NL192860C - Circuit arrangement for modifying the dynamics magnitude of an input signal such as, for example, an audio signal. - Google Patents

Description

1 192860

Circuit arrangement for modifying the dynamics magnitude of an input signal such as, for example, an audio signal

The present invention relates to a circuit arrangement for modifying the dynamics magnitude of an input signal, comprising a frequency-selective dynamics modifier with a series circuit fed with the input signal, consisting of a frequency-selective circuit having a transmission frequency band and a blocking frequency band, wherein the transmission frequency band determines the frequency band of the input signal within which the modification of the dynamics magnitude takes place, and wherein blocking signal components of the input signal 10 are damped in the output signal of the frequency selective circuit; and a dynamics modifier, for performing the dynamics modification of signal components within the passband or shifting the angular frequency of the passband according to a control signal, and comprising a control signal generating circuit having a rectifier, for determining the output signal of the frequency selective dynamics modifier deriving from a first control signal component that is a measure of the pass signal components and of the damped blocking band signal components (claim 1).

The present invention further relates to such a circuit arrangement, wherein the dynamics modifier is particularly suitable for effecting a shift of the cross-band angular frequency according to a control signal size, and wherein the control signal generating circuit with the rectifier member is suitable for deriving the complete control signal from the output signal of the frequency-selective dynamics modifier (claim 13).

Circuit devices that modify the dynamics magnitude of input signals are compression circuits (compressors) that compress the dynamics magnitude, and expansion circuits (expanders) that expand the dynamics magnitude. The invention is particularly useful for the treatment of audio signals, but can also be applied to other signals.

Circuit devices of the type described in the opening paragraph are known from German Patent Specification 2,035,479.

The known device is a two-way circuit. wherein the input signal is input into a main road and into a further road, and the output signals of these two roads are weighted together to form the output sigras 1 'of the circuit arrangement. The known circuit arrangement is of the sliding band type. Far away from the circuit is a variable filter whose angular frequency is shifted by the control. This is an elaboration of known base circuit antennas further explained below to modify the dynamics magnitude of input signals.

The known device is sensitive to control by unwanted signals, mainly signal components or noise in the blocking frequency band. Such disturbances cause modulation effects in the frequency spectrum of the output signal from the circuit device.

The object of the invention is to curb these adverse modulation effects and to provide a circuit arrangement in which the influence of the unwanted signal components is reduced.

For this purpose, the invented circuit arrangement is characterized by at least one further control signal generating circuit to which the input signal, the output signal of the frequency selective dynamics modifier or the output signal of the circuit arrangement is applied; comprising a rectifier member; and which is capable of generating a further control signal component which is combined with the first control signal component for generating the control signal, 45 so that the modification of the dynamics magnitude by the dynamics modifier is less dependent on high level blocking band signal components (claim 1), or the further circuit arrangement mentioned in the preamble, is characterized in that the control signal generating circuit comprises a series circuit consisting of a blocking band signal components highlighting means, a limiting means for determining the maximum amplitude of the blocking band signal components 50 in the control signal, and a blocking band signal components. the highlighter for canceling the operation of the blocking band signal component highlighter at signal levels below the threshold of the limiter, making the dynamics magnification modification less dependent on the dynamics modifier is aware of high level blocking band signal components (claim 13).

The dynamics operation of the dynamics modifier of the circuit arrangement is so responsive to increasing levels of the linearly summed combination of the passband signal components and the blocking band signal components that the dynamics operation of high level input signals 192860 2 is less responsive to blocking band signal components. That is, the low level circuitry of the input signal functions primarily as a conventional compressor or expander. However, at high level input signals, the compressor or expander operation is modified by the (further) control circuits of the invention, so that the aforementioned adverse noise and signal modification effects that occur in the prior art device are suppressed. Thus controlling the modulation problem according to the invention is hereinafter referred to as the term "modulation control".

Advantageous embodiments of the invention are defined by the subclaims.

The following is an explanation of the general state of the art in the art.

Compression members and complementary expansion members are often used together (a compander system) to effect noise reduction: the signal is compressed before transmission or recording and expanded from the transmission channel after reception or playback. However, compression means can be used per se to reduce the dynamics size, for example to adapt to the capacity of a transmission channel, without expansion following it, namely when the compressed signal is sufficient for the end target. In addition, compression means are used by themselves in certain products, especially audio products, which are intended to transmit or record compressed broadcasts or pre-recorded signals only. Expansions are used separately in certain products, in particular audio products intended to receive or play back already compressed broadcasts or pre-recorded signals only. In certain products, particularly audio signal recording and playback products, a single device is often configured for switching operation as a compression means for recording signals and as an expansion means for playing compressed broadcasts or pre-recorded signals.

The degree of compression or expansion can be expressed in dB. For example, 10 dB means

compression that an input dynamics magnitude of N dB is compressed to an output magnitude of (N - 10) dB. In a noise suppression system, 10 dB of compression, followed by 10 dB of complementary expansion, is said to provide 10 dB of noise reduction.

The invention particularly relates to a circuit for modifying the dynamics magnitude of an input signal which circuit has a bi-linear characteristic (in which "linear" in this connection means constant gain), which characteristic consists of: 1) a linear part at low level up to a threshold value, 2) a non-linear part (with changing gain) at an intermediate level above the threshold value and up to an end point, which provides a predetermined maximum compression ratio or expansion ratio, 35 and 3) a linear high level part with a gain different from the gain of the low level part.

The characteristic is called a bi-linear characteristic because there are two parts with at least almost constant gain.

40 In practice, the threshold and end point are not always well-defined "points". The two transition areas where the intermediate level portion merges into the low level portion and the high level portion, respectively, may each vary in shape from a smooth curve to a steep curve depending on the steering characteristics of the compression member and the expansion organ.

Attention is drawn to the fact that a circuit with a bi-linear characteristic is a different 45 from a circuit belonging to one of two classes, namely: (a) a logarithmic or non-linear circuit with either a fixed or a changing slope and without a linear part, which means that the gain changes over the entire dynamics range; (b) a circuit with a characteristic of two or more parts of which only one part is linear ("uni-linear").

The invention also applies to uni-linear circuits, as will be explained below. A circuit with a bi-linear characteristic has special advantages and is widely used.

The threshold can be set above the input noise level or the transmission channel noise level to exclude the possibility of noise control of the circuit. The high level portion with substantially constant gain avoids nonlinear handling of strong signals that would otherwise introduce 55 distortion.

Two well known types of bi-linear circuits are referred to here as shearband and fixed band (or split band or multiband) chains.

3 192860

Shearband chains evoke the specified desired characteristic for the case of high-frequency audio compression or expansion by applying high-frequency support (for compression) or suppression (for expansion) through a high-pass filter with a variable lower angle frequency. As the signal level in the high frequency band increases, the filter corner frequency 5 shifts upward to narrow the supported or suppressed band and exclude the useful signal from the support or suppression. Examples of such chains are found in U.S. Pat. Nos. Re 28,426, 3,757,254, 4,072,914, 3,934,190 and in Japanese Patent Application 55,529 / 71. Such chains can also be configured to operate at a low frequency, in which case the low-frequency support or suppression is obtained by a low-pass filter with a variable top angle frequency.

