Electrical audio signal processing systems and devices – Binaural and stereophonic – Broadcast or multiplex stereo
Patent
1995-01-05
1997-06-10
Isen, Forester W.
Electrical audio signal processing systems and devices
Binaural and stereophonic
Broadcast or multiplex stereo
381 18, 395 238, H04H 500
Patent
active
056384513
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
For the transmission and storage of audio signals in digital form, different coding methods for achieving bit rate reduction have become known so far (DE 3639753 C2) which are used for the coding of a monophonic or stereophonic audio channel. If the bit rate of two audio channels that belong together is to be reduced, each individual channel by itself can be subjected to a bit rate-reducing coding and can subsequently be transmitted or stored. The bit rate reduction, however, can be made more effective by not only utilizing the masking characteristics of the human ear in each individual audio channel taken by itself for the bit rate reduction but, in addition, by also utilizing the inertia of the hearing sensation in stereophonic hearing as well as the stereophonic masking characteristics of the human ear (NL 9000338).
For some applications (such as, for example, for future HDTV applications), however, it is intended to transmit, record or reproduce more audio channels of a multi-channel signal than the usual two (stereophonic) used so far. Naturally, in such a case all audio channels can be individually subjected to a bit rate-reducing coding before they are transmitted or stored. Nevertheless, the bit rate necessary for the transmission of multi-channel audio signals increases along with the number of channels that are to be transmitted. Because of the very high costs for the additionally required channel capacity compared to stereophonic transmission, this circumstance does not result in an easy implementation of such a multi-channel transmission method.
SUMMARY OF THE INVENTION
It is the object of the invention to create a method which necessitates only a relatively small increase in the data rate when the number of channels is expanded.
This object is solved, according to the invention, in that for the bit rate reduction of audio signals having more than two audio channels, the psychoacoustic masking by at least a portion of the remaining audio channels or the redundancy of individual audio channels among themselves is utilized for each individual audio channel, to the effect that
only those portions of the considered audio channel are transmitted or stored that, in the reproduction types or modes that can be selected from, are not masked by the audio signals of other audio channels or are contained in the audio channels for stereophonic reproduction, and
the used portions are transmitted or stored with such a low resolution that, in the reproduction types or modes that can be selected from, the quantization noise generated by quantization remains masked by the totality of all audio channels.
Advantageous modifications and developments of the method according to the invention ensure compatibility with existing systems.
The invention is based on the consideration that when the number of channels to be transmitted is expanded to more than only two audio channels, the masking characteristics of the human ear should still be utilized further for the coding of these audio channels beyond the masking characteristics in the individual channel or stereo channel. In this process, the masking by all other audio signals can be utilized for each individual audio channel of the audio channels to be transmitted or stored.
By means of such a procedure, the data rate for the transmission of the additional audio channels that exceed the two base audio channels of a stereo signal that are normally to be transmitted, can be considerably reduced if suitable coding is used.
For these additional audio channels only those portions of the respective audio signals are then transmitted
that are not masked by the audio signals of other audio channels, and
these portions are only transmitted with such a low resolution and thus also data rate that the quantization noise generated by quantization remains masked.
If a sub-band coding method is used, the portions to be transmitted can be separated from the portions that are not to be transmitted by deciding on a sub-band basis, while sorting out can t
REFERENCES:
patent: 5285498 (1994-02-01), Johnston
Warner R. Th.: "Eine Neue Codiertechnik fur Surround-Stereo-Surround (4-2-4)". In: Rundfunktechnische Mitteilungen, vol. 35, No. 1, Jan. 1991, Norderstedt, DE, pp. 10-16.
W.R. Th. ten Kate et al.: "Matrixing of Bit Rate Reduced Audio Signals". IN: IEEE International Conference on Acoustics, Speech and Signal Processing, vol. 2, Mar. 23, 1992, San Francisco, US, pp.205-208.
Suganami et al.: "A sound Reproduction and Transmission System for HDTV". In: Fourth International Colloquium on Advanced Television Systems, Jun. 25, 1990, Ottawa, CA, pp. 3A.7.2-3A.7.14.
Johnston et al.: "Sum-Difference Stereo Transform Coding" In: IEEE International conference on Acoustics, Speech and Signal Processing, vol. 2, Mar. 23, 1992, San Francisco, US, pp. 569-572.
James Johnston: "Perceptual Transform Coding of Wideband Stereo Signals". In: IEEE International Conference on Acoustics, Speech and Signal Processing, vol. 3, May 23, 1989, Glasgow, GB, pp. 1993-1996.
Institut Fuer Rundfunktechnik GmbH
Isen Forester W.
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