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Filterbank structure and method for filtering and separating an information signal into different bands, particularly for audio signal in hearing aids
| Details |
Inventors: Brennan, Robert; Schneider, Anthony Todd;
Assignee: dspfactory Ltd. (Waterloo, CA)
Primary Examiner: Kuntz; Curtis
Assistant Examiner: Ni; Suhan
Attorney, Agent or Firm: Bereskin & Parr
A filterbank structure is provided which provides a flexible compromise between the conflicting goals of processing delay, filter sharpness, memory usage and band interaction. The filterbank has an adjustable number of bands and a stacking which provides for a selectable shift of band frequencies to one of two discrete sets of center frequencies. The width of the bands and hence the number of the bands is selected depending upon acceptable delay, memory usage, and processing speed required. The flexibility in terms of stacking of the bands provides twice the number of potential band edge placements, which is advantageous for hearing loss fitting, especially at low frequencies. The same filter coefficients can be used for analysis and synthesis, to reduce memory usage. |
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DETAILED DESCRIPTION We claim: 1.
An oversampled filterbank for filtering an information signal, the filterbank having a filterbank structure comprising a filter means defining a filter bandwidth, said filter means filtering said information signal and separating said information signal into a plurality of frequency band signals, each representing one of a plurality of uniformly spaced frequency bands within said filter bandwidth, said frequency bands being stacked in one of an even and an odd manner and said frequency bands overlapping, such that the summation of the unmodified frequency band responses of the plurality of said frequency bands sums to a function within a predetermined passband ripple over said filter bandwidth, wherein the filter means includes a selection input enabling at least one of the following to be selected: (i) the number of frequency band signals, (ii) the bandwidth of said frequency bands, (iii) selection of stacking of said frequency bands in one of an even and an odd manner, (iv) the degree of overlap between said frequency bands; (v) an oversampling factor by which said frequency band signals are sampled above the theoretical minimum of critical sampling.
2.
A filterbank as claimed in claim 1, wherein the selection input enables at least one of the number of frequency bands and whether said frequency bands are stacked in an even or odd manner to be selected, said number of frequency bands being equal to N, and the filter means comprises: (a) a first analysis filterbank means for separating said signal into the plurality of N separate frequency band signals; (b) processing means for receiving and processing each of said separate frequency band signals to provide N separate processed frequency band signals; and (c) a second synthesis filterbank means for receiving and recombining the N separate processed frequency band signals into a single output signal, wherein both of the first analysis filterbank means and the second synthesis filterbank means are connected to the selection input, the processing means being coupled between the first analysis filterbank means and the second synthesis filterbank means
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Audio Signal Processing 