In fixed band chains, the frequency spectrum is split into a number of bands by associated band-pass filters and the compression or expansion in each band is accomplished by an amplification controller (either an auto-responsive diode-type limiter or a controlled limiter ) in the case of a compressor in some form of an inverse or complementary expansion member circuit. Examples of such circuits are found in U.S. Pat. Nos. 3,846,719 and 3,903,485 and in the Journal of the Audio Engineering Society, vol. 15, No. 4, October 1967, pp. 383-388. These fixed band chains provide independent operation in the different frequency bands.

It is known to construct bi-linear compression and expansion members of both the shear belt and the fixed belt type using only a single signal path. However, it is generally preferred to construct such devices by providing a main signal circuit which is linear in dynamics magnitude with a combining circuit in the main circuit, and a second circuit which derives its input signal from the input signal or the output signal of the second chain and whose output is connected to the combining chain. The second circuit includes a limiter (self-acting or controlled) and the limited signal from the second chain amplifies the main chain signal in the combining circuit for the case of compression but presses the main chain signal for the case of expansion. The bounded second road signal is smaller than the main road signal in the upper part of the input dynamics range. The main chain and the second chain are preferably individually identifiable signal paths and this is also the easiest. More than one second chain is usually provided in the case of fixed band devices. A bi-linear device with a main chain and second chains is often referred to as a double-way device.

Such known double-way compression and expansion means are particularly advantageous in that they can accomplish the desired type of transfer characteristic in an accurate manner without problems of distortion of strong signals. The low level portion with practically constant gain is accomplished by giving the second path a threshold above the noise level: below this threshold, the second path is linear. The intermediate level portion is created by the region over which the limiting action of the second path becomes partially effective and the high level portion with substantially constant gain occurs after the limiter has become fully effective so that the second path signal ceases to and becomes negligible compared to the main road signal. At the highest part of the input dynamics range, the output signal of the circuit is effective, only the signal passed through the main linear path, i.e., which is linear with respect to the dynamics range.

Examples of these known circuits are found in U.S. Pat. Nos. 3,846,719, 3,903,485 and Re 28,426. There are also known analog circuits that achieve similar 45 results but in which the second road has properties opposite to limiter properties and in which the output of the second road suppresses the main road signal for compression and amplifies the main road signal for expansion (U.S. Pat. Nos. 3,828,280 and 3,875,537).

The invention can be applied to any of these known bi-linear circuits in order to obtain the 50 associated advantages. The invention is not limited to bi-linear circuits, but can also be used to improve the operation of the aforementioned un-linear circuits. As discussed below, the invention can also be applied to logarithmic circuits provided that a deviation from a logarithmic transfer function can be allowed. However, the preferred embodiments relate to bi-linear circuits and except where this is stated in so many words 55, this description only concerns bi-linear circuits.

As stated earlier, it is not essential to achieve the desired shape of the bi-linear characteristic using the aforementioned "dual path" techniques. Alternatives exist that operate with 192860 4 single roads, as described in U.S. Pat. Nos. 3,757,254, 3,967,219, 4,072,914, and 3,909,733 and Japanese Patent Application 555.29 / 71, to name a few examples. Although these alternative circuits usually cannot produce such good results as double road chains or can be less convenient and therefore less cheap, they can still generally give equivalent results. Accordingly, the invention also applies to these known circuits.

The invention also relates to known compression and expansion devices in which series-connected (e.g. multi-stage) bi-linear chains are used. Such circuits are described in Belgian patent 889,428.

In compression and expansion devices, especially frequency-selective or multi-band devices, it is clearly desirable that strong signals in one frequency range should not adversely affect the behavior of signals in another frequency range . Filtration and equalization used in the various circuits has been the normal mode of handling this problem, both in logarithmic devices and in specialized devices such as the uni-linear and bi-linear circuits described f5. In these known circuits, the DC control signal that controls the variable gain / attenuator (for example, a variable gain device such as a voltage controlled amplifier (VCA) or a variolosser, such as a FET attenuator), or else a variable filter, is formed from the linear additive combination of the passband signals and the stopband signals reaching the control circuit. The invention effectively changes this simple combination in a level dependent manner so as to optimize the performance of the compressor or expander with respect to passband versus stopband signals. Non-linear operations are performed including rectification of the signals in different parts of the spectrum, and analyzes are made of the relative and / or absolute amplitude values. The final control can be formed by choosing one of the signals, by choosing two or more of the signals, or by performing non-linear operations, such as limiting at least one of the signals.

A side effect is that the transfer characteristic from input level to output level of the device is modified at a certain frequency or combination of frequencies. The overall effect is immaterial and may even go unnoticed at the predominant frequency in bi-linear systems. However, in logarithmic systems, the effect of modulation control is mainly active in the portion of the high-level dynamics magnitude, which deviates from a purely logarithmic characteristic. This may or may not be important in a particular application.

The invention stems from the observation that ideally in compressors and in expanders the compression or expansion responds only to the levels of signals within desired frequency pass bands and not to the levels of signals at other frequencies the latter of which can be said that they are in the stop bands. For example, in an ideal circuit, the compression or expansion should not be affected by the levels of signals outside the passband of the fixed band or the passband of the sliding band (whether or not in its rest position). In the case of a shift band chain in accordance with the invention, the amount of the variable band frequency shift does not exceed what is necessary to ensure that a dominant control signal is not amplified (in the case of compression) above a reference level.

As applied to bi-linear chains, in particular such chains in the double-way embodiment, the invention further benefits from an inherent property of such chains: at a high level of the input signal, the main road signal is considerably stronger than the signals or the signal in the other way or roads. As a result, manipulations of the strong signal on the other road or side road 45 are at least virtually inaudible and, with the exception of phase shifts, they are at least not measurable (negligible level changes). This property of bi-linear chains is most easily understood in the context of a double-way chain. However, the principle also applies to single-way bi-linear chains in which two or more signal components are present on the same path, rather than in separately designated paths.

The invention exploits the above data findings on the properties of bi-linear circuits. When compared with bi-linear compressors and expanders known in the art, the invention provides additional manipulation of the signal (modulation control) in the region where the input signal has a high level, where the overall response of the compressor or expander is linear. The comparatively weak noise component of the signal is manipulated in this additional manner only at high signal levels, thereby ensuring that all effects relevant to the signal channel are overshadowed by the strong main signal component.

In double-way bi-linear circuits, an effect of the invention is to modify the side-way transfer characteristic such that the side-way characteristic itself becomes bi-linear instead of smoothing at a high level of the input signal or return to zero. This is a consequence of the proportional aspect of the modulation control. That is, at a high entry level, the level in the side road does not drop below a chosen proportional part of the level in the main road (for example, a 5 quart or a tenth). This is acceptable because the signal in the side road remains considerably weaker than the signal on the main road at a high level of the input signal, and because the stop band is usually phase shifted significantly from the main road signal channel.

For the same reasons, the invention can be implemented in uni-linear chains that have a linear response at a high signal level.

From another point of view, the operation of the invention is to increase the level of stopband signal components in the output signal of the device at a high signal level, but not so much as to cause problems with the recording or transmission channel as they are relatively speaking are still weak. Increasing the level of such stopband signal components is not in itself a particularly advantageous thing, but is necessary in order to obtain an amplification of the dynamic operation as well as a further reduction of noise in the passband. Raising the level of stopband signals in the output signal of the device at a high signal level is achieved by lowering the level of the stopband signal components in the control signal channel at a high signal level, or otherwise arranging things so that the control signal is generated as if the stopband signal components in the signal used for obtaining the control signal at a high signal level had a lower level (for example, by filtering and limiting in the control circuits or by a frequency-dependent suppression provision for the control signal).

