DE19963648B4 - Overload protection in a signal processing unit - Google Patents

Abstract

Method for overmodulation protection of an input signal (E) in at least one channel of a signal processing unit, on a transmission path (3) lying between a signal input (1) and a signal output (6), wherein the input signal (E) is processed in a signal processor (4) and processed in a limiting amplifier (35) is attenuated or amplified, wherein when a signal amplitude is exceeded on the transmission path (3) with increasing signal amplitude higher (lower) signal amplitudes in comparison to lower (higher) signal amplitudes stronger attenuatable (amplifiable) and the amplitude selective attenuation (amplification) the limiter amplifier (35) in dependence on volume settings (g _vol ) and / or filter settings (g _F ) is adjustable.

Description

The The invention relates to a method for overdrive protection of a signal in at least one channel of a signal processing unit and a Signal processing unit

One such method for overdrive protection is used, for example, when used in a digital audio system despite overcharge control overrides in the signal processing chain through the settings of the sound influencing Filter, for example, to adjust the depth, altitude, or Equalizer and / or volume control, caused.

in the normal operating conditions become the gain and damping factors within the signal processing chain as a function of the input signal amplitude and the settings of all sound-influencing filter stages such balanced, that always a sufficient headroom for the Signal processing available stands. In all cases, in which it is not possible is, due to the signal characteristics and the preset sound settings To provide this headroom, is the Risk of oversteer. Such an override leads to strong non-linear distortions and thus high harmonic distortion.

• 1. Begrenzerverstärker mit dynamisch einstellbarer amplitudenunabhängiger Pegelabsenkung (oder in Ausnahmefällen Pegelanhe bung).
• 2. Begrenzerverstärker mit fest eingestellter amplitudenselektiver Pegelanhebung/Pegelabsenkung, wobei in der Regel hohen Amplituden gedämpft und niedrige Signalamplituden angehoben werden.

From the prior art it is known to limit the amplitude of the processed signal. To limit the signal amplitude to a predetermined maximum value, a limiter amplifier is provided. Such limiter amplifiers can be divided into two functional classes:

• 1. Limiter amplifier with dynamically adjustable amplitude-independent level reduction (or in exceptional cases level increase).
• 2. Limiter amplifier with fixed amplitude-selective level increase / level reduction, usually with high amplitudes attenuated and low signal amplitudes are increased.

A limiter amplifier according to functional class 1 restricts the output amplitude of a signal by lowering the overall amplification factor accordingly in the case of very high signal amplitudes. Thus, for example, determine large, only briefly occurring signal amplitudes, the maximum modulation of the digital audio system. Since the limiter amplifier reduces the overall amplification factor to avoid overshoot by signal peaks, quiet audio signal passages with small signal amplitudes are reproduced even more quietly for a certain time. The disadvantage of this method is therefore the fact that the playback volume changes depending on the signal level.

at a limiter amplifier the second class of function, this disadvantage of changing occurs Playback volume dependent on from the signal level not on. A limiter amplifier with fixed set Level increase / decrease is dimensioned so that medium and high signal amplitudes are "truncated" or "rounded". Therefore occurs even with signal amplitudes with comparatively low modulation an elevated one Distortion factor on.

From the DE 38 03 291 A1 a method is known for overdrive protection of an input signal in at least one channel of a signal processing unit on a lying between a signal input and a signal output transmission path, wherein the input signal is processed attenuated or amplified in a Begrenzerverstärker. When a signal amplitude on the transmission path is exceeded, higher (lower) signal amplitudes become more attenuable with increasing signal amplitude in comparison with lower (higher) signal amplitudes

Of the Invention is based on the object, a method for overdrive protection in a signal processing unit where the dynamics, d. H. the difference between maximum and minimum volume, largely is maintained without the playback volume depending on changes from the signal level, if briefly overdriven of the digital (audio) system occurs. At the same time should be avoided in the event of oversteer Be that stronger in the saturation region goes and / or that such signal amplitudes, which not at all an override guided would have been "cut off". In both make The goal is to avoid high harmonic distortion.

