WO2006053684A2

WO2006053684A2 - Signal processing unit and signal processing method

Info

Publication number: WO2006053684A2
Application number: PCT/EP2005/012102
Authority: WO
Inventors: Hanno Kahnt; Stephan Braun
Original assignee: Fachhochschule, Jena
Priority date: 2004-11-18
Filing date: 2005-11-11
Publication date: 2006-05-26
Also published as: DE102004055738A1; DE102004055738B4; WO2006053684A3

Abstract

The invention relates to a signal processing unit for a signal processing path (1) for altering a first property of a received signal (s1), comprising an output module (2, 3) for the output of the signal (s2), altered in the signal processing path (s1), as output signal (s3), whereby the signal processing path (1) carries out a change to a second property of the received signal (s1) according to a first transmission function and whereby the output module (2, 3) comprises an adjustable amplifier (2), arranged downline of the signal processing path (1), to which the altered signal (s2) is supplied and which amplifies the same according to a second transmission function relating to the second signal property and provides the same as an output signal (s3) and an adjuster module (3) which adjusts the second transmission function of the amplifier as the inverse of the first transmission function.

Description

Signal processing unit and signal processing method

The invention relates to a signal processing unit and a signal processing method, in particular for audio signals.

In the processing of audio signals with sound filters, e.g. the increase or decrease of height or depth portions, inevitably takes place a change in the volume. However, to accurately evaluate the effect of the achieved sound change, a volume comparable to the unaffected signal is required. Therefore, a manual volume correction is performed, which is complex and inaccurate.

It is also known to reduce the signal level in an audio system depending on a source of interference, e.g. the ambient volume, readjust (DE 24 56 445 C3). DE 689 17 710 T2 and DE 102 25 145 A1 describe a controlled influencing of sound filters as a function of a signal level. DE 42 37 005 A1 discloses a method for receiving side reduction of volume differences when switching between stored and / or broadcast moderately transmitted audio program signals, in which a corresponding characteristic value is specified for the signals. Depending on the characteristic value, the volume is then set during the program change. DE 199 48 172 A1 describes a method in which the level of a signal is lowered prior to processing as a function of its amplitude and raised after the signal processing in order to enable distortion-free signal processing.

Proceeding from this, it is the object of the invention to provide a signal processing unit for a signal processing path for changing a first property of a supplied signal, with which an undesired by the signal processing path change a second property of the supplied signal can be avoided. Furthermore, a corresponding signal processing method is to be provided. According to the invention, this object is achieved by a signal processing unit for a signal processing path for changing a first property of a supplied signal, with an output module for outputting the signal changed by the signal processing path as an output signal, wherein the signal processing path causes a change of a second property of the supplied signal according to a first transfer function and wherein the output module comprises an adjustable amplifier downstream of the signal processing path to which the modified signal is applied, amplifies it according to a second transfer function with respect to the second signal characteristic and outputs it as an output signal, and an adjustment module which adjusts the second transfer function of the amplifier inversely to the first transfer function ,

With this signal processing unit can thus be compensated for the unwanted change of the second characteristic of the supplied signal by means of the amplifier whose second transfer function is set by the control module. Thus, the unwanted change of the second signal characteristic is eliminated, so that when, for example, audio signals are processed, the changed and amplified signal has the same volume as the supplied signal. This can immediately assess the effect of the achieved sound change. In addition, the dynamics of the applied signal are maintained (the dynamics of the input signal and the output signal are the same), so that there is no undesirable deterioration of the signal dynamics.

The amplifier is preferably designed to affect only the second signal characteristic. Thus, only the change of the second signal property is effected by means of the amplifier and otherwise carried out no further changes of the signal.

The change in the second characteristic of the applied signal preferably occurs in the signal processing path during the desired change of the first signal characteristic.

For example, the control module can detect the setting of an actuator of the signal processing path (e.g., the setting of a sounder in a signal processing path for audio signals) and set the second transfer function depending thereon.

Furthermore, it is possible that the control module detects the supplied signal and the signal changed by means of the signal processing path and causes the setting of the second transfer function as a function of the two signals. This makes it possible to realize a very exact compensation of the change of the second signal property. In particular it is it is possible to use the signal processing unit according to the invention in already existing signal processing paths (in the case of audio signals, for example, equalizer, distortion, mixer, tone generator, dynamic compressor or vocal processor).

