How to process audio for immersive audio playback

Abstract

1. A method (1000) of generating multiple audio channels from audio including height and non-height audio channels for reproduction on an immersive loudspeaker system having at least one height loudspeaker (5) in a listening environment, the method comprising: applying (1500) a virtual height filter (1300) to a portion of each height channel (1010) to attenuate spectral components of the height channel that emanate directly from the loudspeaker (1;2;3;4) and amplify spectral components of the height channel that are reflected from a roof or an area near the roof in the listening environment when reproducing the height channel by one of the loudspeakers to generate multiple virtual height filtered audio signals that are added to corresponding non-height audio channels for reproduction by a corresponding loudspeaker; and reproducing the remaining portion of each height audio channel on the at least one height loudspeaker (5).

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to the following priority applications: U.S. Provisional Application No. 63 / 291,598, filed on December 20, 2021 (Docket No. D21147AUSP1), U.S. Provisional Application No. 63 / 353,778, filed on June 20, 2022 (Docket No. D21147AUSP2), and European Patent Application No. 22179943.0, filed on June 20, 2022 (Docket No. D21147AEP).

[0002] Technical Field The present disclosure relates to the field of audio processing. In particular, the present disclosure relates to a method for generating at least two audio channels from an immersive audio format audio including a plurality of front and rear height audio channels and a plurality of front and rear non-height audio channels for playing the plurality of audio channels in an immersive loudspeaker system. The present disclosure further relates to an apparatus including a processor configured to perform the method, a vehicle including the apparatus, a program, and a computer readable storage medium. [Background technology]

[0003] Vehicles typically include a loudspeaker system for audio playback. The loudspeaker system in the vehicle may be used to play audio, for example, from tapes, CDs, audio streaming services, or applications running in the vehicle's automobile entertainment system or remotely via a device connected to the vehicle. The device may be, for example, a portable device connected to the vehicle wirelessly or with a cable. For example, streaming services such as Spotify and Tidal have recently been integrated into the automobile entertainment system either directly into the vehicle's hardware (commonly known as the "head unit") or via a smartphone using Bluetooth or Apple CarPlay or Android Auto. The loudspeaker system in the vehicle may be used to play terrestrial and / or satellite radio. A conventional loudspeaker system for a vehicle is a stereo loudspeaker system. A stereo loudspeaker system may include a total of four loudspeakers, a front pair of loudspeakers and a rear pair of loudspeakers for the front and rear passengers, respectively. However, more recently, with the introduction of DVD players in vehicles, surround loudspeaker systems have been introduced into vehicles to support the playback of DVD-Audio formats.

[0004] Immersive audio is becoming mainstream in cinemas and home listening environments. As immersive audio is becoming mainstream in cinemas and homes, it is natural to assume that immersive audio will also be reproduced in vehicles. Dolby Atmos music is already available through various streaming services. Immersive audio is often differentiated from surround audio formats by the inclusion of one or more overhead or height audio channels. Thus, overhead or height loudspeakers are used to reproduce immersive audio.

[0005] FIG. 1 shows a view of the interior of a vehicle 100. The vehicle 100 includes a loudspeaker system including loudspeakers 10, 11, 30, 31, 41, 42, 43, 44. The loudspeakers are shown only for the left side of the vehicle 100. Except for the loudspeakers 10 and 11, corresponding loudspeakers may be symmetrically arranged on the right side of the vehicle 100. In particular, the loudspeaker system of FIG. 1 includes tweeter loudspeakers 41, 42 and 43, full-range front and rear loudspeakers 30 and 31, a center loudspeaker 10, a low-frequency effects loudspeaker or subwoofer 11, and a height loudspeaker 44. The tweeter loudspeaker 41 is located near the dashboard of the vehicle. The tweeter loudspeaker 42 is located low on a front pillar of the vehicle 100. However, the tweeter loudspeakers 41, 42, 43 as well as the full range front loudspeaker 30 and rear loudspeaker 31 may be positioned in any location suitable for a particular implementation. The height loudspeaker 44 is positioned in the roof of the vehicle, in this example above the driver's seat.

[0006] While high-end vehicles may include multiple overhead or elevation loudspeakers, some vehicles still use a limited number of elevation stereo loudspeakers. In fact, elevation loudspeakers dramatically increase the complexity of the loudspeaker system in the vehicle. The elevation loudspeakers need to be placed on the roof of the vehicle, which is typically not suitable for this purpose. For example, vehicles typically have low roofs that limit the available height for placement of elevation loudspeakers. Furthermore, vehicles are often sold with the option of installing a sunroof to expose windows in the roof of the vehicle, making the incorporation or placement of many elevation loudspeakers on the roof a difficult industrial design challenge. Additional audio cabling may also be required for such elevation loudspeakers. The placement of multiple overhead or elevation loudspeakers is also a concern when considering vehicle safety and the placement of, for example, airbags at the same or nearby locations of the overhead or elevation loudspeakers. For all these reasons, integrating multiple elevation loudspeakers in a vehicle can be costly due to space and industrial design constraints. On the other hand, using only a limited number of height loudspeakers dramatically limits the spatial resolution of the sound in the height plane of the vehicle. Summary of the Invention [Problem to be solved by the invention]

[0007] It would be advantageous to reproduce immersive audio content in an immersive loudspeaker system having at least one height loudspeaker. In the context of this disclosure, an "immersive loudspeaker system" is a loudspeaker / speaker system that includes at least one height loudspeaker (e.g. located above the listener's head, i.e. in the so-called height plane) and multiple front and rear non-height loudspeakers (e.g. located below the listener's head, i.e. in the so-called base plane).

[0008] It is advantageous to create a perception of pitch with satisfactory spatial resolution by playing the immersive audio content over an immersive loudspeaker system that includes at least one height loudspeaker, such that the user's audio experience is enhanced without the need for more than two overhead loudspeakers. [Means for solving the problem]

[0009] An aspect of the disclosure provides a method of generating multiple audio channels from immersive format audio including multiple front and rear height audio channels and multiple front and rear non-height audio channels for reproducing the multiple audio channels in an immersive loudspeaker system including at least one height loudspeaker and multiple front and rear non-height loudspeakers. The method includes applying a virtual height filter to a portion of each front and rear height audio channel of the multiple front and rear height channels. The virtual height filter is configured to at least partially attenuate spectral components of at least one of the front and rear height audio channels that emanate directly from a loudspeaker through which the height channel is reproduced when the at least one of the front and rear height audio channels is reproduced by a corresponding loudspeaker of the front and rear non-height loudspeakers. The virtual height filter is also configured to at least partially amplify spectral components of the height channel that are reflected from a roof or an area near the roof in the listening environment to generate multiple front and rear virtual height filtered audio signals. The method further includes adding each front and rear virtual height filtered audio signal of the plurality of front and rear virtual height filtered audio signals to a corresponding front and rear non-height audio channel of the plurality of front and rear non-height audio channels to generate a summed audio signal for playback by a corresponding front or rear non-height loudspeaker. The method further includes reproducing a remaining portion of each front and rear height audio channel of the plurality of front and rear height channels with the at least one height loudspeaker.

[0010] In the context of this disclosure, the term "channel" refers to an audio signal, optionally plus metadata, in which the location is encoded as a channel identifier, e.g., left front or upper right surround. "Channel-based audio" is audio formatted for playback through a given set of loudspeaker zones with associated nominal locations, e.g., 5.1, 7.1, etc. The term "object" or "object-based audio" refers to one or more audio channels with parametric source descriptions, such as apparent source location (e.g., 3D coordinates), apparent source width, etc.

[0011] When the portion of the height channel is reproduced from one of the non-height loudspeakers without filtering, the sound may radiate along various paths. Some sounds may radiate along a direct path from the non-height loudspeaker to the listening position (e.g., to the passenger's or driver's ears). Some other sounds may radiate along a reflected path from the on-height loudspeaker to the listening position. For example, some sounds may be reflected from the roof or a near-roof area inside the listening position and thus radiate from the roof or a near-roof area to the listening position. Sounds radiating along a direct path are undesirable when the height channel is reproduced by a non-height loudspeaker. By applying a virtual height filter to the portions of the height channel, the spectral components of the portions of the height channel that are reflected from the roof or near the roof are amplified, while the spectral components of the portions of the height channel that are emitted directly towards the loudspeaker are attenuated. Configured as above, the method compensates for undesired direct sounds and introduces perceptual height cues into the audio signals being fed to the non-height loudspeakers, thereby improving the positioning and perceived quality of the virtual height signal. For example, a directional auditory model has been developed to create a virtual height filter that improves the perceived quality of the playback when used to process the audio being played by the non-height loudspeakers. In addition, by directly playing back the remaining parts of the height audio channels with at least one height loudspeaker, a desired balance of the front and rear height audio channels between the non-height loudspeakers and the at least one height loudspeaker can be achieved for improved spatial resolution in the height plane providing an improved immersive listening experience. The improved spatial resolution in the height plane is achieved by using a single height loudspeaker or only two height loudspeakers.

[0012] In one embodiment, the respective portions of the plurality of front and rear elevation channels may be a function of one or more of the position of the at least one elevation loudspeaker along the length of the listening environment, or a desired balance distribution of the plurality of audio channels among the loudspeakers of the immersive loudspeaker system.

[0013] In one embodiment, applying a virtual height filter to a portion of each of the plurality of front and rear height audio channels may include applying a virtual height filter to a portion of the front height audio channel proportional to a position of the at least one height loudspeaker away from the front and toward the rear of the listening environment.

