Apparatus and methods for enhancement of speech

• US 20080177532A1
• Filed: 01/22/2007
• Published: 07/24/2008
• Est. Priority Date: 01/22/2007
• Status: Active Grant

• Current Assignee: DSP Group Ltd. (Synaptics Incorporated)
• Original Assignee: DSP Group Ltd. (Synaptics Incorporated)
• Inventors: Gur, Arie, Greiss, Israel
• Granted Patent: US 8,229,106 B2
• Time in Patent Office: Days
• US Class Current: 704/200.1
• CPC Class Codes: G10L 21/0364 for improving intelligibility
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

A method for improving the intelligibility of an incoming telephone signal, including boosting loudness of at least one band of poorly heard frequencies of the signal within at least one band of intensities of the signal, the band lying below a predetermined intensity level at which telephone standard conformance testing is performed, thereby to generate a differentially boosted telephone signal. Alternatively or in addition, intelligibility of sibilants in a narrow band telephone signal is enhanced, by doubling the sampling rate of the narrow band signal by interpolation, thereby to provide a narrow band interpolated signal, generating a harmonic extrapolation signal by harmonically extrapolating from the narrow band interpolated signal thereby to estimate the missing portions of the telephone signal, the harmonic extrapolation comprising a sequence of pulses located at peaks of the interpolated signal, generating a missing energy estimator measure estimating energy missing at high frequency bands of the telephone signal, continuously modulating the amplitude of the pulses in said sequence of pulses based on said missing energy estimator measure, thereby to generate a modulated signal, passing the modulated signal through a shaping filter thereby to obtain a shaped signal, and summing the shaped signal with the interpolated signal.

Claims

1. Apparatus for improving the intelligibility of an incoming telephone signal, the apparatus comprising:

a frequency band and intensity dependent loudness modifier operative to boost loudness of at least one band of poorly heard frequencies of the incoming telephone signal within at least one band of intensities of the incoming telephone signal, said band lying below a predetermined intensity level at which telephone standard conformance testing is performed, thereby to generate a loudness boosted signal,

wherein said loudness modifier is also operative to boost loudness of at least one band of poorly heard frequencies of the incoming telephone signal at said predetermined intensity level wherein the loudness is boosted at the predetermined intensity level only to the extent allowed by the telephone standard.

4. Apparatus according to claim 1 which resides interiorly of a telephone receiver.

5. Apparatus according to claim 1 wherein the band of poorly heard frequencies in which loudness is boosted within said at least one band of intensities is programmable.

6. Apparatus according to claim 1 wherein the band of intensities at which the loudness of a band of poorly heard frequencies is boosted, is programmable.

7. Apparatus according to claim 1 and wherein said loudness modifier is operative to attenuate loudness of at least one band of frequencies of the incoming telephone signal within at least one band of intensities of the incoming telephone signal lying below a threshold intensity level below which the signal is considered background noise.

9. Apparatus according to claim 1 wherein operation of the loudness modifier is determined at least partly as a function of a loudness estimate determined by filtering the incoming telephone signal, measuring the energy of the filtered signal, and smoothing the measured energy over time.

10. Apparatus according to claim 1 wherein the extent of boosting is a non-linear function of the intensity level of the incoming telephone signal.

11. Apparatus according to claim 10 and also comprising a compression table storing desired levels of boosting as a function of intensity level of the incoming telephone signal.

12. Apparatus according to claim 1 wherein operation of the loudness modifier is determined at least partly as a function of a loudness estimate determined recursively by measuring the energy of the telephone signal after its loudness has been modified by the loudness modifier.

13. Apparatus according to claim 9 wherein at least one of the extent of loudness modification and the direction of loudness modification effected by the loudness modifier at at least one intensity level is determined as a function of said loudness estimate.

2. A method for improving the intelligibility of an incoming telephone signal, the method comprising:

boosting loudness of at least one band of poorly heard frequencies of the incoming telephone signal within at least one band of intensities of the incoming telephone signal, said band lying below a predetermined intensity level at which telephone standard conformance testing is performed, thereby to generate a dynamically boosted telephone signal.

3. Apparatus according to claim 2 and wherein the loudness is boosted within said intensity band to an extent which exceeds the extent allowed by the telephone standard at said predetermined intensity level.

