AM-FM separation using auditory-motivated filters

Abstract

A new approach to the joint estimation of sine-wave amplitude modulation (AM) and frequency modulation (FM) is presented based on the transduction of frequency modulation into amplitude modulation by digital filters, being motivated by the hypothesis that the auditory front end uses a similar transduction mechanism in measuring sine-wave FM. An AM-FM estimation algorithm is derived which uses the amplitude envelope of the output of two transduction filters of piecewise-linear spectral shape. The piecewise-linear constraint is then relaxed, allowing a wider class of transduction filters for AM-FM separation. The particular class of Gaussian filters is shown to yield a closed form solution to AM-FM estimation. Solution stability analysis and error evaluation are performed, and the FM transduction method is shown to typically compare favorably with the Teager energy operator and the Hilbert transform for AM-FM estimation. Finally, the amenability of cochlear gammatone-filter pairs to separate AM and FM is demonstrated.