Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04S—STEREOPHONIC SYSTEMS 
  • H04S7/00—Indicating arrangements; Control arrangements, e.g. balance control
  • H04S7/30—Control circuits for electronic adaptation of the sound field
  • H04S7/302—Electronic adaptation of stereophonic sound system to listener position or orientation
  • H04S7/303—Tracking of listener position or orientation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R5/00—Stereophonic arrangements
  • H04R5/02—Spatial or constructional arrangements of loudspeakers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R27/00—Public address systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04S—STEREOPHONIC SYSTEMS 
  • H04S3/00—Systems employing more than two channels, e.g. quadraphonic
  • H04S3/002—Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04S—STEREOPHONIC SYSTEMS 
  • H04S3/00—Systems employing more than two channels, e.g. quadraphonic
  • H04S3/008—Systems employing more than two channels, e.g. quadraphonic in which the audio signals are in digital form, i.e. employing more than two discrete digital channels
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R2430/00—Signal processing covered by H04R, not provided for in its groups
  • H04R2430/01—Aspects of volume control, not necessarily automatic, in sound systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04S—STEREOPHONIC SYSTEMS 
  • H04S2400/00—Details of stereophonic systems covered by H04S but not provided for in its groups
  • H04S2400/11—Positioning of individual sound objects, e.g. moving airplane, within a sound field
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04S—STEREOPHONIC SYSTEMS 
  • H04S2400/00—Details of stereophonic systems covered by H04S but not provided for in its groups
  • H04S2400/13—Aspects of volume control, not necessarily automatic, in stereophonic sound systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04S—STEREOPHONIC SYSTEMS 
  • H04S7/00—Indicating arrangements; Control arrangements, e.g. balance control
  • H04S7/30—Control circuits for electronic adaptation of the sound field

Definitions

• the present invention relates to multi-channel audio systems. Background and Prior Art
• Multi-channel audio systems are distinguished from stereophonic audio systems by the number of channels of audio information and the corresponding number of loudspeakers used for playback. While stereophonic systems are characterised by two channels, common multi-channel audio systems have 5 or more channels.
• One of the goals of multi-channel audio systems is to provide a listener with the immersive experience of a conductor or an artist on stage.
• SPL sound pressure level
• an apparatus for reproducing a multi-channel audio signal consisting of one or more sound objects in which each sound object is present in a plurality of channels comprising:
• a plurality of first loudspeakers provided spaced around a first arc forward of a predetermined listening zone, each of the first loudspeakers facing towards the listening zone and substantially equidistant therefrom;
• a plurality of second loudspeakers provided spaced around a second arc behind the listening zone, each of the second loudspeakers facing towards the listening zone;
• An amplifier arranged to produce an amplified signal from each channel in the audio signal, each amplified signal being provided to a corresponding first or second loudspeaker;
• each sound object is reproduced by one or more loudspeakers such that the SPL at a point spaced from the apparatus is less than the SPL at the listening zone.
• the SPL at a point spaced from the apparatus the same distance as each first loudspeaker is spaced from the listening zone is 15 dB less than the SPL at the listening zone.
• the number of first and second loudspeakers is at least 13, the number of first loudspeakers being greater than the number of second loudspeakers.
• the plurality of second loudspeakers are provided closer to the listening zone than the first loudspeakers.
• the apparatus further comprises an enclosure provided behind the listening zone, the amplifier and second loudspeakers being housed within the enclosure.
• the apparatus further comprises a subwoofer housed within the enclosure.
• each first loudspeaker is provided within a corresponding enclosure, the enclosures of adjacent first loudspeakers being coupled together.
• the multi-channel audio signal is produced by the method of any one of claims 5 to 8.
• the step of de-correlating the phase of each width signal comprises adding to each width signal a different phase offset, and altering the phase offset of each width signal with a period T.
• the substantially Gaussian distribution follows a user-configurable standard deviation.
• the user-configurable standard deviation is configurable for each sound object signal.
• the method further comprises the step of normalising the amplitudes of the width signals such that the amplitude of sum of the width signals is equal to the amplitude of the sound object signal.
• the method further comprises processing each sound object signal to produce a depth-corrected signal, and producing the plurality of width signals from the depth-corrected signal.
• Figure 1 is a top view, partially cut away, of an apparatus for reproducing a multichannel audio signal according to one embodiment of the invention
• Figure 2 is a perspective rear view of the apparatus in Figure 1;
• Figure 3 is a perspective front view of the apparatus in Figure 1;
• FIG. 1 is shows room sound pressure levels (SPL) when the apparatus of Figure 1 is in use;
• Figure 5 is shows comparable room SPL using conventional stereophonic loudspeakers and audio system
• Figure 6 is shows comparable room SPL using conventional multi-channel loudspeakers and audio system.
