Method and apparatus to measure differential phase and frequency modulation distortions for audio equipment

Method of measuring dynamic frequency response of a device, wherein the device has an input and an output, comprising:

• coupling a lower frequency signal and a higher frequency signal to the input of the device, wherein the lower frequency signal spans an output range of the device, and wherein the higher frequency signal is varied, and measuring amplitude of one or more cycles of the higher frequency signal in a localized portion of the output range of the device to provide the measurement of dynamic frequency response at the output of the device.

Method of measuring phase or frequency modulation on an amplitude modulated signal from an audio device, wherein the audio device has an input and output, comprising:

• coupling the amplitude modulated signal to the input of the audio device, wherein the amplitude modulated signal includes a carrier signal with a residual carrier level, and
• coupling the output of the audio device to a phase or frequency detector or to a spectrum analysis system for measuring the phase or frequency modulation of the carrier signal of the amplitude modulated signal at the output of the audio device.

Method of measuring distortion on an amplitude modulated signal from an audio device, wherein the audio device has an input and output, comprising:

• coupling an amplitude modulated signal to the input of the audio device, and
• coupling a spectrum analyzer or spectral analysis system to the output of the audio device to measure extra sidebands beyond the first set of sidebands near a carrier of the amplitude modulated signal to provide measuring distortion of the amplitude modulated signal from the output of the audio device.