WO2016162613A1

WO2016162613A1 - Method and device for controlling the tone of a sound signal

Info

Publication number: WO2016162613A1
Application number: PCT/FR2016/050720
Authority: WO
Inventors: Laurent Gagliardini
Original assignee: Peugeot Citroen Automobiles Sa
Priority date: 2015-04-10
Filing date: 2016-03-31
Publication date: 2016-10-13
Also published as: FR3034928B1; FR3034928A1

Abstract

The invention relates to a method for controlling the tone of a sound signal. Said sound signal is detected inside a playback region at a sound intensity characterized by a sound intensity index. Said tone control method includes applying a filter bank to said sound signal. Said filter bank includes a plurality of filters designed to amplify or attenuate said sound signal on the basis of adjustments carried out by the user. According to the invention, said tone control method also includes applying an increase in calibration to each filter of the filter bank. Each of said increases is configured such that the sound intensity index of the sound signal detected in the playback region is, on average, constant.

Description

METHOD AND DEVICE FOR MONITORING THE TONE OF A SOUND SIGNAL

[001] The invention relates generally to the control of the tone of sound signals, that is to say the control of the sound spectrum of the signals - more or less serious or acute - according to settings made by a user . In particular, the tone control method according to the present invention is aimed at controlling the tone of sound signals emitted inside a vehicle cabin by a car radio or any audio system.

[002] Indeed, audio systems able to broadcast a sound signal in a listening volume, including a closed listening volume such as a vehicle interior, include a number of settings options offered to the user . The adjustment possibility which concerns the present invention concerns the adjustment of the tone of the sound signal, that is to say the adjustment of the sound spectrum of the signals restored in the listening volume.

[003] Thus, the tone control, as known to those skilled in the art, can be achieved through processing performed on the sound signal before its return in the listening volume.

[004] The controls used today consist of filter banks that amplify, respectively attenuate, certain frequency bands of the sound signal according to the settings made. This known technique has the disadvantage that, during the adjustment, there is a confusion for the listener between the increase, respectively the decrease, in the perceived loudness level and the tone change. This leads to an abuse of these controls.

[005] Moreover, the use of particular tone control functions, such as the adaptive loudness - adaptive loudness according to the anglicized expression known to those skilled in the art - or the control of the replay level of the audio tracks , require a good control of the perceived sound levels so that the quality of the return of the sound signal is satisfactory.

[006] There is therefore a need for a tone control method adapted to change the tone of a sound signal without inducing the aforementioned drawbacks. For this purpose, the present invention proposes a method the implementation of which makes it possible to carry out a control of tone while maintaining a constant level of perceived loudness in the listening volume.

[007] For this purpose, the present invention relates to a tone control method of a sound signal, said sound signal being perceived within a listening volume with a loudness characterized by an intensity index sound, said tone control method comprising applying a filter bank to said sound signal, said filterbank comprising a plurality of filters configured to amplify or attenuate certain frequency bands of said sound signal according to settings made by the sound 'user. Said tone control method according to the invention is characterized in that it furthermore comprises the application of a gain to each of the filters of the filterbank, each of said gains being configured so that the index of the sound intensity of the sound signal perceived in the listening volume is, on average, kept constant.

According to a preferred embodiment of the method according to the invention, the sound intensity index is a function of the mean quadratic sound pressure in the listening volume.

[009] In particular, said gains, denoted G _ctrl , can be written according to the following equation:

where IS ((p _ear ^2> L, R) represents the loudness rating calculated from the sound pressure spectrum (p _ea r ^2> L, R> ^{and s} ^is the CTRI I ^e spectrum of the considered filter .

The sound intensity index may especially be the overall sound level weighted sound signal in the listening volume.

[001 1] According to another embodiment, the sound intensity index can be the loudness of the sound signal in the listening volume.

According to a particular embodiment of the method according to the invention, said method for controlling the tone of a sound signal, said sound signal having a constant spectrum per frequency band (pink noise), is intended to be implemented. an audio system capable of reproducing the sound signal in the listening volume, said audio system being characterized by a known transfer function. When the intensity index sound is a weighted global level, the gain applied to each filter in the filter bank satisfies the following equation:

where G _ctrl is the gain, i corresponds to a frequency band, the bandwidth of the audio system is divided into frequency bands corresponding to one-third octave, and Ntiers is the third-octave number of the bandwidth considered. , Tc; _{LR i} represents the transfer function corresponding to the average audio frequency response of the audio system, said average being for example calculated at the various places concerned and for the right and left channels, P _¾ is a weighting function of the spectrum (weighting A or B for example), and S _{ctrl i} is the spectrum of the filters applied to the sound signal.

According to a particular application of the method according to the invention, the listening volume is a passenger compartment of a motor vehicle.

