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Abstract

An apparatus for deriving a compressed digital signal from a digital input signal by compressing the digital input signal in a selected one of at least two compression modes. The compressed digital signal has a different bit rate in each of the compression modes. The apparatus includes a receiving circuit that receives the digital input signal at the same sampling frequency in all compression modes. The apparatus also includes a low-pass filter that has a cut-off frequency set according to the selected one of the compression modes. The low-pass filter receives the digital input signal and provides a bandwidth-limited signal. Finally, the apparatus includes a compressor circuit that derives the compressed digital signal from the bandwidth-limited signal. In an alternative embodiment, the apparatus comprises a circuit that receives the digital input signal at the same sampling frequency in each of the compression modes. The apparatus also includes a block dividing circuit that divides the digital input signal in time into blocks. Each block has a block length; and the block lengths of the blocks have a maximum block length that depends on the selected one of the compression modes. The maximum block length is greater in the compression modes in which the digital output signal has a lower bit rate. Finally, the apparatus includes a compressor circuit that derives the compressed digital signal from the blocks of the digital input signal.

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First Claim