Another advantage of the invention is that in listening tests "pump effects" of single-ended compressors and expanders are significantly reduced if they are not completely removed. Thus, in addition to its application in complementary noise suppression systems, the invention is particularly useful for use in standalone compressors and expanders (i.e. compressors used to compress signals that are not subsequently expanded, and expanders used for expanding signals that had not been compressed before).

It is in the background of the invention that while various practical embodiments of noise suppression circuits have been found to be successful, such circuitry deviates from the ideal to some extent in use because the problem of stopband signals which over-control compression and expansion occurs. The effect of such shortcomings appears in several interrelated ways: 1) a reduction in the noise suppression effect in a portion of the passband of the noise suppression system; 2) noise modulation effects (for example, the level of a signal at one frequency modulates the noise level in another part of the holiday spectrum); 3) signal modulation effects (eg the level of the signal at one frequency modulates the level of a signal at another frequency); 4) cross modulation effects (e.g., interfering modulation products arising from either of the last two aforementioned modulation effects or from both).

The extent to which these shortcomings are discernible depends on the type of circuitry used in the noise suppression system, the recording and playback equipment, the recording / 45 playback channel or medium, and the nature of the signal material. In many cases, the shortcomings are at least virtually imperceptible except with the aid of test equipment. It is nevertheless desirable to address these shortcomings. Since the aforementioned shortcomings of the known compressors, expanders and noise suppression systems are related to modulation effects, either of signals or of noise, the invention described herein for suppressing such shortcomings is referred to as modulation control.

The severity of these modulation effects largely depends on the uniformity of the transmission channel between the compressor and the expander. For example, in magnetic tape recording and playback systems, there is a frequency response phenomenon known as "head shocks"

Even in professional systems, especially those operating at 76 cm / s, the playback response 55 below 100 Hz is not uniform due to the relationship between the signal wavelength on the tape and the size of the play head being of the same order and size to be. If the compressor / expander system is sensitive to signals in the head-shock region, such signals may control the expander 192860 6 in a non-complementary manner such that signals or noise at a higher frequency, for example, up to 3 kHz , are modulated by the signals in the range of 100 Hz or lower.

Prior art fixed band circuits (single band and multiband) have utilized various filtering techniques to minimize control of compression and expansion by unwanted signals. According to these techniques, narrow filters (for example with steep sides) are placed in the signal path or in the control circuit (of the limiter).

However, the use of signal path filters that are steeper than 6 dB / octave (eg single pole filters) in multiband compressors and expanders causes amplitude and phase effects such that when the total signal spectrum is combined again, there are amplitude and phase errors . This problem is greatly exacerbated when using filters steeper than 12 dB / octave. However, a filter steepness of only or 12 dB / octave cannot adequately protect against all unwanted signals. In the examples of multiband (fixed band) bi-linear circuits in U.S. Pat. No. 3,846,719 and in Journal of the Audio Engineering Society, vol. 15, No. 4, October 1967, p.

15 383-388, filters are used with a steepness of 12 dB / octave in the signal path of three of the four fixed bands. Only by using a complex filter characteristic in the frequency band adjacent to the steep filters can a flat overall frequency response be obtained. Such a solution is clearly not generally applicable.

In the logarithmic multiband (fixed band) compressor / expander circuit described in Rundfunktechn. Mitteilungen, 22 (1978), No. 2, pp. 63-74, the input signal is divided into four bands by single pole filters. However, the control chains for each band use steep 18 dB / octave filters. Also, a steep control chain filter (12 dB / octave) is used in a single fixed band compressor / expander chain sold under the brand name "dbx II". However, the use of steep control chain filters results in an undue amplification of high level signals outside the passband of the control chain filter when no large amplitude signals are present within this passband, which in turn results in a possible overdrive of the transmission channel unless also in the signal channel steep cut-off filters are used.

A prior art method, referred to as spectral beveling, is described in Belgian Patent 889,427, in Audio, May 1981, pp. 20-26 and in Nomination 30 J-6 and its preprinting. presented at the meeting of the Audio Engineering Society in New York, NY in November 1981. Spectral beveling also relates to the suppression of modulation effects resulting from compressor and expander non-complementality due to transmission channel errors. According to the spectral bevel technique, steep filtering is provided at least in the compressor at a frequency well within the normal passband of the system 35 and within the flat response region of the transmission channel. Although the spectral bevel succeeds in reducing the disturbing signal modulation effects caused by channel irregularities, it does not address the problem of an undue frequency shift in shear band systems or of an undue damping in fixed band systems .

Thus, the invention aims to minimize control of expansion and compression by unwanted signals without the associated side effects and / or complexity of the prior art.

Although measurable modulation effects are not totally suppressed by the invention, the effects of the invention in audio applications are complemented by psychoacoustic masking effects such that the noted effects are inaudible to most listeners and most of the music 45 material. That is, only the modulation of a signal (or signals) sufficiently frequency-separated from the modulating signal is noticed by human hearing. Such modulation is reduced to a minimum by the invention. Although the modulation of a signal (or of signals) by another signal that is close in frequency is less likely to be affected or improved by the invention, such phenomena are not likely to be perceived by hearing as a result. of two related effects: a) a weak signal that is close to a strong signal in terms of frequency is masked by the strong signal such that the weak signal is inaudible, or b) if the nearby signal is heard before the compression or leveled by 55 the compressor is increased such that it becomes audible there is a psychoacoustic tolerance of modulation effects due to the small frequency distance.

Thus, human hearing is unable to distinguish modulation effects of signals at nearby frequencies 7 192860 and thus the invention need not be fully effective for such signals.

The operating conditions for the invention have been determined by a fixed belt or shear belt compressor or expansion circuit incorporating a variable circuit member which is usually controlled by a DC control signal operating primarily in the lower portion of the total dynamics range. According to the invention, in the upper part of the dynamics magnitude modulation controllers, they are used to prevent the operation of the variable circuit from becoming greater than is necessary to provide the nominally desired suppression of dominant signals, whether these signals have frequencies in the passband or in the stop band. In practice, controlling the operation of the variable circuit member usually means acting on the controller controlling the chain member.

The modulation control may take the form of active or passive control signal limiting devices operating at a high signal level, or of means utilizing circuits that detect the presence of the high level signals and generate signals which counteract the increase in the control signal level . Such a control signal limitation can take place in one or more frequency-selective control signal channels: if more than one means are present for selecting or combining the control signals, such that the variable chain element is provided with an optimal control signal. When using a high level signal detection circuit or a modulation control generator, it can operate in various ways that will measure signal levels in at least the upper part of the dynamics range. For example, the modulation control signal can be derived from the input signal or the output signal of the compressor or expander. The modulation control signal effectively provides a reference for the DC control signal applied to the variable circuit element (VCA or voltage controlled filter). The reference signal is combined with opposite phase to the DC control signal (eg with opposite sign or the like to counteract) which control signal is generated primarily in response to stopband signal components to provide a limit as to how large the control signal to the variable chain element may be responsive to signals in the stopband, i.e. outside the passband of the fixed band or the slider band. In practice, this boundary can be made relatively "hard" or relatively "soft". That is, progressive increases in the control signal may abort relatively suddenly or otherwise be allowed to continue at a reduced speed.

The modulation control signal can also be derived from the variable chain (VCA or variable filter) by measuring the voltage or current components of the variable chain and, if necessary, equalization to generate a signal useful in providing a boundary at the point how large the control signal to the variable circuit can become in response to signals in the stopband.

