The Frequency-Amplitude-Modulation Encoding (FAME) strategy is outlined m the ar

Question

The Frequency-Amplitude-Modulation Encoding (FAME) strategy is outlined m the article of the currently assigned supplementary reading, starting with a description of the FM and AM components of a sound signal s(t): A signal, s(t), can be approximated by a sum of N band-limited components, x(t), containing both amplitudes and frequency modulations s (t) almostequalto sigma^N _k = 1 x_k (t) = sigma^N _k = 1 A_k (t) cos [2 pi f _ck t + 2 pi integral^t _0 9k (tau) d tau + theta_k] where A_k (t) and g_k (t) are the kth band's amplitude and frequency modulations, whereas f_ck and theta_k are the k the band's center frequency and initial phase, respectively. The application of this technique to encoding stimulation patterns of the cochlear electrodes requires removal of the center frequency f_ck. Why is this so? in doing so. doesn't the technique effectively throw away a fundamental component of the acoustic information? Explain why you agree or disagree. What additional information or speech cues does this technique attempt to provide that is not provided with, e.g., "n-of-m" encoding?

Explanation / Answer

i)By removing the center frequency from the subband signals and additionally limiting the frequency modulation's range and rate, the FAME strategy transforms the fast-varying temporal fine structure into a slowly varying frequency modulation signal which improves cochlear implant performance in noise.Reduced FM for cochlear implant users can be provided by removing the center frequency from the subband signal. The center frequency removal might be acceptable because, presumably, it would already be encoded by the position of the stimulating electrode

ii)The amplitude modulation cue cannot support robust speech recognition in noise.A FAME strategy extracts and encodes both formant transition and fundamental frequency cues.The AM-only strategy encodes these cues either indirectly in the time domain (e.g., fundamental frequency) or crudely in the frequency domain (e.g., formant transition), particularly when the number of bands is low. FAME strategy contains more acoustic information.

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