Method and apparatus for filtering and compressing sound signals

• US 20020015503A1
• Filed: 08/07/2001
• Published: 02/07/2002
• Est. Priority Date: 08/07/2000
• Status: Active Grant

• Current Assignee: Ototronix, LLC
• Original Assignee: Audix Technology Company Limited (Audix Corporation)
• Inventors: Hou, Zezhang
• Granted Patent: US 6,873,709 B2
• Time in Patent Office: Days
• US Class Current: 381/94.3
• CPC Class Codes: H04R 2225/43 Signal processing in hearing aids to enhance the speech intelligibility
• CPC Class Codes: H04R 25/356 Amplitude, e.g. amplitude shift or compression
• CPC Class Codes: H04R 25/407 Circuits for combining signals of a plurality of transducers
• CPC Class Codes: H04R 25/505 using digital signal processing
• CPC Class Codes: H04R 3/00 Circuits for transducers , loudspeakers or microphones

Abstract

Improved approaches are disclosed to filter and compress sound signals so as to achieve not only speech audibility and intelligibility at low levels but also preserves spectrum contrast at high levels. According to one aspect of the invention, gain amounts for different frequency bands are individually constrained based on signal levels for the frequency bands. Hence, the gain amounts for each of the frequency bands may or may not be constrained depending on the corresponding signal levels. As a result, the most critical information for speech intelligibility, speech clarity, and speech quality can be made available to hearing impaired people over wide range of signal level. The invention is particularly useful for hearing aids or other sound systems for the hearing impaired.

Claims

1. A method for processing sound signals for hearing impaired persons, said method comprising:

(a) filtering a sound signal to obtain channel signals for at least two channels;

(b) determining an estimated signal level for each of the channel signals;

(c) determining an initial gain amount for each of the channel signals;

(d) constraining the initial gain amount for each of the channel signals against gain amounts associated with at least one neighboring channel based on the corresponding estimated signal levels; and

(e) amplifying the channel signal in accordance with the corresponding constrained initial gain amount.

2. A method as recited in claim 1, wherein said constraining (d) comprises:

(d1) comparing the estimated signal level to at least one threshold level to obtain comparison information; and

(d2) constraining the initial gain amount for the channel signal against at least one gain amount associated with at least one neighboring channel based on the comparison information.

3. A method as recited in claim 1, wherein the channel signal pertains to a frequency band, and

wherein said method further comprises:

(f) combining the amplified channel signal with other amplified channel signals from other frequency bands of the sound signal.

4. A method as recited in claim 3, wherein said constraining (d) comprises:

(d1) comparing the estimated signal level to at least one threshold level to obtain comparison information; and

(d2) constraining the initial gain amount for the channel signal against the gain amount associated with at least one neighboring channel based on the comparison information.

5. A method as recited in claim 1, wherein said constraining (d) operates to average the initial gain amount for the channel signal with at least one other gain amount associated with a neighboring channel.

6. A method as recited in claim 5, wherein the average operation is weighted average.

7. A method as recited in claim 5, wherein the neighboring channel is a channel adjacent to the channel.

8. A method as recited in claim 5, wherein the neighboring channel pertains to a lower frequency band that is adjacent to the frequency band for the channel.

9. A method as recited in claim 1, wherein said constraining (d) operates to average the initial gain amount for the channel signal with a plurality of other gain amounts associated with neighboring channels.

10. A method as recited in claim 9, wherein the average operation is weighted average.

11. A method as recited in claim 9, wherein the neighboring channels are channels adjacent to the channel.

12. A method as recited in claim 11, wherein the neighboring channels include at least one channel at a lower frequency band that is proximate to the frequency band for the channel, and at least one channel at a higher frequency band that is proximate to the frequency band of the channel.

14. A method as recited in claim 13, wherein said determining comprises:

comparing the signal level estimate for the channel signal to a first threshold amount; and

constraining the suitable gain amount for the channel signal when said comparing determines that the signal level estimate exceeds the first threshold amount.

15. A method as recited in claim 13, wherein said determining comprises:

producing an initial gain amount for the channel signal;

comparing the signal level estimate for the channel signal to a first threshold amount;

producing the suitable gain amount as the initial gain amount when said comparing determines that the signal level estimate is less than the first threshold amount; and

constraining the initial gain amount and then producing the suitable gain amount as the constrained initial gain amount when said comparing determines that the signal level estimate is greater than the first threshold amount.

16. A method as recited in claim 15, wherein said constraining operates to average the initial gain amount for the channel signal with at least one other gain amount associated with a neighboring channel.

17. A method as recited in claim 16, wherein the average operation is weighted average.

18. A method as recited in claim 16, wherein the neighboring channel is a channel adjacent to the channel.

19. A method as recited in claim 13, wherein said determining comprises:

producing an initial gain amount for the channel signal;

comparing the signal level estimate for the channel signal to a first threshold amount and a second threshold amount;

producing the suitable gain amount as the initial gain amount when said comparing determines that the signal level estimate is less than the first threshold amount;

constraining the initial gain amount to a first extent and then producing the suitable gain amount as a first constrained initial gain amount when said comparing determines that the signal level estimate is greater than the first threshold amount and less than the second threshold amount; and

constraining the initial gain amount to a second extent and then producing the suitable gain amount as a second constrained initial gain amount when said comparing determines that the signal level estimate is greater than the second threshold amount, the constraining to second extent being more constraining than constraining to the first extent.

