ISO0WHh.png

4) Are there more ways to optimise recording in this way?

5) As next step, I am using this command to create a spectrogram

  sox test.wav -n remix - rate .25k spectrogram -x 1776 -y 512 -c 125Hz

Could the latter command also be optimised or should calibration
correction take place here?

6) When calibration is used, does the spectrogram reflect dB properly or
is more processing needed?

Thanks,

Pander

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