Applies to: EUTs with analogue or digital inputs and analogue or digital outputs.
Aim: To measure the THD+N of the EUT against frequency.
Method
A -1dBFS sinusoidal stimulus is applied to the EUT, successively at each octave frequency between
20Hz and half the upper band-edge frequency. The output of the EUT is passed through a standard
notch filter at the frequency of the stimulus, and also through a low-pass filter at the upper band-edge
frequency (or at 20kHz, whichever is the lower). The RMS amplitude of the residual is measured for
each stimulus frequency.
The results are presented graphically, with THD+N (in % relative to the amplitude of the stimulus)
being plotted for each channel against stimulus frequency.
The test is then repeated with a stimulus amplitude of â€"20dBFS, the results being overlaid on the
original graph.
AES17 - THD+N vs Freq (-1dBFS).png
AES17 - THD+N vs Freq (-20dBFS).png