U.S. Philips Corporation

Koninklijke Philips Corporation N.V.

Eric Kathmann

Robert J Sluijter

Rakesh Taori

Johannes W Bergmans

Friedhelm Wuppermann

Adrianus Wilhelmus Maria Van Den Enden

Antonius J Bogers

Fransiscus M De Bont

Mark A Russell

In a method of encoding a source signal by determining Line Spectral Frequencies (LSFs) for representing Linear Predictive Coding (LPC) filter coefficients, real zeros are determined in associated polynomials P&Prime; and Q&Prime; in cos(m&ohgr;), with each polynomial being a series of Chebyshev polynomials, a search for real zeroes being performed by evaluating the associated polynomials in a series of steps of a real variable u, an approximation of cos(m&ohgr;) as a function of the real variable u being employed.

Method of calculating line spectral frequencies

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.

Transmission system for quasi periodic signals

A digital transmission system wherein only certain of the samples in a series of signal samples are transmitted by the transmitter to a receiver over a channel. In addition, various characteristic parameters of the series of signal samples are determined in the transmitter and transmitted to the receiver. The characteristic parameters are used at the receiver to reconstruct the missing single samples by assigning to them values such that the resulting reconstructed series of signal samples approximates the characteristic parameters as closely possible. If the series has a periodicity having a period longer than the time duration of the series of signal samples, reconstruction of the series may have a considerable interpolation error. By determining such period in the transmitter and transmitting it over the channel to the receiver, where the same periodicity is introduced into the reconstructed series of signal samples, the interpolation error is considerably reduced.

Transmission system with reconstruction of missing signal samples

For avoiding error propagation as a result of decision feedback equalization, the data to be transmitted are coded with a coder 2 which has a transfer function substantially inverse to the transfer function of the channel 4. Consequently, instantaneous decisions about the received symbol may be made at the receiver 6 without intersymbol interference causing a disturbance. If the channel transfer function differs from the transfer function of the precoder 2, intersymbol interference will again occur, so that the symbol error rate will increase. In order to restrict this increase of the symbol error rate as much as possible, the receiver comprises a cascaded circuit of an adaptive filter 18 which has an inverse transfer function to that of the channel and a decoder 21 which has an inverse transfer function to that of the precoder 2.

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Eindhoven, Netherlands

Eric Kathmann