Electrical audio signal processing systems and devices – Binaural and stereophonic – Pseudo stereophonic
Patent
1996-09-12
1997-12-23
Isen, Forester W.
Electrical audio signal processing systems and devices
Binaural and stereophonic
Pseudo stereophonic
381 23, H04S 502
Patent
active
057013462
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention refers to a method of coding a plurality of audio signals, comprising the steps of combining at least two signals by joint stereo coding so as to obtain a jointly coded signal, whereupon the jointly coded signal is decoded so as to provide simulated decoded signals, which are combined by matricization in a compatibility matrix together with additional signals so as to provide signals that are compatible with existing decoders.
The present invention especially deals with a multichannel coding technique for audio signals which is adapted to be used in connection with the coding standard MPEG-2.
DESCRIPTION OF THE PRIOR ART
The future MPEG-2 audio standard does not represent a fundamentally new coding algorithm, but defines extensions of the coding algorithms according to the standards MPEG-1 layer I, II and III. Although MPEG-1 decoders are not capable of decoding an MPEG-2 bit stream, the extension to a multichannel system including up to 5 full-range audio channels with an additional low-frequency channel and up to 7 multispeech channels permits a so-called downward compatibility for MPEG-1 standard decoders.
When MPEG-2 coding for several audio channels is carried out, one central channel, one left and one right basic channel and one left as well as one right so-called "surround" channel are typically coded, a low-frequency improvement channel for the independent transmission and reproduction of low-frequency information being selectively provided.
When the MPEG-2 standard is used, importance is attached to a so-called "downward compatible" transmission, i.e. the coding is to be carried out such that the coded signal can be decoded by already existing dual-channel decoders of the MPEG-1 standard. For this purpose, the left and right basic channels L, R of the MPEG-1 standard are replaced by matricized signals Lc, Rc that are produced by a compatibility matrix. The left compatible signal Lc is obtained from the left basic channel, the central channel and the left surround channel by multiplying these signals with different matrix coefficients and by adding them afterwards. The bit stream thus produced is adapted to be decoded by an MPEG-1 decoder, the central information and the surround information being, however, not contained separately in the MPEG-1-decodable compatible signals Lc, Rc.
The dual-channel signal obtained by matricization includes all relevant signal components for permitting downward-compatible decoding. Hence, it will suffice in most cases to transmit, in addition to these compatible signals, three further channels within the framework of the multichannel extension data stream. The missing up to two channels are reconstructed in the decoder by inverse matricization, or a so-called dematricization.
For utilizing the multichannel irrelevance, joint stereo decoding techniques are used, such as joint stereo coding which is based on the "intensity stereo coding technique". All jointly coded signals are replaced by scaled embodiments of a single transmitted signal. This is done in such a way that the acoustically relevant signal properties, viz. e.g. the energy or the time envelopes of the signals, are largely preserved.
The production of downward compatible signals and the simultaneous utilization of multichannel irrelevance by using joint stereo coding techniques entail, however, the following problems: When the compatible signals Lc, Rc are produced first by matricization and when "intensity stereo" coding, or IS coding, is then applied to the residual channels, these signals are no longer in harmony with the "compatible" signals. Hence, a dematricization operation in the decoder will result in completely different reconstructed channel signals which are audibly distorted in comparison with the original signals.
This problem can be solved by using IS coding first and by producing the compatible signals by matricization subsequently. This enforces the consistency of all signals taking part and, consequently, it has the effect that correct dema
REFERENCES:
patent: 5291557 (1994-03-01), Davis et al.
International Search Report of the PCT/EP95/00378.
International Standard ISO/IEC 11172-3, 1993, pp. V, VI, 5, 6 (English trlation).
Stettner: Mehrkanal-Stereoton zum Bild fur Kino und Fernsehen, In: Rundfunktechnische Mitteilungen, edition 35 1991, vol. 1, pp.1-9.
IEEE International Conf. on Acoustics, Speech and Processing, vol. 2, Mar. 23, 1992, San Francisco, California, U.S.A., pp. 205-288, "Matrixing of bit rate reduced audio signals," (English translation).
Brandenburg Karlheinz
Eberlein Ernst
Grill Berhard
Herre Jurgen
Seitzer Dieter
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Isen Forester W.
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