[0014] In one embodiment, applying a virtual height filter to a portion of each of the plurality of front and rear height audio channels may include applying a virtual height filter to a portion of the rear height audio channel proportional to a position of the at least one height loudspeaker away from the rear and towards the front of the listening environment.

[0015] In one embodiment, reproducing a remaining portion of each of the plurality of front and rear height audio channels with the at least one height loudspeaker may include reproducing a remaining portion of each of the plurality of front height audio channels proportional to a position of the at least one height loudspeaker away from the rear and towards the front of the listening environment.

[0016] In some embodiments, reproducing a remaining portion of each of a plurality of front and rear elevation channels with the at least one height loudspeaker may include reproducing a remaining portion of each of a plurality of rear channels proportional to a position of the at least one height loudspeaker away from the front and toward the rear of the listening environment.

[0017] In an embodiment, the audio in the immersive audio format may further include front right and front left non-height audio channels, rear right and rear left non-height audio channels, upper front right and upper front left height audio channels, and upper rear right and upper rear left height audio channels. The front virtual height filtered audio signals may be added to the corresponding front right and front left non-height audio channels. The rear virtual height filtered audio signals may be added to the corresponding rear right and rear left non-height audio channels. These summations produce four summed audio signals for playback by the corresponding front right and front left, and rear right and rear left non-height loudspeakers.

[0018] In some embodiments, the immersive loudspeaker system may include a single overhead loudspeaker.

[0019] In one embodiment, the top front right elevation audio channel, the top rear right elevation audio channel, the top front left elevation audio channel, and the remaining top rear left elevation audio channel may be summed together and played by a single upper (overhead) loudspeaker.

[0020] In one embodiment, the immersive loudspeaker system may include two overhead loudspeakers, for example an overhead right elevation loudspeaker and an overhead left elevation loudspeaker.

[0021] In one embodiment, the remaining portions of the top front right elevation audio channel and the top back right elevation audio channel may be summed together and played by an upper right elevation loudspeaker. Similarly, the remaining portions of the top front left elevation audio channel and the top back left elevation audio channel may be summed together and played by an upper left elevation loudspeaker.

[0022] In an embodiment, the virtual height filter may have a filter transfer function, and the method further includes determining the filter transfer function of the virtual height filter from one or more parameters identifying the filter transfer function.

[0023] In an embodiment, the method may further include storing the one or more parameters in a processor as a look-up table or as an analytical function.

[0024] In an embodiment, the virtual height filter may have a filter transfer function that has a peak at a first frequency and a notch at a second frequency that is higher than the first frequency.

[0025] In some embodiments, at least two of the front and rear non-height loudspeakers may be spaced laterally apart with respect to the listening position. The method may further include determining a filter transfer function for the virtual height filter based on a relative distance of the at least two loudspeakers from the listening position and an elevation of the roof or near-roof area with respect to the listening position.

[0026] In some embodiments, at least two of the front and rear non-height loudspeakers may be spaced laterally apart relative to a listening position. The method may further include obtaining a plurality of filter transfer functions for a plurality of virtual height filters based on a range of relative distances of the two non-height loudspeakers from the listening position and a range of elevations of a roof or near-roof area relative to the listening position, and selecting a filter transfer function from the plurality of filter transfer functions.

[0027] In an embodiment, the selected filter transfer function may be an average of said multiple filter transfer functions.

[0028] In one embodiment, selecting a filter transfer function from the plurality of filter transfer functions may include selecting one or more parameters identifying a selected filter transfer function based on an average distance of the at least two loudspeakers from a listening position and based on an average elevation of a roof or near-roof area relative to the listening position.

[0029] In an embodiment, the obtaining, selecting, applying, adding and reproducing steps of the above-mentioned method may be applied iteratively for each selected filter transfer function until the filter transfer function provides a maximum perception of sonic sonic quality for the reproduction of the at least two channels.

[0030] In some embodiments, the method may further include applying a gain to the virtual height filter, hi some embodiments, the gain may be user configurable.

[0031] In one embodiment, the listening environment is a vehicle.

[0032] Another aspect of the present disclosure provides an apparatus comprising a processor and a memory coupled to the processor, the processor configured to perform any of the methods described in the present disclosure.

[0033] Another aspect of the present disclosure provides a vehicle equipped with such an apparatus.

[0034] Another aspect of the present disclosure provides a program including instructions that, when executed by a processor, cause the processor to perform a method for processing audio, and also a computer-readable storage medium having such a program stored thereon. [Brief description of the drawings]

[0035] Embodiments of the present disclosure are illustrated by way of example, and not by way of limitation, in the accompanying drawings in which like reference symbols refer to similar elements and in which: [Figure 1]1A-1C are schematic diagrams illustrating an interior left side view of a vehicle having a loudspeaker system arranged in accordance with one embodiment of the present disclosure. [Diagram 2] 1 is a flowchart illustrating an example of a method for generating multiple audio channels from audio in an immersive audio format according to an embodiment of the present disclosure. [Diagram 3] 1 illustrates generally an example of a method for generating multiple audio channels from audio in an immersive audio format according to an embodiment of the present disclosure. [Figure 4] 1 shows a schematic top view of a vehicle with a single height loudspeaker. [Diagram 5] 1A-1C are schematic diagrams illustrating a top view of a vehicle having a loudspeaker system arranged in accordance with an embodiment of the present disclosure. [Figure 6] 1 illustrates a schematic diagram of exemplary sound paths within a vehicle; [Figure 7] 1A-1C illustrate several examples of virtual height filters according to some embodiments of the present disclosure; [Figure 8] 1 illustrates generally an example of a method for generating multiple audio channels from audio in an immersive audio format according to an embodiment of the present disclosure. [Figure 9] 1 shows a schematic top view of a vehicle with two height loudspeakers. [Figure 10] 1 illustrates a schematic diagram of an example of energy distribution of an immersive loudspeaker system according to an embodiment of the present disclosure. [Figure 11] 1 illustrates a schematic diagram of an example of energy distribution of an immersive loudspeaker system according to an embodiment of the present disclosure. [Figure 12] FIG. 1 is a schematic diagram of an example of an apparatus for performing methods according to embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] In order to provide a thorough understanding of the present disclosure, numerous specific details are described below. However, the present disclosure may be practiced without these specific details. Also, well-known parts may be described in less exhaustive detail. The drawings are schematic and include parts relevant to understanding the present disclosure, while other parts may be omitted or merely suggested.

[0037] FIG. 2 shows a flow chart illustrating an example of a method 1000 for generating multiple audio channels from audio in an immersive audio format (e.g., an immersive bitstream) according to an embodiment of the present disclosure. The audio in the immersive audio format includes multiple front and rear elevation audio channels and multiple front and rear non-elevation audio channels. The method 1000 may be used to play the generated multiple audio channels in a listening environment using an immersive loudspeaker system. The listening environment may be a room, an audio studio, a vehicle, or any other closed or partially closed environment suitable for listening to audio. In the present disclosure, it is assumed that the listening environment is a vehicle. The vehicle may be any type of passenger or non-passenger vehicle, for example, used for commercial purposes or to transport cargo. However, other types of listening environments other than vehicles may also be envisioned. An immersive loudspeaker system is a loudspeaker / speaker system having at least one elevation loudspeaker and multiple front and rear non-elevation loudspeakers, as described above. The at least one elevation loudspeaker is located above the listener's head (in the case of a vehicle, above the heads of any passengers and / or drivers), and the non-elevation loudspeaker is located below the listener's head (in the case of a vehicle, below the heads of any passengers and / or drivers).

[0038] For example, referring to FIG. 4, a top view of a vehicle 4000, in this example a passenger car with four seats, is depicted in schematic form. The passenger car 4000 is an example of a listening environment. The passenger car 4000 has four seats 4100, 4200, 4300, and 4400. The vehicle 4000 is equipped with an immersive loudspeaker system having five loudspeakers 1-5. The immersive loudspeakers of the vehicle 4000 include one height loudspeaker 5, two front loudspeakers 1 and 2, and two rear loudspeakers 3 and 4. The loudspeaker on the left side of the vehicle 4000 and its counterpart on the right side of the vehicle 4000 are arranged to be symmetrically reflective with respect to a central axis 4500 that crosses the center of the vehicle 4000 along its length. However, other arrangements of the loudspeakers 1-4 are possible. The height loudspeaker 5 is arranged approximately in the middle of the vehicle 4000 along the longitudinal direction of the vehicle. This is shown diagrammatically by dashed arrows 105 showing the value of factor c increasing from 0 at the rear of the vehicle 4000 to 1 at the front of the vehicle 4000. In the middle of the vehicle 4000, the value of factor c is 0.5. The factor c may be used to calculate the part of the height channel that is filtered by applying a so-called "virtual" filter based on the position of the height loudspeaker 5, by the method described with reference to FIG. 3, and to calculate the remaining part of the same height channel that is reproduced by the height loudspeaker 5. It will be understood that each of the seats 4100, 4200, 4300, and 4400, and therefore the potential listeners located therein, may be symmetrically off-center with respect to any pair of the front loudspeakers 1 and 2 and the rear loudspeakers 3 and 4. For example, the driver sitting in the driver's seat 4100 is symmetrically off-center between the front loudspeakers 1 and 2. The driver is on the right side of the vehicle 4000 and closer to loudspeaker 1 than to the corresponding loudspeaker 2. 1 and 4 show the driver's seat on the left side of the vehicle (left side as one faces the forward direction of travel). However, it is understood that the location of the driver's seat within the vehicle may vary in different regions. For example, in the UK, Australia and Japan, the driver's seat is located on the right side of the vehicle relative to the vehicle's direction of travel.