The present invention also provides a device for controlling the tone of a sound signal, comprising means for receiving a sound signal, as well as electronic means for implementing the method for controlling the tone of a signal. sound as briefly described above.

The present invention also provides an audio system for a motor vehicle, comprising means for synthesizing a sound signal and means for restoring said sound signal to a listening volume, also comprising a control device. as briefly described above.

In addition, the present invention also relates to a motor vehicle, comprising a passenger compartment forming a listening volume and an audio system as briefly described above.

Other features and advantages of the invention will appear on reading the detailed description of the embodiments of the invention, given by way of example only, and with reference to the drawings which show: FIG. 1, a graph showing a first example of a spectrum of a filter bank according to the state of the art;

FIG. 2, a graph showing a second example of spectrum of a filter bank according to the state of the art;

FIG. 3, a graph showing a first example of a spectrum of a filter bank according to the invention;

FIG. 4, a graph showing a second example of a spectrum of a filter bank according to the invention;

FIG. 5, a graph showing an exemplary "target" transfer function, in the context of an implementation of the method according to the invention.

In what follows, the described embodiments are more particularly related to an implementation of the tone control method of a sound signal according to the invention, for an application within a motor vehicle. However, any implementation in a different context, in particular in any type of sound signal reproduction system, is also covered by the present invention.

The present invention, as mentioned above, relates firstly to a tone control method capable of maintaining a constant perceived loudness when tone control operations are applied to the sound signal by a user acting on the loaded audio system. the restoration of said sound signal.

According to the state of the art, the tone controls consist of a filter bank. They generally consist of two or three controls to act, respectively, on the bass and treble level or on the bass, midrange or treble level. In some cases, the number of these checks can be increased. We then speak of graphic equalizers. Nevertheless, the architecture and the operating principle remain the same.

At the heart of audio systems that can be installed in interiors of motor vehicles, the tone control is generally performed upstream of the amplification and relate to sound signals, called "media", from the radio, d a CD, a device connected by a USB port ... etc. By way of example, FIGS. 1 and 2 show spectra of filter banks implemented in the state of the art. These known filters can be of different types: in FIG. 1 is thus represented the spectrum of a "peaking EQ" filter, and in FIG. 2 is represented the spectrum of a "shelf" filter, according to the Anglo-Saxon names. known to those skilled in the art.

Figures 3 and 4 show spectral banks of tone control filters performed according to the method according to the invention.

As is apparent from the analysis of these Figures 3 and 4, the invention consists in applying a gain to each of the filters implemented on the sound signal to be processed, so that the sound intensity of the sound signal perceived to be constant on average, regardless of the sound signal to be reproduced by the audio system. For this, it is assumed, known to those skilled in the art, that said sound signals have on average the spectrum of a pink noise within a certain bandwidth.

Thus, considering in particular the return of a sound signal inside a vehicle cabin, the tone control method according to the invention allows that inside the cabin, the the intensity of the sound signal, as perceived in the cockpit, is constant, on average.

To achieve this result, a gain is applied to each filter of the filter bank implemented on the sound signal to be processed. This calibration gain, or this correction, is based on a modeling of the form:

[0027] (Pear ² > L, R = _C ² _L , _R X ² (1) where:

(Pear ² > L, R represents the spectrum of the mean squared sound pressure in the listening volume (the average in the right and left places in a vehicle cabin),

TC, L, R represents the transfer function corresponding to the average audio frequency response of the audio system, x ² is the spectrum of the sound signal reproduced. In the context where a tone control is applied to the sound signal, the transfer function becomes:

, L, R, Ctrl-Tc, L, RS _c trl (2) is the control spectrum applied to the sound signal.

[0030] According to the invention, an indication of loudness, denoted IS ((p _ear ^2> L, R) ^is considered. This index is a psycho-acoustic variable which can in any case be connected to the sound pressure, This sound intensity index forms an indicator that may simply correspond to an overall sound level in dB (A), as defined by IEC 61672-1, or it may be a more complex indicator such as loudness, defined by the ISO 532 standard, which quantifies in a more refined way the perception of the sound intensity in the human being.In both cases, the index of loudness characterizes the perceived loudness in the volume of according to the invention, it must be, on average, kept constant.

The calibration gain for the tone control, noted a _ctrl , applied to each filter, is such that:

[0032] IS _"P ear ^2> L, R) = I _(ctrl _(P ear ^2> L, R _ct rl) (3)

By construction, in connection with equations (1), (2) and (3), the sound intensity index depends both on the sound signal and on the transfer function corresponding to the system response. audio.