In particular, the adjustment module determines the value of a predetermined evaluation parameter in the case of both detected signals and sets the second transfer function as a function of the two values. As an evaluation parameter, e.g. the RMS value, the arithmetic mean or the peak value of the signal are selected. For audio signals, the RMS value is preferably selected.

The adjusting module can form the ratio of the value of the predetermined evaluation parameter of the supplied signal to the value of the predetermined evaluation parameter of the changed signal and set this ratio as a gain factor of the second transmission function. Such a ratio formation can be realized very easily and simply, so that the signal processing unit according to the invention can be constructed inexpensively.

In particular, the adjusting module can filter the signals in order to determine the value of the predetermined evaluation parameter. This is particularly advantageous in the case of audio signals since this makes it possible to carry out a weighting of the spectral components of the signal in accordance with the spectral sensitivity of the ear.

Furthermore, the adjusting module may add a predetermined offset before the ratio formation to the value of the changed signal. This ensures that the ratio is certainly less than 1 when no signal or a very low level signal is supplied. It can thus be ensured that noise (in the absence of supplied signal) is not undesirably amplified by the amplifier.

The signal processing path can have at least one actuating element with which the effect of the signal processing path can be changed. With the actuator can be, for example, adjust the change of the first signal property, which, however, usually leads to a change of the first transfer function. In this case, the adjusting module preferably adjusts the second transfer function whenever the effect of the signal processing path is changed by means of the adjusting element. Particularly preferred is the embodiment in which the control module always adjusts the second transfer function only when the effect of the signal processing path is changed.

In particular, the positioning module may comprise a sample-and-hold element in which a value for setting the second transfer function is stored, which is given a new value is replaced when the effect of the signal processing path is changed by means of the actuator. This can be ensured in a simple manner that always the desired compensation of the change of the second signal property is achieved.

Of course, the control module can also adjust the second transfer function continuously according to the previously described types.

In particular, the signal processing unit is designed as an audio signal processing unit and the control module sets the second transfer function as a function of the rms values of the supplied signal and of the changed signal. Thus, an automatic level tracking is achieved in such a way that the supplied signal and the output signal have the same volume.

Preferably, the signal processing path is part of the signal processing unit according to the invention.

The signal processing unit can be designed as hardware and / or software. The hardware can be an analog and / or digital circuit. In particular, the software can also be implemented as a software plug-in.

The second transfer function of the amplifier may in particular be an amplification factor whose value may be greater than, equal to or less than 1. If the value is less than 1, the amplifier will attenuate.

The object is further achieved by a signal processing method for a signal processing path for changing a first property of a supplied signal, comprising the steps:

Amplifying the signal changed by the signal processing path and outputting as an output signal, wherein the signal processing path causes a change of a second property of the supplied signal according to a first transfer function, the gain of the changed signal is performed according to a second transfer function with respect to the second signal property, and wherein the second transfer function is set inverse to the first transfer function.

With this method, the unwanted change of the second signal property can be completely compensated. In particular, with audio signals, it is possible that the supplied signal and the output signal have the same volume, so that the performed by means of the signal processing path sound change can be well assessed. Preferably, the supplied signal and the changed signal are detected and in response to the two signals, the adjustment of the second transfer function is effected. Thus, the inventive method can be applied to existing signal processing lines.

In particular, the value of a predetermined evaluation parameter can be determined for both detected signals, and the second transfer function is set as a function of the two values. This can cause a very good compensation of the unwanted change of the second signal property.

In particular, the ratio of the value of the predetermined evaluation parameter of the supplied signal to the value of the predetermined evaluation parameter of the changed signal is formed and this ratio is set as an amplification factor of the second transfer function. Thus, the setting of the gain can be realized in the simplest way.

Before the ratio formation, a predetermined offset can be added to the value of the changed signal. This ensures that the amplification factor is less than 1 when no signal is applied and noise is only generated by the signal processing path. Such noise is then not amplified, but reduced due to the gain of less than 1 in an advantageous manner.