14. Apparatus according to claim 2 and also comprising:

a low pass filter receiving and filtering said incoming telephone signal thereby to provide a low passed signal; and

a virtual bass reconstructor operative to compute an envelope estimate by band-pass filtering an absolute value of the low passed signal and passing said band-passed filtered absolute value into a summation operator for summation with said loudness boosted signal.

15. Apparatus according to claim 14 and also comprising a programmable multiplier operative to multiply said envelope estimate by a programmed factor.

8. Apparatus for enhancing the intelligibility of sibilants in a narrow band telephone signal, the apparatus comprising:

a sample rate doubler doubling the sampling rate of the narrow band telephone signal by interpolation, thereby to provide an interpolated signal;

a harmonic extrapolator producing a harmonic extrapolation of missing portions of the telephone signal, the harmonic extrapolation comprising a sequence of pulses located at peaks of the interpolated signal;

a missing energy estimator generating a missing energy estimator measure estimating energy missing at high frequency bands of the telephone signal;

a continuous amplitude modulator continuously modulating the amplitude of the pulses in said sequence of pulses based on said missing energy estimator measure, thereby to generate a modulated signal;

a shaping filter which converts the modulated signal into a shaped signal; and

a summer summing the shaped signal with the interpolated signal.

16. A method for enhancing the intelligibility of sibilants in a narrow band telephone signal, the method comprising:

doubling the sampling rate of the narrow band telephone signal by interpolation, thereby to provide a narrow band interpolated signal;

generating a harmonic extrapolation signal by harmonically extrapolating from the narrow band interpolated signal thereby to estimate the missing portions of the telephone signal, the harmonic extrapolation comprising a sequence of pulses located at peaks of the interpolated signal;

generating a missing energy estimator measure estimating energy missing at high frequency bands of the telephone signal;

continuously modulating the amplitude of the pulses in said sequence of pulses based on said missing energy estimator measure, thereby to generate a modulated signal;

passing the modulated signal through a shaping filter thereby to obtain a shaped signal; and

summing the shaped signal with the interpolated signal.

17. A method according to claim 16 wherein said step of generating a missing energy estimator measure comprises:

passing the narrow band telephone signal through a zero-crossing identification unit and subsequently through a low pass filter thereby to generate an LPF output; and

multiplying the LPF output by an estimate of the energy of the high frequency portion of the narrow band telephone signal thereby to obtain said energy estimator measure,

and wherein said step of continuously modulating comprises multiplying an amplitude function of said sequence of pulses by said energy estimator measure.

18. A method according to claim 16 wherein the estimate of the energy of the high frequency portion is generated by:

passing the narrow band telephone signal through a high pass filter comprising a differentiator, thereby to generate a high pass filtered signal; and

subtracting from the high pass filtered signal an estimate of the noise level of the filtered narrow band telephone signal.

19. A method according to claim 16 wherein said shaping filter comprises a bandpass filter.

20. A method according to claim 16 wherein said peaks comprise positive peaks.

21. A method according to claim 16 wherein said peaks comprise negative peaks.

22. A method according to claim 16 wherein said peaks comprise all positive peaks and all negative peaks.

23. A method according to claim 16 wherein said shaping filter comprises a high pass filter.

24. A method according to claim 16 wherein random noise is added to the harmonic extrapolation signal.

25. A method according to claim 16 wherein said step of generating a missing energy estimator measure comprises:

passing a pulse train signal located at peaks of the interpolated signal via a low pass filter; and

multiplying the filtered pulse train signal by an estimate of the energy of a high frequency portion of the narrow band telephone signal thereby to obtain said energy estimator measure.

26. A method according to claim 24 and also comprising:

doubling the sampling rate of the differentially boosted telephone signal by interpolation, thereby to provide an interpolated signal;

producing a harmonic extrapolation of missing portions of the differentially boosted telephone signal, the harmonic extrapolation comprising a sequence of pulses located at peaks of the interpolated signal;

generating a missing energy estimator measure estimating energy missing at high frequency bands of the differentially boosted telephone signal;

continuously modulating the amplitude of the pulses in said sequence of pulses based on said missing energy estimator measure, thereby to generate a modulated signal;

passing the modulated signal through a shaping filter thereby to obtain a shaped signal; and

summing the shaped signal with the interpolated signal.