Frequency & amplitude modulation

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Frequency Modulation (Derivative Estimates) is defined as

Frequency modulation is estimated based on time and frequency derivatives across frequencies. If the frequency derivatives are much higher than the time derivatives, we say that FM is low and visa versa. Visually, FM is an estimate of the (absolute) slope of frequency traces in reference to the horizontal line. Note: SAP2 calculates an absolute estimate of FM, but it is easy to change the definition to obtain signed FM.


Amplitude Modulation: AM is simply the overall time-derivative power across all frequencies within a range. Units of AM are 1/t, SAP2011 does not scale AM, and time units are defined by the ‘advance window’ parameter.

Amplitude modulation captures changes in the amplitude envelope of sounds. It is positive in the beginning and negative at the end of each sound, with the sound unit being either a syllable or a change of vocal state within a syllable.