[0039] The immersive loudspeaker system may for example be a surround loudspeaker system with two additional height loudspeakers as shown with reference to Fig. 1. The loudspeaker system shown in Fig. 1 is a loudspeaker system with five front or surround loudspeakers, two left audio loudspeakers (e.g. left and left surround), two right audio loudspeakers (e.g. right and right surround), a centre loudspeaker, one LFE loudspeaker and two overhead loudspeakers (left and right overhead loudspeakers). The two left audio loudspeakers correspond to loudspeakers 30, 31 (for mid-range or full-range frequencies), 41, 42 and 43 (for high-range frequencies). The centre loudspeaker corresponds to loudspeaker 10. The LFE loudspeaker corresponds to loudspeaker 11. The left overhead loudspeaker corresponds to loudspeaker 44.

[0040] Alternatively, the immersive loudspeaker system may be a surround loudspeaker system having a single height loudspeaker as shown, for example, with reference to FIG.

[0041] Alternatively, in another example, the immersive loudspeaker system may be a surround loudspeaker system having two height loudspeakers, for example as shown with reference to FIG.

[0042] Referring to Fig. 5, a top view of another exemplary vehicle 5000 is shown diagrammatically. The vehicle 5000 may be a six or seven-seater vehicle distributed in three different rows. The vehicle 5000 may be, for example, a sports utility vehicle (SUV) or a minibus. The vehicle 5000 has six seats 5110, 5120, 5130, 5140, 5150, and 5160. For the vehicle 5000, a typical 7.1.2 loudspeaker system may be implemented. The loudspeaker system shown in FIG. 5 has three left loudspeakers 5210, 5230, and 5250 (e.g., left and two left surrounds), three right loudspeakers 5220, 5240, and 5260 (e.g., right and two right surrounds), a center loudspeaker 5270, an LFE loudspeaker 5280, a left mid overhead loudspeaker 5235, and a right mid overhead loudspeaker 5125.

[0043] In some embodiments, the audio in an immersive audio format may be audio rendered in an immersive audio format.

[0044] The immersive audio format of the (e.g., rendered) audio may include at least one elevation channel. In an embodiment, the immersive audio format may be an object-based audio format that supports elevation, such as a Dolby Atmos format. In another embodiment, the immersive audio format may be a channel-based audio format that supports elevation, such as an XYZ audio format, where X≧2 is the number of front or surround audio channels, Y≧0 is a low-frequency effects or subwoofer audio channel, if present, and Z≧1 is the at least one elevation audio channel. In an embodiment, the object-based audio format (e.g., supporting elevation) may be rendered or pre-rendered into a corresponding channel-based audio format to generate loudspeaker feeds that correspond to the channels of the channel-based audio format.

[0045] The method illustrated in Figure 2 will now be described with reference to Figure 3, which illustrates generally an example of a method for generating multiple audio channels from audio in an immersive audio format according to an embodiment of the present disclosure. The immersive loudspeaker system illustrated in Figure 3 has the same number and type of loudspeakers as shown in the vehicle 4000 illustrated with reference to Figure 4.

[0046] With reference to FIG. 3, the audio in the immersive audio format may include eight audio channels: non-elevation front channels 1050 and 1100 (e.g., left and right front channels), non-elevation rear channels 1125 and 1150 (e.g., left and right rear channels or left and right surround channels), and four elevation channels 1020, 1010, 1030 and 1040 (e.g., upper front left channel TFL, 1020, upper front right channel TFR, 1010, upper rear left channel TRL, 1030, upper rear right channel TRR, 1040). The example loudspeaker system of FIG. 3 is a surround loudspeaker system with loudspeakers 1, 2, 3 and 4 and a single overhead loudspeaker 5 (Voice of God). The same loudspeaker system is shown in a vehicle 4000 with reference to FIG. 4. However, a similar loudspeaker system may be used indoors or in another listening environment. In the example of Figure 3, loudspeaker 1 is used for reproduction of audio in an immersive audio format of channel 1050 and a portion of the virtual filtered height channel 1200. In the example of Figure 3, loudspeaker 2 is used for reproduction of audio in an immersive audio format of channel 1100 and a portion of the virtual filtered height channel 1175. The method 1000 generates a plurality of audio channels 1011, 1018, 1033, 1063, and 1065 from the audio in an immersive audio format, as described herein below. Since a plurality of audio channels 1011, 1018, 1033, 1063, and 1065 are generated from the eight channels 1050, 1100, 1125, 1150, 1020, 1010, 1030, and 1040 of the immersive audio format, it can be said that the eight channels of the immersive audio format are downmixed to said plurality of five audio channels 1011, 1018, 1033, 1063 for playback by corresponding loudspeakers 1, 2, 3, 4, and 5.

[0047] 2 and 3, the method 1000 includes applying 1500 virtual height filters 1400, 1300, 2500 and 2600 to a portion of each of a plurality of front and rear height channels 1020, 1010, 1030 and 1040, so as to at least partially attenuate spectral components of the portion of the height channel that emanate directly from the non-height loudspeakers when one of the front and rear height audio channels (either channels 1020, 1010, 1030 or 1040) is reproduced by one of the front non-height loudspeakers 1 and 2 or the rear non-height loudspeakers 3 and 4, and at least partially amplify spectral components of the portion of the height channel that are reflected from a roof or a roof-proximate area within the listening environment, which in this example is a vehicle, to generate a plurality of front virtual height filtered audio signals 1200 and 1175 and rear virtual height filtered audio signals 1225 and 1250. 2 , the method 1000 further includes adding 1700 each of the plurality of front virtual height filtered audio signals 1200 and 1175 to a corresponding front non-height audio channel 1050 and 1100 to generate a summed audio signal 1011 and 1018 for playback by the corresponding front loudspeakers 1 and 2. The method 1000 further includes adding 1700 each of the rear virtual height filtered audio signals 1225 and 1250 to the non-height audio channels 1125 and 1150 to generate a summed audio signal 1033 and 1063 for playback by the corresponding loudspeakers 3 and 4. The method 1000 further includes reproducing 1750 a remaining portion of each of the plurality of front and rear height channels 1020, 1010, 1030 and 1040 using the at least one height loudspeaker 5. From FIG. 3 it can be seen that the remaining portions of the front and rear height channels 1020 , 1010 , 1030 and 1040 are summed to a signal 1065 which is fed to the height loudspeaker 5 .

[0048] In some embodiments, the portions of the front and rear height channels to which the virtual height filter is applied are a function of the position of the at least one height loudspeaker along the length of the vehicle. In some embodiments, the portions of the front and rear height channels to which the virtual height filter is applied are a linear function of the position of the at least one height loudspeaker along the length of the vehicle. For example, as shown in FIG. 4, a height (or overhead) loudspeaker 5 may be located in the middle of the vehicle 4000 along the length of the vehicle 4000 and along the axis 4500. As mentioned above, in the example of FIG. 4, the height loudspeaker 5 is located in the middle of the vehicle 4000. The position of the height loudspeaker 5 is shown diagrammatically in FIG. 4 by the value of the multiplication factor. If the height loudspeaker 5 is located in the middle along the length of the vehicle 4000, then c=0.5. In this example, with reference to FIG. 3, when the height (or overhead) loudspeaker 5 is located in the middle of the vehicle along the length of the vehicle, 50% of the energy of each height channel 1020, 1010, 1030 and 1040 may be "virtually" filtered by the corresponding virtual filter 1400, 1300, 2500 and 2600, and 50% of the remaining energy may be reproduced by the height loudspeaker 5. This example is represented diagrammatically with reference to FIG. 10. FIG. 10 shows diagrammatically an example of the energy distribution of an audio system in the loudspeaker system of the vehicle 4000 of FIG. 4 by using the exemplary method of FIG. 3. If c=0.5 when the height loudspeaker 5 is located in the middle of the vehicle 4000, the audio signal fed to the height loudspeaker 5 is 0.5TFL+0.5TFR+0.5TRL+0.5TRR. The audio signal fed to loudspeaker 1 is L+(0.5TFL) filter , i.e., equal to the energy of the non-height front left channel plus half the energy of the top front left channel filtered by the virtual filter 1400. The audio signal fed to loudspeaker 2 is R+(0.5TFR) filteri.e., equal to the energy of the non-height front right channel plus half the energy of the top front right channel filtered by the virtual filter 1300. The audio signal fed to the loudspeaker 3 is S +(0.5TRL) filter i.e., equal to the energy of the non-height rear (or surround) left channel plus half the energy of the top rear left channel filtered by the virtual filter 2500. The audio signal fed to the loudspeaker 4 is S +(0.5TRR) filter , i.e. equal to the energy of the non-height rear (or surround) right channel plus half the energy of the upper rear right channel filtered by the virtual filter 2600. The energy distribution is such that it conserves energy between the loudspeakers of the loudspeaker system, i.e. the distribution is energy neutral. This effect is shown diagrammatically in FIG. 10 by the loudspeakers enclosed in dashed lines. The sounds in the height plane are distributed between the "virtual" loudspeakers enclosed in dashed lines, and the listener has the perception that the sounds in the height plane, i.e. the sounds associated with the height channels of the immersive audio format, are emitted by such virtual loudspeakers. The sounds in the height plane have an improved spatial resolution compared to the conventional method of using a single height loudspeaker. It can be said that the listener's perception of the sounds in the height plane is that of the sounds produced by a helicopter, i.e. as if the audio were emanating from all directions surrounding the listener, even by using a single height loudspeaker. In typical prior art solutions, i.e. solutions without redistribution of the height channel between the height and non-height loudspeakers of an immersive loudspeaker system and without "virtual" filtering of the parts of the height channel that are fed to the non-height loudspeakers, a helicopter effect is not produced, but the sound is perceived as emanating simply from the physical location of a single height loudspeaker.

