Other

Lucent Technologies Inc.

Dror Nahumi

Willem Bastiaan Kleijn

The arrangement of the invention allows for modifying amplitude, frequency or phase characteristics, for example, of an audio or video signal in a compressed signal system without altering the encoder or decoder employed by each conferee in communications information conferencing. A control network inserted between the encoder and decoder permits demultiplexing the compressed bitstream signal into sensitive parameters of the signal to be controlled, as well as into those parameters whose characteristics are not of concern. The control is then effected on the parameters of concern, in a way so as to eliminate the signal degradation associated with general tandeming signal decoding and coding operations of all characteristics in establishing the scaling control desired.

Volume control arrangement for compressed information signals

Simplified methods of searching a codebook table are provided. These methods perform a codebook search for a plurality of pulses, one pulse at a time, in order of increasing to decreasing pulse significance, wherein pulse significance is defined as the relative contribution a given pulse provides to minimizing the mean-squared error between the source signal and the quantized sequence of pulses.

Optimized pulse location in codebook searching techniques for speech

The apparatus of the invention eliminates objectionable popping and clicking when switching between conferees in a communications conferencing system employing signal compression techniques to reduce bandwidth requirements. The apparatus operates with the conventional audio decoder of such system, and with its conventional audio encoder of the type employing a look-ahead-buffer in converting a frame of sampled voice or data to a compressed bit stream. The apparatus of the invention employs its own audio decoder and audio encoder in broadcasting the digital signal samples to the various conferees on the system, but its audio encoder is devoid of any look-ahead-buffer, to achieve synchronization and time matching between the audio encoder delay and its relevant bit stream.

Delay synchronization in compressed audio systems

An improved method of speech coding for use in conjunction with speech coding methods wherein speech is digitized into a plurality of temporally defined frames, each frame including a plurality of sub-frames, and the digitized speech is partitioned into periodic components and a residual signal. For each of a plurality of sub-frames of the residual signal, the improved method of speech coding selects and applies a time shift T to the sub-frame by applying a matching criterion to (a) the current sub-frame of the residual signal, and (b) a sample-to-sample (subframe-to-subframe) pitch delay determined by applying linear interpolation to known pitch delays occurring at or near frame-to-frame boundaries of previous frames. The matching criterion is applied by minimizing .epsilon., where: ##EQU1## (r(n-T)) is the residual signal of the current frame shifted by time T, r(n-D(n)) is the delayed residual signal from a previously-occurring frame, n is a positive integer, r is the instantaneous amplitude of the residual signal, and D(n) is the sample-to-sample pitch delay determined by applying linear interpolation to known pitch delay values occurring at or near frame-to-frame boundaries.

RCELP coder

In a speech coding system which encodes speech parameters into a plurality of frames, each frame having a predetermined number of bits, a predefined number of bits per frame are employed to transmit a speech parameter delta. The speech parameter delta specifies the amount by which the value of a given parameter has changed from a previous frame to the present frame. According to a preferred embodiment disclosed herein, a speech parameter delta representing change in pitch delay from the present frame to the immediately preceding frame is transmitted in the present frame, and the predefined number of bits is in the approximate range of four to six. The speech parameter delta is used to update a memory table in the speech coding system when a frame erasure occurs.

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Dror Nahumi