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Input electronic signal to sound card input ?

Discussion in 'Electronic Design' started by boki, Oct 14, 2004.

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  1. boki

    boki Guest

    Dear All,
    I want to implement a simple A/D conversion by PC sound card
    input channel(Line in / MIC in), therefore I can employ it as a high
    resolution A/D processor :D ?

    What is the limit/problem in hardware?

    Thank you very much for your comments.

    Best regards,
  2. Rolavine

    Rolavine Guest

    From: (boki)
    The net must be filled with informtaion about doing this, have you looked?

    If you use the mic input it prob. has a dc voltage on it to power an electret
    mic, so line in is a better choice. Either way the input with be ac coupled by
    a series cap on the card. The line in should be good for about 300 mv rms input
    (100mv is normal preamp out in hi fi). Any cheap card in a pc is noisy so you
    prob. won't get as high a usable resolution as you might suspect. There are
    some scope programs for PC's that use the sound card you should find one and
    check it out to see the limits of this input.

    Here is a link to a free sound card scope program on on the net,
    I never used it

  3. Iwo Mergler

    Iwo Mergler Guest

    The soundcard input is a high pass at a few tens of
    Hz. It doesn't work at DC and badly at low frequencies

    It's not as high resolution as you may think. 16 bit
    is not really achievable inside a PC and most soundcards
    are not even close, anything below the first 12 bits or
    so is random numbers.

    Otherwise it's possible and done quite regularily.

  4. Spajky

    Spajky Guest

    could be (if you can record music on pc, why not!)

    max usable frequency response 20Hz-20KHz /around 95dB noise signal
    ratio max for cheaper models like mine Ensonic AudioPci128 .... on
    line input (150mV/47k); conversion 16-bit, 44,1kHz sampling ...
    Mic input is Mono & in the midle ring on the stereo 3mm jack is that
    phantom power; when used an ordinary mono jack, it shorts that, so on
    the hot (input) you do not have any DC current!

    not sure for line in ... (for Mic in for sure!)
    on mine there is at 19kHz -3dB drop which drastically increases
    reaching frequencies above 20kHz; on the other hand there at low end
    is same with drop @ 25Hz, but drop increases much much slower & you
    can handle 10Hz @ -10dB drop & becomes unuseable lower than 5Hz!
    this I regularly use to make snapshots for my site´s electronics
    articles .... for pics there I used for cards input only a resistors
    voltage divider (trimmer pot.) ...

    since I have an audio Led VU meter connected to my audio card & is
    calibrated (has worse frequency ratio than the audio card), I could
    approx. calculate signal drop at frequencies I stated for that audio

    Hope I helped ...
  5. David Jordan

    David Jordan Guest

    It's maybe not as bad as you think... I tried an experiment a while
    ago. Audition lets you zoom in on the amplitude scale and take very
    accurate measurements of the signal level. I set a signal generator so
    Audition read -6dB at 1kHz and swept the frequency while monitoring
    the sig gen voltage with a 'scope to make sure it didn't change.

    The table below is a listing of amplitude error (in dB) vs. frequency.
    The two left hand columns are for a 'Soundblaster Live Platinum 5.1'
    and the two right hand columns are for a Soundblaster USB widget I got
    for about 30ukp.

    Freq Right Left Right Left
    10 -0.13 -0.13 -1.88 -1.88
    20 -0.09 -0.09 -0.57 -0.58
    40 -0.08 -0.08 -0.18 -0.18
    70 -0.04 -0.04 -0.05 -0.06
    100 +0.00 -0.01 +0.0 +0.0
    200 +0.00 +0.01 +0.04 +0.04
    400 +0.00 -0.01 +0.02 +0.01
    700 +0.00 +0.00 +0.01 +0.01
    1000 +0.00 +0.00 +0.0 +0.0
    2000 -0.03 -0.02 -0.04 -0.04
    3000 -0.09 -0.09 -0.06 -0.06
    4000 -0.08 -0.08 -0.01 +0.0
    5000 +0.02 +0.02 +0.02 +0.03
    6000 +0.07 +0.07 -0.03 -0.01
    7000 +0.08 +0.08 -0.08 -0.06
    8000 -0.04 -0.04 -0.08 -0.05
    9000 -0.10 -0.10 -0.02 +0.01
    10000 -0.13 -0.13 -0.01 +0.03
    12000 -0.01 -0.02 -0.12 -0.07
    14000 +0.02 +0.01 -0.07 -0.02
    16000 -0.11 -0.11 -0.20 -0.15
    18000 -0.04 -0.05 -0.27 -0.24
    20000 -0.54 -0.54 -0.92 -0.92
    21000 -1.44 -1.59 -2.20 -2.20
    22000 -3.8 -4.0 -8.60 -5.40
    23000 -13.0 -9.0 -16.0 -12.5
    24000 -23.0 -22.0 -24.0 -24.0

    That looks pretty good to me! Notice the VERY sharp antialias filter
    that starts at 20kHz.
    This is true, I can see around 3 bits worth of noise - around 120uV. I
    wonder about the 24bit Audigy devices, the are external so it would be
    possible to get the noise down very low. I would hope to see >16bits
    of resolution from one of these. They also sample at 192kHz but I
    don't know if you still get the full 24bits of resolution at that

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