ETF and 1/2 duplex laptop problem solved?

Discussion in 'Archived Threads 2001-2004' started by ThomasW, Jan 10, 2002.

  1. ThomasW

    ThomasW Cinematographer

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  2. BruceD

    BruceD Screenwriter

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    Actually, for all half-duplex soundcards (many notebooks), all you need to do is download the "CD test signal" image file on the ETF website and then burn a CD.

    Best of all its FREE.

    Then use this burned CD as a source signal from the CD player for the microphone to use as an input signal to ETF.
     
  3. ThomasW

    ThomasW Cinematographer

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    Bruce

    It takes a full duplex setup to make mls measurements. Since most laptops don't have full duplex audio, the little device from Blaster solves the problem.

    The free CD from ETF works for everything but mls measurements
     
  4. BruceD

    BruceD Screenwriter

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    Thomas,

    I haven't tried it yet as I have a full-duplex soundcard in my laptop, but this issue is specifically discussed on the ETF website.

    Their recommendation for half-duplex operation of the ETF mls system is to use mls test signals on a CD. They provide the CD image of the mls signals for download.

    Did I miss something? Is the CD image not mls signals? As I said I haven't tried the CD yet, but I did download the CD image file.
     
  5. ThomasW

    ThomasW Cinematographer

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    Bruce

    I'm a tad confused about this myself. I bought the program earlier in the week, but haven't had time to play with it since we're building a couple of subs....

    The CD contains approx 12 min of 19Khz test signal and approx 12 min of what sounds like pink noise.

    I'd be delighted if the CD were the only thing needed.
     
  6. BruceD

    BruceD Screenwriter

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    It appears from this blurb about CD use on the first page that the CD may be all you need.
    CD use
    I know when I've used the program in full-duplex mode, the mls test signals produced by the software sound just like pink noise to me.
    Hopefully I will have time to try it out this weekend.
     
  7. BruceD

    BruceD Screenwriter

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    Please see the help menu in the ETF program for an exact step by step walk-thru including diagrams of cable setups and example windows

    Here is a brief part of it:

    CD player (Left LINE-OUT) -> stereo Y connector on PC (LINE-IN)

    try both left and right connections on the Y connector to see which one works.

    1) Select "New Measurement" , then "Normal Transfer Function"

    2) Check the text box labeled "Test CD"

    3) Play the test signal on the CD player

    4) the PC audio mixer may need to be set to the sound card for correct input

    5) Click level check to see if the input is strong enough

    6) repeat level check while CD track 1 "MLS signal" is playing on the CD and adjust levels with mixer if necessary

    7) when levels are properly set, the calibartion window will show a new instruction

    . . . . . . .

    Also, the Radio Shack SPL meter mic-correction files typically don't work with the free version of the ETF5 program.

    I haven't tested the CD half-duplex method of using the software, but hope to try it out this weekend and report back.
     
  8. ThomasW

    ThomasW Cinematographer

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    Bruce

    Yup that's how to use the CD but.....

    True mls measurements are made with a very short duration shaped tone burst that's measured in real time. This eliminates room interaction. Using the CD playing continuously won't be accurate because of the room interaction with the speaker.

    If someone needs to low-ball their measuring, then the CD is better than nothing. But the little device from Sound Blaster will allow full duplex from a 1/2 duplex soundcard.
     
  9. BruceD

    BruceD Screenwriter

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    Agreed, you actually don't use the CD continuously when taking measurements, just play track 1 (like the software generated signal it's probably just multiple 10 second bursts).

    You can also adjust the windowing of the FFT analysis to control the time element of the impulse response curve you're evaluating, so this shouldn't really be an issue.

    I still have to burn the CD and try it.
     
  10. Pete Mazz

    Pete Mazz Supporting Actor

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    That CL unit looks nice! I would think it would also have a much better S/N ratio since it's external.

    Pete
     

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