U.S. Philips Corporation

Fransiscus M De Bont

Friedhelm Wuppermann

Robert J Sluijter

Eric Kathmann

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

In a transmission system a signal is encoded in an encoder (7) and the encoded signal is transmitted by a transmitter (2) via a transmission medium (4) to a receiver (6). In the encoder, analysis parameters of the input signal are determined by an analyzer (8) and quantized by a quantizer (14). The transmitter transmits quantization level numbers to the receiver (6), and in the receiver decoded analysis parameters are derived by interpolating level numbers of two subsequent sets of analysis parameters, and subsequently determining the corresponding analysis. By interpolating the level numbers instead of the analysis parameters themselves, a substantial amount of computational complexity is saved.

Signal transmission system in which level numbers representing

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 from a one dimensional codebook 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, the selection is done in two stages. First a preselection of a small number of excitation sequences is made by selecting only every L.sup.th codebook entry for preselecting a plurality of excitation sequences. Thereafter, with this small number of excitation sequences, a full complexity search is made in which all excitation sequences surrounding the preselected ones are involved in the selection.

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Eindhoven, Netherlands

Fransiscus M De Bont