Audio processing method for immersive audio playback - Patents.com

Abstract

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) and reproducing the at least two audio channels using a non-immersive speaker system of at least two audio speakers (1, 2) in a vehicle, comprising: applying (1500) a virtual height filter (1300) to the height channel (1010) such that, when the height channel is reproduced by one of the speakers, a virtual height filtered audio signal (1175) is generated by attenuating spectral components of the height channel that emanate directly from the speakers (1; 2) and amplifying spectral components of the height channel that are reflected from a roof or an area close to the roof of the vehicle, and mixing (1700) the virtual height filtered audio signal with at least one of the two non-height audio channels.

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 (Reference No. D21147AUSP1), U.S. Provisional Application No. 63 / 353,778, filed on June 20, 2022 (Reference No. D21147AUSP2), and EP Application No. EP22179943.0, filed on June 20, 2022 (Reference No. D21147AEP).

[0002] 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 audio in an immersive audio format and reproducing the at least two audio channels using a (non-immersive) speaker system. The present disclosure further relates to an apparatus comprising a processor configured to perform the method, a vehicle comprising the apparatus, a program and a computer readable storage medium. [Background technology]

[0003] Vehicles are typically equipped with a speaker system for audio playback. The speaker system in a vehicle may be used to play audio, for example, from tapes, CDs, audio streaming services, or applications running on the vehicle's in-car entertainment system or remotely via a device connected to the vehicle. The device may be, for example, a portable device connected wirelessly or by cable to the vehicle. For example, streaming services such as Spotify and Tidal have recently been integrated directly into the vehicle's hardware (usually known as the "head unit") or into the in-car entertainment system via a smartphone using Bluetooth, Apple CarPlay, or Android Auto. The vehicle's speaker system may also be used to play terrestrial radio and / or satellite radio. A conventional vehicle speaker system is a stereo speaker system. A stereo speaker system may include a total of four speakers, a front pair of speakers and a rear pair of speakers for the front and rear passengers, respectively. However, more recently, with the introduction of DVD players in vehicles, surround speaker systems supporting the playback of DVD audio formats have been introduced in vehicles. FIG. 1 shows an interior view of a vehicle 100. The vehicle 100 has a surround speaker system including speakers 10, 11, 30, 31, 41, 42 and 43. The speakers are shown only for the left side of the vehicle 100. Corresponding speakers may be symmetrically placed on the right side of the vehicle 100. In particular, the surround speaker system of FIG. 1 includes a pair of tweeter speakers 41, 42 and 43, a pair of full-range front speakers 30 and rear speakers 31, a center speaker 10, and a Low Frequency Effects speaker or subwoofer 11. The tweeter speaker 41 is located near the dashboard of the vehicle. The tweeter speaker 42 is mounted low on the front side pillar of the vehicle 100.However, the tweeter speakers 41, 42, 43 as well as the full-range front and rear speakers 30, 31 may be positioned in any location suitable for a particular implementation.

[0004] Immersive audio is becoming mainstream in cinemas and home listening environments. Now that immersive audio is becoming mainstream in cinemas and homes, it is natural to think that immersive audio will also be played in cars. Dolby Atmos Music is already available on various streaming services. Immersive audio is often distinguished from surround audio formats by including overhead or height audio channels. Therefore, overhead or height loudspeakers are used to play immersive audio. Although luxury cars may be equipped with such overhead or height speakers, most conventional vehicles use stereo speaker systems or more advanced surround speaker systems as shown in Figure 1. In fact, height speakers dramatically increase the complexity of the vehicle's speaker system. Height speakers must be installed on the roof of the vehicle, which is usually not suitable for this purpose. For example, vehicles usually have low roofs, which limits the height at which height speakers can be installed. In addition, vehicles are often sold with the option of installing a sunroof (a window on the roof of the vehicle that opens), and installing height speakers on the roof is difficult from an industrial design perspective. Also, such height speakers may require additional audio cabling. For these reasons, integrating height speakers into a vehicle can be costly due to space and industrial design constraints. Summary of the Invention

[0005] It may be advantageous to play immersive audio content over a non-immersive speaker system, such as a stereo speaker system or a surround speaker system. In the context of this disclosure, a "non-immersive speaker system" is a speaker / speaker system that comprises at least two speakers but does not (or does not have) overhead speakers, i.e. does not have height speakers.

[0006] It would be advantageous to create the perception of height by playing immersive audio content over a non-immersive speaker system such that the user's audio experience is enhanced without the use of overhead speakers.