These The object is achieved by a method with the features of claim 1 and a signal processing unit according to claim Second

advantageous versions and further developments are specified in the subclaims.

The method according to the invention for overmodulation protection of an input signal in at least one channel of a signal processing unit is based on a level reduction by a limiter amplifier in the event of imminent overdriving. The essential idea of the invention is that the current settings of the transfer characteristic of the limiter amplifier according to the set signal strength (volume), after the settings (sound-influencing) filter and the current signal level on the Übertra judge the route. The invention provides that in normal operating conditions, ie when there is no overload, the signal processed in a signal processor is not changed and only when there is the danger of overdriving, the transfer characteristic of the Begrenzerverstärkers the new situation is adjusted. The signal adaptive and thus dynamic adjustment of the transfer characteristic of the limiter amplifier, which depends on the set signal strength and the settings of the filters, is characterized in that when a signal strength and / or filter value and / or a signal amplitude on the transmission path is exceeded (this includes the signal processor) As the signal amplitude increases, higher signal amplitudes are attenuated more than low signal amplitudes.

at short-term high signal amplitudes is the modulation of the signal is changed by the limiter amplifier. This modulation change However, this only affects high signal amplitudes. The signals Small and medium amplitudes are not affected by the scheme. For an audio system, this means that the playback volume for this Signal level does not change. As a result, the signal-to-noise ratio does not change. The unchanged transmission Small and medium signal level advantageously avoids this Occurrence of harmonics caused by the use of a fixed limiter with non-linear transfer function occur. For an audio signal means that the harmonic distortion is small and mean signal amplitudes are not increased. The system thus avoids an override, without occurring during normal operation signal amplitudes of affected by the scheme.

So leads for example such improved overdrive protection in a signal processing unit for digital audio signals a much improved listening experience. Especially at the limit of full scale (0 dB full scale) the regulation a non-linear perceived as particularly disturbing Distortion of the audio signal while maintaining the dynamics and the Playback volume.

Around to adapt the arrangement to special requirements is provided that the withdrawal the dynamic damping (Gain) is freely adjustable. It should be possible, the return the dynamic damping (Gain) in one or more stages or continuously. The reset time for the taking back the dynamic damping (Gain) should also be freely selectable be.

Especially Cheap is to turn the scheme into a digital signal processor (DSP) too integrate. Since the scheme in this case in the form of a computer program, this means For example, with the help of a DSP algorithm, is realized, the implementation effort is very low.

It has been considered favorable proved that the limiting amplifier with the amplitude-selective attenuation (amplification) has a transfer characteristic, starting from a straight course S-shaped or even stepwise changeable is. In particular, a stepped History of the transfer characteristic makes it possible that only the signal amplitudes, which really too overdrive guided would have muted be while all other signal amplitudes that are not overdrive guided would have be transferred unchanged. In such a characteristic curve, however, harmonics generated, which for example influence an audio signal, that the listening impression massively deteriorated. An S-shaped or at least approximate S-shaped History of the transfer characteristic represents a compromise between unchanged transmission small and medium signal amplitudes and reduction of harmonic content at high signal amplitudes.

In In practice, it is advantageous that the Begrenzerverstärker off consists of two stages. In this two-stage design is provided the first stage for amplitude-selective amplification and the second Stage to a constant lowering of the entire signal, regardless of the amplitude of the signal. The transfer characteristic is the first Stage designed so that small signal amplitudes of the input signal reinforced be while size Amplitudes of the input signal are not amplified and remain largely unchanged. In conjunction with the additional amplitude independent damping the second stage leads this means that small amplitudes of the input signal remain almost unchanged and only big ones Amplitudes of the input signal, which would lead to an override, are attenuable.