[0049] In one embodiment, applying the virtual height filter to a portion of each of the plurality of front and rear height channels includes applying the virtual height filter to a portion of the front height channel proportional to a position of the at least one height loudspeaker away from the front and toward the rear of the listening environment. For example, with reference to FIG. 4, the value of c may decrease as the position of height loudspeaker 5 approaches the rear of the vehicle 4000. In the example of FIG. 3, the portion of the top front left and right channels (TFL and TFR) that feed loudspeakers 1 and 2 increases proportionally as the value of c decreases. That is, in this particular example, such portion increases by a factor 1-c.

[0050] Further, in one embodiment, applying the virtual height filter to a portion of each of the plurality of front and rear height channels includes applying the virtual height filter to a portion of the rear height channel proportional to a position of the at least one height loudspeaker away from the rear and toward the front of the listening environment. For example, with reference to Figure 4, the value of c may increase as the position of height loudspeaker 5 moves toward the front of vehicle 4000 and away from the rear. In the example of Figure 3, the portion of the upper rear left and right channels (TRL and TRR) that feed loudspeakers 3 and 4 increases proportionally as the value of c increases. That is, in this particular example, such portion increases by a factor c.

[0051] Similarly, in one embodiment, reproducing a remaining portion of each of the plurality of front and rear elevation audio channels with the at least one height loudspeaker includes reproducing a remaining portion of each of the plurality of front elevation audio channels that is proportional to a position of the at least one height loudspeaker away from the rear and toward the front of the listening environment. For example, with reference to Figure 4, the value of c may increase as the position of the height loudspeaker 5 moves toward the front of the vehicle 4000 and away from the rear. In the example of Figure 3, the remaining portions of the upper front left and right channels (TFL and TFR) feeding the height loudspeaker 5 increase proportionally as the value of c increases, i.e., in this particular example, such remaining portions increase by a factor c.

[0052] Similarly, in one embodiment, reproducing a remaining portion of each of the plurality of front and rear height audio channels with the at least one height loudspeaker includes reproducing a remaining portion of each of the plurality of rear height audio channels that is proportional to a position of the at least one height loudspeaker away from the front and toward the rear of the listening environment. For example, with reference to Figure 4, the value of c may decrease as the position of the height loudspeaker 5 moves toward the rear of the vehicle 4000 and away from the front. In the example of Figure 3, the remaining portion of the upper rear left and right channels (TRL and TRR) feeding the height loudspeaker 5 increases proportionally as the value of c decreases, i.e., in this particular example, such remaining portion increases by a factor 1-c.

[0053] It is understood that the embodiments described with reference to Fig. 3, Fig. 4 and Fig. 10 are merely examples of how the distribution of energy from the height channel to the non-height loudspeakers may be implemented. In a practical implementation, the portion(s) of the height channel filtered by the virtual filter feeding the non-height loudspeaker may not depend on the position of the height loudspeaker. In a practical implementation, the portion(s) of the height channel filtered by the virtual filter feeding the non-height loudspeaker may be determined based on the best performance of the loudspeaker system, for example based on the best immersive audio experience for the listener. Similarly, in embodiments of the present disclosure, the factor c may be adjusted for the best immersive audio experience for the listener, for example instead of based on the position of the at least one height loudspeaker. It is also understood that the embodiments of the present disclosure are not limited to the use of the factor c as shown in Fig. 3. Other linear or non-linear functions of the position of the height loudspeaker or other parameters of the height and / or non-height audio channels, such as, for example, volume level, equalization level, dialogue enhancement, may be envisaged. Other ratios of the portion of the height channel that is virtually filtered and the remaining portion of the height channel that is reproduced by the height loudspeaker may be selected depending on the appropriate implementation.

[0054] In an embodiment, the portion of the front and rear height channels to which the virtual height filter is applied is a function of a desired balance distribution of the multiple audio channels between the loudspeakers of the immersive loudspeaker system. The desired balance distribution may provide the best immersive audio experience for the listener. For example, during a calibration or testing phase, it may be found that a particular ratio of the portion of the height channel that is virtually filtered and the remaining portion of the height channel reproduced by the height loudspeaker provides the desired height spatial resolution, i.e., spatial resolution in the height plane.

[0055] In another embodiment, the portions of the front and rear height channels to which the virtual height filter is applied are a function of both the desired balance distribution of the multiple audio channels among the loudspeakers of the immersive loudspeaker system and the position of said at least one height loudspeaker along the length of the vehicle. The desired spatial resolution in the height plane may be a function of the position of the height (or overhead) loudspeakers.

[0056] Generally, as described above, the selection of the portions of the front and rear height channels that are filtered by the virtual height filter is made based on empirical data or experimentation that provides the best performance of the immersive loudspeaker system.

[0057] In some embodiments, the portion of the front or rear height channel to which the virtual height filter is applied may be a function of the position of the listener (driver or passenger) relative to the position of the height (or overhead) loudspeakers. In some embodiments, the portion of the front or rear height channel to which the virtual height filter is applied may be dynamically adjusted / triggered in response to changes in the listener's position relative to the position of the height (or overhead) loudspeakers. For example, the listener's position may be adjusted in the height or base plane, and the portion of the front or rear height channel to which the virtual height filter is applied may be changed based on this adjustment. For example, the adjustment of said portion may be triggered by an adjustment of the seat in any direction in the vehicle.

[0058] The virtual height filter 1300 is configured to at least partially attenuate spectral components of the portion of the height channel 1010 that emanate directly from loudspeaker 2 when the portion of the height channel 1010 is reproduced by loudspeaker 2. The virtual height filter 1300 is further configured to at least partially amplify spectral components of the portion of the height channel 1010 that emanate directly from loudspeaker 1 when the portion of the height channel 1020 is reproduced by loudspeaker 1. The virtual height filter 1400 is further configured to at least partially amplify spectral components of the portion of the height channel 102 ... The virtual height filter 2500 is configured to at least partially attenuate spectral components of the portion of the height channel 1030 that emanate directly from the loudspeaker 3 when the portion of the height channel 1030 is reproduced by the loudspeaker 3. The virtual height filter 2500 is further configured to at least partially amplify spectral components of the portion of the height channel 1030 that emanate directly from the loudspeaker 4 when the portion of the height channel 1040 is reproduced by the loudspeaker 4. The virtual height filter 2600 is further configured to at least partially amplify spectral components of the portion of the height channel 1030 that emanate directly from the loudspeaker 4 when the portion of the height channel 1040 is reproduced by the loudspeaker 4. The virtual height filter 2600 is further configured to at least partially amplify spectral components of the portion of the height channel 104 ... roof or roof-proximate area of ​​the vehicle to generate the virtual height filtered audio signal 1250.

[0059] For further explanation, reference is made to FIG. 6. FIG. 6 shows, in a schematic manner, exemplary paths 6300 and 6400 that a sound reproduced by a loudspeaker 6000 may travel from the loudspeaker 6000 to a listening position 6100 (e.g., in a vehicle). The loudspeaker 6000 may be, for example, any of the non-height loudspeakers shown with reference to the loudspeaker systems of FIG. 1 and FIG. 3. In particular, the loudspeaker 6000 may be any of the front or rear (or surround) left, right loudspeakers shown. Preferably, the loudspeaker 6000 may be any high-frequency loudspeaker associated with any of the left, right or surround loudspeakers, such as, for example, the loudspeakers (e.g. tweeters) 41, 42 and 43 shown in FIG. 1, since height cues are typically more prevalent in high frequency signals than in low frequency signals. The listening position 6100 may be at the ear / head of a passenger or driver of the vehicle. The sound reproduced by the loudspeaker 6000 may radiate along a reflected path 6300, shown by a dashed line in FIG. 6, and along a direct path 6400, shown by a solid line in FIG. 6. The reflected path 6300 is an indirect path from the loudspeaker 6000 to the listening position 6100, and is formed by the sound being reflected from a surface 6500 located above the listening position 6100. Inside the listening environment, the surface 6500 may be the ceiling of a room or an area close to the ceiling of a room. Inside the vehicle, the surface 6500 may be the roof of the vehicle or an area close to the roof of the vehicle. The area close to the roof may be the upper inner part of the front or rear windshield of the vehicle, or the upper inner part of a side window of the vehicle. In general, the surface 6500 may be any part of the interior of the vehicle that is located at a higher elevation (e.g., above) than the listening position during the reproduction of the sound. It is desirable for the sound to radiate along the reflected path 6300 to increase the perception of the elevation of the sound. However, some sound from the loudspeaker 6000 will travel along the direct path 6400 and reduce the perception of sound coming from positions on the surface 6500 where the sound is reflected towards the listening position 6100.The amount of this undesired direct sound compared to the desired reflected sound may be a function of the directional pattern of the loudspeaker 6000. A non-height loudspeaker located about halfway through the overall interior height of the vehicle (e.g., approximately mid-height of the doors) has been found to improve the perception of pitch.

