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Couple of questions:

  1. If you set the capture sampling rate in ALSA API to say 1000Hz, is the input really sampled at 1000Hz, or does the sound card always sample at its maximum capable sampling rate, removing unwanted samples and returning a PCM stream at the required sample rate?

  2. Is there a variable bandwidth (with bandwidth determined by ALSA sample rate) anti-aliasing filter present on the sound card input, or should I put an anti-aliasing filter in the analog audio before providing it to sound card input?

1 Answer 1

1
  1. ALSA configures the sound card for the nearest supported sample rate.

    Which sample rates a sound card supports depends on the hardware.

  2. Anti-aliasing filters depend on the hardware.

2
  • Is there a way to query HW whether anti-aliasing filter is present ?
    – Jean
    Sep 11, 2014 at 17:10
  • 1
    Nothing but a datasheet, if you're lucky.
    – CL.
    Sep 11, 2014 at 17:35

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