A such dynamic adaptation of the transfer characteristic a limiter amplifier can be both channel selective and for multiple channels or for all channels be done together. In a channel selective adaptation takes place in For each individual channel an optimal adaptation of the transfer characteristic of the limiter amplifier to the current level control instead. In general, however, it is sufficient one or two channels to monitor and the adaptation of the transfer function of the limiter amplifier in the other channels to adapt to this one channel.

Furthermore, the invention provides a choice, a level detection and thus the Adap tion of the transfer characteristics of the limiter amplifier broadband or frequency selective perform. This choice offers the advantage that only those areas of the frequency spectrum must be monitored, in which an override is expected. For example, in the case of an audio signal in practice, the main focus is on the low-frequency range of the signal spectrum, where particularly high amplitudes are to be expected. This is the case, for example, with a bang.

On the transmission and signal processing line within a channel, there is one Number of ways to control a signal output and one derived therefrom Correction of the transfer characteristic of the limiter amplifier.

There a certain amount of time is required to have an appropriate transfer function of the limiter amplifier It is advisable to detect an excessive input signal, which is obvious to overdrive in signal processing, already to be detected in the signal input area. This is a first Level detector for picking up the input signal supplied to the signal processor provided when crossing a predetermined amplitude of the input signal, the amplitude-selective damping (Gain) of the limiter amplifier so that the signal at the output of the limiter amplifier a does not exceed the specified value. The level detector is here, for example, directly on the transmission line or arranged at a branching point.

A Forming the level detector as a peak detector has the advantage that such a level detector is very easy to implement and that a measurand immediately for controlling the damping (Gain) of the limiter amplifier lies ahead.

When it has turned out to be particularly advantageous, this level detector assign a first level prediction unit, which takes the form of a appraisal Signal processing in the signal processor exceeded a predetermined Amplitude of a signal at the output of the signal processor and the damping (Gain) of the limiter amplifier so that the signal at the output of the limiter amplifier a does not exceed the specified value. A "predictive" monitoring of the signal at the output of the Signal processor has the advantage of having enough time to identify and Setting the corresponding transfer function the limiter amplifier available is.

A predictive signal analysis is made possible by a time delay element, for Example a signal memory, in the input area on the transmission line is provided in front of the signal processor. For example, during a Caching the input signal a simulation of signal processing this input signal on the transmission path be performed with the current filter settings of the signal processor, at every override is shown. This "predictive" override detection can then be used to measure the necessary amplitude-selective losses (Reinforcements) to avoid overdriving adjust.

In a further embodiment of the invention is instead of the first level detector in the input area or in addition to this level detector another level detector provided, the a crossing a predetermined amplitude of a signal at the output of the signal processor indicating and damping (Gain) of the limiter amplifier so that the signal at the output of the limiter amplifier a does not exceed the specified value. To determine an amplitude of a signal at the output of the signal processor the invention sees two possibilities in front.

So the invention provides a level detector, by the evaluation a saturation unit the signal processor exceeded a predetermined amplitude of the signal at the output of the signal processor detected and the amplitude selective attenuation (amplification) of the limiter set so that a signal at the output of the Begrenzerverstärkers a does not exceed the specified value.

alternative or additionally For this level detector, an extension according to the invention sees another one Level detection, which outputs a signal at the output of the signal processor between the signal processor and the Begrenzerverstärker picks and when crossing a predetermined amplitude of the signal corresponding to the transfer characteristic of the Begrenzerverstärkers chooses. This level detector is advantageously designed as a peak detector.

A so-called "saturation detector", which controls the saturation unit of a signal processor, has the advantage over a peak detector of a much faster data acquisition. To compensate for the duration of the measured value detection, the invention provides that the level detectors each time delay element is assigned, which the input signal of the Begrenzerverstärkers according to the required time for level detection (which depends on the level detector used) and for setting the amplitude selekti attenuation (gain) of the limiter amplifier delayed. This is the only way to guarantee that an overdriven signal will be attenuated according to its overload.

