Harmonic Distortion - Interacoustics Affinity 2.0 Additional Information

3.7.3

Harmonic distortion

The pure tone components are called harmonics and occur at integer multiples of the f undamental
f requency. The output of a hearing aid, however, is rarely a pure tone and the signal will inevitably contain
elements at dif ferent f requencies not included in the input. These components are def ined as distortion
products. As a result, measuring these is called Harmonic Distortion.
Harmonic distortion can be measured f or both microphone and telecoil. It is done by presenting a pure tone
to the hearing aid and analysing the wavef orm of the output to measure the distortion components relative to
the total power of the input signal.
The Total Harmonic Distortion (THD) equals the total sum of all harmonics or in the Af f inity
harmonic. The result is expressed relative to the wanted output signal component in percent.
It is important to know the harmonic distortion to be assured that the output of the hearing aid is not af f ected
by unwanted distortion. Distortion can be compared to the cocktail party effect as harmonics (noise) may
mask the wanted speech signal (f undamental f requency). A hearing aid with high distortion will theref ore not
provide the client with the ideal speech understanding.
Below is an example:
3.7.4
D-0004576-Q – 2022/05
Affinity/Equinox2.0 – Additional Information
elect test
S
View test inf ormation
f or marked f requency
The three bars represent
the total distortion, 2 nd
distortion, and 3 rd distortion
2.0 the 2 nd and 3 rd
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