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What are audio sampling signals?

  1. Jul 5, 2011 #1
    Does anyone know what audio sampling signals? Not Audio sampling but Audio sampling signals

    Thanks.
     
  2. jcsd
  3. Jul 5, 2011 #2
    Do you mean audio sampling or sampled audio?
     
  4. Jul 5, 2011 #3

    berkeman

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    Staff: Mentor

    Can you provide some context to your question? Where did you see this phrase? Can you provide a link?
     
  5. Jul 5, 2011 #4
    That's where the confusion is coming from. I figure it must mean sampled audio signals. Which is now my final assumption. So there is no such a thing as Audio sampling signals, do you think. I thought the words sounded not right because it's implying that signals are used to carry out the sampling.
     
  6. Jul 5, 2011 #5

    berkeman

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    Staff: Mentor

    Well, you could say that the Sample/Hold control signals are "audio sampling signals", right? I'd still like to read the original context...
     
  7. Jul 5, 2011 #6
    I think the OP refers to sampled sound as used in midi interfaces.
    If true, I clearly remember the famous mellotron, pioneered by Robert Fripp in King Crimson. Lenghts of audio tape had recorded sounds which were reproduced after a keystroke. Later on, systems became more complex but the idea stayed the same. Sounds produced by pianos, guitars, horns, etc are sampled, digitized and stored. I'm no expert in midi systems but I think they work on the same principle
     
  8. Jul 6, 2011 #7
    MIDI is the Musical Instruments Digital Interface and is a 7 bit control protocol running at 31.25 Kbits per second. It has nothing to do with audio sampling and merely tells a receiving device note on/off, note number, channel, key velocity, pressure (after touch), pitch bend, modulation, program change and system exclusive parameter changes.

    The mellotron was not pioneered by Robert Fripp; it is/was an instrument consisting of piano-like keys which trigger a tape loop each. Listen to Strawberry Fields by the Beatles (recorder recordings, confusingly) or Nights in White Satin by the Moody Blues (strings and female choir) or Phaedra by Tangerine Dream (more strings) to get a feel for it. Rough and gritty and lovely.

    Audio sampling is the process of recording audio as discrete time domain events. In the case of analogue sampling a BBD (bucket brigade device) is used. It is similar to the CCD in your camera and typically will have 512 capacitors in a row with the audio signal recorded as an instantaneous level at the sample-and-hold input and passed from one cap to its neighbour until it arrives at two outputs in turn, allowing for interpolation by yet another cap with a resistor (low pass filter) to give a reconstituted signal. Quite noisy, but with a distinctive sound - think 1980s indie jangly guitar chorus ( Cocteau Twins).

    Digital audio sampling (go and google Shannon, Nyquist) is the process of converting a signal into discrete numbers by use of an analogue to digital converter and then turning it back into an audio signal using a digital to analogue converter. The signal to noise ratio is governed by the resolution (number of bits) of the converters and a function of the sample rate, and the sample rate governs the bandwidth of the signal and also the signal to noise ratio.

    The Fairlight CMI was the first commercially successful digital audio workstation - a device which allows for sampled and synthesised audio to be sequenced as music.

    It's a big and beautiful subject and there is a lot of accurate material out there on the Interweb - use this post as a diving board.
     
    Last edited: Jul 6, 2011
  9. Jul 6, 2011 #8
    I agree 110% with Berkeman.

    We need more about the context to properly respond; all else is speculation.

    Here is another possibility.

    What is an audio sampling signal?

    It is the signal which tells the sampling circuitry when to sample. In effect it is the clock which issues the 'sample now' command at regular intervals and is also used to move the samples along the recording chain.

    go well
     
  10. Jul 6, 2011 #9
    I should perhaps add to my previous post.

    Sampling occurs at a fixed rate such as 44.1 kHz for video cameras, 48 kHz for CDs and 96 kHz for studio work. Edit see post 11


    So we refer to sampled audio as 44k, 48k or 96k (or some other). I think this signal is the most likely to be meant.
     
    Last edited: Jul 6, 2011
  11. Jul 6, 2011 #10

    cjl

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    Minor nitpick: CDs are at 44.1, DVDs (and I would assume digital video cameras) are at 48.
     
  12. Jul 6, 2011 #11
    You are quite right, that's the trouble with going from memory, especially a creaky one like mine.

    Thank you cjl.
     

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