Around not for every momentarily arriving signal the adjustment of the necessary Damping (amplification) of the limiter to have to adjust will be the settings for maintained a certain amount of time, as long as not an override a new setting of the amplitude selective damping amplification) of the limiter forces. The invention therefore provides, the Begrenzerverstärker a Reset unit to allocate for a return the dynamically adjusted amplitude-selective damping (amplification) ensures.

One embodiment The invention is illustrated in the drawing and will be described below described in more detail. Show it:

1 a block diagram of a first embodiment of a channel of a signal processing unit,

2 a block diagram of a second embodiment of a channel of a signal processing unit,

The 1 shows a block diagram of a first embodiment of a channel of a signal processing unit according to the invention. It shows a signal input 1 to which an input signal E is supplied. The input signal E is a digital audio signal in the example. To the signal input 1 closes a transmission path 3 on the output side with the signal output 6 connected is.

Input side is on the transmission link 3 a signal processor 4 arranged. This is the input signal E '= E supplied. At the output of the signal processor 4 is the signal A 'on. This signal A 'becomes a limiter amplifier 35 supplied as input signal E '' = A '. The output of the limiter amplifier 35 at the same time forms the signal output 6 the signal processing unit. Here the output signal A = A "is tapped.

The at the signal input 1 applied input signal E is at a first branch point 12 from a first level detector 7 tapped. The first level detector 7 is via a data line with an arithmetic unit 14 connected. About this data line is the calculator 14 the signal amplitude g _PL1 communicated to the signal input E. The signal processor 4 is via a data line with a saturation unit 17 connected. This saturation unit 17 is also via a data line with a second level detector 8th connected. This level detector 8th In turn, there is a data line with the calculator 14 connected. About these data lines is the calculator 14 the instantaneous signal amplitude g _SP within individual stages of the signal processor 4 or at the output of the signal processor 4 communicated.

A third level detector 9 engages at a second branch point 13 the signal A 'from the output of the signal processor 4 from. The third level detector 9 is like the level detectors 7 and 8th via a data line with the calculator 14 connected. This data line is used by the level detector 9 the instantaneous amplitude g _{PL2 of} the signal A 'at the output of the signal processor 4 transfer.

Furthermore, the calculator 14 the value of the current volume setting g _vol transmitted. Another input of the calculator 14 is the supply voltage U _Batt .

The calculator 14 represents the signal processor 4 Values for the current filter settings g _F for sound adjustment are available via a data line. In the 1 this is a parameterization unit 23 provided that these filter settings g _F the signal processor 4 provides via a data line.

The calculator 14 provides via a data line to a control device 36 the settings g ₃ for the limiter amplifier 35 to disposal.

The first level detector 7 detected in the signal input range, whether the input signal E in connection with the settings of the sound-influencing filters and the volume adjustment (in the context of a dynamic control of the headroom) is already so high that it obviously leads to overdriving. If this is the case, then the calculator provides 14 that the setting g _{3 of} the limiter amplifier 35 is chosen so that the high signal amplitudes are more attenuated compared to the low signal amplitudes. The attenuation of the high signal amplitudes is ideally chosen so that an override of the signal A at the signal output 6 is avoided. The regulation, ie the signaling of an override by the first level detector 7 to the calculator 14 and the setting of the transfer characteristic of the limiter amplifier 35 through the control device 36 works as forward control, ie as a controller.

The signal E '= E passes through the level-affecting audio processing in the signal processor 4 , To this level-influencing audio processing includes, for example, the setting of the sound-influencing filter g _F , such as for adjustment the treble, bass and / or equalizer controls. An override of the signal S 'within the signal processor 4 or an override of the signal A 'at the output of the signal processor 4 becomes a saturation unit 17 the signal processor 4 displayed.