[0007] One aspect of the disclosure provides a method for generating at least two audio channels from audio in an immersive audio format including at least one height audio channel and at least two non-height audio channels, and reproducing the at least two audio channels using a non-immersive speaker system of at least two audio speakers in a vehicle (or any listening environment). The method includes applying a virtual height filter to at least one height channel. The virtual height filter is configured to at least partially attenuate spectral components of the at least one height channel that emanate directly from the speaker through which the height channel is reproduced when the at least one audio height channel is reproduced by one of the at least two speakers. The virtual height filter is also configured to at least partially amplify spectral components of the at least one height channel that are reflected from a roof or an area proximate to the roof of the vehicle to generate at least one virtual height filtered audio signal. The method further includes generating the at least two audio channels by mixing the at least one virtual height filtered audio signal with at least one of the two non-height audio channels.

[0008] In the context of this disclosure, the term "channel" refers to an audio signal, optionally with metadata whose location is encoded as a channel identifier (e.g., left front or right top surround). "Channel-based audio" refers to audio formatted for playback through a predefined set of speaker zones (e.g., 5.1, 7.1, etc.), which have associated nominal locations. 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.

[0009] When the height channel is reproduced from one of the at least two speakers without filtering, the sounds may radiate along different paths. Some sounds may radiate along a direct path from the speaker to the listening position (e.g., the passenger's or driver's ear), while other sounds may radiate along a reflected path from the speaker to the listening position. For example, some sounds may be reflected from the roof or a region close to the roof in the vehicle and thus radiate from the roof or a region close to the roof to the listening position. When the height channel is reproduced, the sounds radiated along the direct path are undesirable. By applying a virtual height filter to the at least one height channel, the spectral components of the height channel that are reflected from the roof or a region close to the roof are amplified and the spectral components of the height channel that are emitted directly to the speaker are attenuated. The method configured as above compensates for the undesirable direct sounds and improves the localization and perceptual quality of the virtual height signal by introducing perceptual height cues into the audio signal that is fed to one of the at least two speakers. For example, directional hearing models have been developed to create virtual height filters, which, when used to process audio being played through at least two speakers, improve the perceived quality of the playback.

[0010] In some embodiments, the audio in the immersive audio format may further include at least two additional non-height audio channels, and the virtual height filtered audio signal may be mixed with each one of the non-height audio channels to generate four audio channels.

[0011] In some embodiments, the audio in the immersive audio format may include at least two height audio channels, and the virtual height filter may be applied to each one of the at least two height audio channels to generate at least two virtual height filtered audio signals, each one of the virtual height filtered audio signals may be mixed with one of the at least two non-height channels.

[0012] In some embodiments, the audio in the immersive audio format may include four height audio channels and four non-height audio channels. The virtual height filter may be applied to each one of the four height audio channels to generate four virtual height filtered audio signals. Each one of the virtual height filtered audio signals may be mixed with one of the four non-height channels.

[0013] In some embodiments, the virtual height filter may have a filter transfer function, and the method may further include determining the filter transfer function of the virtual height filter from one or more parameters identifying the filter transfer function.

[0014] In an embodiment, the method may further include storing the one or more parameters in a processor as a look-up table or an analytical function.

[0015] In one embodiment, the virtual height filter may have a filter transfer function having a peak at a first frequency and a notch at a second frequency higher than the first frequency.

[0016] In some embodiments, the at least two audio speakers are laterally spaced apart relative to a listening position, and 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 speakers from the listening position and an elevation of the roof or an area near the roof relative to the listening position.

[0017] In some embodiments, the at least two audio speakers are laterally spaced apart from a listening position, and 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 at least two speakers from the listening position and a range of elevations of the roof or an area near the roof relative to the listening position, and selecting a filter transfer function from the plurality of filter transfer functions.

[0018] In one embodiment, the selected filter transfer function may be an average of the multiple filter transfer functions.

[0019] In one embodiment, selecting a filter transfer function from the plurality of filter transfer functions may include selecting one or more parameters identifying the selected filter transfer function based on an average distance of the at least two speakers from the listening position and an average elevation of the roof or an area near the roof relative to the listening position.

[0020] In one embodiment, the obtaining, selecting, applying and mixing method may be applied iteratively to each selected filter transfer function until the filter transfer function provides a reproduction of the at least two channels that maximizes the perception of sonic height.

[0021] In some embodiments, the method may further include applying a gain to the virtual height filter. In some embodiments, the gain may be user configurable. 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 this disclosure.

