U.S. Philips Corporation

Koninklijke Philips Corporation N.V.

Robert J Sluijter

Rakesh Taori

Andreas Johannes Gerrits

Cornelis M Huizer

Hendrik Tjalling Dijkstra

Eric Kathmann

Samir Chennoukh

Hendrik J Kotmans

Gerrit Ary Slavenburg

Albertus Cornelis Den Brinker

Johannes W Bergmans

Friedhelm Wuppermann

Jozef L Van Meerbergen

Hendrik D Hollmann

Augustus Josephus Elizabeth Maria Janssen

Ludovicus M G M Tolhuizen

Fransiscus M De Bont

Mark A Russell

Franciscus J Van Wijk

Fransiscus P Welten

Ludovicus Mgm Tolhuizen

Coding of an audio signal represented by a respective set of sampled signal values for each of a plurality of sequential segments is disclosed. The sampled signal values are analyzed () to determine one or more sinusoidal components for each of the plurality of sequential segments. The sinusoidal components are linked () across a plurality of sequential segments to provide sinusoidal tracks. For each sinusoidal track, a phase comprising a generally monotonically changing value is determined and an encoded audio stream including sinusoidal codes (r) representing said phase is generated ().

Audio coding via creation of sinusoidal tracks and phase determination

Wideband extension of telephone speech for higher perceptual quality. A method for extending the frequency range of a speech signal using wideband extension method with an inverse filter and a synthesis filter where both filters receive LPC coefficients from an LPC estimator. The wideband LPC coefficients are obtained from wideband LSFs. The wideband LSFs are obtained by appending highband LSFs, created by applying a matrix to narrowband LSFs, and lowband LSFs, created by dividing the narrowband LSFs by two. The matrix used to create the highband LSFs is selected from a predetermined list of matrices. The selection is based on either wideband or narrowband reflection coefficients extracted from the narrowband speech signal.

Wideband extension of telephone speech for higher perceptual quality

Described is a transmission system () comprising a transmitter () for transmitting a narrowband audio signal to a receiver () via a transmission channel (). The receiver () comprises a frequency domain bandwidth extender () for extending a bandwidth of the received narrowband audio signal by complementing the received narrowband audio signal with a highband extension thereof. The bandwidth extender () comprises an amplitude extender () for extending the bandwidth of an amplitude spectrum of the received narrowband audio signal by mapping narrowband amplitudes onto highband amplitudes. The bandwidth extender () further comprises a phase extender () for extending the bandwidth of a phase spectrum of the received narrowband signal and a combiner () for combining the extended amplitude spectrum and the extended phase spectrum into a bandwidth extended audio signal. The transmission system () is characterized in that the amplitude extender () comprises an amplitude mapper () and first and second frequency scale transformers (). The first frequency scale transformer. () is arranged for transforming a linear frequency scale of the amplitude spectrum into a logarithmic frequency scale, e.g. the Bark scale. The amplitude mapper () is arranged for mapping according to the logarithmic frequency scale the narrowband amplitudes onto the highband amplitudes. The second frequency scale transformer () is arranged for transforming the logarithmic frequency scale of the extended amplitude spectrum into the linear frequency scale.

Wideband signal transmission system

A transmission system includes a transmitter with a signal encoder and a codebook entry selector. The signal encoder has an input for a signal to be encoded. The codebook entry selector selects a codebook entry for obtaining a synthetic signal giving a best approximation of a signal representative of the input signal. The codebook entry includes samples that can assume more than two values and is identified with a sequence of symbols. A receiver has a decoder with a codebook for deriving the codebook, where the codebook entries corresponding to sequences of symbols that differ in one particular symbol value also differ in one signal sample value.

Encoder and decoder for minimizing effects of transmission errors using a synthetic signal

A transmission system includes a speech decoder, the speech decoder having a detector which determines a level of background noise in a speech signal and a post filter in electrical communication with an output of the decoder when the level of the background noise is equal to or less than a threshold value. A synthesis filter is connected to the output when the level of the background noise is greater than the threshold value.

Transmission system with improved speech decoder

An analyzer determines frequency and amplitudes of an audio signal represented by sinusoids for transmission transmitted to a receiver decoder which includes a synthesizer to reconstruct the audio signal. A pitch detector determines the pitch for transmission to the receiver along with the structure of the spectrum of the speech signal. The structure of the spectrum is often transmitted in the form of LPC parameters. To correct for frequency changes of the periodic component of an audio signal, a frequency change determiner determines a change of the frequency of the periodical component over the analysis period. This change of frequency is transmitted to the decoder for increasing the accuracy of the reconstruction of the audio signal. Further, the frequency change is only used to obtain a more accurate value of the pitch. The frequency change is determined by using a time warper which performs a time transformation such that a time transformed audio signal is obtained with a minimum frequency change.

