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In cochlear implants, the input signal is fed to a set of bandpass filters and is then half-wave rectified and low pass filtered to estimate the envelope signal.

What is the need for doing rectification? Can't we directly take the output of the band pass filter and pass it through a LPF and use that data to stimulate the electrodes?

Do negative values in the envelope cause any variation while stimulating electrodes in cochlear implants?

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If you pass the output of a bandpass filter directly to a lowpass filter, you would often get a zero signal (depending on cutoff frequencies).

Edit: I believe that the filterbank->rectifier->lowpass filter is typically chosen to have a smooth, low-rate energy/power measure, where LPF cutoff << BPF bandwidth. Having a BPF and a LPF in series with no intermediate processing makes little sense for me, then you could just as well pull all of the work with the BPF.

So perhaps your question can be rewritten as "why dont we just hook up a bank of bandpass filters directly to stimulate our hearing nerves?". When you replace biologic parts with artificial parts, it makes sense to try to mimic (our understanding of) the parts that we are replacing.

This text seems relevant: "Each output channel is half-wave rectified to simulate the output of the inner hair cells along the length of the cochlea."

Auditory Sparse Coding

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