This status display is evaluated by the second level detector 8th and signals the overload to the calculator 14 , The calculator 14 causes a corresponding setting g _{3 of} the limiter amplifier 35 through the control device 36 ,

At the output of the signal processor 4 is a level detection by a third level detector 9 intended. This third level detector 9 works like the first level detector 7 as a peak detector. The third level detector signals an override of the signal A 'the arithmetic unit 14 , The calculator 14 again signals after detection of the override of the control device 36 a value for the setting g _{3 of} the transfer characteristic of the limiter amplifier 35 ,

Signal the level detectors 7 . 8th and or 9 in that no overdriving of the audio signal at the output of the signal processor 4 is expected, so ensures a reset unit 18 for a continuous or stepwise withdrawal of the dynamic amplitude-selective attenuation of the signal E "by the limiter amplifier 35 ,

2 shows a block diagram of a second embodiment of a channel of a signal processing unit according to the invention. This embodiment shows an integration of the method according to the invention into a signal processing unit for the dynamic control of dynamic headroom management (DHM). This regulation is usually integrated in a digital signal processor (DSP). The regulation takes place in this case in the form of a computer program, ie for example with the aid of a DSP algorithm.

One Such DHM method ensures that the overall level of the amplifier is improved. additionally the scheme ensures that weak input signals amplified can be without causing overdriving the power amplifier comes when the input signal has high signal amplitudes contains. This cheap Properties are achieved by constantly monitoring the input signal and that reinforcement and attenuation factor on the transmission line be set dynamically.

In all cases in which it is not possible to provide this headroom due to the signal characteristics and the preset sound settings, there is a risk of overloading, which in turn leads to strong nonlinear distortions and thus to high harmonic distortion. It is therefore advantageous to integrate the process according to the invention into this DHM process. The transmission characteristics of the limiter amplifier 35 will be adapted to this procedure.

The 2 shows a block diagram of such an arrangement. It shows a signal input 1* to which an analog audio signal is supplied as input E *. This input E * is in a preamplifier 30 amplified and an analog-to-digital converter 25 supplied and is at the output as a digital signal E before.

Alternatively, a digital input signal may also be applied directly to the signal input 1 be supplied as input signal E.

To the signal input 1 closes a transmission path 3 on the output side with a speaker 38 connected is.

Input side is on the transmission link 3 a level reduction unit 2 arranged. This level reduction unit 2 is with an input of a signal processor 4 connected to which an input signal E 'is supplied. At the output of the signal processor 4 is the signal A 'on. This output signal A 'becomes the level emphasis unit 5 fed. At the output of the level-raising unit is the input of the Begrenzerverstärkers 35 to which the signal E "is supplied. That at the output of the limiter amplifier 35 present signal A '' is a digital-to-analog converter 26 fed. That at the output of the digital-to-analog converter 26 This signal is a variable attenuator 31 fed, then an attenuator 32 with predetermined attenuation and a power amplifier 33 , At the output of the power amplifier 33 is the output signal A *, which is the speaker 38 is supplied.

An analog input signal E *, in the preamplifier 30 amplified and in analog-to-digital converter 25 is converted into a digital input signal E, by a first level detector 7 at a first branch point 12 is present, detected. When falling below a signal threshold, an automatic amplification mechanism is set in motion, which is known in the art under the name "Automatic Gain Control". This procedure is used by the level detector 7 the falling below the signal threshold of the so-called AGC (Automatic Gain Control) unit displayed. This AGC unit signals the preamplifier 30 that this should increase the analog gain g _AD . The advantage of such an automatic gain control is that the quantization gray is reduced on the digital signal path. Is this AGC module 28 implemented, this AGC control takes place simultaneously for the dynamic control of the headroom reserve (DHM).