[0060] Incorporating signal processing to introduce perceptual height cues into the audio signal fed to the loudspeaker 6000 to compensate for undesired direct sounds has been shown to improve the positioning and perceived quality of the virtual height signal. For example, directional hearing models have been developed to create virtual height filters, which when used to process audio reproduced by the loudspeakers, improve the perceived quality of the reproduction. In one embodiment, the virtual height filters are derived from both the physical loudspeaker positions relative to the listening position and the virtual loudspeaker positions (above the listening position). For the physical loudspeaker positions, a first directional filter is determined based on a model of the sound traveling directly from the loudspeaker positions to the listener's ears at the listening position. Such filters may be derived from a database of HRTF (head-related transfer function) measurements or a model of directional hearing, such as a parametric binaural hearing model, a pinna model, or other similar transfer function models that utilize cues that help perceive height. Models that take the pinna model into account are generally useful as they help define how height is perceived, but the filter functions are not intended to isolate the pinna effect, but rather to process the ratio of sound levels from one direction to another, and the pinna model is an example of one such model of a binaural hearing model that may be used, although other models may also be used.

[0061] The inverse of this filter is then determined and used to remove directional cues for audio traveling along a direct path from the physical loudspeaker locations to the listening position. A second directional filter is then determined for the virtual loudspeaker locations based on a model of sounds traveling directly from the virtual loudspeaker locations to the ears of a listener at the same listening position, using the same directional hearing model. This filter is applied directly, providing the directional cues that the ears would receive if the sounds were emanating from the virtual loudspeaker locations above the listening position. In practice, the first directional filter and the second directional filter may be combined to allow for a single filter that at least partially removes (attenuates) the directional cues from the physical loudspeaker locations and at least partially inserts (amplifies) the directional cues from the virtual loudspeaker locations. Such a single filter provides a frequency response curve, referred to herein as a "height filter transfer function," "virtual height filter response curve," "desired frequency transfer function," "height cue response curve," or similar terms, to describe a filter or filter response curve that filters, e.g., attenuates, direct sound components from height sound components in an audio loudspeaker system.

[0062] In terms of the filter model, if P1 represents the frequency response in dB of a first filter that models the sound transmission from a physical loudspeaker location, and P2 represents the frequency response in dB of a second filter that models the sound transmission from a virtual loudspeaker location, then the total response PT of the virtual height filter in dB can be expressed as PT = α(P2-P1), where α is a scaling factor or gain that controls the strength of the filter. At α = 1, the filter is applied to its full extent, and at α = 0, the filter does nothing (0 dB response). In practice, α may be set anywhere between 0 and 1 (e.g., α = 0.5), based on the relative balance between reflected and direct sound. As the level of the direct sound increases compared to the reflected sound, α should also increase in order to give this undesired direct sound path more complete directional cues of the virtual loudspeaker location. However, α should not be so large as to impair the perceived timbre of the audio traveling along the reflected path, which already contains the appropriate directional cues. In general, the exact values ​​of filters P1 and P2 are a function of the azimuth angle of the physical loudspeaker position relative to the listening position and the elevation of the reflected loudspeaker position, which is a function of the distance of the physical loudspeaker position from the listening position and the difference between the height of the roof or near-roof area (surface 6500 in FIG. 6) and the height of the speaker.

[0063] 7 illustrates example curves 7200, 7300, and 7400 of virtual height filters according to some embodiments of the present disclosure. Curves 7200, 7300, and 7400 are depicted in a diagram showing the amplitude of the virtual height filter in decibels (dB) on the vertical axis against frequency in Hertz (Hz) on the horizontal axis.

[0064] Curves 7200, 7300, and 7400 represent the filter transfer functions of three different virtual height filters. FIG. 7 shows that the filter transfer functions 7200, 7300, and 7400 of the three different filters have a peak at a first frequency of about 8000 Hertz and a notch at a second frequency higher than the first frequency of about 12000 Hertz. However, the peak and notch may be at different frequencies. The three different transfer functions may be obtained by applying different scaling factors / different gains to the virtual height filter, as described above. In an embodiment, the gain may be user configurable, such that the "strength" of the virtual height filter may be adjusted by the user according to the particular implementation.

[0065] In an embodiment, as shown with reference to FIG. 2, the method of the present disclosure may further include determining 1800 a filter transfer function of the virtual height filter from one or more parameters that identify the filter transfer function. For example, the one or more parameters may indicate at least one value of a peak, a frequency of the peak, a notch, and a frequency of the notch of the filter transfer function representing the virtual height filter. For example, the parameters may be stored in a memory, or a processor including a memory, for example as a look-up table or an analytical function. These parameters may be retrieved by a processing unit from the memory from which the virtual height filter can be reconstructed. The reconstructed virtual height filter may thus be used and applied to the height channel. By using one or more parameters to identify the filter transfer function, processing of the height channel is simplified as the virtual height filter is described by a small number of parameters rather than being generated locally.

[0066] The two front and / or rear non-height loudspeakers are spaced laterally relative to a listening position (e.g., in the case of a vehicle, a driver or passenger position). In an embodiment, as shown with reference to FIG. 2, the method of the present disclosure may further include determining 1850 a filter transfer function for the virtual height filter based on a relative distance of the two non-height front and / or rear loudspeakers from the listening position and an elevation of the roof or near-roof area relative to the listening position.

[0067] For example, in one embodiment, one or more sensors may be positioned at or near the listening position to measure such relative distances of the at least two front or rear loudspeakers from the listening position, and the elevation of the roof or roof-proximate area relative to the listening position. For example, in one embodiment, such sensors may be embedded within the head restraint of each seat in the vehicle, approximately at the same height as the listener's head. The measurements may be performed during an initial calibration stage of the method, or alternatively, substantially in real-time with the playback of the audio.

[0068] Alternatively, additionally, or optionally, the filter transfer function of the virtual height filter may be based on a predetermined absolute distance between one or more listening positions and each of the non-elevation front and / or rear loudspeakers and a predetermined elevation of the roof relative to the listening positions. For example, the distance between one or more listening positions (e.g., any of the positions at seats 4100, 4200, 4300, or 4400 in FIG. 4) and the pair of non-elevation front loudspeakers 1 and 2 and / or non-elevation rear loudspeakers 3 and 4, as well as the elevation of the roof may be determined / predetermined by environmental characteristics, such as the interior design of the vehicle and the installation of the loudspeakers. The method of the present disclosure may use this predetermined information to obtain the filter transfer function of the virtual height filter. For example, in an embodiment, the step 1800 of determining the filter transfer function of the virtual height filter from one or more parameters may involve accessing the predetermined parameters. For example, the parameters may be obtained / measured for one vehicle of a type and then stored in a memory of an on-board computing system of the same type of vehicle. Such an offline calibration has the advantage that the vehicle does not need to be equipped with sensors to obtain online measurements of the filter transfer functions.

[0069] Alternatively, additionally, or optionally, in an embodiment as shown with reference to FIG. 2, the method 1000 may further include obtaining 1900 a plurality of filter transfer functions for a plurality of virtual height filters, typically before step 1500. The plurality of virtual height filters may be obtained based on a range of relative distances of the plurality of height and non-height loudspeakers from the listening position and a range of elevations of the roof or a near-roof area relative to the listening position. For example, a range of non-height or height loudspeaker-listening position(s) distances may be measured for a plurality of different listening positions and / or a plurality of non-height or height loudspeaker positions, for example during a calibration phase. Similarly, a range of elevations of the roof (or its virtual loudspeaker positions) may be measured for a plurality of different listening positions, for example during a calibration phase. The method 1000 further includes selecting 2000 a filter transfer function from the plurality of filter transfer functions. For example, in one embodiment, the selected filter transfer function may be based on the average distance of the height loudspeakers from the listening position and on the average elevation of the roof or near-roof area (or virtual loudspeaker positions) relative to the listening position. In another embodiment, the selected virtual height filter (the filter transfer function of the) is an average of multiple filter transfer functions. For example, the selected transfer function may be determined by interpolating between multiple filter transfer functions. In yet another embodiment, the method 1000 including steps 1900 and 2000 may be applied iteratively, as shown in FIG. 2, for example during a calibration phase. The application is performed for each selected filter transfer function in each iteration until the selected filter transfer function provides an optimal (e.g. maximum) perception of sound elevation with a desired spatial resolution in the height plane at one or more listening positions. In other words, the method 1000 including steps 1900 and 2000 may be applied iteratively until the (selected) filter transfer function provides a reproduction of said multiple audio channels with a maximum spatial resolution in the height plane.In general, for simpler and more effective audio processing in a particular type of vehicle, a single filter transfer function may be selected that performs well on average for the majority of listening positions / loudspeaker positions and elevations of the roof or near-roof area (or elevations of virtual loudspeaker positions). However, the filter transfer function may also be adaptively determined substantially in real time, for example by sensors as described above. Adaptively determining the filter transfer function may provide a more accurate determination of the filter transfer function and therefore provide improved spatial resolution in the height plane.

[0070] In an embodiment, and with further reference to Figure 2, each filter transfer function of the plurality of transfer functions obtained in step 1900 may be determined from one or more parameters stored in memory, e.g., as a LUT or analytical function, as described above. The method may actively / adaptively select the parameters of the filter transfer functions for a particular vehicle type or when a sensor is used.

[0071] In an embodiment, and with further reference to FIG. 2, the step 1800 of determining the filter transfer function of the virtual height filter from one or more parameters (either based on predefined distance / altitude information or based on actual measurements) may be triggered upon detection of a movement of a listener located at one or more listening positions. For example, one or more sensors may be used to detect the movement of the listener. When used inside a vehicle, such sensors may for example be located at each seat of the vehicle. The one or more sensors may be configured to detect the presence of a passenger or driver in the vehicle, thus enabling the use of correct distance information to be used by the processing method to obtain the filter transfer function.

