Pulse or digital communications – Bandwidth reduction or expansion
Reexamination Certificate
1998-01-15
2001-07-24
Ghebretinsae, Temesghen (Department: 2631)
Pulse or digital communications
Bandwidth reduction or expansion
C704S500000
Reexamination Certificate
active
06266368
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a data compression apparatus for data compressing at least a first and a second digital information signal, each of the at least two digital information signals comprising subsequent samples, the apparatus comprising:
means for receiving the first and second digital information signal,
signal combination means for combining the first and second digital information signal so as to obtain a composite information signal,
data compression means for data compressing the composite information signal so as to obtain a data compressed composite information signal,
output means for supplying the data compressed composite information signal, to a data expansion apparatus for data expanding a data compressed composite information signal obtained from at least a first and a second digital information signal, the apparatus comprising
input means for receiving the data compressed composite information signal,
data expansion means for data expanding the data compressed composite information signal so as to obtain a data expanded composite information signal,
retrieval means for retrieving a replica of the first and second digital information signal from the data expanded composite information signal,
output means for supplying the replicas of at least the first and second digital information signals, to a transmitter comprising the data compression apparatus, to a receiver comprising the data expansion apparatus, to a method for data compression, to a method for data expansion and to a record carrier.
Data compressing a stereo audio signal is well known in the art. Reference is made in this respect to EP-A 402,973, document D1 in the list of related documents. The document describes a subband coder, in which each of the left and right hand signal components of the stereo audio signal is A/D converted with a specific sampling frequency, such as 44.1 kHz, and the resulting samples in de form of eg. 24 bits wide words of the audio signal, are supplied to a subband splitter filter. The subband splitter filter splits the audio signal component into a plurality of relatively narrow band subband signals. Using a psycho acoustic model, a masked threshold is derived and blocks of samples of the subband signals are subsequently quantised with a specific number of bits per sample for each block of the subband signals, in response to said masked threshold, resulting in a significant data compression of the audio signal to be transmitted. The data compression carried out is based on ‘throwing away’ those components in the audio signal that are inaudible and is thus a lossy compression method.
In an intensity stereo mode, a further data reduction can be obtained by combining, in the same subband, samples of the subband signals of the left and right hand signal components of the stereo audio signal, by adding them so as to obtain samples of a composite subband signal and carrying out a data compression on the composite subband signal.
The data compression described in document D1 is a rather intelligent data compression method and requires a substantial number of gates or instructions, when realized in hard or software respectively, so that it is expensive. Moreover, the subsequent expansion apparatus also requires a substantial number of gates or instructions, when realized in hardware or software respectively.
SUMMARY OF THE INVENTION
The invention aims at providing a data processing apparatus for data compressing at least a first and a second digital information signal such that the information signals can be data compressed in a more simple way, with a simpler data compressor, such as a lossless coder. Further, the corresponding expander apparatus can also be more simple and less expensive.
The data compression apparatus in accordance with the invention comprises merging means for merging samples of the first and second digital information signal after each other into one datastream so as to obtain said composite information signal, said data compression means having a control input for receiving a control signal, the data compression means being adapted to data compress the composite information signal in response to said control signal, control signal generation means being available, for generating said control signal, said control signal generation means having an input for receiving said composite information signal and being adapted to generate said control signal in response to said composite information signal.
Preferred embodiments of the data compression apparatus, a corresponding data expansion apparatus, a transmitter comprising the data compression apparatus, a receiver comprising the data expansion apparatus and a record carrier, are the subject of the subclaims.
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“A Method For The Construction of Minimum-Redundancy Codes”, by David A. Huffman, Proceedings of The I.R.E., pp. 1098-1103.
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Belk Michael E.
Ghebretinsae Temesghen
U.S. Philips Corporation
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