ETF measurement with Laptop

Discussion in 'Archived Threads 2001-2004' started by Ranga, Mar 4, 2002.

  1. Ranga

    Ranga Stunt Coordinator

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    I am using a Dell Latitude CPi-A laptop with ETF 5.0 demo software and I am not sure if I have the correct connections setup to measure the frequency response. The laptop does have a full-duplex sound card.
    I used two Radio Shack Adapters (274-369), one connected to the LINE-OUT (the headphone jack) and the other to the LINE-OUT/Audio-in jack. Now the connections -
    LINE-OUT jack (Laptop)->BFD 1124's input 1
    BFD 1124 output 1 -> sub-amp line-in
    LINE-OUT/Audio-in (Laptop)-> Ratshack Meter
    LINE-OUT (Laptop) -> LINE-OUT/Audio-in (Laptop) [For sound card calibration).
    In the Mixer, I have set all other playback devices to Mute except the Wave out and selected the LINE-IN in the Recording device setup. However, there is no option to Mute the MIC IN.
    With this setup, the level check shows different values for the Microphone input (-30db) and Soundcard input (-6db). I could not get them set to the same level.
    I then tried the MIC-IN jack on the laptop connected to the Ratshack Meter. Mixer's recording setup was changed to use the MIC-IN jack. With this, both channels were set to -1db. With this setup, when I ran a test measurement, the graph showed a straight line at 100db (almost off the scale).
    Checked ETF documentation which recommends that I remove the LINE-OUT->LINE-OUT/Audio-in connection on the laptop. A level check indicated -39db on the Microphone input channel and -34db on the Soundcard input channel. The 2 test measurements give me these graphs -
    [​IMG]
    This doesn't look anything like what I measured manually -
    [​IMG]
    I did read a post that the connection to the laptop should be to the line-in and NOT the Mic-in. But I could not get the levels set to the same db on both channels.
    Would the line-in be equivalent to the Audio-in on my laptop (the jack is described as a record/playback jack?
    Any other suggestions?
    Ranga
     
  2. Ranga

    Ranga Stunt Coordinator

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    Another question -

    I know it is important to set the volume levels for the playback and recording mixer. Are there are any general recommendations?

    Ranga
     
  3. Matt Barrett

    Matt Barrett Extra

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    Ranga,

    The problem may be that your computer does not have a full duplex sound card?

    The reason the mic input is not used is that it is generally a mono input, thus no feedback loop for sound card correction can be used.

    Using the recording control of the mixer panel, you should have line in selected, the reason mic cannot be “muted” is that there can only be one recording device selected at any time, unlike playback where you can have many at one.

    You should be able to get the levels to around –4 or so without much trouble if everything is working OK, did you do a direct loopback test (R->R and L->L)to see if you can get good levels without the BFD and subwoofer in the picture?
     
  4. Ranga

    Ranga Stunt Coordinator

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    I did confirm that the sound card is full duplex. I did a loopback test and the levels match. However, in loopback mode, when I run the test, I get a straight line graph -
    [​IMG]
    The LINE-IN is muted in the playback mixer.
    Ranga
     
  5. Mike Matheson

    Mike Matheson Second Unit

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    Ranga,

    On the "Record/Play Test Signal", when click on the Mixer button, see if the there is a "Properties" command under the Options menu. Try marking "Recording", note what volume controls will be shown, and try playing around with the levels after you OK out.

    I had a similar problem to what you're describing and realized I hadn't adjusted the "Recording" side of things--only "Playback".

    Hope this helps,

    Mike
     
  6. Ranga

    Ranga Stunt Coordinator

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    Matt

     
  7. Mike Matheson

    Mike Matheson Second Unit

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    Ranga,

    I hope I'm not misunderstanding you again (re-read your post and realized you'd mentioned you HAD set the recording, not just the playback, part of things)--yes, if by "during the measurements" you mean actual testing of the sub you need the RS SPL meter turned ON, and at least on my meter (digital), I needed to set it to the appropriate range (100db) to get readings in the OK range. If the meter's not on you'll still get a graph but it will be fairly flat with a couple small bumps--not at all like a typical sub's in-room response.

    M
     
  8. Matt Barrett

    Matt Barrett Extra

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    I just wanted to back up Mikes statement, the RS meter must be ON to activate it’s internal mic preamp and send a signal out.

    I have the digital meter and I use the 80dB range, then tweak the levels in the mixers to get –4 or so in the “level” windows.

    Lest us know how it goes.
     

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