[0034] However, whatever the sound intensity index used:

On the one hand, the sound signal is represented by a mean spectrum over the bandwidth of the audio system. Pink noise, corresponding to a spectrum having a constant level per third octave, is often considered as a representative signal on average of the sound signals reproduced by standard audio systems. In addition, the sound signal reproduced by an audio system is characterized by its digital sound level expressed in dBFS, typically of the order of -18 dBFS. On the other hand, the transfer function, corresponding to the response of the audio system, is the intended target for the equalization of the sound signal in the listening volume. When there is an automatic physiological filter applicable to the sound signal, the transfer function, corresponding to the response of the audio system, therefore depends on the volume step chosen by the client; in this case we choose the transfer function for an average volume that will be taken as a reference.

In this context, Figure 5 shows an example of "target" transfer function. This transfer function is expressed in dB SPL for a level of 0 dBFS in a given frequency band, corresponding, in general, to one third of an octave. By way of example, for the 1 kHz frequency, the digital audio transfer function of FIG. 5 is equal to 90 dB for an input level of 0 dBFS. The third octave level, for a pink noise calibrated at -18 dBFS and limited to the band 40Hz-16kHz (or 27 third octave), being - 32.3 dBFS, this signal produced in the third octave 1 kHz a level of 90 - 32.3 = 57.7 dBSPL.

Thus, in the case where the sound intensity index used is the overall sound level obtained by weighting the spectrum of the sound signal, the value of the calibration gain to be applied to obtain a constant perceived sound intensity, said sound intensity. being characterized by said sound intensity index, can be calculated analytically according to the different spectra involved.

If the weighting function of the spectrum used, expressed in dB, is designated P, the sound intensity index characterizing the loudness perceived by the listener is:

where the index i indicates the frequency band describing the bandwidth cut in third octave Ntiers. According to a preferred embodiment, third octave bands are used, which have the advantage of being normalized.

In the case where the average spectrum of the sound signal used is a pink noise, the expression above becomes:

where LX is sound level per frequency band of the sound signal considered. When implementing a tone control, the perceived loudness

The gain which makes it possible to keep the level of the perceived loudness constant in the presence of the tone control characterized by its spectrum {s _ctrU } is thus written, according to the invention:

G _ctri = 101ogl0a _ctrl = LP-LP _ctrl = 10log10

The foregoing expression is applied independently for each filter and each level of amplification or attenuation of the filtered frequency band, at the cost of a slight slight inaccuracy resulting from the fact that the transfer function is possibly modified by the presence of other tone controls. However, if the same correction is made for the other controls and these controls concern different frequency bands, then the error is minimal.

It should also be noted that, in the case where a more complex indicator such as loudness is used, the calibration gain can be calculated by iteratively solving equation (3).

In summary, the present invention provides a tone control method mainly providing the application of a gain filters implemented to control the tone of a sound signal for its return by an audio system. Thanks to the application of this gain, the perceived loudness in the listening volume is, on average, constant.

The present invention also provides an audio system comprising means for implementing the tone control method according to the invention, and a vehicle equipped with such an audio system.

It is specified, moreover, that the present invention is not limited to the examples described above and is capable of numerous variants accessible to those skilled in the art.

Claims

Claims:

1. An audio system for a motor vehicle, comprising means for synthesizing a sound signal and means for restoring said sound signal to the passenger compartment of the motor vehicle, said sound signal being perceived inside the passenger compartment with an intensity sound characterized by a sound intensity index, characterized in that it comprises a device for controlling the tone of the sound signal inside the passenger compartment implementing a bank of filters receiving said sound signal, said bank of sound filters comprising a plurality of filters configured to amplify or attenuate said sound signal according to settings made by the user, with a gain applied to each filter of the filter bank, configured so that the sound intensity index of the sound signal perceived in the cockpit is, on average, kept constant.

2. An audio system according to claim 1, characterized in that the sound intensity index is a function of the mean square sound pressure in the passenger compartment.

3. Audio system according to claim 1, characterized in that said gains verify the equation

where ls ((p _ear ² > L, R) represents the sound intensity index calculated from the sound pressure spectrum, (p _ea r ² > L, R> and S _ctrl is the spectrum of the filter considered.

4. Audio system according to claim 3, characterized in that the sound intensity index is the weighted overall sound level of the audible signal in the passenger compartment of the vehicle.

5. Audio system according to claim 3, characterized in that the sound intensity index is the loudness of the audible signal in the passenger compartment of the vehicle.

6. Audio system according to one of claims 4 to 5, said sound signal having a constant spectrum per frequency band, characterized in that the gain applied to each filter of the filter bank satisfies the following equation: G _ctrl =

where G _ctri is the gain, i corresponds to a frequency band, the bandwidth of the audio system being divided into frequency bands corresponding to one-third octave, and Ntiers being the third-octave number of the considered bandwidth , TC, L, R, _I represents the transfer function corresponding to the average audio frequency response of the audio system, Pj is the weighting function of the spectrum of the audio system, and S _{ctrl i} is the spectrum of the filters applied to the sound signal .

7. Motor vehicle, characterized in that it comprises an audio system according to one of claims 1 to 6.