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JP2014060720

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DESCRIPTION JP2014060720
Abstract: [Problem] To provide an integrated active acoustic loudspeaker housing that can be
used singly or in pairs to enhance stereo images. A loudspeaker enclosure (10) comprises a
central channel (16) directed towards the listener, and left and right channels (18L, 18R)
oriented perpendicularly to one another. The signals to be reproduced are i) correlated mono
components between left and right signals, ii) uncorrelated left and right surround components
between left and right signals, iii) uncorrelated left components between mono components and
left signals, and , Iv) separate into the uncorrelated right component between the mono
component and the right signal. The central channel 16 and the lateral channels 18L, 18R may
be arranged alone on the front of the listener or as a pair of loudspeaker enclosures on the left
and right of the listener. [Selected figure] Figure 1
Integrated active acoustic loudspeaker enclosure configurable to be used singly or in pairs to
enhance stereo images
[0001]
The present invention relates to the reproduction of audio signals by a high fidelity device that
presents and enhances stereo effects in front of the listener.
[0002]
Traditionally, the ideal configuration for stereo listening is to place two loudspeaker enclosures
apart from one another to form an isosceles triangle with the listener.
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In this configuration, a stereo image is formed between the two loudspeaker enclosures, i.e.
different sound sources (e.g. different musical instruments) appear and distributed along the axis
connecting the two loudspeaker enclosures It will be.
[0003]
Furthermore, it is desirable that the acoustic environment of the loudspeaker enclosure be
nothing or absorbable to avoid spurious reflections at the walls of the room forming the new
sound source. In any case, it may be desirable for the environment to be symmetrical, at least not
to unbalance the stereo image.
[0004]
The first problem is that such an effect is obtained by a single loudspeaker enclosure placed in
front of the listener.
[0005]
Such loudspeaker enclosures are described, for example, in www.
Theverge. See, for example, Jacob Schulman, XP055064354, XP055064341, and
XP055064344, entitled "Parrot Zikmu Solo Wireless Speaker by Philippe Starck Hands-on,"
published Jan. 10, 2012, on the Internet.
[0006]
Many configurations that group multiple acoustic transducers together in the same loudspeaker
enclosure are described, for example, in US Pat. No. 3,829,624A, US Pat. No. 6,169,812 B1 and
US Pat. No. 7,412,380 B1, and Journal of Audio Engineering Society, Vol. . It is still proposed in
the Christof Faller document entitled "Multiple-Loudspeaker Play-back of Stereo Signals"
published at 54, N.degree. 11, November 2006.
[0007]
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In particular, the loudspeakers can be arranged on the side of the loudspeaker housing so that
they radiate towards the wall.
Loudspeakers are directional, especially in the high range, but accuracy is lost in mono
components and can not be accurately represented in the front direction of the loudspeaker
enclosure. When a means of filtering the signal (amplifying the signal and digitizing the signal
prior to application to the loudspeaker) is available, use a binaural representation type system
based on the psychoacoustic properties of the human ear It is conceivable. Such a technique is a
technique of crosstalk removal and filtering by binaural response, which enables the
loudspeakers to be virtually arranged at any position in the room. These responses also apply to
the mono component, and there is a problem in deforming the mono component. Furthermore,
this solution requires accurate positioning of the listener relative to the loudspeaker housing.
[0008]
Furthermore, systems that use a single loudspeaker enclosure can have a narrow "shape factor"
of the loudspeaker enclosure, since the loudspeakers placed on the side can not be spaced
further than the width of the loudspeaker enclosure. It is even more difficult to achieve. Here, it is
desirable to be able to propose a product that is aesthetically elegant and easy to configure,
which means that the loudspeaker enclosure is made in the form of a very thin column.
[0009]
Finally, a single integrated loudspeaker enclosure tends to be placed on one side of the room
rather than the center of the wall, which unbalances its acoustic environment and represents a
homogeneous stereo image Impair the effectiveness of the processing operation.
[0010]
U.S. Pat. No. 3,829,624 U.S. Pat. No. 6,169,812 U.S. Pat. No. 7,412,380 WO 2008/1139047
[0011]
Jacob Schulman、「Parrot Zikmu Solo Wireless
Speaker by Philippe Starck Hands−on」(URL:www.
