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Soundcard sample rates

Discussion in 'Electronic Design' started by Robert Scott, Nov 11, 2008.

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  1. Robert Scott

    Robert Scott Guest

    Soundcard sample rates may not be what they claim.

    I have been testing different brands of PC soundcards. 44100 and 22050 are two
    of the standard sample rates that most soundcards support. Of course all sample
    rates are only as accurate as the crystal oscillator on the soundcard, so when I
    found several soundcards with a 22050 sample rate that was high by 0.6%, I
    chalked it up to poor crystal accuracy, or maybe ceramic resonators. But then I
    checked the 44100 sample rate on those cards and found it to be right on. I was
    puzzled as to why the 44100 sample rate was not exactly double the 22050 sample
    rate. When I made more careful measurements, it appeared that the 22050 sample
    rates were really trying for 22200, which is a less common standard.

    Does anyone know why they might do that (and not tell anyone!)

    By the way, the soundcard sample rates were all tested by writing a custom
    program to generate an audio tone of a certain frequency based on the assumption
    that the sample rate was the nominal rate requested. The the audio frequencies
    were measured with NIST-traceable means.


    Robert Scott
    Ypsilanti, Michigan
     
  2. Robert Scott

    Robert Scott Guest

    On some soundcards the 44100 and 22050 are exactly in a 2:1 ratio. But a few
    other soundcards are definitely more like 44100 and 22200. No, I did not try
    11025. And yes, I was very careful about the measurements.


    Robert Scott
    Ypsilanti, Michigan
     
  3. If you have requested the sample rate which is not directly supported by
    the sound card hardware, the Win32 API will do the resampling to the
    supported rate automatically, without any obvious indication. The
    integrated sound chipsets typically support for 44.1kHz in hardware; all
    other rates are actually made by the software resampling. Perhaps what
    you see is related to the resampling artifacts for your particular
    hardware/software combination.


    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
    http://www.abvolt.com
     
  4. Ben Bradley

    Ben Bradley Guest

    Not sure if this is the cause of or a similar thing to your
    observation, but the Creative/Soundblaster/SBLive!/Audigy line has had
    at least one lawsuit concerning false claims the company has made
    about the products (that a certain model does 24 bits when in most
    situations it doesn't). Also, many or most of their models have some
    hardware sample-rate-coverter that changes whatever sample rate you're
    using (usually 44.1k) to 48k to do whatever processing it does (volume
    control/mixing?) and then back to 44.1k to go to the computer bus or
    to the D/A or wherever. Bizarre but true.

    Why are you doing this? Do you want to find a good soundcard? If
    so, don't go with any of the "consumer" cards that come with computers
    or on PC motherboards. They're all quite crappy compared to what you
    can get for a few more dollars. Get at least the "semipro" type - the
    minimum would be the Audiophile 2496 (and old but good product, I've
    had one for many years) here:
    http://www.m-audio.com/index.php?do=products.family&ID=PCIinterfaces

    Here's a 'legacy' site (it's been around a long time and I don't
    know when the last time the author updated it) with lots of soundcard
    test data, both consumer and semipro/pro:
    http://pcavtech.com/
     
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