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Use OmniMic to measure frequency response of amplifier?

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  • Use OmniMic to measure frequency response of amplifier?

    Is there any way to get the OmniMic software to "see" the line-in ADC of my E-Mu 0204 USB "sound card?"

    I want to measure the frequency response of electronics like preamps, amplifiers, etc.

  • #2
    Re: Use OmniMic to measure frequency response of amplifier?

    You don't need a microphone to measure volts. You need a full-duplex soundcard. Most comoputers have those these days. Then you need is some software. The software generates a sine sweep from your soundcard output. Plug the output to your "device under test" (DUT). Plug the output of the DUT to the input of the soundcard and record. It would also be appropriate to do a loopback test on the soundard in order to remove the soundcard's effect on the measurement.

    This will work pretty well for a lot of things like ADC's, preamps. Depending on the soundcard, you may be limited to about 900mV input voltage, or more. So for the high voltage output of the amplifier, you can use a voltage divider to do some simple math like "divide by 10", "divide by 100", etc to bring the voltage down to something your soundcard can accept. To more accurately measure an amp, you want a big 8 or 4 ohm resistor connected to simulate the speaker load, or a speaker connected.
    I'm not deaf, I'm just not listening!

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    • #3
      Re: Use OmniMic to measure frequency response of amplifier?

      The OmniMic software and hardware are designed as an integrated system. The OmniMic software does not receive input from any device other than the OmniMic microphone itself.

      In the industry, usually a more complex, expensive system like the Audio Precision (AP) or CLIO system is used for measuring amplifiers, and they provide automated test processes to do that. However, any USB audio interface box can be adapted to measure an amplifier directly, through use of a voltage dividing network, but that network usually needs to be designed for the application, and a dummy load is still required.

      Investigate "RightMark Audio Analyzer" (RMAA) software for performing this testing. RMAA is designed to perform distortion, frequency response, crosstalk, and other measurements on PC sound cards, but in conjunction with the appropriate voltage divider network between the amplifier outputs and the sound card inputs, you can add the amplifier to that signal chain. RMAA will actually perform the analysis and spit out numbers for THD+N%, crosstalk level, IMD+N%, etc.
      Best Regards,

      Rory Buszka
      Product Manager, Dayton Audio

      The best way to predict the future is to create it.

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