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Theverge. com, XP055064354, XP055064341, XP055064344, January 10, 2012) Christof
Faller, "Multiple-Loudspeaker Play-back of Stereo Signals" (Journal of Audio Engineering Society,
Vol. 54, N ° 11, November 2006)
[0012]
One of the objects of the present invention is to be able to optimally represent stereo images
without noticeable deformation of the acoustic signal, and if necessary to adapt the stereo images
to different configurations of the listening room It is thus to compensate for these various
limitations by proposing a compact, multi-channel integrated loudspeaker enclosure that can be
expressed in a parameterizable way.
[0013]
Another object of the invention is to provide two possible configurations: alone, a configuration
in which a single loudspeaker enclosure is placed in front of the listener in the listening room
(hereinafter "solo mode"), or A new type of integrated active loudness that can be used flexibly in
a configuration where two similar loudspeaker enclosures are arranged as a pair, respectively on
the left and right of the listener (hereafter "duo mode") It is providing a speaker case.
[0014]
One of the objects of the present invention is in either mode by simply changing the parameters
of the configuration of the internal processing performed by the algorithm embedded in the
digital signal processor with the same model loudspeaker enclosure To enable the use of a single
loudspeaker enclosure or of two loudspeaker enclosures.
[0015]
Furthermore, in the case of two loudspeaker enclosures (duo mode), the problem of the width of
the acoustic scene not limited by the position of the loudspeaker enclosure not necessarily as far
apart as desirable for a good representation of the stereo image Is raised.
[0016]
Another object of the present invention is by using the space (at the right of the left and right
loudspeakers of the left loudspeaker enclosure) located beyond the loudspeaker enclosure in
such a duo mode configuration , To further expand the acoustic scene to be represented.
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[0017]
To this end, the invention relates to a central channel of the general type disclosed in the abovementioned Schulman document, ie a central speaker with the main loudspeaker of which the
main axis of its own directivity map is oriented in a first direction, The main axis of its own
directivity map is orthogonal to the first direction and oriented in the second direction of the
opposite direction with respect to the left loudspeaker and the right loudspeaker, respectively by
the lateral loudspeakers respectively the left and right lateral A multi-channel integrated active
acoustic loudspeaker enclosure is proposed, comprising a channel.
The audio processing means receives as input the composite stereo signal to be reproduced
including the left signal and the right signal, and distributes the combination of the left and right
signals according to a predetermined distribution between the central and lateral channels.
[0018]
As a feature of the present invention, the audio processing means receives as input the left and
right signals of the composite stereo signal, from which the individual spectral energy levels of
the left and right signals of the composite stereo signal are based on the analysis of the
frequency domain. And a separation means operable to extract at least one right or left
component.
The combining means distributes a combination of signals comprising at least one right or left
component according to a predetermined distribution between the central and lateral channels.
Such coupling means comprise filtering means operable to alter the directivity diagram
represented by each lateral channel to form a direction of cancellation thereon, the pressure
gradient filtering means comprising , Receive at least one right or left component as input.
[0019]
The combining means may further apply a time delay to the signal obtained from the mono
component and distributed to the central channel.
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[0020]
In the first mode of operation, the loudspeaker housing is intended to be used alone in front of
the listener in a first direction towards the listener.
[0021]
In this case, the separating means is operable to extract from the left and right signals of the
composite stereo signal a mono component common to the left and right signals, a pure left
component and a pure right component.
Pressure gradient filtering is a dual pressure gradient filtering that receives either one of the
pure left and right components as an input and provides both the left and right filtered signals as
an output. It is.
The combining means is further operative to distribute the signal obtained from the mono
component to the central channel, to distribute the left filtered signal to the left channel, and to
distribute the right filtered signal to the right channel. It is possible.
[0022]
The combining means may distribute the signal obtained from the mono component to the bass
channel by the omnidirectional bass speaker.
[0023]
The angle of the direction of cancellation with respect to the first direction is less than 10
degrees, preferably less than 5 degrees.
[0024]
Pressure gradient filtering is preferably applied only below the pivot frequency so that the
directivity diagram of each lateral channel itself is kept above the pivot frequency.