In terms of results, the invention, when applied to either fixed band or shear band devices, provides significant immunity to signals outside the pass band of the fixed band or shear band. In the case of sliding band devices, the invention provides an additional but related advantage, namely that the sliding band shifts only as far in response to a dominant signal as is necessary to bring the gain to the signal frequency at substantially the unit, at least for 40 levels at or above a reference level. The reference level is located at or near the top surface of the dynamic operating range of the device, for example within about 6 - 20 dB of the maximum allowable level. Prior art sliding band circuits are prone to excessive shifting such that the angular frequency of the variable filter is pushed further than is necessary with high level signals, which not only causes potential modulation effects but also results in a loss of the effect of the noise reduction in part of the spectrum.

In the simplest embodiment, when applied to two-way shifters with sliding tape, the invention provides for rectifying and smoothing the input or output signal and combining the obtained DC reference signal with the control signal presented to the variable filter. The level of the reference signal can be set for a desired proportionality limit at 50 a dominant second road signal relative to the corresponding component in the main road signal. For example, the modulation control circuit can be run to operate so that, in say, the top 20 dB of the dynamics magnitude, the limiter provides only the attenuation needed to keep the dominant signal component in the second away at a relatively constant ratio to this component in the main road signal (for example, 15 dB lower).

55 When applied to fixed-band two-way circuits, the invention in its simplest embodiment, as with the sliding band version, rectifies and smoothes the input or output signal to generate a modulation control signal that primarily responds to the signal 192860 8 components. with high level of the input signal. However, in the case of fixed band circuits, a steep filter is used in the pass band control circuit to provide a pass band control signal. In addition, a stopband control circuit is used to provide a stopband control signal. The modulation control signal provides a reference for the stopband control signal (ie it counteracts this at high signal levels). The stopband control signal held against the reference is compared to the passband control signal and the two are generally combined to favor the greater via a maximum signal selection circuit which then controls the VCA. The overall effect of the circuit is to provide the required attenuation (total compression rule) in the passband, while avoiding control of the passband attenuation by large signal components in the stopband, and the possibility of undue amplification of signals with a high level in the stopband as it appears at the output of the total compressor is avoided.

In these and other embodiments in which a reference blanking signal is generated, the signal can be derived from the input signal or the output signal because at a high signal level where the invention operates, the input level and the output level are substantially equal. In certain embodiments, the modulation control signal may be subject to filtering or equalization prior to rectification. Such equalization works in conjunction with the fixed or variable filtering or equalization used in the signal chains and in the control chains, to provide total modulation control that is most effective in suppressing control by signal components in the stopband, while simultaneously as little as possible the control by signal components in the passband is disturbed.

Other embodiments of the invention are described below. For example, the amplified AC output signal of the sliding band variable filter can be divided into two or more bandpass channels, each channel exposed to selected threshold thresholds, and rectified and combined to provide a control signal. By selecting suitable thresholds, the DC control circuit of the sliding band compressor or expander has a frequency dependent maximum output signal characteristic which acts to minimize the control of the compressor or expander by signals outside the sliding pass wall.

In a variant that uses only a single control chain channel, a low-frequency gain chain is provided in the control amplifier. This is followed by an amplitude limiter and then a high frequency boost circuit. The resulting AC voltage signal is then rectified and smoothed to form the control signal.

The invention will be explained in more detail below, by way of example, with reference to the drawing, in which: Figure 1 is an example of a set of curves showing the complementary bi-linear compression and expansion properties.

Figure 2 is a circuit diagram of a sliding belt compressor known from the prior art.

Figure 3 is a circuit diagram of a sliding belt expander known from the prior art.

Figure 4 is a circuit diagram of a modification of the schemes of Figure 2 and Figure 3.

Figure 5 is a block diagram of a sliding belt compressor known from the prior art.

Figure 6 is a set of probing tone curves showing the sliding band action of the circuit of Figure 2 and Figure 4.

Figures 7 through 10 are a series of probing tone curves illustrating the effects of modulation control according to the invention performed in a sliding belt compressor.

Figure 11 is a block diagram of a preferred embodiment of the invention performed in a sliding belt compressor.

Figures 12 through 15 are block diagrams of other embodiments of the invention made in sliding belt compressors.

Figure 16 and Figure 17 are block diagrams of a prior art solid 50 band compressor and expander.

Figures 18 through 20 are response curves showing the effects of modulation control according to the invention performed in a sliding belt compressor.

Figure 21 is a block diagram of a preferred embodiment of the invention performed in a fixed belt compressor.

Figure 22 is a block diagram of another embodiment of the invention performed in a fixed belt compressor.

9 192860

Fig. 1 shows exemplary bi-linear complementary compression and expansion transfer characteristics (at a certain frequency) which (for the compression characteristic) indicate the low level part of a practically constant gain, the threshold, the part where the dynamic action takes place, the end point and the high level part with practically constant gain.

Details of a particular two-way sliding band bi-linear circuit are given in Figures 2, 3 and 4. The sliding band embodiments of the invention have been described with reference to this circuit, although the invention is not limited to use in such circuits. FIG. 2, FIG. 3 and FIG. 4 are the same as FIG. 4, FIG. 5 and FIG. 10, respectively, from US Patent Re 28,426, and further details of these circuits, their operation and the underlying theory are set forth therein. Figure 5 is a block diagram of Figure 2 (with or without the modification of Figure 4). The following description of FIG. 2, FIG. 3, and FIG. 4 is largely taken from U.S. Patent Re 28,426.

The circuit in Figure 2 is specifically designed to be included in the recording channel of a home tape recorder, two such circuits being required for a stereo recording device. The input signal is applied at terminal 10 to an emitter follower stage 12 which provides a low impedance signal. This signal is first applied through a straight through main path formed by a resistor 14 to an output terminal 16 and secondly through a second path, the last element of which is a resistor 18 which is also connected to the output terminal 16. Resistors 14 and 18 add the main road and 20 second output signals to fulfill the required compression rule.

The second path consists of a fixed filter 20, a variable cut-off filter 22 containing a FET 24 (these form the filter / limiter), and an amplifier 26 whose output is connected to a double diode limiter 28 and to resistor 18. The non-linear limiter suppresses overshoot of the output signal with sudden increasing input signals. The amplifier 26 secondly raises the signal to such a level that the knee in the characteristic of the limiter or overshoot suppressor 28 containing silicon diodes is effective at the appropriate signal level under transient conditions. The effective threshold of the overshoot suppressor is slightly above that of the previous filter / limiter. Resistors 14 and 18 are sized so that the desired compensating amount of attenuation is then obtained for the signal in the second path.

The output of amplifier 26 is also connected to an amplifier 30 whose output signal is rectified by a germanium diode 31 and is integrated by a smoothing filter 32 to provide the control voltage for the FET 24.

Two simple RC filters are used, although equivalent LC or LCR filters could be used. The fixed filter 20 produces a cutoff frequency of 1700 Hz (now 1500 Hz), below which compression takes place at a decreasing rate. The filter 22 consists of a series capacitor 34 and a parallel resistor 36, followed by a series resistor 38 and a FET 24 whose supply-drain path is connected as a parallel resistor. In the quiescent state with a zero signal at the control electrode of the FET 24, the FET is pinched off and exhibits a practically infinitely large impedance: 40 the presence of the resistor 38 can be disregarded in that case. The cutoff frequency of the filter 22 is thus 800 Hz (now 750 Hz) which, as will be noted, is considerably below the cutoff frequency of the fixed filter 20.