[0072] In an embodiment, the one or more seat sensors or a set of different sensors may be used to detect a new listening position, for example, a new position of the listener's head (or the listener's ear position). For example, a driver or a passenger may adjust his / her seat horizontally and / or vertically for a more comfortable sitting position in the vehicle. In this embodiment, the method may search / obtain (a filter transfer function of) the virtual height filter according to the newly detected listening position. In this way, the correct information may be used according to the new listening position based on a correct set of distance information from a given listener to the loudspeaker and a set of given roof altitude information or based on actual measurements. For example, if / when the given one or more parameters identifying (a filter transfer function of) the virtual height filter are stored as an analytical function or a look-up table (LUT), different analytical functions or different LUTs may correspond to different (e.g., detected) seat or listening positions. These embodiments in which step 1800 may be triggered upon detection of a listener's movement may be combined with the embodiments described above in which the portion of the front or rear height channel to which the virtual height filter is applied may be dynamically adjusted / triggered in response to a change in the listener's position relative to the position of the height (or overhead) loudspeaker. For example, both the parameter or parameters identifying a particular filter transfer function and the portion of the front or rear height to which the particular filter transfer function is applied may be determined upon detection of a new listener position and / or based on the new listener position. The new listener position may be determined using any sensor or set of sensors described above. Thus, an even more accurate and targeted determination of the filter transfer function and the ratio of the portion of the height channel to be filtered and the remaining portion of the height channel to be reproduced by the height loudspeaker may be achieved.

[0073] As mentioned above, the immersive loudspeaker system may comprise two height loudspeakers.

[0074] For example, with reference to FIG. 8, the immersive loudspeaker system includes two height loudspeakers 6 and 7 and four non-height loudspeakers 1, 2, 3 and 4. The two height loudspeakers 6 and 7 may be the upper right height loudspeaker and the upper left height loudspeaker, respectively, as shown in the vehicle 8000 of FIG. 9. FIG. 9 shows a schematic representation of a vehicle 9000. The vehicle 9000 is similar to the vehicle 4000 shown with reference to FIG. 4, but includes an immersive loudspeaker system having two height loudspeakers 6 and 7. As with the vehicle 4000 of FIG. 4, the height loudspeakers 6 and 7 in the example of FIG. 9 are located in the middle of the vehicle 9000 along the length of the vehicle 9000. The middle position of the height loudspeakers 6 and 7 is indicated by a value of 0.5 for the factor c. The (input) immersive audio format used with reference to the example shown in FIG. 8 has eight audio channels, which is the same as that described with reference to FIG. 3 and will not be repeated here.

[0075] A virtual height filter 1300 is applied to a portion of the height channel 1010 to generate a virtual height filtered signal 1175. The virtual height filtered signal 1175 is summed with the non-height channel 1100 to generate signal 1018. A virtual height filter 1400 is applied to a portion of the height channel 1020 to generate a virtual height filtered signal 1200. The virtual height filtered signal 1200 is summed with the non-height channel 1050 to generate signal 1011. A virtual height filter 2500 is applied to a portion of the height channel 1030 to generate a virtual height filtered signal 1225. The virtual height filtered signal 1225 is summed with the non-height channel 1125 to generate signal 1033. A virtual height filter 2600 is applied to a portion of the height channel 1040 to generate a virtual height filtered signal 1250. The virtual height filtered signal 1250 is summed with the non-height channel 1150 to generate signal 1063. Channel signals 1011, 1018, 1033 and 1063 are fed to loudspeakers 1, 2, 3 and 4, respectively, for reproduction. The remaining part of height channel 1020 is fed to height loudspeaker 7 together with the remaining part of height channel 1030. The remaining part of height channel 1010 is fed to height loudspeaker 6 together with the remaining part of height channel 1040. By using two height loudspeakers 6 and 7 and by redistributing the height channels between the height and non-height loudspeakers of the immersive loudspeaker system, the spatial resolution in the height plane is further improved. This is better explained with reference to FIG. 11.

[0076] Figure 11 shows a schematic example of an energy distribution of an audio system in the loudspeaker system of the vehicle 9000 of Figure 9 by using the exemplary method of Figure 8. If c=0.5 when the height loudspeakers 6 and 7 are located in the middle of the vehicle 9000, the audio signal fed to the height loudspeaker 6 is 0.5TFR+0.5TRR and the audio signal fed to the height loudspeaker 7 is 0.5TFL+0.5TRL. The audio signal fed to the loudspeaker 1 is L+(0.5TFL) filter , i.e., equal to the energy of the non-height front left channel plus half the energy of the top front left channel filtered by the virtual filter 1400. The audio signal fed to loudspeaker 2 is R+(0.5TFR) filter i.e., equal to the energy of the non-height front right channel plus half the energy of the top front right channel filtered by the virtual filter 1300. The audio signal fed to the loudspeaker 3 is S +(0.5TRL) filter i.e., equal to the energy of the non-height rear (or surround) left channel plus half the energy of the top rear left channel filtered by the virtual filter 2500. The audio signal fed to the loudspeaker 4 is S +(0.5TRR) filter, i.e. equal to the energy of the non-height rear (or surround) right channel plus half the energy of the upper rear right channel filtered by the virtual filter 2600. The energy distribution is such that it conserves energy between the loudspeakers of the loudspeaker system, i.e. the distribution is energy neutral. This effect is shown diagrammatically in FIG. 11 by the loudspeakers enclosed in dashed lines. The sounds in the height plane are distributed between the "virtual" loudspeakers enclosed in dashed lines, and the listener has the perception that the sounds in the height plane, i.e. the sounds associated with the height channels of the immersive audio format, are emitted by such virtual loudspeakers. The sounds in the height plane have an improved spatial resolution compared to the conventional method of using two height loudspeakers. It can be said that the listener's perception of the sounds in the height plane is the perception of the sounds produced by a helicopter, i.e. as if the audio were emanating from all directions surrounding the listener, even by using two height loudspeakers. Typical prior art solutions, i.e. solutions that do not redistribute the height channel between the height and non-height loudspeakers of an immersive loudspeaker system and that do not "virtually" filter the parts of the height channel that are fed to the non-height loudspeakers, do not produce a helicopter effect, but the sound is perceived as emanating simply due to the physical position of the two height loudspeakers.

[0077] It will be appreciated that the various ways of determining the portion of the height channel based on the virtually filtered height loudspeakers described with reference to the embodiments of Figures 3, 4 and 10 are also applicable to the embodiments of Figures 8, 9 and 11 having two height loudspeakers, and therefore these various methods of determining the portion of the height channel will not be repeated here.

[0078] It is understood that the embodiments described with reference to Figures 8, 9 and 11, as well as the embodiments described with reference to Figures 3, 4 and 10, are merely examples of how the distribution of energy from the height channel to the non-height loudspeakers may be implemented. In a practical implementation, the portion of the height channel to be filtered by the virtual filter feeding the non-height loudspeaker may not depend on the position of the height loudspeaker. In a practical implementation, the portion of the height channel to be filtered by the virtual filter feeding the non-height loudspeaker may be determined based on the best performance of the loudspeaker system, for example based on the best immersive audio experience for the listener. Similarly, in embodiments of the present disclosure, the factor c may be adjusted for the best immersive audio experience for the listener, instead of based on the positions of, for example, the two height loudspeakers. It is also understood that embodiments of the present disclosure are not limited to the use of the factor c as shown in Figure 9. Other linear or non-linear functions of the positions of the height loudspeakers or other parameters of the height and / or non-height audio channels, such as, for example, volume level, equalization level, dialogue enhancement, may be envisaged. Other ratios of the portion of the height channel that is virtually filtered and the remaining portion of the height channel that is reproduced by the height loudspeakers may be selected according to a suitable implementation. For example, c may be equal to 0.25 if the height loudspeakers 6 and 7 are located between the rear and middle of the vehicle 9000. For example, c may be equal to 0.75 if the height loudspeakers 6 and 7 are located between the middle and front of the vehicle 9000. Alternatively, c may also be equal to 0.25 or 0.75 (or any other value suitable for a particular implementation), independent of the position of the loudspeakers 6 and 7.

[0079] In an embodiment, the portion of the front and rear height channels to which the virtual height filter is applied is a function of a desired balance distribution of the multiple audio channels between the loudspeakers of the immersive loudspeaker system. The desired balance distribution may provide the best immersive audio experience for the listener. For example, during a calibration or testing phase, it may be found that a particular ratio of the portion of the height channel that is virtually filtered and the remaining portion of the height channel reproduced by the height loudspeaker provides the desired height spatial resolution, i.e. the desired spatial resolution in the height plane.

[0080] In another embodiment, the portions of the front and rear height channels to which the virtual height filter is applied are a function of both the desired balance distribution of the multiple audio channels among the loudspeakers of the immersive loudspeaker system and the position of said at least one height loudspeaker along the length of the vehicle. The desired spatial resolution in the height plane may be a function of the position of the height (or overhead) loudspeakers.

[0081] Generally, as described above, the selection of the portions of the front and rear height channels that are filtered by the virtual height filter is made based on empirical data or experimentation that provides the best performance of the immersive loudspeaker system.

