Coded data generation or conversion – Digital code to digital code converters
Patent
1996-05-31
1998-04-07
Gaffin, Jeffrey A.
Coded data generation or conversion
Digital code to digital code converters
341106, 381 2, 395 209, D03M 700
Patent
active
057369437
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for determining the type of coding to be selected for coding at least two signals, in which each signal is transformed into the frequency domain and, starting from the spectral values, a similarity measure is determined for the similarity of in each case at least two signals.
In particular, the invention relates to an optimized coding selection for coding two or more signals of which at least two are not independent of one another but contain at least partially redundant or irrelevant information.
2. Description of the Prior Art
In general, in methods for data-reduced coding of digital audio signals the signals are initially transformed from the time domain into the frequency domain. If signals are concerned which are not independent of one another, it is customary to use data-reduced coding which takes account of the redundancy between the two or the plurality of channels.
Such coding has become known as so-called centre/side coding (J. D. Johnston, "Perceptual Transform Coding of Wideband Stereo Signal", IC ASSP, IEEE, 1989, pages 1993 to 1996). In this centre/side coding, on the basis of the left and right channels the sum or centre of the stereo signals is coded, on the one hand, and the difference or side of the stereo signals is coded, on the other hand.
A further type of coding, which has meantime become customary, is the intensity-stereo method which is described in a publication entitled "Subband Coding of Stereophonic Digital Audio Signals", Proc. of the IC ASSP, 1991, IEEE, Toronto, pages 3601 to 3604. In the intensity-stereo method, on the basis of the two channels a monosignal is formed and transmitted with a supplementary information item by the left/right distribution of the signal.
It has already been stated in the applicant's German Patent DE 41 36 825 C1 that in such methods strong interference can occur if the signals have only a relatively slight similarity or are even completely independent of one another. Thus, it is known that a strongly differing composition of the signals in the left and right channels leads in the case of centre/side coding to artifacts which cannot be masked by the signal actually present in the channel. When using the intensity-stereo method, destruction of the spatial sound impression can occur if the left and right channels have spectral values deviating substantially from one another.
In order to face this problem, it is proposed in this printed document to use the spectral values of the signals transformed into the frequency domain to determine a similarity measure on the basis of which switching-over between different types of coding is undertaken. If the spectral values produce a high similarity measure, centre/side coding is used in the method described there, while in the case of a low similarity measure, and thus in the case of a low spectral similarity of the channels under consideration, separate coding of the channels is undertaken. It is likewise known from this patent to use the signals to be coded to calculate the masking threshold by means of a psychoacoustic model, said masking threshold being used to drive a data-reducing stage which is connected downstream of the centre/side coding stage and achieves a data reduction while taking account of the masking.
In its Claim 15, which refers back indirectly to Claim 8, DE 41 36 825 C1 describes only the use of a masking threshold in determining the spectral values which can be set to zero.
Although the method disclosed in German Patent 41 36 825 already achieves a considerable quality enhancement by comparison with unchanged centre/side coding methods and by comparison with unchanged intensity-stereo methods, a further enhancement of the quality of the data to be transmitted is desirable in the case of further reduction of the data rate.
It is therefore the object of the invention, starting from this prior art, to develop a method for determining the type of coding to be selected for coding at least two signals in
REFERENCES:
patent: 5278909 (1994-01-01), Edgar
patent: 5285498 (1994-02-01), Johnston
patent: 5530750 (1996-06-01), Akagiri
patent: 5535300 (1996-07-01), Hall, II et al.
patent: 5581654 (1996-12-01), Tsutsui
Brandenburg Karlheinz
Eberlein Ernst
Grill Bernhard
Herre Jurgen
Seitzer Dieter
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Gaffin Jeffrey A.
Kost Jason L. W.
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