When the signal at the control electrode increases enough to lower the resistance of the FET to less than say 1 kohm, the resistor 38 effectively parallels the resistor 36 and 45 increases the cutoff frequency, which clearly shows the filter pass band narrower. Obviously, the increase in the cutoff frequency is progressive.

The use of a FET is convenient because, within a suitably limited range of signal amplitudes, such a member acts practically as a linear resistor (for signals of both characters), the value of which is determined by the control voltage on the control electrode.

The resistor 36 and the FET are returned to an adjustable runner 46 in a voltage divider containing a temperature compensating germanium diode 48. The runner 46 makes it possible to adjust the compression threshold of the filter 22.

The amplifier 26 includes complementary transistors that provide a high input impedance and a low output impedance. Since the amplifier drives the diode limiter 28, a finite 55 output impedance is provided which is provided by a coupling resistor 50. The diodes 28, as already noted, are silicon diodes and have a sharp knee around 1/2 volt.

The signal on the limiter and thus on the resistor 18 can be short-circuited to earth by means of a switch 53 192860 10 when it is necessary to switch off the compressor.

The amplifier 30 is an NPN transistor with an emitter-time constant network 52 that provides increased amplification at high frequencies. Powerful high frequencies (eg a cymbal beat) will therefore lead to a rapid narrowing of the band in which compression takes place, thus avoiding signal distortion.

The amplifier is connected to the smoothing filter 32 via a rectifying diode 31. The filter includes a series resistor 54 and a parallel capacitor 56. The resistor 54 is connected in parallel to a silicon diode 58 that provides a fast charge of the capacitor 56 for a fast response, coupled with good flattening under stationary conditions. The voltage on the capacitor 56 10 is applied directly to the control electrode of the FET 24.

A complete circuit diagram of the complementary expander is shown in Figure 3, but a full description thereof is not necessary since the circuit is practically identical to that in Figure 2, and therefore, the component values are for the most part not shown in Figure 3.

The differences between Figure 2 and Figure 3 are the following: In Figure 3, the second path derives its input signal from the output terminal 16a, the amplifier 26a is an inverting amplifier, and the signals combined by the resistors 14 and 18 are applied to the input ( base) of the emitter follower 12 whose output (emitter) is connected to terminal 16a. To ensure a low drive impedance, the input terminal 10a is connected to the resistor 14 via an emitter follower 60. Appropriate steps must be taken to prevent a bias from occurring in the expander.

The amplifier 26a is inverted by deriving the output signal from the emitter instead of the collector of the second (PNP) transistor. This change involves moving the resistor 62 with a value of 10 kohm (Figure 2) from the collector to the emitter (Figure 3) which automatically provides a suitable output impedance for driving the limiter. The resistor 50 is therefore omitted in Figure 3.

It should be noted that it is important in tuning a complete noise reduction system to have equally high signal levels on the emitters of transistors 12 in both the compressor and the expander. Measuring connection points M on these emitters are shown in the drawing.

Figure 4 shows a preferred embodiment of a circuit to replace the chain between the 30 points A, B and C in Figure 2 and Figure 3. When the FET 24 is pinched, the second RC network 22 is inoperative and determines the first RC network 20 in that case the response of the second way. The improved circuit combines the phase benefits of having only a single RC section in the quiescent state with the 12 dB per octave attenuation properties of a two-section RC filter in the presence of signal.

In the actual embodiment using MPF 104 type FETs, the resistor 36a with a value of 39 kohm is required to provide a finite feed impedance to act in the FET. In this way, the compression ratio at all frequencies and all levels is kept at a maximum of about 2. The resistor 36a provides the same compression ratio limiting function in the improved circuit as the resistor 36 in the circuit of Figure 2 or Figure 3.

In addition, this resistor provides a low-frequency path for the signal.

Certain details of the circuit in Figures 2, 3 and 4 have been developed over time and more modern embodiments of the circuit have already been published and are well known in the art. For convenience, reference is made here to the specific circuit in U.S. Patent Re 28,426.

45 Figure 5 is a block diagram showing the main elements of the compressor in Figures 2 and 4. The combining circuit 15 represents the combining resistors 14 and 18 in Figures 2 and 3.

The variable band operation of the sliding band device can be studied in Figure 6, which shows a true recording of a CPT response obtained from the circuit of Figure 2 including the circuit of Figure 4. The variable band operation is reproduced by turning off the 50 compressor frequency response by means of a low level CPT (whose level is below the compressor threshold) in the presence of a high level signal: the test tone is detected at the output of the compressor using a tracking filter. The high level signal allows the compressor circuit to operate with the graph showing the effect on filter cutoff frequency.

55 In a shear band device according to the invention, the amplitude of the strong or dominating signal that causes the shear band operation must not cause undue shifting, nor the presence of other high level signals outside the bandwidth of the shear band should cause undue shifting. cause. Overdue means a displacement of the variable filter's crossover frequency beyond what is necessary to provide a shear band compressor characteristic that avoids chasing the dominant signals above a reference level. The absolute value of the reference level is chosen by the designer of the system, but is usually a 10 dB 5 below the usually used highest level value.

Figure 7 shows another set of true records of CPT curves for the case of a sliding band compressor circuit of the same design as that of Figure 2 (with the modification of Figure 4), but with a low level gain of 8 dB and a quenching frequency of the filter in the amount of 800 Hz. The CPT level is at -40 dB, below the compressor threshold. Curves 10 are recorded for a 100 Hz signal at -20, -10, 0, +10 and +20 dB, where 0 dB is the reference level. A curve has also been drawn in case the 100 Hz signal is missing. The recording curves for -10, 0, +10 and +20 dB all start at about 200 Hz. This is also the case for figure 8. In figure 9 and figure 10 curves are also drawn in case the signal is missing.

Referring again to Figure 7, ideally there should be no shift in response to a 100 Hz signal because it is clearly outside the circuit's pass band at its lowest (quench) frequency. Nevertheless, as the level of the signal of 100 Hz increases, the band shifts upwards. The curves for -10, 0, +10 and +20 dB need not slide further than the curve for -20 dB to avoid any significant boost of the 100 Hz signal. The unnecessary shift has two effects: a) a significant noise reduction effect is lost (at 20 playback) because there is no rushing at frequencies where this may otherwise occur, and b) as the amplitude of the 100 Hz signal varies, signals at modulate higher frequencies as the slider varies under its control, resulting in a possible incorrect repair of the signal by the expander if the recording or transmission channel has an irregular frequency response in the vicinity of 100 Hz.

Figure 8 shows a set of true records of CPT curves for the same circuit, but adding the modulation driver as described below. At least virtually no shift occurs for the same levels of the 100 Hz signal as in the situation of Figure 7. The slide band compressor is made practically immune to strong signals outside its pass band. The sliding band response is practically the same as its response below the threshold in the absence of dominant signals.

The effect of the modulation control for sliding belt compressors is further explained by Figures 9 and 10, which also show true records of CPT curves recorded with the same circuit and CPT level as in Figures 7 and 8. In this case, the effect of a dominant signal at 800 Hz, a frequency within the desired active range of the circuit. Ideally, a shift is needed to go just so far that the 800 Hz signal is not rushed above the 0 dB reference level. Thus, in the response of Figure 9 without modulation control, the shift caused by the 800 Hz signal at the levels of -10, 0, +10, and +20 dB is undue. Figure 10 shows the response of the modulation driven circuit: the shift at and above 0 dB is significantly reduced. The effect is progressively less for low 40 signal levels, but it is noticeable to some extent at the -10 dB signal level.

