Electrical audio signal processing systems and devices – Binaural and stereophonic – Broadcast or multiplex stereo
Patent
1994-12-15
1998-09-22
Kuntz, Curtis A.
Electrical audio signal processing systems and devices
Binaural and stereophonic
Broadcast or multiplex stereo
395 212, 395 214, 395 238, 381 1, 381 22, 381 23, H04H 500
Patent
active
058126724
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a method for reducing data in the transmission and/or storage of digital signals of several dependent channels in which scanning values of signals from the time range are transferred blockwise into the frequency range (in spectral values), the spectral value are encoded, transmitted and/or stored, decoded and transmitted back in several channels in the time range.
Methods in which e.g. audio signals are transmitted in frequency-coded manner, are e.g. known from PCT publications WO88/01811 and WO89/08357. Express reference is made to these documents for explaining terms which are not clarified here.
Many known methods for data-reduced coding of digital audio signals code the signals in the frequency range and use for the transmission of the signals from the time range into the frequency range (in spectral values) a suitable imaging procedure, e.g. a FFT, DCT, MDCT, polyphase filter bank or hybrid filter bank.
These methods lead to a high degree of utilization of signal redundancy and irrelevance with respect to the characteristics of the human ear. If during the transmission of signals of several channels the signals are not independent of one another, an additional reduction of the data quantity case of signals in the channels of a quadraphonic or stereophonic audio signal.
A method for the utilization of the redundancy/irrelevance between the two channels of a stereo audio signal is described in the publication by J. D. Johnston, "Perceptual Transform Coding of Wideband Stereo Signals", IEEE, 1989, pp. 1993-1996. In this so-called MS coding (middle/side coding) instead of the left and right channel the sum (=center) and the difference (=side) of the stereo signal is coded. This leads to a saving in the quantity of data to be transmitted.
The dependence of signals of two stereo channels is also utilized in the intensity stereo process known from "Subband Coding of Stereophonic Digital Audio Signals", IEEE 1991, pp.3601 to 3604. In this process the monosignal and an additional information concerning the left/right distribution of the signal are transmitted.
As a result of both these procedures in the case of an unfavorable signal composition high interference levels can occur. For example, a very differing signal composition in the left and right channels in MS coding leads to defects which are not concealed by the signal present in the contained in the right channel, leads to interference on the left channel, which is not concealed and which can therefore be clearly heard. When using the intensity stereo method the spatial sound impression is lost if the left and right channels have a widely differing spectral composition.
Thus, the known methods are only usable if no unfavorable signal composition is to be expected, or if interference can be accepted in favor of reducing the data quantity.
An object of the invention is to provide a method for reducing data in the transmission and/or storage of digital signals of several dependent channels, in which the dependence of the signals in the different channels is utilized and which does not lead to a subjectively perceivable interference of the transmitted signals.
The present invention achieves this object by providing a method for reducing data during the transmission and/or storage of digital signals from N dependent channels, in which scanning values of signals from the time range are transformed blockwise into the frequency rangein spectral values, the spectral values are encoded, transmitted and/or stored, decoded and transmitted back in N channels in the time range, comprising: determining from the spectral values of corresponding blocks of the different channels a quantity which is a measure for the spectral distance between signals of the different channels, and comparing the quantity with a predetermined threshold and performing a common encoding of the signals from the different channels upon the quantity dropping below the threshold.
According to the invention the signals of the differ
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Robbert G. van der et al. "Subband Coding of Stereophonic Digital Audio Signals", IEEE 1991, pp. 3601 to 3604.
J.D. Johnston, "Perceptual Transform Coding of Wideband Stereo Signals", IEEE, 1989, pp. 1993-1996.
Raymond N.J. Veldhuis et al., "Subband Coding of Digital Audio Signals Without Loss of Quality", IEEE 1989, pp. 2009 to 2012.
Herre Juergen
Seitzer Dieter
Fraunhofer-Ges
Kuntz Curtis A.
Nguyen Duc
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