Speech signals have a periodic envelope which can be used for speech separation. The choice of amplitude modulation spectrum (AMS) for speech separation is motivated by biological observations that variations in modulation frequency provides a long term window for characterizing speech information, especially in noisy and reverberant environments.
Suppose the received signal at the microphone is given as:
where is the desired speech signal and is i.i.d zero mean Gaussian noise with variance . The short term spectrum of each frame is computed such that:
The negative frequency components of are set to zero to synthesize a signal where:
The inverse short term spectrum of is the taken, denoted . The AMS is then twice the amplitude of . A sample performance of this algorithm is shown in Figure 1 below:
Figure 1: Speech amplitude modulation detection
The AMS signal can also be used to detect the pitch of speech. However, this approach is very sensitive to noise.
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