Chapter 5 303
Concepts
Audio Measurement Concepts
Audio Distortion Measurement Concepts
Purpose
Audio Distortion measures the amount of Audio distortion contained in the Audio
signal by determining the ratio of harmonic and noise power to fundamental
power.
Measurement Technique
Audio Distortion is defined as:
Equation 5-5
where: P
total
= the power of the total signal,
P
signal
= the power of the wanted audio signal, and
P
total
− P
signal
= total unwanted signal which includes harmonic distortion and
noise.
See Figure 5-12 on page 302. First, the received Audio signal is filtered to remove
DC, then the filtered audio signal is transformed by an FFT into frequency domain.
Next, total power in the total filter band is measured as P
total
, the peak power of
wanted signal is computed as P
signal
, the square root of the ratio of P
total
− P
signal
to
P
total
is calculated. The result is signal’s Audio Distortion. It can be expressed as
dB or %.
%
AudioDistortion
P
total
P
signal
–
P
total
----------------------------------- 100%×=
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