Log-sampled filter system

• US 20060109941A1
• Filed: 10/31/2005
• Published: 05/25/2006
• Est. Priority Date: 10/29/2004
• Status: Active Grant

• Current Assignee: Harman International Industries Incorporated (Samsung Electronics Co. Ltd.)
• Original Assignee: Harman International Industries Incorporated (Samsung Electronics Co. Ltd.)
• Inventors: Keele, D. Broadus Jr.
• Granted Patent: US 7,555,081 B2
• Time in Patent Office: Days
• US Class Current: 375/350
• CPC Class Codes: H03H 17/0261 Non linear filters
• CPC Class Codes: H03H 17/028 Polynomial filters
• CPC Class Codes: H03H 17/06 Non-recursive 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: H03H 2218/04 In-phase and quadrature [I/Q] signals

Abstract

This invention provides a filter system which may be implemented with less hardware and software resources than traditional filters. In addition, the filter system structure reduces the complexities typically associated with filter design by permitting direct specification of the filter frequency response. Thus, the filter system may adaptively change the filter frequency response on the fly without incurring excessive time or computational costs. The filter system may provide a filtered signal output to any subsequent processing system, such as a voice recognition system or audio reproduction system.

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;

series connected multi-rate filter sections coupled between the input channel and the output channel, at least one of the multi-rate filter sections comprising;

a downsampler including a downsampler input and a downsampler output connected to a subsequent multi-rate filter section;

a FIR filter channel coupled to the downsampler output, the FIR filter channel comprising;

a real FIR filter interpolator;

an imaginary FIR filter interpolator coupled in parallel with the real FIR filter interpolator;

a real gain element coupled to the real FIR filter interpolator; and

an imaginary gain element coupled to the imaginary FIR filter interpolator;

a summer connected to the real and imaginary gain elements; and

an upsampler connected to the summer, the upsampler comprising an upsampler input and an upsampler output connected to either a prior multi-rate filter section or to an output signal summer.

2. The multi-rate filter system of claim 1, where the real FIR filter interpolator comprises a tone burst impulse response.

3. The multi-rate filter system of claim 1, where the real FIR filter interpolator and the imaginary FIR filter interpolator each comprise a tone burst impulse response.

4. The multi-rate filter system of claim 3, the filter section further comprises a low pass filter prior to the downsampler.

5. The multi-rate filter system of claim 1, where the real FIR filter interpolator comprises a Cosine tone burst impulse response.

6. The multi-rate filter system of claim 1, where the imaginary FIR filter interpolator comprises a Sine tone burst impulse response.

7. The multi-rate filter system of claim 1, where the real FIR filter interpolator comprises a first impulse response and where the imaginary FIR filter interpolator comprises a second impulse response determined as a Hilbert transformed 90 degree phase shift of the first impulse response.

8. The multi-rate filter system of claim 1, further comprising an initial FIR filter channel coupled between the input channel and the output channel prior to the series connected multi-rate filter sections.

9. The multi-rate filter system of claim 1, where downsampler is a r:

1 downsampler, and where the upsampler is a 1;

r upsampler.

10. The multi-rate filter system of claim 9, where the multi-rate filter sections non-linearly span an audio signal bandwidth.

11. A method of filtering a signal, the method comprising:

processing an input signal through multiple series connected multi-rate filter sections, the processing in at least one of the multi-rate filter sections comprising;

downsampling to generate a reduced rate signal;

filtering the reduced rate signal through a real FIR filter interpolator to generate a real FIR filter interpolator output;

applying a real weight to the real FIR filter interpolator output to generate a real weighted filter output;

filtering the reduced rate signal through an imaginary FIR filter interpolator to generate an imaginary FIR filter interpolator output;

applying an imaginary weight to the imaginary FIR filter interpolator output to generate an imaginary weighted filter output;

summing the real weighted and imaginary weighted filtered outputs to generate an FIR channel output;

upsampling the FIR channel output to generate an increased rate signal;

providing the reduced rate signal to a subsequent multi-rate filter section; and

providing the increased rate signal to either a prior multi-rate filter section or to a output signal summer.

12. The method of claim 11, where the real FIR filter interpolator comprises a tone burst impulse response.

13. The method of claim 11, where the real FIR filter interpolator and the imaginary FIR filter interpolator each comprise a tone burst impulse response.