The first level detector 7 in the signal input area also detects whether the input signal E is already so high that it obviously leads to overdriving. The signal amplitude at the signal input g _PL1 is the arithmetic unit 14 transmitted via a data line. The calculator calculates from this the necessary level reduction g ₁ , which is the level reduction unit 2 is transmitted via a data line. The possibly lowered signal E 'then passes through the level-influencing audio processing in the signal processor 4 , This level-influencing audio processing includes, for example, the setting g _{F of} the sound-influencing filters for setting the treble, the bass, the equalizer output and the volume.

A possible override of a signal S 'within the signal processor 4 becomes a saturation unit 17 the signal processor 4 displayed. This status display is evaluated by the second level detector 8th and signals the overload, ie the signal amplitude g _SP in the signal processor 4 , the calculator 14 , The calculator 14 causes now a level reduction in the level reduction unit 2 for the next audio date. In contrast to the feedforward control by the first control loop, so here only after finding an actual override in the form of a feedback control, a level reduction at the entrance 1 instead of.

It is envisaged that the calculator 14 a detected overdrive example, a microcontroller signals, the filter settings g _F (level-influencing parameters) in the parameterization 23 so changes that in the signal processor 4 no overdriving of the audio signal takes place anymore.

The feedback control of the level reduction at the signal input 1 , which by the second level detector 8th is displayed causes a few samples of digital audio processing in the signal processor 4 actually overdriven.

Both rule principles, ie the intent control one by the first level detector 7 displayed override, as well as the feedback control of a through the level detector 8th Detected overdrive, grab side by side in parallel on the common modulation and control in the calculator 14 and determine the amount of dynamic gain reduction g ₁ in the level reduction unit 2 ,

The calculator 14 now causes each signal A 'in the level-raising unit 5 according to its input side experienced level reduction g _{1 is raised} again with the level increase g ₂ .

The headroom g _H = g _PL2 required in digital signal processing to avoid any overshoot can be calculated from Equation 1 G H = g PL1 + g SP + g 1 (+ g Vol ). (1)

Here g _vol denotes the volume setting, which the calculator 14 provided via a data line.

As long as g _H ≦ 0 dB, no clipping occurs on the digital signal transmission path, since all the gain / attenuation parameters g _AD , g ₁ , g ₂ and g _{DA can} be balanced so that there is sufficient headroom within the signal processing chain. The level reduction g ₁ must always be selected so that g _PL1 + g ₁ (+ g _vol ) ≤ -g _SP .

If g _{H is} greater than 0 dB, then the amplitude-selective attenuation of the limiter amplifier must 35 be changed accordingly, so that overdriving the power output stage 31 . 32 . 33 . 38 is avoided.

As long as the headroom g _H = g _{PL2 is} less than or equal to 0 dB, the limiter amplifier is normally "off". This means that the transfer characteristic of the limiter amplifier 35 is completely linear. If g _H = g _{PL2 is} greater than 0 dB, ie if an override occurs, this becomes the arithmetic unit 14 displayed. The calculator 14 transmitted to the control body 36 of the limiter amplifier 35 in that this changes the amplifier setting g ₃ . This is the case, for example, as shown in the above section, when, due to the feedback control, over-control of fewer samples occurs. The limiter amplifier 35 now has an S-shaped or at least approximately S-shaped course of the transfer characteristics.

As long as g _{H is} greater than 0 dB, the non-linear characteristic of the limiter amplifier is 35 active. Small signal amplitudes are transmitted almost unchanged, while large signal amplitudes are limited to level values below 0 dBFS to any overdriving the power amplifier 31 . 32 . 33 . 38 to avoid. It is obvious that nonlinear distortions of the overall system increase with increasing gain g _H (as long as g _{H is} greater than 0 dB). However, such non-linear distortions of the system can be to that extent be controlled that the transfer characteristics of the limiter amplifier 35 be optimized with regard to psychoacoustic aspects.