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More precisely, pressure gradient filtering processes the left channel with the signal obtained
from the left component and low pass filtering below the pivot frequency as output and then
right with time delay and inversion applied The combination of the signals obtained from the
components is distributed, the right channel is the signal obtained from the right component, and
low pass filtering below the pivot frequency followed by time delay and inversion from the left
component Distribute the obtained signal combination.
[0025]
In the second mode of operation, the loudspeaker enclosure is a first loudspeaker enclosure
intended to be used in connection with a second similar loudspeaker enclosure and the two
loudspeaker enclosures are , Placed on the left and right of the listener respectively.
[0026]
In this case, with respect to the loudspeaker enclosure intended to be placed to the left of the
listener (and with regard to the loudspeaker enclosure intended to be placed to the right of this
same listener mutatis mutandis) The separating means extracts left surround components
forming the left component from the left and right signals of the composite stereo signal.
Pressure gradient filtering is a simple pressure gradient filtering that receives the left surround
component as an input and distributes both the left and right filtered signals as an output.
The combining means distributes the left signal of the composite stereo signal to the central
channel, distributes the left filtered signal to the left channel, and distributes the right filtered
signal to the right channel.
[0027]
Advantageously, the combining means subtracts the left surround component from the left signal
distributed to the center channel.
[0028]
The direction of cancellation of the right hand channel is specifically the direction towards the
second similar loudspeaker enclosure intended to be placed to the right of the listener.
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[0029]
Pressure gradient filtering is preferably applied only below the pivot frequency so that the
directivity diagram of each lateral channel itself is kept above the pivot frequency.
More precisely, pressure gradient filtering distributes as an output the signal obtained directly
from the left surround component to the left channel, and the right channel to low pass filtering
below the pivot frequency, and then Distribute the signal obtained from the left surround
component with applied time delay and inversion.
[0030]
An example of the implementation of the device according to the invention will be described with
reference to the drawings in which the same reference numerals denote the same or functionally
similar elements throughout the drawings.
[0031]
FIG. 1 is an overall isometric view of a loudspeaker enclosure according to the invention, showing
the acoustic architecture of the various loudspeakers used.
FIG. 6 shows as a block diagram the processing steps operated in a single loudspeaker enclosure
configuration.
Figure 5 shows in more detail the filtering performed by the dual pressure gradient filter of
Figure 2;
4a to 4d show various directivity diagrams that can be obtained from the loudspeaker housing
for the transverse signal by modifying several parameters of the dual pressure gradient filtering.
FIG. 6 shows as a block diagram the processing steps operated in a configuration with a pair of
loudspeaker enclosures.
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Fig. 6 shows in more detail the process performed by the pressure gradient filter of Fig. 5; FIG. 6
shows an example of a directivity diagram that can be obtained for these two loudspeaker
enclosures, which enables an enlargement of the sound scene to the listener arranged in front of
the left and right loudspeaker enclosures.
[0032]
General Configuration of Loudspeaker Housing FIG. 1 is a general view of a loudspeaker housing
according to the invention, showing the acoustic architecture of the various loudspeakers used.
[0033]
Loudspeaker housing 10 is shaped to flare outwardly at the bottom thereof, and base 12
supports flat shaped high portion 14 having a cross-section on the order of 3 × 12 cm.
[0034]
The flat high portion 14 carries a first loudspeaker 16, the main radial direction D 1 of the first
loudspeaker 16 being horizontal and perpendicular to the largest dimension of the rectangular
cross section of the high portion 14.
This loudspeaker 16 is hereinafter referred to as a "central loudspeaker" which corresponds to
the "central channel" of the multi-channel loudspeaker enclosure.
[0035]
The loudspeaker housing 10 also includes a left loudspeaker 18L and a right loudspeaker 18R on
the edge of the high portion 14, ie on the narrowest side.
These loudspeakers are oriented in their respective main radial directions D2L and D2R, which
are horizontal and perpendicular to the direction D1. These loudspeakers are hereinafter referred
to as "lateral loudspeakers" corresponding to the left and right "side channels" of the multichannel loudspeaker enclosure.
