MULTI-RATE FILTER SYSTEM
A multi-rate filter system is disclosed. More particularly, a computationally efficient multi-rate filter system for processing an audio stream on a consumer electronics device is disclosed. The multi-rate filter system includes a plurality of multi-rate filtering blocks, at least one block including a linear filter component. At least one multi-rate filtering block may include a nonlinear signal processing components. The multi-rate filter system may include a nonlinear functional block. A method of filtering a signal is also disclosed.
1 . A multi-rate filter system comprising:
an input channel configured to receive an input signal;
an output channel configured to output a filtered signal;
a cascade of multi-rate filter blocks coupled between the input channel and the output channel, at least one of the multi-rate filter blocks comprising:
a bandselector comprising a bandselector input, a highpass bandselector output, a lowpass bandselector output connected to a subsequent multi-rate filter block, and a downsampler connected between the bandselector input and the lowpass bandselector output;
a signal processing block coupled to the highpass bandselector output, the signal processing block comprising a linear filter component; and
a bandcombiner connected to the signal processing block, the bandcombiner comprising two bandcombiner inputs, a bandcombiner output, and an upsampler, the first bandcombiner input connected to the signal processing block, the second bandcombiner input connected to a subsequent multi-rate filter block, and the bandcombiner output connected to a prior multi-rate filter block, the upsampler connected between the bandcombiner inputs and the bandcombiner output.
2 . The multi-rate filter system in accordance with claim 1 , wherein the linear filter component is selected from a group comprising a finite impulse response (FIR) filter, an infinite impulse response (IIR) filter, a Kalman filter, a neural network, a fuzzy logic filter, and combinations thereof.
3 . The multi-rate filter system in accordance with claim 2 , wherein the linear filter component comprises reconfigurable filter parameters.
4 . The multi-rate filter system in accordance with claim 1 , wherein at least one of the signal processing blocks comprises a nonlinear filter component connected to the linear filter component.
5 . The multi-rate filter system in accordance with claim 4 , wherein the nonlinear filter component is selected from a group comprising a compressor, a polynomial, a limiter, and combinations thereof.
6 . The multi-rate filter system in accordance with claim 1 , wherein at least one multi-rate filter block comprises an observer configured to output an observer signal, the observer connected to the signal processing block between the highpass bandselector output and the first bandcombiner input.
7 . The multi-rate filter system in accordance with claim 6 , wherein the observer comprises a power monitor.
8 . The multi-rate filter system in accordance with claim 4 , wherein the nonlinear filter component is configured to respond to an observer signal.
9 . The multi-rate filter system in accordance with claim 1 , further comprising a nonlinear functional block (NLFB) comprising an NLFB input and an NLFB output, a first multi-rate filter block comprising a bandcombiner output, and a second multi-rate filter block comprising a bandcombiner input, the NLFB input connected to the bandcombiner output of the first multi-rate filter block, and the NLFB output connected to the bandcombiner input of the second multi-rate filter block.
10 . The multi-rate filter system in accordance with claim 9 , wherein the nonlinear function block comprises a psychoacoustic function.
11 . The multi-rate filter system in accordance with claim 1 , wherein the downsampler is an m:1 downsampler, and where m is a sample rate and the upsampler is a 1:k upsampler, and where k is a sample rate.
12 . The multi-rate filter system in accordance with claim 11 , wherein m is equal to k.
13 . The multi-rate filter system in accordance with claim 11 , wherein m and/or k are less than or equal to 2, less than or equal to 1.5, less than or equal to 1.33, or less than or equal to 1.25.
14 . The multi-rate filter system in accordance with claim 1 , wherein the multi-rate filter blocks span an audio signal bandwidth.
15 . The multi-rate filter system in accordance with claim 1 , wherein the bandselector comprises a low pass filter connected between the bandselector input and the bandselector lowpass output, and a high pass filter connected between the bandselector input and the bandselector highpass output.
16 . The multi-rate filter system in accordance with claim 15 , wherein the bandselector comprises a complimentary filter pair formed by the low pass filter and high pass filter.
17 . The multi-rate filter system in accordance with claim 15 , wherein the low pass filter is selected from a group consisting of a linear phase FIR filter, a near linear phase FIR filter, a lattice wave filter, and combinations thereof.
18 . The multi-rate filter system in accordance with claim 1 , wherein the bandcombiner comprises a summer connected to the bandcombiner inputs and the upsampler.
19 . The multi-rate filter system in accordance with claim 1 , wherein the bandcombiner comprises a low pass filter connected between the upsampler and the bandcombiner output.
20 . The multi-rate filter system in accordance with claim 1 , further comprising a control channel configured to receive a control signal, wherein at least one multi-rate filter block connected to the control channel.
21 . The multi-rate filter system in accordance with claim 20 , the linear filter component configured to respond to the control signal.
22 . The multi-rate filter system in accordance with claim 4 , wherein the nonlinear filter component is configured to respond to a control signal.
23 . (canceled)
24 . (canceled)
25 . A method for filtering a signal comprising:
processing an input signal with a plurality of multi-rate filter blocks, the processing of at least one multi-rate filter block comprising:
downsampling to produce a downsampled signal;
providing the downsampled signal to a subsequent multi-rate filter block;
processing with a linear filter component to form a linear filtered signal;
processing with a nonlinear filter component to form a nonlinear filtered signal;
combining or selecting the linear filtered signal and/or the nonlinear filtered signal to form a filtered output signal; and
upsampling the filtered output signal to form an increased rate signal.
26 . The method in accordance with claim 25 , further comprising processing at least one increased rate signal with a nonlinear functional block (NLFB) to form a nonlinear processed signal.
27 . The method in accordance with claim 26 , further comprising providing the nonlinear processed signal to a prior multi-rate filter block.
28 . The method in accordance with claim 25 , further comprising providing the increased rate signal to a prior multi-rate filter block.
29 . The method in accordance with claim 25 , wherein the linear filter component is selected from a group comprising a finite impulse response (FIR) filter, an infinite impulse response (IIR) filter, a Kalman filter, a neural network, a fuzzy logic filter, a lattice wave filter, and combinations thereof.
30 . The method in accordance with claim 25 , wherein the nonlinear filter component is selected from a group comprising a compressor, a polynomial, a limiter, and combination thereof.
31 . A method for matching a multi-rate filter system in accordance with claim 1 to a predetermined wideband filter, the method comprising:
assigning the number of multi-rate filter blocks in the multi-rate filter system;
calculating an initial guess for one or more of the multi-rate filter blocks;
optimizing the multi-rate filter blocks towards the wideband filter to form one or more updated multi-rate filter blocks; and
constructing a matched multi-rate filter system from the updated multi-rate filter blocks.
32 . The method in accordance with claim 31 , wherein the step of calculating is performed using a Parks-McClellan algorithm.
33 . The method in accordance with claim 31 , wherein the step of optimizing is performed on one or more bandselectors and one or more bandcombiners included in the multi-rate filter system, and separately on one or more of the signal processing blocks included in the multi-rate filter system.
34 . The method in accordance with claim 31 , further comprising adding a nonlinear function block to one or more of the multi-rate filter blocks.
35 . The method in accordance with claim 34 , further comprising configuring the nonlinear function block to match a psychoacoustic function.