Transmission system for transmitting an audio signal

In an audio transmission system, an input signal is split up into two spectral portions in a transmitter. These spectral portions are coded by their own respective coder. The low-frequency signal portion is coded by a regular narrow-band coder and the high frequency portion is coded using a coder that outputs LPC codes and signal amplitude codes. In the receiver, the low frequency signal portion is reconstructed by a narrow-band decoder and the high frequency portion is reconstructed by applying a high pass filter to a white noise signal and applying an LPC filter that is controlled by the LPC codes to this filtered white noise signal and adjusting the signal amplitude with an amplifier that is controlled using the amplitude codes of the transmitter. The reconstructed low frequency signal and the reconstructed high frequency signal are then combined to yield a reconstructed output signal containing both frequency ranges.

High frequency and low frequency audio signal encoding and decoding system

A transmission system comprising a transmitter with a signal encoder, the signal encoder having an input for a signal to be encoded and a codebook entry selector for selecting a codebook entry for obtaining a synthetic signal giving a best approximation of a signal representative of the input signal, wherein the codebook entry includes a plurality of samples that can assume more than two values and is identified with a sequence of symbols, a receiver having a decoder with a codebook for deriving the codebook entry from the sequence of symbols received from the transmitter, wherein the codebook entries corresponding to sequences of symbols that differ in one particular symbol value also differ in one single sample value.

Encoder for minimizing resulting effect of transmission errors

A speech transmission system with an input speech signal applied to a speech encoder for encoding the speech signal which is transmitted via a communication channel to a speech decoder. Background noise dependent processing elements in the speech encoder and/ or speech decoder are introduced to improve the performance of the transmission system. The parameters of the perceptual weighting filter in the speech encoder are derived by calculating linear prediction coefficients from a speech signal which is processed by means of a high pass filter. An adaptive post filter in a speech decoder is bypassed when the noise level exceeds a threshold value.

Transmission system with improved speech encoder

In a transmission system a variable length encoder is used to reduce the average bitrate of a sequence of symbols. In order to limit the maximum length of the code it is proposed to transmit the sequence of symbols only in coded form if the length of the coded sequence is lower than a predetermined value

Transmission system using a variable length encoder

In a speech encoder (4), a speech signal is encoded using a voiced speech encoder (16) and an unvoiced speech encoder (14). Both speech encoders (14,16) use analysis coefficients to represent the speech signal. The analysis coefficients are determined more frequently when a transition from voiced to unvoiced speech or vice versa is detected. This has been found to achieve significantly improved quality of speech reproduced from the encoded speech signal.

Speech encoding system with increased frequency of determination of

In a harmonic speech encoder (16) a speech signal to be encoded is represented by a plurality of LPC parameters which are determined by a LPC parameter computer (30), a pitch value and a gain value. The speech encoder comprises a (coarse) pitch estimator (38) for determining a coarse pitch, and a refined pitch computer (32) to determine a refined pitch from the coarse pitch value. The refined pitch value is determined in an analysis by synthesis way, in which a refined pitch value is selected which results in a minimum error measure between a representation of a synthesized speech signal and a representation of the original speech signal.

Transmitter with an improved harmonic speech encoder

In a CELP coder a comparison between a target signal and a plurality of synthetic signals is made. The synthetic signal is derived by filtering a plurality of excitation sequences by a synthesis filter having parameters derived from the target signal. The excitation signal which results in a minimum error between the target signal and the synthetic signal is selected. In order to reduce the complexity of the search for the best excitation signal, thee selection is done in two stages. First a preselection of a small number of excitation sequences is made using a reduced complexity synthesis filter. Thereafter, with this small number of excitation sequences, a full complexity search is made. Due to the reduced number of excitation sequences involved in the final selection the required computational complexity is reduced.

Reduced complexity signal transmission system

A transmission system contains a speech coder which utilizes a pitch detector that is arranged to select a characteristic auxiliary signal portion from the signal to be coded in order to improve the quality of the pitch detection. The pitch is found by searching in the speech signal for signal portions that correspond to the characteristics auxiliary signal portion and by calculating the time difference between the respective signal portions.

Transmission system with speech encoder with improved pitch detection

In a transmission system for a quasi-periodic signal, an encoder (12) transmits to a decoder (28) no more than a single period from a total number of periods of the quasi-periodic signal in encoded form. In this decoder (28) the lacking periods of the quasi-periodic signal are reconstructed by means of interpolation. For obtaining an enhanced quality of the reconstructed signal, a signal segment is transmitted that is representative of two successive periods of the quasi-periodic signal. This signal segment may contain two successive periods, but may also be a signal segment having the length of a single period and being determined by a weighted sum of two successive periods.

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Eindhoven, Netherlands

Robert J Sluijter