Frequency modulation (FM) as a computational auditory scene analysis feature refers to the phoneme changes in audio streams. This is accomplished by using a two dimensional cochleagram to corresponding to the FM pattern that we want to pick up. This detection using the cochleagram is done by convolution with a time-frequency kernel.
Consider a two dimensional time-frequency zero mean Gaussian kernel defined as:
To observe a frequency change the Laplacian of the Gaussian filter is used. The Laplacian filter is:
The time-frequency variances are chosen such that the Laplacian corresponds to a receptive fields in the human auditory system. Typically, the time variance is chosen to be bigger than the frequency variance. A sample Laplacian filter for FM is shown in Figure 1 below:
Figure 1: Laplacian filter for frequency change detection
FM is can be used as a feature for speech recognition systems by finding the pitch corresponding to frequency changes.
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