Electrical audio signal processing systems and devices – Noise or distortion suppression – Interpolation
Patent
1985-10-18
1987-01-13
Rubinson, Gene Z.
Electrical audio signal processing systems and devices
Noise or distortion suppression
Interpolation
364571, 455 63, G11B 2024
Patent
active
046370501
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION(s)
This U.S. application stems from PCT International Application No. PCT/DE84/00285 filed Dec. 31. 1984.
The invention relates to a method for suppressing interference in an original signal, in particular an audio signal, comprising a useful signal component and an interference signal component, and to an apparatus for carrying out said method.
As is known, in an electrical signal only the component which lies above the level of the interference signal component present in the signal can be utilized. In particular, in the case of an electroacoustic or audio signal the interference signal component is no longer subjectively perceived in those regions of the signal in which the signal amplitude is above the interference level caused for example by noise. However, to make the interference level inaudible also in the regions of the signal in which the amplitude of the useful signal component is beneath the interference level, it is necessary to carry out a suppression operation to remove the signal regions dominated by the interference level. To avoid then causing any audio physiological interference point the curve ends of the remaining signal regions must then be connected together in suitable manner. However, at the moment there would appear to be no suitable known method for this which can be carried out with an economically acceptable expenditure.
The invention is based on the problem of providing such a method and an apparatus for carrying out said method by which with relatively low expenditure a substantially complete interference suppression can be obtained.
This problem is solved as regards the method in that the original signal is digitally recorded with a sampling frequency corresponding at least to the essential information content of its useful signal component, that the interference signal component is detected and its level stored as reference interference signal with a sampling frequency corresponding at least to a level change rate of the interference signal component under the control of a computer in phase synchronism with the recorded digitized signal, and that the recorded digitized signal is processed with a speed independent of its recording speed and its interference signal component compensated under computer control in dependence upon the stored reference interference signal.
By the digital recording of the generally analog original signal, on the one hand a coding of the signal suitable for the computer-controlled processing is obtained. On the other hand, this recording operation permits the method to be carried out independent of the recording and time. Due to the related possible choice of the processing speed independently of the recording speed the difficulty of a data flow of the digitally recorded signal which is too high for the computer-controlled processing is also eliminated. Likewise, the data flow corresponding to the interference signal component can readily be reduced to a speed suitable for computer-controlled storing because for carrying out the method it suffices to store the level change of the interference signal component which can be detected with a substantially reduced data quantity per time unit. This is because it suffices for the compensation following the readout from the store to know the level of the interference signal component, the detailed variation of the interference signal component not being important.
The main use of the method according to the invention will no doubt lie in commercial music production. For example, by compensating the interference signal component in historic recordings the latter could be made available in modern sound quality.
Preferably the method according to the invention is carried out in that the interference signal component is split into a hum component and a noise component and the corresponding reference interference signals are separately stored. This measure takes account of the different nature of the hum component and the noise component. Whereas the hum component is form
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Rubinson Gene Z.
Schroeder L. C.
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