• Figure 7 is a signal processing diagram showing a method for producing a multichannel audio signal according to one embodiment of the invention.
• FIGS 1 to 3 show an apparatus 10 for reproducing a multi-channel audio signal according to the embodiment.
• the apparatus 10 comprises a plurality of first loudspeakers 12 provided spaced around a first arc 14.
• Each of the first loudspeakers 12 face towards a listening zone 16 provided within the apparatus 10.
• the first loudspeakers 12 are preferably each substantially equidistant from the listening zone 16.
• the first arc 14 is preferably circular as shown in the drawings; however, elliptical or other arcuate curves may also be used.
• a plurality of second loudspeakers 18 are provided spaced around a second arc 20.
• Each of the second loudspeakers 18 faces towards the listening zone 16.
• a listener 22 is shown in Figure 1 in the listening zone 16 facing towards the first loudspeakers 12.
• the terms 'forward' and 'behind' are used relative to the listening zone 16 according to the orientation of the listener 22 shown in Figure 1.
• the first loudspeakers 12 are positioned forward of the listening zone 16 and surround the forward 180° from the listening zone 16.
• the second loudspeakers 18 are positioned behind the listening zone 16.
• thirteen (13) first loudspeakers 12 and five (5) second loudspeakers 18 are used, though other quantities may be used. It is preferred that at the number of first and second loudspeakers should be at least thirteen, however.
• Two low frequency drivers 24 are provided, to either side of and behind the listening zone 16 in an enclosure 26.
• the low frequency drivers 24 are configured as subwoofers.
• the second loudspeakers 18 are also provided in the enclosure 26.
• the second arc 20 shown in Figure 1 has a larger radius than the first arc 14.
• the loudspeakers 18 are positioned closer to the listener 22 than the loudspeakers 12. This reduces the size of the apparatus 10, enabling installation in smaller rooms, without affecting the sound reproduction as experienced by the listener.
• An amplifier 28 produces amplified signals from each channel in the audio signal.
• the audio signal has a separate channel for each loudspeaker 12, 18 and 24.
• the amplifier 28 provides a separate, amplified signal to each loudspeaker and to the subwoofers.
• the amplifier 28 is housed behind the listening zone 16 in the enclosure 26.
• the term amplifier 28 encompasses a multi-channel amplifier, multiple single-channel amplifiers, or a combination of both. Class D amplifiers are preferred for efficiency although other classes may be utilised.
• the apparatus 10 has a base 30 on which the enclosure 26 is mounted.
• Each first loudspeaker 12 is provided in an enclosure 32 mounted to the base 30.
• Adjacent enclosures 32 are connected via plates 34 extending between their top surfaces. When mounted in this manner, the enclosures 32 form a continuous arc.
• the multi-channel audio signal consists of one or more sound objects. Each sound object is present in a plurality of channels of the audio signal as will be described in more detail below.
• each sound object is reproduced by one or more loudspeakers 12, 18.
• the sound from each loudspeaker converges on the listening zone 16. Since each loudspeaker 12 is substantially equidistant from the listening zone 16, sounds from adjacent loudspeakers 12 reproducing a sound object arrive at the listening zone 16 at the same time and will add constructively at the listening zone 16.
• the apparatus 10 reproduces the audio signal, the SPL at a point spaced from the apparatus 10 is less than the SPL at the listening zone 16. Two factors contribute to this effect.
• the listening zone 16 is substantially equidistant from the loudspeakers 12 such that their sound outputs combine within the listening zone 16, while at other locations there will be different path lengths from each loudspeaker resulting in some destructive interference.
• the loudspeakers are located near and oriented towards the listening zone 16, while outside the apparatus 10 the average distance to the loudspeakers increases with increasing distance from the apparatus, resulting in a reduced SPL.
• Figures 4 to 6 show the results of SPL modelling in a 50m 2 room.
• the model was set to produce an SPL of 125dB at the listening zone, and the SPL throughout the room was then calculated.
• Figure 4 shows the SPL using the apparatus 10, in which the SPL at the walls of the room is at least 10 dB and up to 15-20 dB lower than the listening zone.
• Figure 5 shows the SPL using a traditional stereophonic arrangement. The SPL is greatest in this arrangement in the immediate vicinity of the loudspeakers and adjacent walls.
