Total harmonic distortion analyzer

A typical application is to determine the THD of an amplifier by using a very-low-distortion sinewave input and examining the output.

There are several types of distortion analyzers:[citation needed] This type of THD analyzer filters out the fundamental frequency of a signal with a notch filter, leaving only distortion products plus noise; the ratio of this remnant to the signal amplitude is the THD.

Negative feedback from the bridge amplifier to the pre-amp section may be applied to enable the rejection circuit to work more accurately.

A feedback loop from the bridge amplifier output to the pre-amp input helps to eliminate any remaining contribution from the fundamental frequency.

The output from these blocks is measured, typically using an instrumentation amplifier driving an analog or digital meter.