[alsa-devel] Usb audio - unsuported sampling rates

[Gordon Dilan]

Hello,

I'm using an usb mic which(according to it's producer should support up to
48kHz sampling rate). The problem is ALSA allows me to use only 16 kHz for
this device. I do not want to resample the data, I want to sample it at
48kHz in order to be able to record some high pitch sounds 18-20kHz.

I would want to try to do any modifications necessary in order to try
support 48kHz, but I'm not sure where to start.

Some information:

cat /proc/asound/modules
...
 1 snd_usb_audio

arecord --list-devices
**** List of CAPTURE Hardware Devices ****
....
card 1: CameraB409241 [USB Camera-B4.09.24.1], device 0: USB Audio [USB
Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0


when I try to use:  arecord -v -D hw:1,0 -f S16_LE -c 4 -r 48000 gigi.wav
I get this:

Recording WAVE 'gigi.wav' : Signed 16 bit Little Endian, Rate 48000 Hz,
Channels 4
Warning: rate is not accurate (requested = 48000Hz, got = 16000Hz)
         please, try the plug plugin
Hardware PCM card 1 'USB Camera-B4.09.24.1' device 0 subdevice 0
Its setup is:
  stream       : CAPTURE
  access       : RW_INTERLEAVED
  format       : S16_LE
  subformat    : STD
  channels     : 4
  rate         : 16000
  exact rate   : 16000 (16000/1)
  msbits       : 16
  buffer_size  : 8000
  period_size  : 2000
  period_time  : 125000
  tstamp_mode  : NONE
  period_step  : 1
  avail_min    : 2000
  period_event : 0
  start_threshold  : 1
  stop_threshold   : 8000
  silence_threshold: 0
  silence_size : 0
  boundary     : 2097152000
  appl_ptr     : 0
  hw_ptr       : 0


Any sampling rate I would try higher or lower than 16kHz, I will always get
16000 kHz.

Some more information:
lsusb
Bus 001 Device 007: ID 1415:2000 Nam Tai E&E Products Ltd. or OmniVision
Technologies, Inc. Sony Playstation Eye

lsusb -t

/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci_hcd/2p, 480M
    |__ Port 1: Dev 2, If 0, Class=hub, Driver=hub/6p, 480M
        |__ Port 2: Dev 7, If 0, Class=vend., Driver=ov534, 480M
        |__ Port 2: Dev 7, If 1, Class=audio, Driver=snd-usb-audio, 480M
        |__ Port 2: Dev 7, If 2, Class=audio, Driver=snd-usb-audio, 480M


At the moment I'm looking inside ALSA's source code to try to see from
where this limitation of 16000kHz for my device appears, but I have to
admit that I'm kind of lost.
Any pointers on what direction should I go to try make my desired rate
supported would be greatly appreciated!

Thank you and best regards,
Gordon