Psytechnics Limited

British Telecommunications Public Limited Company

Paul Alexander Barrett

Antony William Rix

Simon Richard Broom

Richard Jb Reynolds

Richard John Buchan Reynolds

Ludo Malfait

Phil Gray

Neil Robert Garner

Ludovic Maifait

Andrew Whitefield

Tom Goldstein

This invention relates to generation of a sample error coefficient suitable for use in an audio signal quality assessment system. The invention provides a method of determining a sample error coefficient between a first signal and a similar second signal comprising the steps of: determining a first periodicity measure from the first signal; determining a second periodicity measure from the second signal; generating a ratio in dependence upon said first periodicity measure and said second periodicity measure; and determining a sampling rate error coefficient in dependence upon said ratio.

Generating sample error coefficients

This invention relates to a method of defining an optimised set of test sequences for use with a packet based perceptual quality evaluation processor associated with an edge-device that receives packets containing speech data and converts said packets to a speech signal, the method comprising the steps of: defining a set of quality targets which should be produced when a test sequence of packets is processed by the edge-device; determining a value for a degradation parameter for each quality target wherein a test sequence having a degradation according to said value will substantially produce said quality target when said test sequence is processed by the edge-device.

Generating test sets

The present invention relates to detection of echo in telecommunications networks. The invention provides a method of echo detection comprising the steps of: generating a series of inbound vectors for an inbound signal; generating a series of outbound vectors for an outbound signal; repeating a predetermined number of comparison steps comprising the sub-steps of selecting an outbound vector from the outbound vectors; selecting an inbound vector from the inbound vectors; comparing said outbound vector with said inbound vector and with successive inbound vectors to generate a plurality of similarity metrics; and determining a relative position of the compared outbound vector having maximum correlation with said inbound vector; and counting the number of times each relative position is determined to be the position of maximum correlation.

Signal processing

Non-intrusive speech quality assessment method and apparatus for storing a sequence of intercepted packets associated with a call, each packet containing speech data, and an indication of a transmission time of the packet; storing with each intercepted packet an indication of an intercept time of the packet; extracting a set of parameters from the sequence of packets; and generating an estimated mean opinion score in dependence upon the set of parameters. The extracting step comprises the sub steps of: generating a jitter parameter for each packet of the sequence of stored packets; generating a long term average jitter parameter for the stored packet; and generating a differential jitter parameter in dependence upon the jitter parameter for the stored packet and the long term average jitter parameter.

Quality assessment tool

Non-intrusive speech quality assessment method and apparatus for: storing a sequence of intercepted packets associated with a call, each packet containing speech data, and an indication of a transmission time of the packet; storing with each intercepted packet an indication of an intercept time of the packet; extracting a set of parameters from the sequence of packets; and generating an estimated mean opinion score in dependence upon the set of parameters. The extracting step comprises the sub steps of: generating a jitter parameter for each packet of the sequence of stored packets; and generating a consecutive positive jitter parameter for the stored packet.

A method and apparatus for assessing the perceptual quality of stereo speech signals transmitted via a telecommunications network and recorded acoustically from an acoustic terminal device in which a mono reference signal comprising a single channel is aligned with a degraded stereo signal comprising a left and a right channel; a delay between each channel of said degraded signal and said reference signal is estimated; a noise masking indicator in dependence upon said estimated delays is generated; the level of the stereo signals is adjusted in dependence upon said noise masking indicator; a set of perceptually relevant parameters for each of said reference and degraded signals are generated; the perceptually relevant parameters of the reference signal with the perceptually relevant parameters of the degraded signal to generate a disturbance profile are compared; and a speech quality prediction is generated in dependence upon said disturbance profile.