Figure 11 generally shows a preferred embodiment of the modulation control according to the invention, implemented in a two-way bi-linear sliding belt device. The reference numbers have been kept as much as possible as in Figure 5 for the same and for functionally equivalent elements. The 45 CPT response curves of Figures 7 to 10 are recorded with a sliding tape device as shown generally in Figure 11 with the modulation control sub-chain elements in the dotted line block 100 taken out of the circuit for the response curve without modulation control. For the sake of explanation, the circuit of FIG. 11 is substantially the same in detail as that of FIGS. 2 and 4. The circuit can be modified as described above without affecting the fundamental operation of the modulation control sub-chain.

As shown in FIG. 11, the modulation control sub-circuit derives a calibrated voltage control signal from the input signal of the circuit (or optionally from the output signal of the combining circuit 15), namely, by means of an amplifier 30 ', a rectifier 31' and a smoothing circuit 32a ' . A potentiometer 102 is shown to indicate that the signal from smoothing circuit 32a 'has an adjustable 55 gain. In practice, the gain is usually preset in the design. A combining circuit 33 subtracts the signal supplied by the sub-circuit 100 from the main control signal supplied by the amplifier 30, the rectifier 31 and the smoothing circuit 32a.

1 iizoou 12

The smoothing circuit in Figure 11 is divided into two stages to save on the price of the components. Thus, blocks 32a and 32a 'may be identical and each consist of only a single RC filter section, and block 32b further smoothing the combined control signal may consist of an additional RC filter section.

The signals are rectified (by rectifiers 31 and 31 ') before they are combined by the circuit 33 in order to avoid the ambiguity with the circuit that would occur if AC voltage signals were combined and then rectified (i.e. with AC voltage signals would be two possible stable states).

The arrangement of the embodiment of Figure 11 thus provides a reference level for stabilizing the DC control signal, a reference level that dynamically changes with the input signal level, thereby shifting or transferring part of the dynamic operation of the variable filter to a level region reference level has been determined. The device functions to maintain the maximum amplitude of dominant signals in the noise suppression bypass at a constant ratio to the input signal at high signal levels. The relative level 15 from the modulation control sub-circuit 100 is selected to minimize the sliding action in response to signals outside the sliding band pass band.

Although the embodiment of Figure 11 functions effectively when the input signal for the modulation control sub-circuit 100 is derived from the wide band input (or output) signal, other circuits that provide a measurement of signal levels at the upper end of the dynamics range 20 are possible. For example, even modulation control effects are obtained to some extent if the input signal of the sub-circuit 100 is taken from the output signal of the band pass filter 20. Ideally, amplifiers 30 and 30 'utilize equalization to optimize the overall modulation control effects. (control by passband components as opposed to stopband components), taking into account the combined frequency response effects of the filters 20, 22 and the equalization applied in the control amplifier 26.

When the invention is embodied in serially coupled devices, such as described in Belgian Patent 889,428, a single modulation control sub-circuit can be used to supply a reference signal to each stage. Such a circuit advantageously derives its input signal from the output signal of the last compressor stage when the series-connected stages are arranged in the preferred order such that the first stage has a threshold at the highest level. By deriving the reference signal from the output signal, the low level stage or stages receive the modulation control effect at a lower signal level and thereby enhance the modulation control effect.

As mentioned above, it is also possible to obtain modulation control of sliding band chains by means other than by deriving a control signal reference from the input signal (or output signal). 35 One or more control signals can be derived from the output signal of the variable filter and so limited that results are obtained that are comparable to those obtained with the suppression device as indicated in figure 11: the essential result is the same, namely desensitizing the dynamic circuit modification operation for high level signals within the stopband. Figures 12, 13 and 14 are directed to such embodiments in which limitation 40 is used.

In the embodiment of Figure 12, the control signal generating means (blocks 30, 31 and 33 in Figure 5) is split into three paths by amplifiers 30, 116 and 124, filters 110, 118 and 126, respectively, a high-frequency path, a medium-frequency path away and a low frequency road. Each road contains a limiter (112, 120, 128) that has a preset threshold. The limiters can be 45 oppositely connected diodes, such as the diodes 26 in Figure 2. For a high-frequency audio compressor with a performance generally shown in Figures 7 to 10, the filter frequencies may be as follows: filter 126, 200 Hz low pass; filter 118, 200 to 800 Hz band pass; and filter 110, 800 Hz high pass. The output of each limiter is rectified by rectifiers 114, 122 and 130, combined (or selected at maximum value) and applied to the smoothing network 32. Otherwise, the limiting functions can be obtained after rectification. In operation, the low-frequency and medium-frequency bandlimitors are set to minimize the effect on shifting by signals outside the passband. Little or no limitation may be required in the high-frequency path and the control effected by this path can be enhanced by providing the amplifier 30 with a high-frequency boost, as represented by block 52.

55 Figure 13 shows another split road control circuit. In this example, two roads are used, a high-frequency road and a low-frequency road. The high-frequency path is essentially the same as in the embodiment of Figure 12, except that the limiter 112 is omitted. In the low frequency path, an amplifier 132 is included which has a high frequency damping network 134. The amplifier output is applied to a low-pass filter 136 and a limiter 138. The limiter threshold is adjusted along with the different filter and amplifier filter properties to obtain the greatest insensitivity to shear band control by stopband signals. The signals in the two paths are rectified by rectifiers 114 and 140, respectively, and combined at the input to the smoothing circuit 32.

Figure 14 shows a simplified embodiment of the embodiment in figure 13. The high-pass filter 110, the low-pass filter 136 and the amplifier / high-frequency attenuation network 134 are omitted. The high-frequency preamplification network 52 'of amplifier 30 is different from that in the network 52, namely that the high-frequency boost becomes effective at a higher frequency. Thus, only the wide band path amplifier 132 carries low-frequency signals (along with high-frequency signals). The threshold of the limiter 138 is set together with the high frequency drive properties of the network 52 to minimize the effect on shift by stopband signals.

Figure 15 shows an embodiment with a one-way control circuit that contains a frequency-dependent amplifier 141 with a low-frequency boost network 142, followed by a limiter 144 and an amplifier 146 with a high-frequency boost network 148. In operation, first the low-frequency part of the spectrum containing the tends to cause unwanted shift, first hunted and then limited. The limiter 144 is preferably syllabic with its own feedback amplifier, rectifier, controlled gain smoothing element (such as blocks 276, 280, 282, and 270 in Figure 17). The amplifier 146, which includes a high-frequency boost network 148, restores any high-frequency emphasis that may be required. The output of amplifier 146 is then rectified and smoothed by blocks 114 and 32, respectively. In this one-way control circuit, the high level stopband signal components at the rectification at point 114 are significantly attenuated.

For convenience and simplicity, the sliding belt embodiments have been described in connection with a particular design of the sliding belt compressor. The invention is equally applicable to expanders without any change in the second-way noise suppression control circuits shown in the embodiments of Figures 11 to 14. In noise suppression systems using compressors and expanders, it is preferable that the modulation control invention can be applied to both devices to ensure complementarity. The invention is equally applicable to low frequency sliding band chains in which the compression and expansion action is intended to occur in the low frequency range.

