Intermodulation Distortion - Interacoustics Affinity 2.0 Additional Information

2.0
Affinity Additional Information
3.7.4

Intermodulation Distortion

Distortion in moderate
-severe amounts will inevitably have a negative effect on the quality of speech and speech intelligibility. To
assess the distortion product generated by the hearing aid, intermodulation distortion is measured.
Two tones equal in amplitude are presented to the hearing aid; one at the selected frequency difference (f1)
and one at the selected frequency (f2). The HIT440 will make an FFT of the signal produced by the hearing
aid and the 2nd and 3rd intermodulation distortion is calculated.
2nd distortion: the signal at f2 - f1 in relation to the signal at f2.
3rd distortion: the signal at 2*f1 – f2 in relation to the signal at f2.
Below is an example:
Select test
View test information
for marked frequency
The three bars represent the
nd
total distortion, 2 distortion, and
rd
3 distortion
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