High-frequency bandwidth extension in the time domain

• US 8,200,499 B2
• Filed: 03/18/2011
• Issued: 06/12/2012
• Est. Priority Date: 02/23/2007
• Status: Active Grant

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: QNX Software Systems Limited (Canada) (Blackberry Limited)
• Inventors: Nongpiur, Rajeev, Hetherington, Phillip A.
• Primary Examiner(s): Abebe, Daniel D
• Application Number:
  US13/051,725
• Publication Number:
  US 20110231195A1
• Time in Patent Office: 452 Days
• Field of Search: 704/200, 704/223, 704/500, 381/23
• US Class Current: 704/500
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

A system extends the high-frequency spectrum of a narrowband audio signal in the time domain. The system extends the harmonics of vowels by introducing a non linearity in a narrow band signal. Extended consonants are generated by a random-noise generator. The system differentiates the vowels from the consonants by exploiting predetermined features of a speech signal.

Claims

1. A system that extends the high-frequency spectrum of a narrowband audio signal in the time domain:

an interface configured to receive a narrowband audio signal;

a squaring circuit that squares a segment of the narrowband audio signal to extend harmonics of vowels by introducing a non linearity in the received narrowband audio signal in the time domain;

a random noise generator that generates consonants by introducing random-noise in the received narrowband audio signal in the time domain;

a plurality of filters that pass a portion of the frequencies on the non-linearity and the random noise;

a first amplifier that adjusts an envelope of the filtered portion of the random noise to an estimate of a high pass filtered version of the received narrowband audio signal; and

a second amplifier that adjusts an envelope of the filtered portion of the non-linearity to a level of an envelope of the high pass filtered version of the received narrowband audio signal.

2. The system of claim 1, where the first amplifier adjusts the envelope of the filtered portion of the random noise to a variance of unity.

3. The system of claim 2, where the envelope of the filtered potion of the random noise is adjusted to a variance of unity by a gain factor of an absolute value of the high pass filtered version of the received narrowband audio signal smoothed with a leaky integrator filter.

4. The system of claim 1, further comprising a plurality of mixers that select a portion of an output from the first amplifier and a portion of an output from the second amplifier.

5. The system of claim 4, further comprising a summing circuit that sums the portion of the output from the first amplifier and the portion of the output from the second amplifier to generate an extended portion of a high frequency signal.

6. The system of claim 5, further comprising a second summing circuit that sums the extended portion of the high frequency signal with the received narrowband audio signal to generate a bandwidth extended signal.

7. The system of claim 6, further comprising an adaptive filter configured to dampen a background noise detected in the bandwidth extended signal.

8. The system of claim 7, where the adaptive filter comprises an estimating circuit that estimates a high frequency signal to noise ratio of a high pass filtered version of the received narrowband audio signal, and a scalar coefficients estimating circuit.

9. The system of claim 7, further comprising an adaptive shaping filter configured to vary the spectral shape of the output of the adaptive filter configured to dampen a background noise detected in the bandwidth extended signal.

10. The system of claim 9, where the adaptive shaping filter is configured to change a spectrum shape of the output of the adaptive filter configured to dampen a background noise detected in the bandwidth extended signal when a processed signal represents a consonant.

11. A method of extending a high-frequency spectrum of a narrowband signal, comprising:

receiving a narrowband signal at an interface;

evaluating a portion of the narrowband signal to determine a speech characteristic in that portion of the narrowband signal;

generating a high-frequency time domain spectrum based on the determined speech characteristic in the evaluated portion of the narrowband signal; and

combining the generated high-frequency time domain spectrum with the narrowband signal to create an extended signal,

where the high-frequency time domain spectrum comprises squaring the evaluated portion of the narrowband signal when the speech characteristic in the evaluated portion of the narrowband signal represents a vowel.

12. The method of claim 11, further comprising adaptively passing selective frequencies of the extended signal to suppress a portion of a background noise in the extended signal.

13. The method of claim 12, further comprising shape adjusting the extended signal.

14. The method of claim 11, further comprising adjusting a magnitude of the high-frequency time domain spectrum before combining the high-frequency time domain spectrum with the narrowband signal.

15. A method of extending a high-frequency spectrum of a narrowband signal, comprising:

receiving a narrowband signal at an interface;

evaluating a portion of the narrowband signal to determine a speech characteristic in that portion of the narrowband signal;

generating a high-frequency time domain spectrum based on the determined speech characteristic in the evaluated portion of the narrowband signal; and

combining the generated high-frequency time domain spectrum with the narrowband signal to create an extended signal,

where the high-frequency time domain spectrum comprises a random generated signal when the speech characteristic in the evaluated portion of the narrowband signal represents a consonant.

16. The method of claim 15, further comprising adaptively passing selective frequencies of the extended signal to suppress a portion of a background noise in the extended signal.

17. The method of claim 16, further comprising shape adjusting the extended signal.

18. The method of claim 15, further comprising adjusting a magnitude of the high-frequency time domain spectrum before combining the high-frequency time domain spectrum with the narrowband signal.