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[0036]
The central loudspeaker 16 is advantageously a loudspeaker combining distributed vibration
mode and piston mode operation, for example the BMR model of HiWave Technologies. The
lateral loudspeakers 18L and 18R are advantageously distributed vibration mode loudspeakers
with a high form factor (ie very long, very narrow shape), for example the HARP model from
HiWave Technologies.
[0037]
In essence, in a loudspeaker with distributed vibration mode or DML (Disturbed Mode
Loudspeaker), the flat diaphragm is pushed by the vibration according to the complex figure, in
this complex figure the vibration The amplitudes and phases of the various points of the plate are
distributed uncorrelatedly, ie the diaphragm is considered to be pushed by random vibrations
over the range of its surface, which is the whole spectrum with minimal distortion Makes it
possible to obtain excellent acoustical expressions over a range of On the other hand, in
conventional piston mode operation, the membrane is subjected to coherent oscillations, ie
movements whose displacement amplitude and phase are in principle constant over the entire
range of the diaphragm.
[0038]
The central loudspeaker 16 and the lateral loudspeakers 18L and 18R are used together to
represent the mid / treble portion of the spectrum, for example the 350-2000 Hz band of the
acoustic spectrum.
[0039]
A bass channel with bass loudspeaker 20, which may be of the conventional piston type, for
reproduction of the lowest frequency is provided for the representation of the lower part of the
spectrum, for example the 30-350 Hz band (subwoofer).
The bass loudspeaker 20 is mounted, for example, in a closed cavity directed towards the ground
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so as to radiate into a section comprised between the base and the ground (the base is provided
with legs) As a loudspeaker, such an arrangement presents no particular problem given the very
low directivity of the sound waves in the considered frequency band.
[0040]
The acoustic architecture just described with reference to this FIG. 1 will be used in combination
with the digital processing operations specific to each channel, such processing operations being
carried out by the loudspeaker housing towards the listener Used in "Solo" mode with only one
loudspeaker enclosure directed to the "Duo" mode with a pair of loudspeaker enclosures located
on the listener's front and left and right of the listener Depends on what is used in
[0041]
“Solo” Operating Mode with a Single Loudspeaker Enclosure FIG. 2 shows as a block diagram
the processing steps for a single loudspeaker enclosure used in solo mode.
[0042]
Although this scheme is shown as interconnected circuits, it should be noted that the
implementation of the various functions is essentially software based and this representation is
given as an example only.
The software may in particular be implemented by means of a calculation algorithm which is
performed iteratively at sampling frequency for successive signal frames in a chip dedicated to
digital signal processing of DSP type.
[0043]
On the other hand, here and in the following, only specific processing aspects are described for
use in solo mode or duo mode.
For non-specific aspects of the loudspeaker enclosure, such as amplification, equalization,
description of chains etc., an active acoustic loudspeaker enclosure such as that marketed under
the name Zikmu by Parrot, Paris, France Reference will be made to WO 2008/1139047 (Parrot)
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11
which is described. The loudspeaker enclosure described in this document is a multi-channel
active loudspeaker enclosure, in which case the two channels to which the digitized audio signal
is supplied are each a digital signal to be reproduced Have their own chain of power stages,
whose corresponding frequency components are supplied directly after filtering and processing
by the DSP.
[0044]
The first step consists in operating the separation or upmixing of the channels, and such a
technique known per se is that from the composite input signal L, R where the mono and stereo
components are mixed together to the stereo component L Separating the monocomponent C of
'and R'. This separation (block 22) involves the analysis of the signals L and R in the frequency or
time-frequency domain by comparison of the relative spectral energy distribution between the
signals L and R and the threshold value. Then, at a given moment, the same frequency can be in
only one of the three channels L ', R' or C. More precisely, at a given moment, the frequencies of
the same energy of the two channels L and R, whatever their phase, will be in the mono
component C and thus in the stereo components L 'and R' Nothing will be present, pure energy of
higher energy in channel L (R) than in channel R (L) will be in stereo component L '(R') and not in
mono component C Therefore, there will be no stereo in mono component C.