Speech quality assessment with noise masking

This invention relates to measurement of error characteristics of a communication channel. The invention is of particular use for measuring perceived transmission performance of the communication channel. The invention provides a method and apparatus for measuring the transmission error characteristics of a channel employing frame based transmission in which a frame classification indicator is generated for an expected frame, according to data received via said channel, and in which the following steps are repeatedly performed: generating frame classification data relating to the expected frame; updating a statistical representation of the transmission error characteristics according to said frame classification. The invention also provides a method and apparatus for measuring perceived transmission performance of a communications channel in which the perceived transmission performance is generated according to measured transmission error characteristics.

Method and apparatus for transmission error characterization

The present invention relates to a method and apparatus for determining channel degradation information in which a known data sequence is compared to a transmitted version of the known data sequence to provide such information. To assess performance of a public land mobile network, it is convenient if assessment apparatus is located in the network rather than in a mobile station. The invention provides a technique for efficiently sending data characterizing channel degradation caused by the network to mobile station communication channel from the mobile station back to the network, where the channel degradation information is reconstructed.

Method and apparatus for measurement of channel transmission accuracy

This invention relates to the measurement of the accuracy of a communication channel. The invention provides a method and apparatus for determining channel degradation information for a communications channel, in which a known data sequence is generated within a transmitter; a coded data sequence based on the known data sequence is transmitted using the transmission channel; said known data sequence is generated within the receiver; and the known data sequence generated within the receiver is compared with a decoded data sequence based on data received via the channel to provide said channel degradation information; wherein a source encoder in the transmitter has the ability to generate a predetermined output data sequence in response to a predetermined input data sequence; the known data sequence is generated within the transmitter and within the receiver in dependence upon the predetermined output data sequence; and the decoded data sequence is measured prior to source decoding in the receiver.

Communication channel accuracy measurement

A method of measuring the degradation of a data stream owing to the influence of errors thereon is disclosed. Unlike known degradation measures, a measure calculated in accordance with the present invention takes into account the variation in the significance of an error in dependence upon the elements which are affected by it. A particular application of the method to the selection of one of a number of possible speech coding methods for use in transmitting speech across a radio link ( ) from a mobile phone ( ) to a base station ( ) is described.

Method and apparatus for signal degradation measurement

A voice activity detector suitable for deployment in a mobile phone apparatus is disclosed. An advantage of the voice activity detector is that it is better able to provide a decision ( ) as to whether an input signal ( ) consists of noise (which it is not desired to transmit) or comprises speech or information tones (which are required to be transmitted), especially in noisy environments. The voice activity detector includes a number of components, in particular an auxiliary voice activity detector ( ). The auxiliary voice activity detector ( ) distinguishes between noise and speech on the basis that the spectrum of speech changes more rapidly than that of noise. This results in the auxiliary detector ( ) rarely mistaking a speech signal to be a noise signal. Hence, a very reliable noise template ( ) is obtained. For this reason, the auxiliary detector ( ) is also useful in noise reduction applications. The voice activity detector also uses a neural net classifier ( ).

Voice activity detector for calculating spectral irregularity measure on the basis of spectral difference measurements

Speech is distinguished from noise by a spectral comparison of an input signal with a stored noise estimate. Updating of the noise estimate stored in a buffer is permitted during periods when speech is absent under control of an auxiliary detector. In order to improve operation in the presence of signals with strong harmonic components, e.g., signaling tones, an LPC prediction gain is computed from the input (x(i)) and a residual (y(i)) obtained from the input following filtering by a filter having a response complementary to the frequency spectrum of the input, and if the gain exceeds a threshold, buffer updating is suppressed.

Voice activity detector

Speech is distinguished from noise by a spectral comparison of an input signal with a stored noise estimate. Updating of the noise estimate stored in a buffer is permitted during periods when speech is absent under control of an auxiliary detector. In order to improve operation in the presence of signals with strong harmonic components, e.g., signalling tones, an LPC prediction gain is computed from the input (x(i)) and a residual (y(i)) obtained from the input following filtering by a filter having a response complementary to the frequency spectrum of the input, and if the gain exceeds a threshold, buffer updating is suppressed.

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Ipswich, United Kingdom

Paul Alexander Barrett