US 5,490,130 A · Apparatus and method for compressing a digital input signal in more than one compression mode

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.

Claims40

Dependent claims

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 digital input signal being compressed with a different compression ratio in each of the at least two compression modes, the compressed digital signal having a bit rate, the bit rate of the compressed digital signal being different in each of the compression modes, the apparatus comprising:

receiving means for receiving the digital input signal at a fixed sampling frequency, the sampling frequency being invariable between the compression modes;
a low-pass filter having a cut-off frequency set according to the selected one of the compression modes, the low-pass filter receiving the digital input signal and providing a bandwidth-limited signal having a bandwidth defined by the cut-off frequency of the low-pass filter;
and
compressor means for deriving the compressed digital signal from the bandwidth-limited signal.

1 more element

means for receiving the digital input signal at a fixed sampling frequency, the sampling frequency being invariable between the compression modes;
block dividing means for dividing the digital input signal in time into blocks, each block having a block length, the block lengths of the blocks having a maximum block length depending on the selected one of the compression modes, the maximum block length being greater in the compression modes wherein the digital output signal has a lower bit rate;
and
compressor means for deriving the compressed digital signal from the blocks of the digital input signal.

1 more element

Method 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 digital signal being compressed with a different compression ratio in each of the at least two compression modes, the compressed digital signal having a bit rate, the bit rate of the compressed digital signal being different in each of the compression modes, the method comprising the steps of:

receiving the digital input signal at a fixed sampling frequency, the sampling frequency being invariable between the compression modes;
subjecting the digital input signal to low-pass filtering with a cut-off frequency set according to the selected one of the compression modes to provide a bandwidth-limited signal having a bandwidth defined by the cut-off frequency of the low-pass filtering;
and
deriving the compressed digital signal from the bandwidth-limited signal.

1 more element

Method for deriving a compressed digital signal from a digital input signal by compressing the digital input signal using a selected one of at least two compression modes, the digital input signal being compressed with a different compression ratio in each of the at least two compression modes, the compressed digital signal having a bit rate, the bit rate of the compressed digital signal being different in each of the compression modes, the method comprising steps of:

receiving the digital input signal at a fixed sampling frequency, the sampling frequency being invariable between the compression modes;
dividing the digital input signal in time into blocks, each block having a block length, the block lengths of the blocks having a maximum block length depending on the selected one of the compression modes, the maximum block length being greater in the compression modes wherein the digital output signal has a lower bit rate;
and
deriving the compressed digital signal from the blocks of the digital input signal.

1 more element

Dependencies are inferred from the claim text.

Apparatus and method for compressing a digital input signal in more than one compression mode

Life of this patent

Apparatus and method for compressing a digital input signal in more than one compression mode

Life of this patent

Abstract

Claims40