[0045]
As long as the same frequency can be in only one of the three channels L ', R' or C at a given
moment, there is no acoustic interaction other than that provided by the stereo processing In
particular, the interaction between the central loudspeaker 16 assigned to the reproduction of
the mono component C and the lateral loudspeakers 18 L and 18 R assigned to the reproduction
of the stereo components L ′ and R ′ is It is true that it can not exist. Any deformation of the
mono component with the specially processed stereo component is thus avoided.
[0046]
More precisely, the stereo components L 'and R' obtained at the output of the separating stage
22 are the two corresponding filtered components L "and R" applied to the loudspeakers of the
left and right channels 18L and 18R. To provide a stage 24 of the double pressure gradient type
(discussed in more detail with reference to FIG. 3).
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[0047]
For mono component C, mono component C separates the mid / treble portions of the mono
component C spectrum to apply the mid / treble portions of the mono component C to the
central loudspeaker 16 and the bass portion of the same mono component C. Are separated by
crossover filters 26, 28 which separate the bass portion of the mono component C to apply to the
loudspeakers of the bass channel 20.
[0048]
A delay (block 30) can be applied to the signal C supplied by the channel separation stage 22 to
act on the "preceding sound effect" to enhance the stereo effect, such a technique It consists in
delaying (center channel and bass channel) with respect to the stereo channel (transverse
channel), the stereo component arrives first for the mono component and stereo recognition is
enhanced.
[0049]
The relative levels of the different channels, in order to correct possible acoustical incidents of
the loudspeakers, as well as to compensate for differences in loudspeaker sensitivity and / or to
increase or decrease the stereo effect, In particular, the loudspeakers 16, 18L, 18R and 20 may
be used to apply appropriate relative gains to different channels in order to increase or decrease
the level of the stereo signal reproduced by the lateral channels to the central and bass channels.
The signals reproduced by are each subjected to linear filtering equalization (block 32).
[0050]
FIG. 3 illustrates dual pressure gradient filtering effected by block 24.
[0051]
The subject matter is to combine the stereo components L 'and R' to give new components L "and
R" applied to the left and right channels 18L and 18R respectively.
[0052]
The component L 'is applied directly to the filter 34 (simple gain stage).
For that part, the right component R 'is applied to a low pass filter with a typical cutoff frequency
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of 4 Hz.
The output signal of this filter 36 is before being recombined with the output signal of block 34
at 42 to provide a filtered component L "which will be reproduced by the left loudspeaker 18L
after amplification and equalization. Adjustable delays (block 38) and inversions (block 40) are
applied.
[0053]
With respect to the right channel, the right loudspeaker 18R receives components R 'and L' after
processing by the stages 34 ', 36', 38 ', 40' and 42 'acting in the same manner as the stages 3442 described above. The resulting filtered component R "is provided.
[0054]
The dual pressure gradient filtering (ie each of the filtered stereo components is obtained from
the two stereo components L 'and R' applied to the input) is controlled in a controlled manner by
the delays 38, 38. The adjustment of 'allows to change the directivity map of each of the lateral
loudspeakers.
[0055]
Dual pressure gradient filtering thus represents an optimal representation of stereo components
for listeners located in front of a single loudspeaker enclosure and for different configurations of
the listening room (A monocomponent C is represented by the central loudspeaker 16 directed
towards the listener and by the subwoofer 20).
[0056]
4a-4d show various directivity diagrams that can be obtained from the lateral loudspeakers, for
example the left loudspeaker 18L, by modifying several parameters of the dual pressure gradient
filtering.
[0057]
Without any filtering, the directivity of the left loudspeaker 18L is as shown in FIG. 4a, where the
loudspeaker is directional in the high-tone part of the spectrum (a solid line for frequencies
above 4000 Hz) Note that in figure A), the mid / bass part is omnidirectional (dotted figure B for
frequencies in the range of 350-4000 Hz).
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[0058]
By adjusting the value of the delay applied by block 38, and by the inversion performed by block
40, the combination of the two right and left signals L 'and R' for the signal reproduced only on
the left side The directivity map reproduced by L ′ ′ can be shown to correspond to that
shown in FIG. 4b, in the mid / bass range, the diagram has two sides separated by valleys
defining the direction of cancellation Δ Including the robe.