Out 2 goes on to show that this is the delimiter 35 applied output signal A '' is converted back into an analog signal before it in the attenuator 31 is dampened again. The calculator 14 ensures that the signal is again attenuated with the analog attenuation g _{DA in} accordance with its gain g _{AD which has} been experienced on the input side.

The signal attenuated in this way becomes an attenuator in the example 32 supplied, _wherein the attenuation g _att for an adaptation to the fixed and constant gain g _{amp of} the final amplifier 33 provides.

The overall volume of the signal thus results from the fact that the gain or attenuation in both the digital and in the analog part of the transmission path 3 is set. The best signal properties result from the fact that the analog input signal E * is pre-amplified as far as possible (gain g _DA ) before the signal is converted into a digital signal. For analog amplifiers 30 The gain can be changed between 0 and 31 dB in 1 dB increments. Therefore, in the digital level emphasis unit 5 and / or in the attenuator 31 also a corresponding attenuation g _DA can be set. In addition, the volume setting g _Vol must be taken into account, which in the signal processor 4 , in the level raising unit 5 or in the attenuator ( 31 ) is applied to the signal.

The fixed damping g _{att of} the attenuator 32 in the example is -10 dB. The fixed gain g _{amp of} the analogue power amplifier 33 is 26 dB in the embodiment.

1*

signal input (Analogous)

1

signal input

2

Level reduction unit

3

transmission path

4

signal processor

5

Level boost unit

6

signal output (Digital)

7

first level detector

8th

second level detector

9

third level detector

12

first branching point

13

second branching point

14

calculator

17

saturation unit

18

Reset unit

23

parameterization

25

Analog-to-digital converter

26

Digital-to-analog converter

28

Automatic Gain Control (AGC)

30

preamplifier

31

attenuator (Changeable)

32

attenuator (firmly)

33

Power amplifier (fixed)

35

Limiter amplifier (changeable)

36

control device

38

speaker

e

input (Digital)

A

output (Digital)

e '

input signal processor

A '

output signal processor

S '

signal in the signal processor

A ''

output limiter

E ''

input limiter

e *

input (Analogous)

A *

output (Analogous)

g _AD

Amplification analog

g _DA

Damping analog

g _PL1

signal amplitude at the signal input

g _SP

signal amplitude in the signal processor

g _F

filter settings

g _Vol

Volume adjustment

g ₁

Attenuator

g _att

damping

g ₂

level increase

g _amp

reinforcement

g ₃

attitude of the limiter amplifier

g _PL2

signal amplitude at the output of the signal processor

g _H

headroom

V _Batt

supply voltage

Claims (16)

