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Theoretically Highest Quality of PCM Audio

Discussion in 'General Electronics' started by Radium, Nov 9, 2003.

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  1. Radium

    Radium Guest

    What is the theoretically highest possible:

    1. Frequency Response (range of frequencies)

    2. SNR

    3. Dynamic Range

    4. SPL

    5. Musical Pitch (highest acceptable frequency)

    of PCM audio?
  2. Dbowey

    Dbowey Guest

    what sampling rate do you have in mind?
  3. Based on what theory? Based on what PCM audio? Red Book? DVD-A?
    Some arbitrary, non-standard interconnect? The main system bus of a
    computer that processes said PCM audio?

    Since one can (and does) use PCM at all levels and scales of physical
    analysis (electron microscopy, earthquake analysis, radar, etc), then the
    limitations are going to come from what you define to be "audio", in the
    context of "PCM audio".

    Once you define your terms, the answers to all of your questions can be
    simply derived.
  4. Les Cargill

    Les Cargill Guest

    Google up "Shannon Theorem".
  5. Dick Pierce

    Dick Pierce Guest

    Sorry, but he DID define his terms. "PCM audio," meaning "pulse
    code modulation audio" is sufficiently unambiguous to answer
    his question. We don't have to know DVD, red book or anything

    The maximum bandwidth possible without the introduction of
    unwanted artifacts must be less than 1/2 the sampling rate.

    The two are equivalent when the signal is the maximum undistorted
    signal the medium can accept. In such a case, the dynamic range,
    as defined as the ratio between the smallest unmabiguously encodable
    sample measured over the bandwidth of the system and the maximum
    undistorted signal is approximately 6.02 dB per bit.

    Sorry, SPL is irrelevant, because it includes factors not relevant
    to the PCM process, such as amplifier gain, loudspeaker efficiency,
    distance from the speaker, and any other factors that has nothing
    to do with "PCM"

    Sorry, but this is a case where your use of the terminology is murky.
    "pitch" is defined as the psychoacoustic perception as it relates
    to the frequency of a tone. As to the highest possible frequency,
    assuming base-band usage, is simply less than 1/2 the sampling rate.
  6. Radium

    Radium Guest

    Sampling rate = 2(highest frequency)

    Bit resolution = dynamic range/2

    bytes per second = information per time

    The high sample rate and bit resolution the better the audio quality.

    The shortest amount of time is 10^-43 second. What is the maximum # of
    bits that can squeezed into this sml amt of time?
  7. He doesn't seem to have defined it well enough for you to give him a
    precise answer.
    Again, you appear to have to infer definitions, so perhaps the
    original poster was not precise enough.
    Peter J. Kootsookos

    "I will ignore all ideas for new works [..], the invention of which
    has reached its limits and for whose improvement I see no further

    - Julius Frontinus, c. AD 84
  8. There are no inherent limits, the current state of the art is 24/192.
    This gives theoretical limits of 141dB SNR, which is the same as
    dynamic range, and 0.0001Hz to 95kHz frequency response, with 95kHz of
    course being the upper limit.
  9. Dick Pierce

    Dick Pierce Guest

    Fine, you just answered your own question.
    Wrong. number of bits required to represent a dynamic range
    of x dB is about x/6.02.
    Not so, you just stated so yourself. Once you have exceeded the
    requirements for dynamic range and bandwidth, NO increease in
    sampling rate or bits will give you any better resolution.
    Are you REALLY serious or are you just a troll?
  10. Arny Krueger

    Arny Krueger Guest

    unlimited. You got the bits...
    unlimited. You got the bits...
    unlimited. You got the bits...
    unlimited but irrlevant. You got the bits...
  11. There is no theoretical limit.
    However there are different standards which specify the performance, and
    the different hardware limitations.

    The today's state of art in the pro audio is ~24kHz, ~120dB, ~0.0005%

    Vladimir Vassilevsky

    DSP and Mixed Signal Design Consultant
  12. Jerry Avins

    Jerry Avins Guest

    Unlimited frequency response just by adding bits? Surely not to the word
    length! One could argue that doubling the sample rate doubles the number
    of bits, but it doesn't seem you meant that.


  13. If I am given a 16-bit fixed-point number of uniform quantization, I
    can surely say that the maximum theoritic dynamic range I can get is
    96.329 dB (assuming a voltage ratio and an constant impedance). If I
    am told the sampling rate is a uniform 8 KHz, I can say that the
    maximum unaliased frequency I can derive is theoritically, less than 4
    KHz. Rather than say there is no therotical limit, let's just say we
    don't have enough information to determine the limit.

    Maurice Givens
  14. Nope. If you are given even a 1-bit quantization, you can have any
    dynamic range by multiple oversampling. If the sample rate is 8 kHz, you
    can have multiple channels combined into one stream of any bandwidth.
    Vladimir Vassilevsky

    DSP and Mixed Signal Design Consultant
  15. Dbowey

    Dbowey Guest

    Vlad posted:
    So get real. That isn't what is being discussed.
  16. malcolm

    malcolm Guest

    wont the noise start adding up as well and ruin the SNR !
  17. Not if you declare your 8kHz system to have infinite (or at
    least arbitrarily large) SNR (by making the number of bits per
    sample arbitrarily large).
  18. Not if you shape it so that most of it is outside the audio band.
    That's how SACD works, and indeed it has very poor dynamic range above
  19. Arny Krueger

    Arny Krueger Guest

    It's exactly what I meant.
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