On the other hand, in the treble range, typically above 4000 Hz, the low pass filter 36 blocks the
signal so that the dual pressure gradient filter has no particular effect in this range of the
spectrum (see Figure A). Not changed).
[0059]
The angle θ between the axis D1 corresponding to the direction of cancellation Δ and the
direction of the listener (direction orthogonal to the main direction D2L of the loudspeaker 18L)
is given by the relationship sin θ = cxD / a, where a is the loudspeaker The width of the housing
(ie the distance between two loudspeakers 18L and 18R, typically around 12 cm), c is the speed
of sound propagation and D is the delay introduced by the delay stage 38 .
This relationship is true at distances from the loudspeaker enclosure much longer than a, and the
listener is typically a few meters from the loudspeaker enclosure.
[0060]
The directivity diagram is of course symmetrical with respect to the signal reproduced on the
right by the right loudspeaker 18R.
[0061]
Having the direction of cancellation allows the stereo to be amplified in various ways.
[0062]
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In the first case shown in FIG. 4b, the angle θ is as small as 3 to 4 degrees, so that when the
listener 44 is in the main method D1 of the loudspeaker housing, the direction of cancellation Δ
for the left channel is It is near the listener's right ear 46R, and similarly, the direction of
cancellation of the right channel is near the listener's left ear 46L.
Thus, the left ear will mainly capture the stereo component L ', the right ear will mainly capture
the right component R', and the listener will be as if the loudspeakers are placed on both sides of
the listener's head You will hear the stereo information clearly.
[0063]
The first case is particularly suitable for situations in which there is no acoustic reflection, or in
which those acoustic reflections are symmetrical.
[0064]
The direction of cancellation Δ can be moved further away from the axis D1 (FIG. 4c) or even
further to θ = 90 degrees (FIG. 4d) by increasing the delay, as in the latter case, The directivity
diagram is placed completely on one side of the loudspeaker enclosure, the radiation being
maximum on one side.
In this case, for example, if the loudspeaker enclosure 10 is arranged in the vicinity of the wall
48 of the listening room, it is well suited to a configuration that exhibits a significant risk of
acoustic reflection on one side of the loudspeaker enclosure 10 .
[0065]
"Duo" operating mode with a pair of loudspeaker enclosures Figs. 5-7 show that the loudspeaker
enclosures according to the invention are used with other similar loudspeaker enclosures, and
the left and right loudspeaker enclosures 10 and 10 ' Fig. 8 illustrates how the processing of the
signal can be changed if the pairs are arranged on both sides of the listener 44 according to the
conventional configuration (shown schematically in Fig. 7), where two loudspeaker housings Are
respectively placed on the left and right in front of the listener.
[0066]
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16
In this case, the acoustic architecture shown in FIG. 1, that is, the individual configurations of the
various loudspeakers are not changed, and the operation in solo mode or duo mode is a
modification of the digital signal processing operated in the DSP. Note that it only results from
[0067]
Switching from one mode of operation to the other is thus quite simple and will not require
physical modification of the loudspeaker housing.
[0068]
The process applied in duo mode is to magnify the conventional stereo image formed between
the two loudspeaker enclosures 10 and 10 ', in particular to expand the sound scene (this is two
loud It is particularly advantageous if the loudspeaker enclosures 10 and 10 'are arranged
relatively close to one another, so as not to introduce distortion into the represented signal, and
in particular, without enriching the mono components. Have the purpose of
[0069]
With this configuration, the separation stage or upmix (block 50) is a left surround component
SL for the loudspeaker enclosure 10 located to the left of the listener, and likewise a loudness
located to the right of the listener Extract the surround channel including the right surround
component SR for the speaker enclosure 10 '.
[0070]
The surround components are obtained by analysis of the stereo components of the signals L, R
applied to the input in order to extract a new signal containing information which is not highly
correlated between the left L and right R signals.
[0071]
These surround components include the part of the information that is mixed to the very right or
the very right, as well as the part of the reverberation and the "surround" information in a narrow
sense, for example, the noise of the audience in the case of recording on the stage , Exists.