Method for overdriving protection of an input signal (E) in at least one channel of a signal processing unit, on one between a signal input (E) 1 ) and a signal output ( 6 ) lying transmission path ( 3 ), wherein the input signal (E) in a signal processor ( 4 ) and stored in a limiter amplifier ( 35 ) is attenuated or amplified, wherein when a signal amplitude on the transmission path ( 3 ) with increasing signal amplitude higher (lower) signal amplitudes are more attenuable (amplifiable) compared to lower (higher) signal amplitudes and the amplitude-selective attenuation (amplification) of the limiting amplifier ( 35 ) depending on volume settings (g _Vol ) and / or filter settings (g _F ) is adjustable. Signal processing unit with at least one channel, each channel having a signal input ( 1 ) for applying an input signal (E), a signal output ( 6 ) for picking up one on an over transmission line ( 3 ) between the signal input ( 1 ) and the signal output ( 6 ) transmitted output signal (A), one on the transmission line ( 3 ) arranged signal processor ( 4 ) and one between the signal processor ( 4 ) and the signal output ( 6 ) limiting amplifier ( 35 ), wherein at least one level detector ( 7 . 8th . 9 ) on the transmission line ( 3 ) is provided for monitoring a signal amplitude, and the attenuation (gain) of the limiter amplifier ( 35 ) when a signal amplitude on the transmission path is exceeded ( 3 ) is adjustable so that with increasing signal amplitude higher (lower) signal amplitudes are more attenuable (amplifiable) compared to lower (higher) signal amplitudes, wherein the amplitude-selective attenuation (gain) of the limiter amplifier ( 35 ) depending on volume settings (g _Vol ) and / or filter settings (g _F ) is adjustable. Signal processing unit according to claim 2, characterized in that the limit amplifier ( 35 ) applied signal (E '') is a digital signal. Signal processing unit according to claim 2 and 3, characterized in that the limiter amplifier ( 35 ) having the amplitude-selective attenuation (gain) has a transfer characteristic which, starting from a straight course, is at least approximately S-shaped or stepwise variable. Signal processing unit according to one of claims 2 to 4, characterized in that the limiter amplifier ( 35 ) is designed so that the amplitude-selective attenuation (amplification) is channel-selective or mutually adjustable for several channels. Signal processing unit according to one of claims 2 to 5, characterized in that the limiter amplifier ( 35 ) is designed so that the amplitude-selective attenuation (amplification) is frequency-selective or broadband. Signal processing unit according to one of claims 2 to 6, characterized in that a first level detector ( 7 ) for picking up the signal processor ( 4 ) supplied input signal (E) is provided, which when exceeding a predetermined amplitude of the input signal (E), the attenuation (gain) of the Begrenzerverstärkers ( 35 ) so that the signal (A '') at the output of the limiter amplifier ( 35 ) does not exceed a predetermined value. Signal processing unit according to claim 7, characterized in that the first level detector ( 7 ) in the signal input area at a first branch point ( 12 ) on the transmission line ( 3 ) between the signal input ( 1 ) and the signal processor ( 4 ) is arranged. Signal processing unit according to claim 7, characterized in that the first level detector ( 7 ) in the signal input area on the transmission link ( 3 ) between the signal input ( 1 ) and the signal processor ( 4 ) is arranged. Signal processing unit according to claim 7, 8 or 9, characterized in that the first level detector ( 7 ) is designed as a peak detector. Signal processing unit according to one of claims 7 to 10, characterized in that the first level detector ( 7 ) a first level prediction unit ( 10 ) in the form of an estimate of a signal processing in the signal processor ( 4 ) a possible exceeding of a predeterminable amplitude of a signal (E '') at the input of the limiter amplifier ( 35 ) and the attenuation (gain) of the limiter amplifier ( 35 ) controls so that the signal (A '') does not exceed a predetermined value. Signal processing unit according to one of claims 2 to 11, characterized in that a second level detector ( 8th ) provided by the evaluation of a saturation unit ( 17 ) of the signal processor ( 4 ) exceeding a presettable amplitude of a signal (A ') at the output of the signal processor ( 4 ) and the attenuation (gain) of the limiter amplifier ( 35 ) so that the signal (A '') at the output of the limiter amplifier ( 35 ) does not exceed a predetermined value. Signal processing unit according to one of claims 2 to 12, characterized in that a third level detector ( 9 ) is provided, which is a signal (A ') at the output of the signal processor ( 4 ) and, when a predeterminable amplitude of the signal (A ') is exceeded, the attenuation (gain) of the limiting amplifier ( 35 ) so that the signal (A '') at the output of the limiter amplifier ( 35 ) does not exceed a predetermined value. Signal processing unit according to claim 13, characterized in that the third level detector ( 9 ) at the output of the signal processor ( 4 ) on the transmission line ( 3 ) is arranged. Signal processing unit according to claim 13, characterized in that the third level detector ( 9 ) at the output of the signal processor ( 4 ) at a branching point ( 13 ) on the transmission line ( 3 ) is arranged. Signal processing unit according to one of the preceding claims, characterized in that the limiter amplifier ( 35 ) for dynamic amplitude-selective damping (amplification) in a signal processing unit for dynamic control of the drive reserve (DHM) is integrated.