RU2121175C1 - Dynamic-companding device for noise reduction - Google Patents

Abstract

FIELD: multichannel tape recorders. SUBSTANCE: device provides combination of dynamic and companding noise reduction in single device with possibility to change signal envelope in given way. Dynamic noise clipping unit is inserted before expander. This results in possibility to decrease noise level in pauses by approximately 15 dB. EFFECT: increased noise reduction. 3 dwg

Description

 The invention relates to the field of information storage, in particular to noise reduction systems in sound reproducing technology.

 A widely known compander noise reduction system using compressor and expander blocks connected through a noise introducing unit (for example, magnetic tape) (Radio Journal, Moscow, DOSAAF, 1992, 6, p. 57-58). Side systems (DOLBY A, B, C, SR, DBX) provide noise masking with sound signals, i.e. when there is sound, noises are not heard.

 Basically, noises are felt by ear in the pauses between musical fragments or individual sounds, especially in the case of implementation in multi-channel tape recorders, when there are long pauses between sound signals.

 Known systems contain two main units - a compressor and an expander (made, for example, in the form of non-linear amplifiers). (M.V. Gitlits. Magnetic recording in information transmission systems, M .: Energoizdat, 1978, pp. 93-96, Journal of Radio, M., DOSAAF, 1983, 5, pp. 36-40). Such systems provide a noise level of 10 dB below the natural sound level. At the peak level, noise is not heard due to masking sound.

 However, the known system does not provide a sufficient level of noise reduction.

 The objective of the present invention is to provide a device which, when combined with a compander and dynamic noise suppressors, in a predetermined manner changes the shape of the signal envelope and simplifies the implementation of such a device.

 The invention is illustrated by the drawing, in which Fig. 1 shows a block diagram of a device, and in Figs. 2 and 3 are timing diagrams of signals of a known compander noise suppressor and a proposed dynamic dynamic noise suppressor, respectively.

 The compander-dynamic noise suppressor contains a compressor unit 1, connected through a noise introducing medium 2 (for example, recording and reproducing channels of an analog tape recorder), with a dynamic noise limiting unit 3, the output of which is connected to the input of the expander 4, which restores sound signals to initial levels.

 For convenience, we agree that the beginning and end of the sound signal are at a level of about -65 dB (figa). When passing through a compressor with an gain of, for example, 15 dB, the start and end levels of the signal increase to -50 dB, and the shape of the envelope line changes (Fig.2b). Next, the signal passes through the link, making noise, for example, is recorded on a magnetic tape (pigv). As can be seen, in the well-known compander noise suppressor (figure 2), the beginning and end levels of sound lie above the noise level by 10 dB.

 In a conventional compander squelch, the signal passes through the expander, bringing the signal to its original state (Fig.2d), while achieving a gain in noise of about 10 dB in pauses.

 Compander-dynamic noise reduction works as follows.

 The original signal (Fig.3A) after the compressor (Fig.3b) and recording onto magnetic tape (Fig.3c) from the reproducing magnetic head (not shown) falls on the dynamic filter 3, which without distortion passes signals above about -55 dB (open ), and signals less than -55 dB reduces by 15 (closed) (Fig. 3d). Then the signal cleared in pauses is fed to the expander (Fig. 3d), while the sound levels are restored to the initial state, and the noise level is reduced by another 15 dB compared to the compander noise suppressor. As a result, a noise reduction level of about 90 dB is achieved before the start of sound signals.

 The signal processing according to the new structure (called PGA) can be performed both over the entire spectrum of the sound range similar to the DbX system, and in parts of the range to the Dolby B NR, Dolby C or Dolby A systems.

 As a result, in comparison with conventional compander noise suppressors (Fig. 2), the gain is -15 dB in the pauses between sound signals and can be significantly increased.

 This device is especially effective when used as part of multi-channel tape recorders, where there are rather long pauses between the playback signals on individual channels. In this case, the DNL filters and non-linear amplifiers can be optimized accordingly to provide the specified noise reduction levels.

 It should be noted that DNL systems are already known that provide noise reduction in a certain range (see above). Operational amplifiers in such systems have a large gain, which is selected from the amplitude of the noise and the degree of compression-expansion.

 However, at present, a technical solution is unknown that uses a combination of known noise reduction systems to solve the problem of significantly reducing noise levels, for example, in pauses, in multi-channel applications.

 As illustrated above, in the compander-dynamic noise suppressor, after the link introducing noise, a dynamic noise limiter with a sensitivity of, for example, -55 dB is turned on, that is, in the absence of a signal at the level of -60 dB it is closed and reduces noise by about 15 dB (to -75 dB), whereas when a signal appears at about -55 dB, it opens and passes the signal without distortion, and closes again after the signal ends.

 Especially effective is the implementation of non-linear blocks (compressor, expander, dynamic noise limiter) using signal-driven active elements in amplifier feedback circuits (RU, C1, 2018181).

 All this ensures the effective use of a combination of compander and dynamic noise suppressors in the proposed technical solution.

Claims (1)

 A compander noise suppressor comprising a compressor, the output of which is connected to a noise introducing link, and an expander, characterized in that a dynamic noise limiting unit is introduced connected between the noise introducing link and the expander input.

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