MULTI-RATE FILTER SYSTEM

• US 20150010170A1
• Filed: 01/09/2013
• Published: 01/08/2015
• Est. Priority Date: 01/10/2012
• Status: Abandoned Application

• Current Assignee: Cirrus Logic International Semiconductor Ltd. (Cirrus Logic Incorporated)
• Original Assignee: Actiwave AB (Cirrus Logic Incorporated)
• Inventors: Lindahl, Erik, Risberg, Pr Gunnars, Toth, Landy, Lindblom, Ludvig
• Application Number:
  US14/371,020
• Publication Number:
  US 20150010170A1
• Time in Patent Office: Days
• US Class Current: 381/119
• CPC Class Codes: H03H 17/0261 Non linear filters
• CPC Class Codes: H03H 17/0283 Filters characterised by the filter structure H03H17/0202, H03H17/0219 - H03H17/0248 take precedence
• CPC Class Codes: H03H 17/0294 Variable filters; Programmable filters
• CPC Class Codes: H03H 17/0621 with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing
• CPC Class Codes: H04R 2430/00 Signal processing covered by H04R, not provided for in its groups
• CPC Class Codes: H04R 2430/03 Synergistic effects of band splitting and sub-band processing
• CPC Class Codes: H04R 3/04 for correcting frequency response

Abstract

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.

Claims

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.

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.

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.