14. The method of claim 13, the filter section further comprises a low pass filter prior to the downsampler.

15. The method of claim 11, where the real FIR filter interpolator comprises a Cosine tone burst impulse response.

16. The method of claim 11, where the imaginary FIR filter interpolator comprises a Sine tone burst impulse response.

17. The method of claim 11, where the real FIR filter interpolator comprises a first impulse response and where the imaginary FIR filter interpolator comprises a second impulse response determined as a Hilbert transformed 90 degree phase shift of the first impulse response.

18. The method of claim 11, further comprising an initial FIR filter channel coupled between the input channel and the output channel prior to the series connected multi-rate filter sections.

19. The method of claim 11, where the downsampling step is implemented by a r:

1 downsampler, and where the upsampling step is implemented by a 1;

r upsampler.

20. The method of claim 19, where the multi-rate filter sections non-linearly span an audio signal bandwidth.

21. A product comprising:

a machine-readable medium; and

instructions stored on the medium for execution by a processor in a filtering system, where the instructions cause the filtering system to perform a method comprising;

downsampling to generate a reduced rate signal;

filtering the reduced rate signal through a real FIR filter interpolator to generate a real FIR filter interpolator output;

applying a real weight to the real FIR filter interpolator output to generate a real weighted filter output;

filtering the reduced rate signal through an imaginary FIR filter interpolator to generate an imaginary FIR filter interpolator output;

applying an imaginary weight to the imaginary FIR filter interpolator output to generate an imaginary weighted filter output;

summing the real weighted and imaginary weighted filtered outputs to generate an FIR channel output;

upsampling the FIR channel output to generate an increased rate signal;

providing the reduced rate signal to a subsequent multi-rate filter section; and

providing the increased rate signal to either a prior multi-rate filter section or to a output signal summer.

22. The product of claim 21, where the real FIR filter interpolator comprises a tone burst impulse response.

23. The product of claim 21, where the real FIR filter interpolator and the imaginary FIR filter interpolator each comprise a tone burst impulse response.

24. The product of claim 21, where the real FIR filter interpolator comprises a Cosine tone burst impulse response.

25. The product of claim 21, where the imaginary FIR filter interpolator comprises a Sine tone burst impulse response.

26. A filter comprising:

an input channel configured to receive an input signal;

an output channel configured to output a filtered signal;

multiple FIR filter channels which implement a filter response, the FIR filter channels coupled to the input channel and to a signal summer, where the signal summer generates the filtered signal, and where each FIR filter channel comprises;

a filter gain element coupled to the input channel;

a real FIR filter interpolator comprising a first filter input coupled to the filter gain element and a first filter output coupled to the signal summer;

an imaginary FIR filter interpolator comprising a second filter input coupled to the filter gain element and a second filter output coupled to the signal summer;

where each filter gain element specifies a portion of the filter response in linear frequency.

27. The filter of claim 26, where each FIR filter interpolator comprises a constant width tone burst impulse response.

28. The filter of claim 27, where each constant width tone burst impulse response has a different frequency.

29. The filter of claim 28, where the different frequencies are approximately equally spaced.

30. A filter comprising:

an input channel configured to receive an input signal;

an output channel configured to output a filtered signal;

multiple FIR filter channels which implement a filter response, the FIR filter channels coupled to the input channel and to a signal summer, where the signal summer generates the filtered signal, and where each FIR filter channel comprises;

a filter gain element coupled to the input channel;

a real FIR filter interpolator comprising a first filter input coupled to the filter gain element and a first filter output coupled to the signal summer;

an imaginary FIR filter interpolator comprising a second filter input coupled to the filter gain element and a second filter output coupled to the signal summer;

where each filter gain element specifies a portion of the filter response in log-spaced frequency.

31. The filter of claim 30, where each FIR filter interpolator comprises a variable width tone burst impulse response.

32. The filter of claim 31, where each variable width tone burst impulse response has a different frequency.

33. The filter of claim 32, where each variable width tone burst impulse response comprises an equal number of cycles.

34. The filter of claim 31, where each variable width tone burst impulse response is initially aligned.

35. The filter of claim 31, where each variable width tone burst impulse response is centrally aligned.

36. The filter of claim 30, where each real FIR filter interpolator comprises a tone burst, where each tone burst of each real FIR filter interpolator is substantially the same.

37. The filter of claim 36, where each tone burst of each real FIR filter interpolator is identical.

38. The filter of claim 30, where each imaginary FIR filter interpolator comprises a tone burst, where each tone burst of each imaginary FIR filter interpolator is substantially the same.

39. The filter of claim 38, where each tone burst of each imaginary FIR filter interpolator is identical.