Calibrating the Soundcard

Once the audio input and output have been selected (or left as default if using the default OS settings) REW is ready to make a calibration measurement of the soundcard's frequency response. This will be used to remove the soundcard's response from room measurements.

Making the Soundcard Calibration Measurement

  1. Connect the soundcard's line output directly to its line input - use the channel that will be used to make system measurements, which should be the same one that has been selected in the Input Channel control.
  2. Press the Measure... button on the Soundcard Settings panel and follow the instructions in the help panel
  3. The measurement result should be fairly flat but will probably roll off at the lowest and highest frequencies and will often have some ripple at the high end. This measurement is from a laptop's internal card which rolls off fairly rapidly below 20Hz (graph vertical scale is 1dB/division):
    Laptop soundcard measurement 1dB/div

    This is a measurement from another laptop soundcard, showing better low frequency response and a smoother high frequency response:
    Laptop soundcard measurement 1dB/div


  4. Some results from the measurement are shown in the measurement notes:
    Laptop soundcard measurement results

  5. If the measurement looks like this:
    Bad soundcard calibration result

    it is probably due to a feedback loop from the Line In to the output. This can happen if the soundcard has some feature for record monitoring - for example, on the Soundblaster Live 24-bit External there is a "Monitor" feature for the Line In that must be turned off to get correct results, on some other Creative soundcards (e.g. Audigy 2 ZS) there is a Record Advanced Controls setting for "Record without monitoring" that must be selected.
  6. Having obtained a measurement it needs to be saved as a calibration file. Press the Make Cal... button in the Soundcard Settings and choose a name and location for the file. The file is saved and then automatically re-loaded as a calibration file to use for all subsequent measurements. On the next startup the file will be loaded automatically with a confirmation message like this one:
    Soundcard Cal confirmation message

  7. To check that the calibration has been successful:
  8. Remove the loopback connection and connect the soundcard to the SPL meter and AV processor/equaliser

Note that soundcard measurements made from the Soundcard Settings panel use the full sweep range to half the soundcard sample rate, regardless of the sweep end frequency setting, and the soundcard calibration file is NOT applied to such soundcard measurements

Note also that the soundcard calibration file is only valid for the sample rate at which it was measured, if the sample rate is changed the soundcard should be re-measured at the new sample rate

Setup information and example measurements for the Creative Soundblaster Live! 24-bit USB External soundcard can be found here.

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