[0082] In some embodiments, the portion of the front or rear height channel to which the virtual height filter is applied may be a function of the position of the listener (driver or passenger) relative to the position of the height (or overhead) loudspeakers. In some embodiments, the portion of the front or rear height channel to which the virtual height filter is applied may be dynamically adjusted / triggered in response to changes in the listener's position relative to the position of the height (or overhead) loudspeakers. For example, the listener's position may be adjusted in the height or base plane, and the portion of the front or rear height audio channel to which the virtual height filter is applied may be changed based on this adjustment. For example, the adjustment of said portion may be triggered by an adjustment of the seat in any direction in the vehicle.

[0083] Any other suitable immersive audio formats and / or loudspeaker configurations suitable for a particular implementation may be envisioned.

[0084] For example, in addition to the example (input) channels shown with reference to Figures 3 and 8, the audio in an immersive audio format may also include a center (C) channel and / or a low frequency effects (LFE) channel (not shown in either Figure 3 or Figure 8). As explained above, because height cues are typically more prevalent in high frequency signals than in low frequency signals, the center channel and / or LFE channel, when present, are typically not mixed / summed with the virtual filtered height channel but are instead fed directly to the corresponding loudspeakers (e.g., center and LFE loudspeakers).

[0085] In some embodiments (not shown), when a center channel is present in the input immersive audio format, the center channel may be mixed / added together with the non-height front left and front right channels. In such embodiments, adding the virtually filtered height channel(s) to the non-height audio channel(s) (i.e., the front left and / or front right channels) may be performed after mixing the front left and front right channels with the center channel. In other words, in such embodiments, the non-height channel signals that are added to the virtually filtered signal are already mixed with the center channel.

[0086] Similar considerations are applicable to a loudspeaker configuration such as that shown in FIG. 5, which also includes Middle Left (ML) and Middle Right (MR) loudspeakers 5230 and 5240.

[0087] In some embodiments, non-height channels, e.g., front left and front right channels and / or rear left and rear right channels, are processed before being mixed with the corresponding virtually filtered portion of the height channel. For example, the front left and front right channels and / or rear left and rear right channels may be processed to compensate for off-center listening positions of passengers / drivers in a vehicle. Compensation for off-center listening positions may be performed using the algorithm described in EP 1994795 B1, which is incorporated herein by reference in its entirety. In EP 1994795 B1, it was shown that it is possible to simultaneously "virtual center" two symmetrically off-center listening positions from the same pair of (stereo) loudspeakers. This follows the same principle as reducing the phase difference of the interaural phase difference (IDP) of a single listening position. In the case of two listening positions, the phase difference of the resulting IDPs for each of the two listening positions is simultaneously reduced so that each IDP at each listening position has a value between -90 degrees and 90 degrees over the desired frequency range. By compensating for off-center listening positions and mixing the filtered portions of the height channels with the corresponding compensated front and / or rear non-height channels, panning of the content of the portions of the height channels across the front and / or rear loudspeakers may be prevented.

[0088] Exemplary Computing Device Methods of generating multiple audio channels from audio in an immersive audio format for playing multiple audio channels in an immersive loudspeaker system comprising at least one height loudspeaker and multiple front and rear non-height loudspeakers have been described. Additionally, the present disclosure relates to an apparatus for performing these methods. Additionally, the present disclosure relates to a vehicle that may comprise an apparatus for performing these methods. An example of such an apparatus 1440 is shown diagrammatically in FIG. 12. The apparatus 1440 may comprise a processor 1410 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), one or more application specific integrated circuits (ASICs), one or more radio frequency integrated circuits (RFICs), or any combination thereof) and a memory 1420 coupled to the processor 1410. The memory 1420 may store, for example, an analytical function (or a set thereof) representing one or more parameters that identify a filter transfer function of a virtual height filter for different listening positions and / or roof elevations and / or different vehicles, or a look-up table (or a set thereof). The processor may be configured to perform some or all of the steps of the methods described throughout this disclosure, for example, by retrieving a set of analysis functions and / or LTUs from the memory 1420. To perform the method of generating multiple audio channels, the device 1440 may receive as input channels of (e.g., rendered) audio in an immersive audio format, such as a height channel and one or more front or surround audio channels 1425. In this case, the device 1440 may output two or more channel signals 1430 for playback of the channel signals in an immersive loudspeaker system.

[0089] The device 1440 may be a server computer, a client computer, a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a cell phone, a smart phone, a web appliance, a network router, a switch or bridge, or any machine capable of executing instructions (sequential or otherwise) that specify actions to be taken by the device. Additionally, although only a single device 1440 is shown in Figure 12, the present disclosure relates to any collection of devices that individually or jointly execute instructions to perform any one or more of the methodologies described herein.

[0090] The present disclosure further relates to a program (e.g., a computer program) comprising instructions that, when executed by a processor, cause the processor to perform some or all of the steps of the methods described herein.

[0091] The present disclosure also relates to a computer-readable (or machine-readable) storage medium having the above program recorded thereon, where the term "computer-readable storage medium" includes, but is not limited to, data repositories in the form of solid-state memories, optical media, and magnetic media, for example.

[0092] The embodiments described herein may be implemented in hardware, software, firmware, and combinations thereof. For example, the embodiments may be implemented on a system having electronic circuits and components, such as a computer system. Examples of computer systems include desktop computer systems, portable computer systems (e.g., laptops), handheld devices (e.g., smartphones or tablets), and networking devices. A system for implementing the embodiments may comprise, for example, at least one of an integrated circuit (IC), a programmable logic device (PLD), such as a field programmable gate array (FPGA), a digital signal processor (DSP), an application specific IC (ASIC), a central processing unit (CPU), and a graphics processing unit (GPU).

[0093] Certain implementations of the embodiments described herein may include a computer program product including instructions that, when executed by a data processing system, cause the data processing system to perform any of the methods of the embodiments described herein. The computer program product may include a physical medium, such as a non-transitory medium that stores the instructions, e.g., magnetic data storage media including floppy disks and hard disk drives, optical data storage media including CD-ROMs and DVDs, and electronic data storage media including ROMs, flash memories, e.g., flash RAMs or USB flash drives. In another example, the computer program product includes a data stream including the instructions, or a file including the instructions stored in a distributed computing system, e.g., one or more data centers.

[0094] The present disclosure is not limited to the above-described embodiments and examples. Numerous modifications and variations can be made without departing from the scope of the present disclosure, which is defined by the appended claims.

[0095] Various aspects of the present invention can be understood from the following enumerated example embodiments (A-EEE and B-EEE).

[0096] A method for generating discrete channels from an immersive bitstream, comprising: identifying one or more elevation channels and one or more non-elevation channels of the immersive bitstream; processing the one or more height channels using a virtual height filter and a non-standard blending technique; and mixing the processed one or more elevation channels with the one or more non-elevation channels. method.

[0097] B-EEE1. A method (1000) for generating at least two audio channels from audio in an immersive audio format including at least one height audio channel (1010) and at least two non-height audio channels (1050, 1100), for playing said at least two audio channels on a non-immersive loudspeaker system of at least two audio loudspeakers (1, 2) in a vehicle, the method comprising: at least partially attenuating spectral components of the at least one height channel (1010) that emanate directly from the loudspeakers (1, 2) when the at least one audio height channel is reproduced by one of the at least two loudspeakers and at least partially amplifying spectral components of the at least one height channel that are reflected from a roof or a roof-proximate area within the vehicle to generate at least one virtual height filtered audio signal (1175); mixing (1700) the at least one virtual height filtered audio signal (1175) with at least one of the two non-height audio channels to generate the at least two audio channels (1008, 1016), method. B-EEE2. The method (1000) according to B-EEE1, wherein the audio in the immersive audio format further comprises at least two further non-height audio channels (1125, 1150), and the virtual height filtered audio signal (1175) is mixed with each of the non-height audio channels (1050, 1100, 1125, 1150) to generate four audio channels (1008, 1016, 1032, 1064). B-EEE3. A method according to any one of B-EEE1 to 3, wherein the audio in the immersive audio format comprises at least two height audio channels (1010, 1020), and the virtual height filter (1300, 1400) is applied to each of the at least two height audio channels (1010, 1020) to generate at least two virtual height filtered audio signals (1175, 1200), each of the virtual height filtered audio signals (1175, 1200) being mixed with one of the at least two non-height channels (1100, 1050). B-EEE4. 4. The method of claim 1, wherein the audio in the immersive audio format comprises four height audio channels (1010, 1020, 1030, 1040) and four non-height audio channels (1050, 1100, 1125, 1150), and wherein the virtual height filters (1300, 1400, 2500, 2600) are applied to each of the four height audio channels (1010, 1020, 1030, 1040) to generate four virtual height filtered audio signals (1175, 1200, 1225, 1250), each of the virtual height filtered audio signals (1175, 1200, 1225, 1250) being mixed with one of the four non-height channels (1100, 1050, 1125, 1150). B-EEE5. A method according to any one of B-EEE1 to 4, wherein the non-immersive loudspeaker system is a stereo or surround loudspeaker system. B-EEE6. A method according to any one of B-EEE1 to B-EEE5, wherein the virtual height filter has a filter transfer function, the method further comprising determining the filter transfer function of the virtual height filter from one or more parameters identifying the filter transfer function. B-EEE7. A method according to any one of B-EEE1 to 6, wherein the virtual height filter has a filter transfer function having a peak at a first frequency and a notch at a second frequency higher than the first frequency. B-EEE8. The method of B-EEE 6 and 7, wherein said one or more parameters indicate a value of at least one of a peak, a first frequency, a notch and a second frequency of said filter transfer function. B-EEE 9. The method of any one of B-EEE1 to 8, wherein the at least two audio loudspeakers (1, 2) are spaced laterally relative to a listening position. B-EEE 10. The method of B-EEE9, further comprising determining (1800) a filter transfer function for the virtual height filter based on the relative distances of the at least two loudspeakers from a listening position and the elevation of a roof or near-roof area relative to the listening position. B-EEE 11. A method according to B-EEE 9, comprising: obtaining (1900) a plurality of filter transfer functions for a plurality of virtual height filters based on a range of relative distances of the at least two loudspeakers from a listening position and a range of elevations of the roof or an area proximate to the roof relative to the listening position; and selecting (2000) a filter transfer function from the plurality of filter transfer functions. method. B-EEE 12. The method of claim 11, wherein the selected filter transfer function is an average of the plurality of filter transfer functions. B-EEE 13. A method according to claim 11, when dependent on any one of claims 6 to 8, wherein selecting one filter transfer function from the plurality of filter transfer functions comprises selecting one or more parameters identifying the selected filter transfer function based on an average distance of the at least two loudspeakers from a listening position and based on an average elevation of the roof or an area close to the roof relative to the listening position. B-EEE 14. A method according to any one of B-EEE11 to 13, wherein the obtaining (1900), selecting (2000), applying (1500) and mixing (1700) steps are applied iteratively for each selected filter transfer function until the filter transfer function provides a reproduction of the at least two channels with the maximum perception of the sonic sophistication. B-EEE 15. A method according to any one of claims 6 to 14, further comprising storing said one or more parameters in a processor as a look-up table or as an analytical function. B-EEE 16. A method according to any one of B-EEE1 to 15, further comprising applying a gain to the virtual height filter. B-EEE 17. The method of B-EEE 16, wherein said gain is user configurable. B-EEE 18. A method according to any one of B-EEE1 to 17, wherein the immersive audio format audio is audio rendered in the immersive audio format, and / or the immersive audio format is Dolby Atmos, or any XYZ audio format, where X≧2 is the number of front or surround audio channels, Y≧0 is a low frequency effects or subwoofer audio channel, if present, and Z≧1 is the at least one height audio channel. B-EEE 19. Apparatus configured to carry out the methods described in any one of B-EEE 1 to 18. B-EEE 20. A vehicle including a loudspeaker system of at least two audio loudspeakers (1, 2), further comprising the apparatus of B-EEE 19. B-EEE 21. A program comprising instructions which, when executed by a processor, cause the processor to carry out a method according to any one of B-EEE 1 to 18. B-EEE 22. A computer-readable storage medium storing the program described in B-EEE 21.