[0072]
These components are extracted by analysis and comparison in the frequency domain of the
individual spectral energy levels of the signals L, R applied to the input, as described above.
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[0073]
With regard to the loudspeaker enclosure 10, the surround signal SL (SR) is reproduced by the
left loudspeaker 18L and the right loudspeaker 18R of this loudspeaker enclosure 10 (which is
itself located to the left of the listener) 2 It is applied to a simple pressure gradient filtering stage
52 to provide one filtered surround component SLL and SLR.
[0074]
Similarly, with respect to the loudspeaker enclosure 10 ', the right surround component SR is
reproduced by the left loudspeaker 18L and the right loudspeaker 18R of this loudspeaker
enclosure 10' (which is itself located to the right of the listener respectively) Filtered to give two
filtered components SRL and SRR.
[0075]
With respect to the loudspeaker housing 10, the central channel of the loudspeaker 16 is
supplied with the component coming from the left signal L from which the surround component
SL has been subtracted by the blocks 54 and 56.
[0076]
Similarly, with respect to the loudspeaker enclosure 10 ', the central channel of the loudspeaker
16 is supplied with the component coming from the right signal R with the surround component
SR subtracted by the blocks 54 and 56.
[0077]
Thus, in a conventional manner, but without interference between the surround components of
the signal and the components of the stereo signal which are not surround components, the
surround components are reproduced by the lateral channels (loudspeakers 18L and 18R) and
The components of the no stereo signal are reproduced by the center channel (loudspeaker 16).
[0078]
As in solo mode, to enhance the stereo, the delay introduced by block 30 acts on the lead effect
by delaying the left (right) channel relative to the left (right) surround channel The surround
component can arrive first relative to the standard stereo component, thus enhancing stereo
recognition.
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[0079]
The linear filtering stage 32 makes it possible, if necessary, to correct the acoustical incidents of
the various loudspeakers, in order to compensate for differences in loudspeaker sensitivity, as
well as to increase or decrease the stereo effect. Allows the level of stereo lateral channels to be
increased or decreased for mono and bass channels.
[0080]
FIG. 6 shows in more detail the process performed by the (simple) pressure gradient filter 52.
[0081]
The pressure gradient filter 52 comprises a direct filter 34, ie a simple gain stage, and the direct
filter 34 is a filtered SLL from the surround component SL applied to the input (from the
surround component SR applied to the input Provide the filtered component SRL).
For the component SLR (SRR), the application of the surround component SL (SR) to the low pass
filter 36 and the subsequent application to the delay stage 38 and the inversion stage 40 result.
[0082]
The operation of stages 34, 36, 38 and 40 is the same as that described with reference to FIG. 3
for the solo mode, the only difference is that the filter here is a single input filter.
[0083]
By adjusting the value D of the delay applied by block 38, and for inversion by block 40, the
directivity diagram of the surround signal at the loudspeaker enclosure 10 arranged to the left of
the listener 44 is described above. Can be shown to be similar to that shown in FIGS. 4b-4d,
where the direction of cancellation .DELTA. Is the same as the main direction D1 of the
loudspeaker enclosure and the one described above in connection with the solo mode. Form the
angle θ determined by the relation sin θ = cxD / a in a manner.
[0084]
As shown in FIG. 7, in duo mode, it is particularly advantageous to give a value of 90 degrees to
the angle θ, as a result of which the direction of cancellation Δ in FIG. B of the loudspeaker
housing 10 arranged on the left The direction of cancellation Δ ′ of the view B ′ of the
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loudspeaker enclosure 10 ′ directed to the right towards the loudspeaker enclosure 10 ′
situated to the right of the listener and likewise likewise to the listener It is turned to the left
towards the loudspeaker housing 10 arranged on the left.
[0085]
The radiation diagram of the surround mixture in the low / mid range (A or A ') or in the high
range (B or B') is to be placed completely on one side of the loudspeaker enclosure, two The
maximum radiation beyond the area in which the loudspeaker enclosure is arranged enables the
acoustic scene from representing the content to be extended beyond this area.
Finally, in order to fit when the wall is on one side of the loudspeaker enclosure, the level of the
surround signal can be adjusted to reduce the reverberation effect resulting from this proximity.
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