Re: [SoX-users] Confused about SOX and ALSA

[Jan S. <ha...@st...>]

On Dec 11 17:57:21, pf...@fa... wrote:
> I have a high sample rate (250 khz) USB microphone.

May I ask what kind of microphone this is exactly,
and what ultrasounds you plan to record with it?

> I've tried to record from it using matlab, audacity and the command tool
> arecord. However, to no avail. All these tools return the same error:
> the sample rate is wrong.

I'm afraid this has nothing to do with SoX.
Ask on _their_ mailing lists.

But I wouldn't be surprised if a recording tool refused
to record at 250 kHz. It is also possible that it's SoX
doing the resampling for you - on my old MacBook
(which surely cannot record at 250000 Hz), I get

  $ rec -r 250000 file.wav
  fCoreAudioDriverUID AppleHDAEngineInput:1
  rec WARN formats: can't set sample rate 250000; using 44100
  
  Input File     : 'default' (coreaudio)
  Channels       : 2
  Sample Rate    : 44100
  Precision      : 32-bit
  Sample Encoding: 32-bit Signed Integer PCM

  In:0.00% 00:00:01.70 [00:00:00.00] Out:413kk [    |    ]    Clip:0   ^C
  Aborted.

  $ soxi file.wav
  
  Input File     : 'file.wav'
  Channels       : 2
  Sample Rate    : 250000
  Precision      : 32-bit
  Duration       : 00:00:01.65 = 412896 samples ~ 123.869 CDDA sectors
  File Size      : 3.30M
  Bit Rate       : 16.0M
  Sample Encoding: 32-bit Signed Integer PCM


> However, using sox, I can record without problems. Generating a
> spectrogram from sound with a known frequency confirms that the sample
> rate is indeed 250khz - also the files contain (give or take some
> samples) the correct number of samples.

You don't a spectrogram for that, plain old soxi(1) will tell you.
Also, the sample rate has nothing to do with the "known frequency"
of the sound you are recording.

> So, my question is, why can i record using sox
> but not any of the other tools.

Ask _them_.

> In case it helps, I have attached the sox output below.

You also need to attach the command line you used.

> ----------------
> rec:      SoX v14.4.1
> 
> Input File     : 'hw:2,0' (alsa)
> Channels       : 1
> Sample Rate    : 250000

Hm, this looks like the device _is_ actually set to 250000.
In the example above, the devie is actually set to 44100,
and it's SoX resampling for me (to 250000).

	Jan

> Precision      : 16-bit
> Sample Encoding: 16-bit Signed Integer PCM
> Endian Type    : little
> Reverse Nibbles: no
> Reverse Bits   : no
> 
> rec INFO sox: Overwriting `test.wav'
> 
> Output File    : 'test.wav'
> Channels       : 1
> Sample Rate    : 250000
> Precision      : 16-bit
> Sample Encoding: 16-bit Signed Integer PCM
> Endian Type    : little
> Reverse Nibbles: no
> Reverse Bits   : no
> Comment        : 'Processed by SoX'
> 
> rec INFO channels: has no effect in this configuration
> rec INFO sox: effects chain: input       250000Hz  1 channels
> rec INFO sox: effects chain: highpass    250000Hz  1 channels
> rec INFO sox: effects chain: vol         250000Hz  1 channels
> rec INFO sox: effects chain: spectrogram  250000Hz  1 channels
> rec INFO sox: effects chain: dither      250000Hz  1 channels
> rec INFO sox: effects chain: output      250000Hz  1 channels
> In:0.00% 00:00:04.33 [00:00:00.00] Out:1.07M [      |      ]       
> Clip:0    ^C
> Aborted.