Electrical audio signal processing systems and devices – Binaural and stereophonic – Quadrasonic
Reexamination Certificate
1998-05-21
2001-08-14
Isen, Forester W. (Department: 2644)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Quadrasonic
C381S020000, C381S023000, C704S500000, C704S200100
Reexamination Certificate
active
06275589
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and an apparatus for error masking in multi-channel audio signals, in particular an MPEG-2 audio decoder.
BACKGROUND
For audio coding, the MPEG-2 standard provides for a spatial representation by multi-channel reproduction (multi-channel sound). The multi-channel sound in this case comprises three channels L, C, R (Left, Centre, Right), which are arranged spatially in front of the listener, and two channels LS, RS (Left Surround, Right Surround), which are arranged spatially behind the listener. In addition, a sixth channel for special effects is provided. In order to ensure backwards compatibility with MPEG-1 signals, the signals of the multi-channel sound channels are matrixed. The stereo signals L
0
and R
0
calculated in the process are then transmitted as MPEG-1-compatible stereo signal and the remaining three audio signals are transmitted as supplementary data.
Before being matrixed, the audio signals generally have their levels reduced in order to prevent overdriving. Thus, a value of L
0
=2.4 would result, for example, in the case of matrixing in accordance with L
0
=L+0.7C+0.7LS without attenuation, i.e. for L, C, LS=1. In order to balance again the reduction at the encoder end, an option that is provided in the MPEG-2 standard is for a decoder to raise the output levels again. If, however, a transmission error then occurs in the multi-channel section, the decoder cannot carry out the reverse matrixing. In that case, only the MPEG-1-compatible signal component, i.e L
0
and R
0
, will be decoded. The auditory impression can therefore be disturbed in various ways during the changeover to MPEG-1 decoding. Thus, sudden changes in volume may occur, for example, since level raising is not carried out in MPEG-1 decoding.
SUMMARY OF THE INVENTION
The invention is based on the object of specifying a method for error masking in multi-channel audio signals. This object is achieved by means of the method specified in claim
1
.
The invention is based on the further object of specifying an apparatus for carrying out the method according to the invention. This object is achieved by means of the apparatus specified in claim
7
.
In principle, the method for the level matching of multi-channel audio signals, at the encoder end mono or stereo signals and supplementary signals being produced from the multi-channel audio signals by means of matrixing, and the mono or stereo signals being coded in accordance with a first coding standard and the supplementary signals being coded in accordance with a second coding standard, and at the decoder end the mono or stereo signals and supplementary signals being decoded and subjected to inverse matrixing, in order to obtain the multi-channel audio signals again, consists in the an fact that in the event of errors being detected in the supplementary signals, a portion of the multi-channel audio signals is cross-faded to the mono or stereo signals and/or a further portion of the multi-channel audio signals is set to zero.
In an advantageous manner, the multi-channel audio signals are in this case attenuated at the encoder end prior matrixing. Then, at the decoder end, level raising of the stereo signals is effected prior to the cross-fading of the multi-channel audio signals, the level raising at the decoder end then being reversed again after a period of time.
In this case, it may be particularly advantageous if the level raising is reversed in the event of errors being detected over a plurality of frames.
The first coding standard may be, in particular, the MPEG-1 standard and the second coding standard may be, in particular, the MPEG-2 standard.
A further advantageous development provides for the accoustics for the reproduction area to be calculated, the level raising being carried out in such a way that the deviation of the accoustics before and after the level raising is minimal.
Furthermore, in the event of multi-channel sound errors, a changeover and/or cross-fading to a pseudo-accoustics method may preferably be effected.
In principle, apparatus for the reproduction of multi-channel audio signals, having a first decoder for decoding mono or stereo signals and a second decoder for decoding supplementary signals, and an inverse matrixing device, to which the decoded signals are fed in order to produce the multi-channel audio signals, consists in the fact that a changeover switch is provided to which are fed the mono or stereo signals from the first decoder and an error signal from the second decoder and the multi-channel audio signals from the inverse matrixing device, a changeover from the multi-channel audio signals to the mono or stereo signals being effected when the error signal appears.
In this case, the changeover switch is preferably arranged upstream of the synthesis filter which is present at the decoder end.
It is furthermore advantageous if a unit for conflicting level raising is provided by which the level of the mono or stereo signal is raised in the event of an error.
It is particularly advantageous if, furthermore, a timer is provided which enables the level raising by the unit to be switched off after a period of time.
Furthermore, it may be advantageous to provide a unit by which the current accoustics are calculated, this value being fed to the unit for level raising.
REFERENCES:
patent: 5701346 (1997-12-01), Herre et al.
patent: 5920833 (1999-06-01), Dierke
patent: 6023490 (2000-02-01), Ten Kate
patent: 4409368A1 (1995-09-01), None
patent: WO93/19541 (1993-09-01), None
Deutsche Thomson-Brandt GmbH
Isen Forester W.
Pendleton Brian
Shoneman D. T.
Tripoli J. S.
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