Envelope-based amplitude mapping for cochlear implant stimulus
An envelope based amplitude mapping achieves the signal compression required to provide a natural sound level without the high processor loading or waveform alteration. In one embodiment, the output of a family of parallel bandpass filters is processed by an envelope detector, followed by decimation. The resulting reduced data rate envelope is log mapped to produce a scaling factor for the original high data rate bandpass filter output sequence. The resulting scaled signal determines the current level for stimulation of the cochlea for each frequency band, which stimulation achieves a log mapping of the sound amplitude effect similar to natural hearing, while reducing processor load, and preserving waveform shape.
1. An Implantable Cochlear Stimulation (ICS) system including envelope based amplitude mapping, comprising:
an implantable part including a cochlear electrode array; and
a speech processor including a microphone and a signal processor, wherein the microphone converts acoustic energy into an electrical signal provided to the signal processor, and wherein the signal processor includes
a bandpass filter for filtering the electrical signal to generate at least one filtered signal;
an envelope detector for computing at least one envelope signal from the at least one filtered signal;
a decimator for computing at least one decimated signal from the at least one signal envelope,
a log mapper for computing at least one mapped signal from the at least one decimated signal; and
a multiplier for computing at least one output signal from the at least one mapped signal and the at least one filtered signal;
wherein the multiplier multiplies the at least one mapped signal and the electrical signal to produce an output signal for the cochlear electrode array.
2. An Implantable Cochlear Stimulation (ICS) system including envelope based amplitude mapping, comprising:
an implantable part including a cochlear electrode array; and
a speech processor including a microphone and a signal processor, wherein the microphone converts acoustic energy into an electrical signal that is presented to the signal processor, and wherein the signal processor includes:
a bandpass filter for filtering the electrical signal to generate at least one filtered signal;
an envelope detector for computing at least one envelope signal from the at least one filtered signal;
a decimator for computing at least one decimated signal from the at least one signal envelope;
a log mapper for computing at least one mapped signal from the at least one decimated signal; and
a multiplier for computing at least one output signal from the at least one mapped signal and the at least one filtered signal;
wherein the log mapper for computing the at least one mapped signal comprises a mapping function F′(x), wherein F′(x) is F(x)/x, and
wherein x is the decimated signal, and wherein F(x) is the desired mapping between the at least one filtered signal and the at least one output signal.
3. The system of claim 2 wherein F(x) is a compressive mapping of x.
4. The system of claim 3 wherein the compressive mapping of x is a log mapping.