Speech band sampling rate expansion

Details Speech band sampling rate expansion Speech band sampling rate expansion

2000-07-03

2003-01-14

Dorvil, Richemond (Department: 2654)

Data processing: speech signal processing, linguistics, language

Audio signal bandwidth compression or expansion

C704S206000, C704S230000

Reexamination Certificate

active

06507820

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The invention relates to the band expansion of speech for telephones, in particular for mobile telephones.
DESCRIPTION OF RELATED ART
FIG. 1
of the accompanying drawings is an exemplary illustration of a wide-band speech signal having a bandwidth of around 8 kHz. Although most of the information carried by the speech signal is contained in components of the speech signal having frequencies up to 4 kHz, as can be seen clearly from the diagram, nevertheless significant information is contained in components of the speech signal having frequencies in the range approximately 4-8 kHz.
An exemplary illustration of an equivalent narrowband speech signal having a bandwidth of around 4 kHz is also shown in FIG.
1
.
The bandwidth of speech carried by the existing telephone system infrastructure is generally limited to around 4 kHz. Although speech signals having a bandwidth of 4 kHz are intelligible, the loss of the higher frequencies from the speech signal results in the speech produced by telephones sounding unnatural.
Many suggestions have been made previously to enhance the quality of speech signals in telephone systems by bandwidth expansion of the narrowband speech signal.
One conventional way of creating a wide-band speech signal from a narrowband speech signal relies on the characteristics of speech and uses pitch periodicity and the spectral envelope of the narrowband speech signal to estimate the pitch periodicity and the spectral envelope of the missing wide-band signals frequencies.
However, algorithms which estimate the pitch periodicity and the spectral envelope of the missing wide-band signals frequencies tend to introduce unwanted artefacts which reduce speech quality.
Spectrum expansion methods that utilise aliasing effects resulting from sampling rate conversion and subsequent digital filtering for spectrum shaping have also previously been proposed.
One example of this technique shows a narrowband speech signal sampled at 8 kHz is expanded by an interpolator with 16 kHz sampling. The resulting signal is fed to two parallel filter paths. In the first filter path the interpolated signal is filtered with a low pass filter to obtain the original input signal. In the second filter path the interpolated signal is filtered with a shaping filter to generate a signal in the frequency range 4-7 kHz. The signals resulting from the two parallel filter paths are then level adjusted and added together to obtain the desired wide-band signal.
However, although the circuit configuration used in this method is relatively simple when compared with the previously used methods based on estimates of the spectral envelope and periodicity of the speech signal, the method set out in this paper still involves extensive filtering and requires level adjustment of the signals in the different filter paths prior to the summation of the filtered samples from each path to obtain the wide-band output speech signal.
SUMMARY OF THE INVENTION
The prior art proposals to expand speech bandwidth for telephones have the drawback that they are fairly complex and computationally intensive. In addition prior art proposals which seek to estimate the higher band frequencies can introduce unwanted artefacts into the signal, therefore degrading the speech quality.
The present invention seeks to provide a method of expanding the speech bandwidth for telephones which provides improved speech quality when compared with the narrowband speech signal.
Embodiments of the method in accordance with the invention have the advantage that they can be implemented with low complexity.


REFERENCES:
patent: 4835791 (1989-05-01), Daoud
patent: 4896356 (1990-01-01), Millar
patent: 4901307 (1990-02-01), Gilhousen et al.
patent: 4941178 (1990-07-01), Chuang
patent: 5325318 (1994-06-01), Harris et al.
patent: 5406635 (1995-04-01), Jarvinen
patent: 5455888 (1995-10-01), Iyengar et al.
patent: 5581652 (1996-12-01), Abe et al.
patent: 0 696 110 (1996-02-01), None
patent: 0 838 804 (1998-04-01), None
patent: 1 008 984 (2000-06-01), None
patent: 1 409 799 (1975-10-01), None
patent: 2 280 827 (1995-02-01), None
Karelic et al (“Compression Of High-Quality Audio Signals Using Adaptive Filterbanks And A Zero-Tree Coder”, Convention of Electrical and Electronics Engineers in Israel, Mar. 1995).*
Ferreira (“A New Frequency Domain Approach To Time-Scale Expansion Of Audio Signals”, IEEE International Conference on Acoustics, Speech and Signal Processing, May 1998).*
Liang et al (“Combining A Biconical With A Polarizer To Expand Bandwidth”, Antennas and Propagation Society International Symposium, Jun. 1995).*
Crochiere et al (“Multirate Digital Signal Processing”, Prentiss-hall © 1990).*
Yasukawa, H: “Spectrum Broadening of Telephone Band Signals Using Multirate Processing for Speech Quality Enhancement”,IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, vol. E78-A No. 8, Aug. 1995, pp. 996-998.
Novelty Search performed by RWS Group of Tavistock House, Tavistock Square London WC1H 9LG, England on May 26, 1999.
Betts, John, Search Report for United Kingdom Patent Application No. GB 9915831.3, Dec. 21, 1999.
Soliman, Ahmed, International Search Report for International Patent Application No. PCT/EP00/05765, Sep. 29, 2000.

Affiliated with

Also associated with

Rating

Speech band sampling rate expansion does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Speech band sampling rate expansion, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Speech band sampling rate expansion will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3061502