To determine the value of the predetermined evaluation parameter, the signals can be filtered. Thus, for example, a weighting of the spectral components of the signal can be carried out. This is particularly advantageous for audio signals, since these can then be weighted according to the spectral sensitivity of the ear, so that a constant volume is adjustable.

In addition to the effective value as an evaluation parameter, which is particularly useful in the case of audio signals, the arithmetic mean value or the peak value of an evaluation parameter, for example, can still be used.

In particular, the signal processing path can have at least one adjusting element with which the effect of the signal processing path on the first signal property can be changed, and the second transfer function is always set when the effect of the signal processing path is changed by means of the actuating element. For this purpose, the value for setting the second transfer function is preferably stored and always replaced by a new value, if by means of the actuator the effect of Signal processing path is changed. In this way, it can be easily ensured that always the desired compensation of the change of the second signal characteristic is performed.

Particularly preferably, the signal processing method processes audio signals and the second transfer function is set as a function of the effective value of the supplied signal and of the changed signal. This can be a constant volume realize.

The signal processing unit according to the invention can in particular be developed so that the specified signal processing method and its developments are realized.

The signal processing method according to the invention can be realized as a computer-implemented method. In particular, the refinements of the signal processing method according to the invention can also be implemented as a computer-implemented method. In this case, the method can then be carried out by means of a computer or another computer. The individual steps are carried out under control of a central processing unit of the computer or the computer and using the existing memory and possibly necessary input and output units in a conventional manner.

In particular, the computer-implemented method can be implemented as an extension program or as a so-called plug-in program, which serves to expand a predetermined software product by the functionality provided by the computer-implemented method. The predetermined software product can be, for example, known audio editing programs that are already installed on the computer or computer. The extension program can be added to such an already installed audio editing program without re-installing the complete audio editing program. The expansion program can also be used to extend mixers, equalizers, or their respective software, or as a subprogram on DSP-based audio platforms (DSP = Digital Signal Processing).

Furthermore, a computer program product is provided which comprises software code for carrying out the steps of the signal processing method according to the invention or of its further developments when the computer program product is executed on a computer. The computer program product can in particular be stored on a data medium. Preferably, the computer program product is designed as an extension program to a predetermined software product to enhance the functionality provided by the computer program product.

The invention will be explained in more detail by way of example with reference to embodiments in conjunction with the accompanying drawings. Show it:

Fig. 1 is a schematic diagram of a first embodiment of a signal processing unit, and

2 is a schematic diagram of a development of the signal processing unit of FIG. 1.

As can be seen from FIG. 1, a signal processing path 1 is supplied with a signal s1 to be changed, which signal is changed by the signal processing path 1 and output as a modified signal s2 to an amplifier 2 downstream of the signal processing path 1. The amplifier 2 amplifies the changed signal s2 and outputs it as an amplified output signal s3. The signal processing path, for example, performs an increase or decrease in the height components (first signal characteristic) of the supplied audio signal s1, which at the same time entails an undesirable reduction (according to a first signal level transfer function) of the signal level (second signal characteristic), whereby the changed signal s2 is lower than the supplied signal s1. The gain of the amplifier 2 is adjusted so that the level of the output signal s3 is raised so that the volume of the output signal s3 corresponds to the volume of the supplied signal s1.

The adjustment of the corresponding amplification factor (second transfer function for the signal level) is effected by means of a control module 3.

The control module 3 comprises a first filter 4 to which the supplied signal s1 is supplied and a rms value measuring unit 5 downstream of the first filter 4. Furthermore, the control module 3 comprises a second filter 6, to which the changed signal s2 is supplied, and a second filter 6 downstream effective value measuring unit 7.