20. A method as recited in claim 19, wherein said constraining operates to average the initial gain amount for the channel signal with at least one other gain amount associated with a neighboring channel.

21. A method as recited in claim 20, wherein the average operation is weighted average.

22. A method as recited in claim 19,

wherein said constraining to the first extent operates to average the initial gain amount for the channel signal with at least one other gain amount associated with a neighboring channel, and

wherein said constraining to the second extent operates to average the initial gain amount for the channel signal with a plurality of other gain amounts associated with neighboring channels, the number of other gain amounts being greater by at least one more than that used with said constraining to the first extent.

23. A method as recited in claim 22, wherein the average operation is weighted average.

25. A method as recited in claim 24, wherein said method further comprises:

filtering a sound signal to obtain a plurality of channel signals, including the channel signal.

27. A system as recited in claim 26, wherein said signal processing unit is a digital signal processor.

13. A method for amplifying sound signals in a multi-band sound processing system, said method comprising:

receiving a signal level estimate for a channel signal corresponding to a particular frequency band of a sound signal; and

determining a suitable gain amount for the channel signal based on the signal level estimate,

wherein, when the signal level estimate has a high level, the suitable gain amount is constrained to preserve spectrum contrast across frequency bands, thereby preserving speech clarity and intelligibility.

24. A method for amplifying sound signals in a multi-band sound processing system, said method comprising:

receiving a signal level estimate for a channel signal corresponding to a particular frequency band of a sound signal; and

determining a suitable gain amount for the channel signal based on the signal level estimate,

wherein, when the signal level estimate has a high level, the suitable gain is constrained to limit variation of gain difference across frequency bands, thereby preserving speech clarity and intelligibility.

26. A system for processing sound signals for hearing impaired persons, said system comprising:

a microphone to convert a sound pressure signal into an electronic sound signal;

a signal processing unit operatively connected to said microphone, said signal processing unit operates to filter the electronic sound signal to obtain channel signals for at least two channels, determine an estimated signal level for each of the channel signals, determine an initial gain amount for each of the channel signals based on the estimated signal level, constrain the initial gain amounts for the channel signals by combining the initial gain amount with other gain amounts associated with neighboring channels to produce constrained gain amounts, amplify the channel signals in accordance with the constrained initial gain amounts, and combine the amplified channel signal into a processed electronic sound signal; and

a receiver to convert the processed electronic sound signal to a sound pressure signal.

28. A system for amplifying sound signals in a multi-band sound processing system, said system comprising:

a microphone to convert a sound pressure signal into an electronic sound signal; and

a signal processing unit operatively connected to said microphone, said signal processing unit operates to filter the electronic sound signal to obtain channel signals for at least two channels with different frequency bands, receive a signal level estimate for each of the channel signals, and determine a suitable gain amount for each of the channel signals based on the signal level estimate corresponding to each of the channel signals,

wherein, when the signal level estimate has a high level, the suitable gain is constrained to preserve spectrum contrast across frequency bands.

29. A system for amplifying sound signals in a multi-band sound processing system, said system comprising:

a microphone to convert a sound pressure signal into an electronic sound signal; and

a signal processing unit operatively connected to said microphone, said signal processing unit operates to filter the electronic sound signal to obtain channel signals for at least two channels with different frequency bands, receive a signal level estimate for each of the channel signals, and determine a suitable gain amount for each of the channel signals based on the signal level estimate corresponding to each of the channel signals,

wherein, when the signal level estimate has a high level, the suitable gain amount is constrained to limit variation of gain difference across frequency bands.

30. A hearing aid device, comprising:

a microphone for picking up a sound signal;

signal processing circuitry operatively connected to said microphone, said signal processing circuitry operating to process the sound signal to produce a modified sound signal; and

an output device that produces an output sound in accordance with the modified sound signal,

wherein said signal processing circuitry operates to filter the sound signal into a plurality of channel signals of different frequency bands, obtain signal level estimates for each of the channel signals, and determine suitable gain amounts for the channel signals based on the signal level estimates, and

wherein, in determining each of the suitable gain amounts, when the signal level estimate has a high level, the corresponding suitable gain amount is constrained against gain amounts associated with one or more other channel signals.

31. A hearing aid device as recited in claim 30, wherein the constraining of one or more of the suitable gain amounts serves to preserve spectrum contrast across frequency bands, thereby preserving speech clarity and intelligibility.

32. A hearing aid device as recited in claim 30, wherein the constraining of one or more of the suitable gain amounts serves to limit the variation of gain difference across frequency bands, thereby preserving speech clarity and intelligibility.

33. A computer readable medium including at least computer program code for processing sound signals, said computer readable medium comprising:

computer program code for filtering a sound signal to obtain a channel signal for a channel;

computer program code for determining an estimated signal level for the channel signal;

computer program code for determining an initial gain amount for the channel signal based on the estimated signal level;

computer program code for constraining the initial gain amount based on the estimated signal level; and

computer program code for amplifying the channel signal in accordance with the constrained initial gain amount.

34. A computer readable medium as recited in claim 33, wherein said computer program code for constraining comprises:

computer program code for comparing the estimated signal level to at least one threshold level to obtain comparison information; and

computer program code for constraining the initial gain amount for the channel signal against a gain amount associated with at least one neighboring channel based on the comparison information.

35. A computer readable medium as recited in claim 33, wherein the channel signal pertains to a frequency band, and

wherein said computer readable medium further comprises:

computer program code for combining the amplified channel signal with other amplified channel signals from other frequency bands of the sound signal.