Claims

1. 1. A method of generating multiple audio channels from audio in an immersive audio format including multiple front and rear height audio channels and multiple front and rear non-height audio channels for reproduction of the multiple audio channels in a listening environment using an immersive loudspeaker system including at least one height loudspeaker and a plurality of front and rear non-height loudspeakers, the method comprising: - applying a virtual height filter to a portion of each front and rear height audio channel of the plurality of front and rear height audio channels to at least partially attenuate spectral components of the one height audio channel that emanate directly from a non-height loudspeaker when the one of the front and rear height audio channels is reproduced by a corresponding loudspeaker of the plurality of front and rear non-height loudspeakers, and to at least partially amplify spectral components of the one height audio channel that are reflected from a roof or a roof-proximate area in the listening environment to generate a plurality of front and rear virtual height filtered audio signals; adding each front and rear virtual height filtered audio signal of the plurality of front and rear virtual height filtered audio signals to a corresponding front and rear non-height audio channel of the plurality of front and rear non-height audio channels to generate a summed audio signal for playback by a corresponding front and rear non-height loudspeaker; and reproducing, with the at least one height loudspeaker, a remaining portion of each front and rear height audio channel of the plurality of front and rear height channels. method.

2. 2. The method of claim 1, wherein the portion of each front and rear height audio channel of the plurality of front and rear height channels is a function of one or more of: a position of the at least one height loudspeaker along a length of the listening environment, or a desired balance distribution of the plurality of front and rear height audio channels among loudspeakers of the immersive loudspeaker system.

3. 3. The method of claim 2, wherein the portions of each front and rear height audio channel are a linear or non-linear function of a position of the at least one height loudspeaker along a length of the listening environment.

4. 2. The method of claim 1 , wherein applying the virtual height filter to a portion of each front and rear height audio channel of the plurality of front and rear height audio channels comprises applying the virtual height filter to a portion of the front height audio channel proportional to a position of the at least one height loudspeaker away from a front and toward a rear of the listening environment.

5. 2. The method of claim 1 , wherein applying the virtual height filter to a portion of each front and rear height audio channel of the plurality of front and rear height audio channels comprises applying the virtual height filter to a portion of the rear height audio channel proportional to a position of the at least one height loudspeaker away from a rear and towards a front of the listening environment.

6. 2. The method of claim 1 , wherein reproducing a remaining portion of each front and rear height audio channel of the plurality of front and rear height audio channels with the at least one height loudspeaker comprises reproducing a remaining portion of each front height audio channel proportional to a position of the at least one height loudspeaker away from a rear and toward a front of the listening environment.

7. 2. The method of claim 1 , wherein reproducing a remaining portion of each front and rear height audio channel of the plurality of front and rear height audio channels with the at least one height loudspeaker comprises reproducing a remaining portion of each rear height audio channel proportional to a position of the at least one height loudspeaker away from a front and toward a rear of the listening environment.

8. 2. The method of claim 1, wherein the audio in the immersive audio format further includes front right and front left non-height audio channels, rear right and rear left non-height audio channels, upper front right and upper front left height audio channels, and upper rear right and upper rear left height audio channels, and wherein the front virtual height filtered audio signals are added to corresponding front right and front left non-height audio channels and the rear virtual height filtered audio signals are added to corresponding rear right and rear left non-height audio channels to generate four summed audio signals for playback by corresponding front right and front left, and rear right and rear left non-height loudspeakers.

9. The method of claim 1 , wherein the immersive loudspeaker system includes a single upper loudspeaker.

10. the immersive loudspeaker system includes a single upper loudspeaker; 9. The method of claim 8, wherein the remaining portions of the top front right elevation audio channel, top rear right elevation audio channel, top front left elevation audio channel, and top rear left elevation audio channel are summed together and played by the single top loudspeaker.

11. The method of claim 1 , wherein the immersive loudspeaker system includes an upper right elevation loudspeaker and an upper left elevation loudspeaker.

12. 9. The method of claim 8, wherein remaining portions of the upper front right and upper rear right elevation audio channels are summed together and played by an upper right elevation loudspeaker, and the remaining portions of the upper front left and upper rear left elevation audio channels are summed together and played by an upper left elevation loudspeaker.

13. The method of claim 1 , wherein the virtual height filter has a filter transfer function, the method further comprising determining the filter transfer function of the virtual height filter from one or more parameters identifying the filter transfer function.

14. The method of claim 1 , wherein the virtual height filter has a filter transfer function having a peak at a first frequency and a notch at a second frequency higher than the first frequency.

15. The method of claim 13 , wherein the one or more parameters indicate a value of at least one of a peak, a first frequency, a notch, and a second frequency of the filter transfer function.

16. 2. The method of claim 1 , wherein the at least two of the front and / or rear non-height loudspeakers are spaced laterally with respect to a listening position, the method further comprising determining a filter transfer function for the virtual height filter based on a relative distance of the at least two loudspeakers from the listening position and an elevation of a roof or near-roof area with respect to the listening position.

17. At least two of the front and rear non-height loudspeakers are spaced laterally relative to a listening position, and the method includes: obtaining a plurality of filter transfer functions for a plurality of virtual height filters based on a range of relative distances of the two loudspeakers from the listening position and a range of elevations of a roof or near-roof area relative to the listening position; selecting a filter transfer function from the plurality of filter transfer functions. The method of claim 1.

18. 20. The method of claim 17, the selected filter transfer function is an average of said plurality of filter transfer functions; or selecting a filter transfer function from the plurality of filter transfer functions includes selecting one or more parameters that identify a selected filter transfer function based on an average distance of the two loudspeakers from the listening position and based on an average elevation of a roof or near-roof area relative to the listening position. method.

19. 20. The method of claim 17, wherein the obtaining, selecting, applying, adding, and reproducing steps are applied iteratively for each selected filter transfer function until the filter transfer function provides a maximum perception of sonic sonic sonicity for the reproduction of the generated multiple audio channels.

20. The method of claim 13 , further comprising storing the one or more parameters in a processor as a look-up table or as an analytical function.

21. The method of claim 1 , further comprising applying a gain or a user configurable gain to the virtual height filter.

22. 2. The method of claim 1 , wherein the immersive audio format audio is audio rendered in the immersive audio format, and / or the immersive audio format is Dolby Atmos, or any XYZ audio format, where X≧2 is a number of front or surround audio channels, Y≧0 is a low-frequency effects or subwoofer audio channel, if present, and Z>1 is the plurality of front and rear height audio channels.

23. The method of claim 1 , wherein the listening environment is a vehicle.

24. Apparatus configured to carry out the method of any one of claims 1 to 23.

25. 25. A vehicle including an immersive loudspeaker system comprising at least one elevation loudspeaker and a plurality of front and rear non-elevation loudspeakers, the vehicle further comprising the apparatus of claim 24.

26. A program comprising instructions which, when executed by a processor, cause the processor to carry out a method according to any one of claims 1 to 23.

27. A computer-readable storage medium storing the program according to claim 26.

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