By means of the filter 4 and the rms value measuring unit 5, an effective value Ui of the supplied signal s1 is determined, and by means of the filter 6 and the rms value measuring unit 7 an effective value U _{2 of} the changed signal s2 is determined. The filters 4 and 6 are the same here, their time constants also being equal and substantially greater than the longest period in the supplied signal s1. The filters 4 and 6 are used to weight the spectral signal components in the RMS values U ₁ and U ₂ according to the spectral sensitivity of the ear of a listener. The adjusting module 3 further includes a quotient forming unit 8, which determines the ratio of the effective value or the root mean square value U ₁ to the effective value U ₂ and applies this to the amplifier 2 as a gain factor. Thus, the level of the changed signal s2 is just multiplied by the inverse ratio which exists due to the signal processing path 1 between the level of the changed signal s2 and the level of the supplied signal s1. In other words, the signal processing path 1 has a first transfer function (U ₂ ZU ₁ ) for the signal level and the second transfer function of the amplifier 2 with respect to the signal level (second signal property) is just inversely set (U ₁ ZU ₂ ) to the first transfer function. Thus, the undesired change of a second signal characteristic (in this case the signal level) which takes place when the desired change is carried out by means of the signal processing path 1 (for example the change in the spectral composition of the supplied signal s1 or the addition of further signal components to the signal s1) Inversely set transfer function of the amplifier 2 completely compensated. There is therefore an automatic level tracking, so that the output signal s3 (= U _{1 to} ₂ x s2) always has the level of the supplied signal s1, regardless of the change carried out by means of the signal processing line 1. As amplifier 2 can in a hardware implementation, for example, a voltage controlled amplifier (VCA) or an analog multiplier.

2, a development of the embodiment of Fig. 1 is shown. To avoid unnecessary repetition, the same elements are denoted by the same reference numerals and reference is made to their description with reference to FIG. 1.

In contrast to the embodiment of Fig. 1, in the signal processing unit of Fig. 2 between the second RMS 7 and the quotient forming unit 8, an offset unit 9 is arranged, which adds to the determined effective value U ₂ a predetermined value (offset), so that a value U ₃ , which is greater than U ₂ is obtained. This ensures that at very low signal levels, as given for example in the case of a missing supplied signal s1 due to the noise, the ratio UiZU _{3 is} certainly less than 1. Thus, in this case, no undesired raising of the signal level of the changed signal s2 by means of the amplifier 2 is effected.

Furthermore, the signal processing unit of FIG. 2 has a sample-and-hold circuit 10 downstream of the quotient-forming unit 8, in which the desired ratio value U ₁ ZU _{3 is} stored. The sample and hold circuit 10 applies the stored ratio value U _{1 to} ₃ and to the amplifier 2 and takes a new ratio instead of the even stored one Ratio always only when the signal processing path is changed such that there is a modified signal processing (indicated by the dashed line 11). This can be achieved, for example, by monitoring an actuating element 12 of the signal processing path 1 and only accepting the new ratio value into the sample-and-hold element 10 when the actuating element 12 (for example a sound plate) changes.

Of course, embodiments are possible in which no filters 4 and 6 are provided. Instead of the rms value measuring units 5 and 7, it is also possible to provide units with which other evaluation parameters are determined. As further evaluation parameters, for example, the arithmetic mean or the peak value can be selected. Further, it is possible that a filter unit is provided between the quotient forming unit 8 and the amplifier 2.

The signal processing unit can be realized as hardware and / or software.

The signal processing methods that can be implemented by the described signal processing units can each be implemented as a computer-implemented method. In particular, the computer-implemented method may be implemented as an extension program that serves to extend a predetermined software product (such as widely-used audio editing programs) around the functionality provided by the computer-implemented method. The computer-implemented method can thus be designed as a so-called plug-in program. Such a plug-in program can be used in known audio editing programs and, for example, mixing consoles and equalizers. Furthermore, it is also possible to design the computer-implemented method as a subroutine. Such a subroutine can be used, for example, in DSP-based audio platforms.

Claims

claims

A signal processing unit for a signal processing path (1) for changing a first characteristic of a supplied signal (s1), comprising an output module (2, 3) for outputting the signal processing path (s1) changed signal (s2) as an output signal (s3), wherein the signal processing path (1) effects a change of a second property of the supplied signal (s1) in accordance with a first transfer function and wherein the output module (2, 3) has an adjustable amplifier (2) arranged downstream of the signal processing path (1) to which the changed signal (s2) which amplifies it according to a second transfer function with respect to the second signal characteristic and outputs it as an output signal (s3), and an adjusting module (3) which adjusts the second transfer function of the amplifier (2) inversely to the first transfer function.

