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Total Harmonic Distortion Analysis

Real world audio devices introduce distortion in addition to the desired response.  Total Harmonic Distortion (THD) is a measure of this quantity.

THD is the ratio of the harmonic power to the fundamental power.  It is expressed as a percentage.  The lower the THD value, the "cleaner" the response.  A typical THD measurement will use a 1kHz reference test tone.  This reference signal is passed through the audio device under test,and its THD computed from the spectrum

Key Settings: 
Mode:    Real-Time
Views: Spectrum,   Time Series
Amplitude axis:   Logarithmic
Frequency axis:   Linear
Standard Weighting:  Flat
Mic compensation:    None
Sampling rate:   44100Hz
FFT size:    8192
Decimation:   1
Averaging size:   10
Smoothing Window:  Hanning
Sampling Format:  16 bit, Mono

Procedure:
  • Connect a 1kHz test tone to the imput of the device under test.
  • Connect the output of the device under test to the input of your sound card.
  • Run the analyzer for sufficient time to allow the spectrum response to settle.
  • Select <Total Harmonic Distortion> under the <Utilities> menu item.