Distortion Measurement Description
Last updated: January 16, 2009
How is a Distortion measurement made?
Distortion is an audio quality measurement that compares the audio signal level from the mobile at a specified (desired) frequency to the level of signals present at other frequencies. The audio signals from the mobile are typically measured after digital demodulation of the traffic channel.
The test set makes two measurements to determine distortion. First, the test set measures the total audio signal level into the Audio Analyzer. Next, a precise notch filter is then used to remove the signal at the specified frequency. The remaining signal level indicates the level of unwanted signals (distortion). Distortion is expressed as a percentage of the total audio signal.
Distortion can be measured in the range of 100 Hz to 10 kHz. For information on using the Audio Analyzer, see
Audio Analyzer Measurement Description
.
The distortion measurement can be used to perform the audio harmonic distortion test. For example, in the AMPS system two audio signals are used: a 1004 Hz tone and the 6000 Hz SAT. The 1004 Hz tone is notched out to make the measurement.
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