Frequency Reassignment for Coherent Modulation Filtering

Modulation filtering is a technique for filtering slowly-varying envelopes of frequency subbands of a signal, without affecting the signal´s phase and fine-structure. Coherent modulation filtering is a promising subtype of such techniques where subband envelopes are determined through demodulation of the subband signal with a coherently detected subband carrier. In this paper we propose a coherent modulation filtering technique that detects the carriers using the frequency reassignment (FR) operator from time-frequency reassignment. We show how this technique avoids the use of finite differences in the computation of instantaneous frequency (IF), and that it estimates IF more accurately than a past technique as a result. We confirm that the FR-enhanced technique retains the desirable modulation filtering properties (superposition and the preservation of zero-crossings) and show that it performs better on the same single-channel music source separation task than the past technique