Method and apparatus to evaluate audio equipment for dynamic distortions and or differential phase and or frequency modulation effects

Abstract

A system is provided to analyze distortion in an electronic or electromechanical device, which may include testing with one or more modulated signals and/or with one or more demodulators. In one embodiment a change in pitch (or frequency) is measured at an output of the device. One or more signals from a demodulator output may be measured for an amplitude, noise, phase, aliasing, spurious signal, and/or frequency modulation effect. In another embodiment a musical signal may be used as a test signal. Providing additional test signals to the device can induce a cross-modulation distortion signal (or time varying cross-modulation distortion signal) from an output of the device. Also utilizing at least one additional filter, filter bank, demodulator and or frequency converter and or frequency multiplier provides extra examination of distortion. Also frequency and/or phase response can be measured with the presence of a de-sensing signal and or another signal that induce near slew rate limiting or near overload condition of the device under test. Another system is provided to analyze modulation index differences between input and output signals for a test signal including modulation. Another system includes providing a nested or layered modulated signal and/or a nested or layered demodulation apparatus or method.