Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Reexamination Certificate
2000-09-07
2003-09-09
To, Doris H. (Department: 2655)
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
C704S500000, C704S503000
Reexamination Certificate
active
06618700
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The subject invention relates generally to communication systems and more particularly to a method and apparatus for improving communication between a cellular phone and a phone on the PSTN network whenever a digital speech compression algorithm is followed by an compander conversion, which is typical.
2. Description of Related Art
In the prior art, situations arise where a digital cellular phone (e.g., GSM, PCS- 1800, IS-54) is connected to a telephone on the public switched telephone network (PSTN). Such cellular systems typically employ a speech coder followed by a compander, such as a &mgr;-Law or A-Law conversion, in order to interface to the PSTN network. Due to the “poor” quantization characteristics of A-Law and to a lesser extent of the &mgr;-Law conversion, at very low levels (hardly audible), the output of the speech coder are transformed into an annoying audible noise after the A/&mgr;-Law conversion at the receiving PSTN phones. The problem becomes worse as the bit-rate of the speech coding algorithm decreases and is most noticeable if a level adjustment (increase) takes place after the A/&mgr;-Law decoding.
SUMMARY OF THE INVENTION
It has been discovered that annoying audible noise during speech intervals can be eliminated by adding a fixed number in the digital domain to the output of the speech coder. In this manner, signal samples shifting around zero are moved away from the area of “poor” quantization of the compander. The invention would typically be a part of the speech decoder algorithm, as a post operation. However, it can be used as successfully, as a stand alone block between any speech decoding algorithm and the A-Law or &mgr;-Law conversion (compander). Adding a fixed number to the output of the speech decoder is inaudible, and does not degrade speech quality in any way. The technique eliminates the problem for any bit-rate. The effect is dramatic and will solve the noise problem for most existing standards. Alternatively, the constant added to the output of the speech coder is confined to a small value added to the speech coder output so that during the silence period between speech, when the output of the coder falls slightly below zero or slightly above zero, the constant value moves the entire speech coder output during the silence period slightly above zero or slightly below zero.
REFERENCES:
patent: 4507792 (1985-03-01), Yamakido et al.
patent: 5121391 (1992-06-01), Paneth et al.
patent: 5177734 (1993-01-01), Cummiskey et al.
patent: 5267262 (1993-11-01), Wheatley, III
patent: 5666659 (1997-09-01), Kernahan et al.
patent: 5692105 (1997-11-01), Leppänen et al.
patent: 5734967 (1998-03-01), Kotzin et al.
patent: 5784406 (1998-07-01), DeJaco et al.
patent: 5878329 (1999-03-01), Mallinckrodt
patent: 5926505 (1999-07-01), Long
patent: 5943365 (1999-08-01), Long et al.
patent: 0 381 215 (1990-08-01), None
patent: 2064276 (1981-06-01), None
patent: WO 00/07178 (2000-02-01), None
Su Huan-Yu
Thyssen Jes
Farjami & Farjami LLP
Mindspeed Technologies Inc.
Opsasnick Michael N.
To Doris H.
LandOfFree
Speech coder output transformation method for reducing... 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 coder output transformation method for reducing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Speech coder output transformation method for reducing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3079786