Figure 16 shows a block diagram of a fixed-band bi-linear compressor and expander design in a two-way configuration. The fundamental aspects of the system are described in U.S. Pat. Nos. 3,846,719 and 3,903,485 and in Journal of the Audio Engineering Society, Vol. 15, No. 4, October 1967, pp. 383-388.

In the known embodiment of Figure 16, the second-way networks 250 provide four bands. The bands 1, 3 and 4 have common 12 dB / octave input filters: a low-pass filter 252 at 80 Hz at 40 the input of band 1, a high-pass filter 254 at 3 kHz at the input of band 3 and a high-pass filter 256 at 9 kHz at the entrance of band 4. Each of the filters is followed by an insulating stage 258 with an emitter follower. A band 2 has a frequency response that is complementary to that of bands 1 and 3. Such a response is obtained by adding (in the adder 260) the outputs of the emitter followers 258 in bands 1 and 3 and subtract this sum from the total input 45 signal (in a subtractor 262). The output of the emitter follower 258 in each of the bands and the output of the subtractor 262 are applied to the respective limiters 264 and 264 '. The limiters 264 and 264 'are identical except that the limiters 264' in bands 1 and 2 have a time constant twice that of bands 3 and 4. The output signals from bands 1 to 4 are combined with the signal on the main road in a combination means 50 266. The output of the compressor is presented to a noise input channel to be sent to the complementary expander in which the output of the identical second-way networks is subtracted from the input signal to thus obtaining the complementary expansion characteristic.

Figure 17 shows further details of the limiters 264 and 264 '. Each includes a 55 FET attenuator 270 that operates in response to a control signal. The attenuator output is amplified by a signal amplifier 272 whose gain is adjusted to obtain the desired low-level signal gain. The output signals of all bands are combined 192860 14 with the main signal in such a way that a low-level output signal is delivered from the compressor that is uniformly 10 dB higher than the input signal up to about 5 kHz, above which the level increase gradually on increases to 15 dB at 15 kHz.

The FET attenuator is controlled by a control signal auxiliary circuit which provides a compression threshold of 40 dB below the peak operating level. The control auxiliary circuit includes a control signal amplifier 276 followed by a phase splitter 278 driving a two-phase rectifier 280. The DC voltage obtained is applied to a smoothing network 282 whose output signal is the control signal. The network 282 includes a first RC integrator, an emitter follower, and an RC end integrator that interact with diodes such that both the first integrator and the end integrator have a non-linear characteristic provided by the diodes. Rapid, large changes in the signal amplitude are passed quickly, while small changes are propagated slowly. This dynamic smoothing action provides optimum results with respect to modulation effects, low-frequency distortion and distortion components generated by the control signal. The chain achieves rapid recovery and low signal formation.

Figure 18 shows actual recording on a sheet writer of a response graph below the compression threshold of a fixed band compressor with a low level gain of 8 dB and a pass band filter frequency of 800 Hz high pass. Within the active frequency range of the device (determined by the angular frequency of 800 Hz), a boost is obtained up to levels of about -10 dB (relative to a 0 dB reference level).

Figure 19 shows the effect on compression when a high level signal (+10 dB) is present at 100 Hz, which frequency is well below the 800 Hz angular frequency of the filter. The strong 100 Hz signal in the stopband effectively blocks the compressor and prevents any compression within the passband. The result is that the desired noise reduction in the passband is omitted. In addition, if the 100 Hz signal is intermittent, the compression in the passband will be effected or lost with the controlling 100 Hz signal, which will cause noise modulation and / or signal modulation.

Figure 20 shows the effect of adding a modulation control auxiliary circuit as described below to a fixed band circuit. Compression is restored in the pass range even when the strong (+10 dB) signal occurs at 100 Hz. The modulation control auxiliary circuit effectively desensitizes the fixed band circuit to the strong stop band signal.

Figure 21 generally shows the preferred embodiment of the invention as applied to one belt of a fixed belt bi-linear two-way compressor of the type described in connection with Figure 16. Two additions to the described circuit have been made to provide modulation to obtain guidance. A modulation control auxiliary circuit 198, similar to that in the sliding belt 35 embodiment of Figure 11, is provided and includes a rectifier 208 'and a first smoothing stage 210a'. The modulation control can be supplied optionally from the output signal of the compressor. Elements 208, 208 'and 210a, 210a' can be identical (but separate). The level of the modulation control signal from the smoothing circuit 210a 'is adjusted by an attenuator 212 or any other suitable means and is combined by means of the opposite sign circuit 214 with the dust band DC voltage control signal from the smoothing circuit 210a. In addition, the output of an FCA 204 and an amplifier 206 is applied to a filter 216 which preferably has the same angular frequency as the filter 202, although this is not essential: the comparative graphs in Figures 19 and 20 were made with a simple 6 dB / octave low pass filter 216 with an angular frequency of 3 kHz. Nevertheless, the filter 216 should ideally have a relatively steep cutoff characteristic, for example, 12dB or 18dB per octave (with a two or three pole filter, respectively) with approximately the same cutoff frequency as the filter 202. The output signal of the filter 216 is aligned and smoothed by blocks 218 and 220 to form the passband control signal. The smoothing provided by blocks 210a, 210a 'and 210 "may be a preliminary filter stage followed by further smoothing in the circuit 210b. The output of the passband filter channel is presented to a maximum selector 222 which is its other input receives the output from the combiner 214, the modulation-controlled stopband control signal In its simplest form, the maximum selector comprises two diodes that transmit the greater of the two input signals: more sophisticated circuits utilize operational amplifiers to eliminate the diode voltage drops and increase accuracy.

In operation, the signals in the stopband are subject to the operation of the auxiliary circuit 198 if there are no dominant signals within the passband where the compression operation is desired. Although a strong signal, such as that of +10 dB at 100 Hz, allows a large control signal to be generated by the

Claims (15)