2. Signal processing unit according to claim 1, wherein the control module (3) detects the supplied signal (s1) and the changed signal (s2) and in response to the two signals (s1, s2) causes the setting of the second transfer function.

3. signal processing unit according to claim 2, wherein the adjusting module (3) determines the value (Ui, U ₂ ) of a predetermined evaluation parameter of the two detected signals (s1, s2) and in

Dependence of the two values (U ₁ , U ₂ ) sets the second transfer function.

4. signal processing unit according to claim 3, wherein the adjusting module (3) the ratio of the value (U ₁ ) of the predetermined evaluation parameter of the supplied signal (s1) to the value (U ₂ ) of the predetermined evaluation parameter of the changed signal (s2) forms and this ratio as the gain of the second transfer function.

5. signal processing unit according to claim 4, wherein the adjusting module (3) before the ratio formation to the value (U ₂ ) of the changed signal (s2) adds a predetermined offset.

6. Signal processing unit according to one of claims 3 to 5, wherein the adjusting module (3) for determining the value (U ₁ , U ₂ ) of the predetermined evaluation parameter filters the signals (s1, s2).

7. A signal processing unit according to any one of claims 3 to 6, wherein the predetermined evaluation parameter is the effective value, the arithmetic mean or the peak value.

8. Signal processing unit according to one of the above claims, wherein the signal processing path (1) has at least one adjusting element with which the effect of

Signal processing path (1) is variable, and the adjusting module (3) adjusts the second transfer function whenever the action of the signal processing path (1) is changed by means of the adjusting element.

9. Signal processing unit according to claim 8, wherein the adjusting module (3) comprises a sample-and-hold member (10) in which a value for setting the second transfer function is stored, wherein the sample-and-hold member (10) has a new value stores, if by means of the actuator, the effect of the signal processing path (1) is changed.

10. Signal processing unit according to one of the above claims, wherein the signal processing unit is designed as an audio signal processing unit and the adjusting module (3) adjusts the second transfer function as a function of the effective values (U ₁ , U ₂ ) of the supplied signal (s1) and the changed signal (s2) ,

11. Signal processing unit according to one of the above claims, wherein the signal processing path (1) is part of the signal processing unit.

12. A signal processing method for a signal processing path for changing a first characteristic of a supplied signal, comprising the steps of: amplifying the changed signal and outputting as an output signal, wherein the signal processing path causes a change of a second property of the supplied signal according to a first transfer function, the gain of the changed signal is performed according to a second transfer function with respect to the second signal property, and wherein the second transfer function is set inversely to the first transfer function.

13. The method of claim 12, wherein the supplied signal and the changed signal are detected and the adjustment of the second transfer function is effected in response to the two signals.

14. The method according to claim 13, wherein the value of a predetermined evaluation parameter of the two detected signals is determined and the second transfer function is set as a function of the two values.

15. The method of claim 14, wherein the ratio of the value of the predetermined evaluation parameter of the supplied signal to the value of the predetermined

Evaluation parameter of the changed signal is formed and this ratio is set as the gain of the second transfer function.

16. The method of claim 15, wherein before the ratio formation to the value of the changed signal, a predetermined offset is added.

17. The method according to any one of claims 14 to 16, wherein the signals are filtered to determine the value of the predetermined evaluation parameter.

18. The method according to any one of claims 14 to 17, wherein the predetermined evaluation parameter is the effective value, the arithmetic mean or the peak value.

19. The method according to any one of claims 12 to 18, wherein the signal processing path has at least one adjusting element, with which the effect of the signal processing path is variable, and the second transfer function is always set when the action of the signal processing path is changed by means of the actuating element.

20. The method of claim 19, wherein a value for setting the second transfer function is stored and replaced by a new value when the effect of the signal processing path is changed by means of the actuator.

21. The method according to any one of claims 12 to 20, are processed in the audio signals and the second transfer function in response to the RMS values of the supplied signal and the changed signal is set.

22. The method according to any one of claims 12 to 21, wherein the method is implemented as a computer¬ implemented method.

23. The method of claim 22, wherein the computer-implemented method is implemented as an extension program that serves to expand a predetermined software product by the functionality provided by the computer-implemented method.

A computer program product comprising software code for performing the steps of any of claims 12 to 21 when the computer program product is executed on a computer.