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PCM and Non-PCM audio RRS feed

  • Question

  • Can Microsoft explain how they define the terms PCM and Non-PCM in your docs. Is Non-PCM simply compressed audio and PCM non compressed? If so that would mean that a wav file having 32 bit float data is PCM?
    Friday, February 22, 2019 12:49 AM

All replies

  • WAVE_FORMAT_PCM and WAVE_FORMAT_EXTENSIBLE/KSDATAFORMAT_SUBTYPE_PCM both mean "uncompressed data in integer format." WAVE_FORMAT_IEEE_FLOAT and WAVE_FORMAT_EXTENSIBLE/KSDATAFORMAT_SUBTYPE_IEEE_FLOAT both mean "uncompressed data in floating-point format."

    If you have a question about a particular doc, please provide a link to the doc in question.


    Matthew van Eerde

    Friday, February 22, 2019 5:25 PM
    Moderator
  • https://docs.microsoft.com/en-us/windows-hardware/drivers/audio/background-of-non-pcm-support

    It is implied in Microsoft docs that all audio data can be split into two types: PCM and non-PCM. I have  never seen a clear definition of what it means. I understand that plain uncompressed ineger samples is PCM and also compressed integer such as ADPCM. Beyond that it gets a bit fuzzy. I'm assuming Microsoft have a clear definition that is used in documentation.

    Is this a case where there is no actual definition in practice?

    Friday, February 22, 2019 6:55 PM
  • That documentation is from Windows XP and is obsolete.

    ADPCM and LPCM are both forms of compression, so they would not full under any reasonable definition of "PCM."


    Matthew van Eerde

    Friday, February 22, 2019 6:57 PM
    Moderator
  • The library of congress told me that it's PCM https://www.loc.gov/preservation/digital/formats/fdd/fdd000016.shtml

    I just want the definition that Microsoft are using so that I'm clear about it.

    Saturday, February 23, 2019 12:23 AM
  • > I just want the definition that Microsoft are using

    We use different definitions in different places, depending on whether the distinction between integer and floating-point or between compressed and uncompressed is more important.


    Matthew van Eerde

    Saturday, February 23, 2019 12:42 AM
    Moderator