192860 blocks 208 and 210a (and 210b), that control signal is opposed by the modulation control auxiliary signal so that the gain of the VCA 204 is not depressed to cause a loss of compression in the passband. On the other hand, if a signal of 100 Hz occurs in the level range of -20 dB, the counteracting action is significantly reduced, and the stop band-5 control signal in that case controls the operation of the compressor correctly each time the signal conditions are such that the through-band control signal compressor does not control. If strong signals are present within the passband in the active region, the narrow filter channel output, the passband control circuit will control the maximum selector and allow the VCA to respond accordingly. A circuit arrangement for modifying the dynamics magnitude of an input signal, comprising a series-fed frequency-selective dynamics modifier with a series circuit, comprising a frequency-selective circuit having a pass frequency band and a block frequency band, the pass frequency band being the frequency band of the input signal determines within which the modification of the dynamics magnitude takes place, and wherein blocking signal components of the input signal are contained attenuated in the output signal of the frequency selective circuit; and a dynamics modifier for performing the dynamics modification of signal components within the passband or a shift of the angular frequency of the passband according to a control signal's dimension, and comprising a control signal generating circuit having a rectifier for the output of the frequency selective dynamics modifier deriving a first control signal component which is a measure of the passband signal component and of the damped blocking band signal components, characterized by at least one further control signal generating circuit (100; 192 860 16 116-122; 136-140; 198), to which the input signal, the output signal of the frequency selective dynamics modifier when the output of the circuit device is applied; comprising a rectifier member (31 '; 122; 140; 208'); and which is capable of generating a further control signal component which is combined with the first control signal component to generate the control signal, whereby the dynamics magnification modification by the dynamics modifier is less dependent on high level blocking band signal components. Circuit arrangement according to claim 1, characterized in that the first control signal component and each further control signal component are combined by a combiner (114, 122, 130, 32; 114, 10, 140, 32; 216, 218 ', 210), which is the largest of the control signal components select. Circuit arrangement according to claim 1, characterized in that the dynamics modifier comprises a variable gain or damping member (204) or a variable filter (22). Circuit arrangement according to claim 1, characterized in that the further control signal generating circuit comprises means (128; 138; 232) for non-linear processing of the blocking band signal components. Circuit arrangement according to claim 1 or 2, characterized in that the control signal generating circuit and the at least some further control signal generating circuit have at least one limiter (112; 120; 128; 138), and at least one frequency selective circuit (110; 118; 126; 136; 52; 52 '), wherein the at least some limiter preferably acts on the blocking band signal components such that the contribution of high level blocking band signal components to the control signal is reduced. Circuit arrangement according to claim 5, characterized in that the control signal generating circuit comprises a first frequency selective circuit (110) which selects passband signal components, as well as a second frequency selective circuit (52) for increasing the level of passband signal components, and that the further control signal generating circuit includes a third frequency selective circuit (126; 136) which selects blocking band signal components as well as the limiter (128; 138). Circuit arrangement according to claim 6, characterized in that the control signal generating circuit comprises a second limiter (112), and a second further control signal generating circuit comprising a third limiter (120) and a fourth frequency selective circuit (118) is provided. wherein the fourth frequency selective circuit selects signal components in a frequency band just below the pass band. Circuit arrangement according to claim 5, characterized in that the control signal generating circuit comprises the frequency selective circuit (52 ') which increases the level of passband signal components, and in that the further control signal generating circuit has an all-frequency transmissive characteristic and comprises the limiter (138). Circuit arrangement according to any one of claims 5 to 8 for audio signals, characterized in that the dynamics modifier has a variable filter (22), which variable filter provides an increase or decrease in a high or low frequency range of the signal band wherein the control signal at an increasing level causes a shift of the angular frequency of the variable filter to narrow the raised or lowered area. Circuit arrangement according to claim 1 for audio signals, characterized in that the dynamics modifier has a variable filter (22), which variable filter causes an increase or decrease in a high or low frequency range of the signal band, the control signal increasing by 45 level shifts the angular frequency of the variable filter to narrow the raised or lowered region, and the at least some further control signal generating circuit (100) generates the further control signal component, counteracting the first control signal component, control signal component dynamically changes with the level of the input or output signal, and has a means (102) for adjusting the gain of the further control signal component. The level of the modulation control auxiliary circuit relative to the input signal or the output signal is adjusted so as to obtain a dynamic reference signal (relative to the input signal) of sufficient level to result in a significant insensitivity of the compressor operation to strong passband signals. The comments made with regard to equalizing control and modulation control amplifiers in connection with sliding band chains also apply to fixed band embodiments. Thus, optionally filter equalizers 224 and 226 may be inserted in the respective paths to the rectifiers 208 and 208. However, the possibilities are to advantageously operate one frequency dependent characteristic against another in the case of the fixed band versions smaller than with the sliding band: this is why an extra control chain in the fixed band case is needed (three 20 chains versus two). It is also possible to obtain modulation control of fixed band chains by means other than deriving a control signal reference from the input signal (or output signal) of the compressor or expander. One or more control signals can be derived from the output of the controllable element (attenuator or VCA) and can be limited in order to achieve results corresponding to those obtained by means of the opposing embodiment according to figure 21. Figure 22 is focused on such limiting embodiments. In the embodiment of Figure 22, the control signal generating member (blocks 276, 278, 280, and 282 in Figure 17) is split into two paths, one with an amplifier 228, a steep cutoff filter (as in the embodiment of Figure 21), and a rectifier 218, and the other with an amplifier 230, a limiter 30 232 and a rectifier 218 '. The threshold of the limiter 232 which may consist of, for example, oppositely connected diodes) is chosen such that the limiting action starts at a relatively high level, namely at about the same level where the output from the combiner 214 begins to become dominant in the embodiment according to Figure 21. The output signals of the rectifiers 218 and 218 'may be combined and applied to a smoothing circuit 210, the output signal of which is presented as the control signal to the VCA 204, or the rectifier output signals of which may be applied to (or can serve as) a maximum selector chain (such as block 222 in Figure 21) and its output is applied to a smoothing network 210. In operation, the embodiment of Figure 22 functions in a similar manner to the embodiment of Figure 21. 40 Circuit arrangement according to claim 1, for audio signals, characterized in that the dynamics modifier has a variable gain or damping member (204) provided with a first further control signal generating circuit (198) for generating a first further control signal component, the first further circuit having means (212) for adjusting the gain of the first further control signal component, the first further control signal component dynamically changing with the level of the input signal or of the output signal and the first control signal component for generating a modified first control signal component 17 counteracts 192860 that a second further control signal generating circuit (216, 218, 210a ") is provided for generating a second further control signal component, said second further circuit having at least one filter (216) for transmitting signals into the transmission frequency band, which filter has a filter characteristic steeper than that of the frequency selective circuit (202), and which provides a means (222) for selecting the largest from the modified first control signal component and the second further control signal component as the control signal. Circuit arrangement according to claim 1 or 2 for audio signals, characterized in that the dynamics modifier comprises means (204) with variable gain or damping, the control signal generating circuit having a filter (216) for transmitting signals in the pass-through. frequency band, which filter has a filter characteristic steeper than that of the frequency selective circuit (202), and the further control signal generating circuit has a limiter (232), which is preferably active on signals in the blocking band. 13. Circuit arrangement for modifying the dynamics magnitude of an input signal, comprising a frequency-selective dynamics modifier with a series circuit fed with the input signal, comprising a frequency-selective circuit having a transmission frequency band and a blocking frequency band, the transmission frequency band being the frequency band of the input signal determines within which the modification of the dynamics magnitude takes place, and wherein blocking signal components of the input signal are contained in the output signal of the frequency selective circuit; and a dynamics modifier for outputting the angular frequency of the passband according to a control signal size, and comprising a control signal generating circuit having a rectifier for deriving the output signal from the frequency selective dynamics modifier control signal, characterized in that the control signal generating circuit comprises a series circuit consisting of a blocking band signal component highlighter (141, 142), a limiter (144) for determining the maximum amplitude of the blocking band signal components in the control signal, and a blocking band signal components de-highlighting means (146, 148) for canceling the operation of the blocking signal component components highlighting at signal levels below the threshold of the limiting means, so that the dynamics magnification modification by the dynamics modifier is less dependent on blocking high level band signal components. Circuit arrangement according to any one of claims 1 to 13, characterized in that this arrangement is a two-way circuit with a bi-linear or a un-linear characteristic, comprising a main road, and a further road comprising the frequency-selective dynamics modifier ( 20, 22, 26) and includes the control signal generating means, the further road having a limiting characteristic with a limiting threshold value, so that the output signal level of the further road in the upper part of the input dynamics range is smaller than the output signal level of the main road, and wherein the further path has a further threshold value at input levels above the limiting threshold value, the gain of the further path at input signal levels above the value of the further threshold value remaining substantially constant, so that the further path has a bi-linear characteristic. Circuit arrangement according to claim 14, characterized in that the amplification of the further road in the upper 20 dB of the dynamics range is selected such that the output level of the further road is approximately 15 dB below that of the main road. Hereby 18 sheets drawing