• Figure 6 shows the SPL in typical multi-channel systems with loudspeakers at the periphery of the room. As shown, the SPL throughout the room and the walls is relatively even.
• the preferred method of producing an audio signal according to the embodiment involves three process stages applied to the track for each sound object - depth, width and pan - described below with reference to Figure 7.
• Each track, or sound object signal is filtered via a low pass second order MR filter 102, a low shelf second order MR filter 104 and a high shelf second order MR filter 106.
• These filters 102, 104 and 106 are applied in order to represent frequency variations that occur when the distance to a sound source increases.
• a gain stage 108 provided at the output of the filter 106, produces two depth-corrected output signals, referred to as direct and reverberant signals.
• filters 102, 104 and 106 and gain stage 108 are given below for a depth parameter d having a value between 0 and 1, where 0 is close to the listener and 1 is far away:
• the direct signal is passed to the Width stage described below.
• the reverberant signal is processed using an acoustic space simulator 110.
• the simulator 110 adds a configurable amount of reverberation. Balancing the amplitudes of the direct and reverberant signals, for example in the gain stage 108, provides an additional sense of depth.
• the simulator 110 uses a 1 input, n outputs algorithm. The n outputs have similar energy content, but are de-correlated using feedback delay networks with a different time constants for each output.
• n outputs enable them to be played by adjacent loudspeakers without affecting the listener 22's location of the sound object (which is located by the direct signal), whilst contributing to focussing acoustic energy at the listening zone 16 and providing a sense of depth.
• n ⁇ 13 and the n outputs may be mapped to all channels in the audio signal, with several of them being fed by the same output.
• the n outputs may be mapped to a subset of these channels using, for example, standard audio panning techniques. Width:
• the direct signal from the depth stage is input to a fourth order crossover filter 112 that splits the signal into two bands: a low frequency (LF) part, and a high frequency (H F) part.
• the f a is approximately 500 Hz, but nothing prevents use of a lower frequency.
• the gain stages 114 apply gains to each of the k signals following a Gaussian distribution, whose standard deviation is controlled by an adjustable Width parameter. It is preferred that the gains of the gain stages 114 are normalised such that the sum of the k gain stage 114 outputs does not show any amplitude deviation from the HF input signal. The greater the value of the Width parameter, the more even the distribution of gains applied by the gain stages 114. This results in more control over the SPL outside the apparatus 10.
• k is an odd number, so that the middle of the k signals has a greater amplitude than the other of the k signals, which aids the listener 22 to locate the sound object.
• values of k other than 5 may be used.
• Each of the k signals passes through one of k all-pass FI R filters 116.
• Each FIR filter 116 alters the phase of the incoming signal with a spectral period T and a different initial phase offset compared to the other FI R filters 116 to produce one of k width signals, shown in Figure 7 at 118.
• the k width signals are de-correlated in phase due to the effect of the filters 116.
• Phase oscillation patterns such as sinusoids can be used, as well as other phase oscillation patterns.
• the effect of the Width processing stage is to produce k width signals with relative phase properties to enable their playback on k adjacent loudspeakers of the apparatus 10, without creating frequency cancellations in the listening zone 16.
• Figure 7 shows the LF part being summed to the middle signal of the k signals.
• the LF part could be applied to more than one of the k signals or follow the same gain/pan distribution as the H F part described above.
• Pan
• the k width signals are each passed through a second order MR low shelf filter 120 and gain stage 122 to produce k pan signals.
• the filter 120 provides a low-frequency gain correction that reduces the change in tonality of a sound object when panned across loudspeakers 12, 18.
• the gain of the filter 120 is -3dB when an object is equidistant to its two closest speakers.
• the listener's ability to locate the sound object is unaffected: the listener will determine the location of a sound object based on the loudest apparent source of sound; the de-correlated signals to either side of the loudest signal for each sound object to not affect the listener's location of the sound object since de-correlated sound has no apparent location to a listener.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Multimedia (AREA)
• Stereophonic System (AREA)
• Stereophonic Arrangements (AREA)
• Circuit For Audible Band Transducer (AREA)

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• 2015
  • 2015-04-28 ES ES15165526.3T patent/ES2686275T3/es active Active
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  • 2015-04-28 EP EP15165526.3A patent/EP3089477B1/en active Active
• 2016
  • 2016-04-28 JP JP2018507774A patent/JP2018518923A/ja active Pending
  • 2016-04-28 BR BR112017023292-8A patent/BR112017023292A2/pt active Search and Examination
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• 2018
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