[0022] Another aspect of the present disclosure provides a vehicle equipped with such an apparatus.

[0023] Another aspect of the present disclosure further provides a program comprising instructions which, when executed by a processor, cause said processor to perform an audio processing method, and a computer-readable storage medium having stored thereon such a program. [Brief description of the drawings]

[0024] Embodiments of the present disclosure are illustrated by way of example, and not by way of limitation, in the accompanying figures, in which like reference symbols refer to similar elements and in which: [Figure 1] FIG. 1 shows a schematic diagram of an interior view of a vehicle with a speaker system arranged according to one embodiment of the present disclosure. [Diagram 2] FIG. 2 is a flow chart illustrating an example method for generating at least two audio channels from audio in an immersive audio format according to one embodiment of the present disclosure. [Figure 2A] FIG. 2A illustrates a schematic diagram of an example of a method for generating at least two audio channels from audio in an immersive audio format according to an embodiment of the present disclosure. [Diagram 3] FIG. 3 shows a schematic diagram of a vehicle. [Figure 4] FIG. 4 shows a schematic top view of a vehicle with a speaker system arranged according to one embodiment of the present disclosure. [Diagram 5] FIG. 5 shows a schematic example of sound paths in a vehicle. [Figure 6] FIG. 6 illustrates several examples of virtual height filters according to some embodiments of the present disclosure. [Figure 7] FIG. 7 illustrates a schematic diagram of an example of a method for generating four audio channels from audio in an immersive audio format according to an embodiment of the present disclosure. [Figure 8] FIG. 8 illustrates a schematic diagram of an example of a method for generating two audio channels from audio in an immersive audio format according to an embodiment of the present disclosure. [Figure 9] FIG. 9 illustrates a schematic diagram of an example of a method for generating four audio channels from audio in an immersive audio format according to an embodiment of the present disclosure. [Figure 10] FIG. 10 illustrates a schematic diagram of an example of a method for generating six audio channels from audio in an immersive audio format according to an embodiment of the present disclosure. [Figure 10A] FIG. 10A illustrates a schematic diagram of an example of a method for generating eight audio channels from audio in an immersive audio format according to one embodiment of the present disclosure. [Figure 11] FIG. 11 is a schematic diagram illustrating an example of an apparatus for carrying out a method according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Numerous specific details are described below to provide a thorough understanding of the present disclosure. However, the present disclosure may be practiced without these specific details. Also, well-known parts may be described without exhaustive details. The figures are schematic and include parts relevant to understanding the present disclosure, while other parts may be omitted or merely suggested.

[0026] FIG. 2 is a flow chart illustrating an example of a method 1000 for generating at least two audio channels from audio in an immersive audio format according to an embodiment of the present disclosure. The audio in the immersive audio format comprises at least one height channel and at least two non-height channels. The method 1000 may be used to play the generated at least two audio channels on a non-immersive speaker system of at least two audio speakers in a vehicle. The vehicle may be any type of passenger or non-passenger vehicle used for commercial purposes or for transporting cargo, for example. The examples provided in the present disclosure assume that the playback of the generated at least two audio channels is performed in the vehicle. However, the generated at least two audio channels may be played in any other type of listening environment suitable for a particular implementation, for example, a closed or partially closed listening environment (e.g., a room).

[0027] As an example, referring to FIG. 3, a vehicle 3000 (in this example, a four-seater car) is depicted in a schematic manner. For simplicity, the arrangement of speakers is not shown in FIG. 3, but is shown in the more detailed interior view of the vehicle 100 in FIG. 1. The car 3000 has four seats 3110, 3120, 3130 and 3140. Considering the speaker system shown in FIG. 1, for speakers 30, 31, 41, 42, 43, corresponding speakers (not shown) would be placed on the right side of the vehicle 3000. Referring to FIG. 3, the speaker groups on the left side of the vehicle 3000 and the respective corresponding speaker groups on the right side of the vehicle 3000 are placed in a reflection symmetrical manner with respect to a central axis 3150 that crosses the center of the vehicle 3000 along its length. It is understood that each of the seats 3110, 3120, 3130 and 3140, and therefore potential listeners located therein, may be off-center with respect to any pair of speakers consisting of speakers 30, 31, 41, 42, 43 (not shown in FIG. 3) and their respective corresponding speakers on the right side of the vehicle (also not shown in FIG. 3). For example, a driver sitting in the driver's seat 3110 will be off-center with respect to speakers 30, 41, 42 and the corresponding right side speaker (not shown). The driver will be closer to speakers 30, 41 and 42 than the corresponding speaker on the right side of the vehicle 3000. In FIG. 1 and FIG. 3, the driver's seat is shown on the left side of the vehicle 3000 (left side with respect to the driving direction forward). However, it is understood that the location of the driver's seat in a vehicle may vary from region to region. For example, in the UK, Australia or Japan, the driver's seat is located on the right side of the vehicle with respect to the driving direction forward of the vehicle.

[0028] The non-immersive speaker system may for example be a stereo speaker system or a surround speaker system as illustrated with reference to FIG.

[0029] In some embodiments, the audio in an immersive audio format may be audio rendered in an immersive audio format.

[0030] The immersive audio format of the (e.g., rendered) audio may include at least one height channel. In an embodiment, the immersive audio format may be an object-based audio format that supports elevation, such as the Dolby Atmos format. In another embodiment, the immersive audio format may be a channel-based audio format that supports elevation, such as the XYZ audio format, where X≧2 is the number of front or surround audio channels, Y≧0 is a low-frequency effect or subwoofer audio channel, if present, and Z≧1 is at least one height 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 speaker feeds corresponding to the channels of the channel-based audio format. The speaker system shown in Figure 1 is a typical 5.1 speaker system for playing 5.1 audio, with five front or surround speakers, two left audio speakers (e.g., left and left surround), two right audio speakers (e.g., right and right surround), a center speaker, and one LFE speaker. The two left audio speakers correspond to speakers 30, 31 (for mid-range or full-range frequencies), 41, 42 and 43 (for high-range frequencies). The center speaker corresponds to speaker 10. The LFE speaker corresponds to speaker 11.

[0031] For example, referring to FIG. 4, a top view of another exemplary vehicle 4000 is shown. The vehicle 4000 may be a 6-seater or 7-seater vehicle distributed in three different rows. The vehicle 4000 may be, for example, a Sport Utility Vehicle (SUV) or a minibus. The vehicle 4000 has six seats 4110, 4120, 4130, 4140, 4150 and 4160. A typical 7.1 speaker system may be implemented in the vehicle 4000. The speaker system shown in FIG. 4 has three left speakers 4210, 4230 and 4250 (e.g., left and two left surrounds) and three right speakers 4220, 4240 and 4260 (e.g., right and two right surrounds), a center speaker 4270, and an LFE speaker 4280.

[0032] The method diagrammatically shown in FIG. 2 will now be described with reference to FIG. 2A as well.

[0033] Referring to FIG. 2A, the audio in the immersive audio format may include non-height channels 1050 and 1100 (e.g., left and right channels) and a height channel 1010 (single in this example). The speaker system in the example of FIG. 2A is a stereo speaker system with speakers 1 and 2. In this example, speakers 1 and 2 are used to play the audio in the immersive audio format on channels 1050, 1100 and 1010. The method 1000 generates two channels 1008 and 1016 from the audio in the immersive audio format, as described below. Since the two channels 1008 and 1016 are generated from the three channels of the immersive audio format, it can be said that the three channels of the immersive audio format are downmixed to two channels for playback.

[0034] 2 and 2A, the method 1000 includes applying 1500 a virtual height filter 1300 to the height channel 1010. The virtual height filter 1300 is configured to at least partially attenuate spectral components of the height channel 1010 that emanate directly from one of the speakers 1 or 2 when the height channel 1010 is reproduced by one of such speakers 1 or 2. The virtual height filter 1300 is further configured to at least partially amplify spectral components of the height channel 1010 that are reflected from a roof or a region near the roof of the vehicle to generate a virtual height filtered audio signal 1175. The method 1000 further includes mixing 1700 the virtual height filtered audio signal 1175 with the non-height audio channels 1050 and 1100 to generate two audio channels 1008 and 1016 for reproduction by the speakers 1 and 2. 2A shows the virtual height filtered audio signal 1175 being mixed with both non-height channels 1050 and 1100. However, the virtual height filtered audio signal 1175 may be mixed with only one of the non-height channels 1050 and 1100. Mixing the virtual height filtered audio signal 1175 with only one of the non-height channels 1050 or 1100 to generate two channels for playback is sufficient to create a perception of height or elevation without the use of height / overhead speakers.

[0035] For further explanation, reference is made to FIG. 5. FIG. 5 shows, in a schematic manner, example paths 5300 and 5400 along which sound reproduced by a speaker 5000 travels from the speaker 5000 to a listening position 5100 in a vehicle. The speaker 5000 may be any of the speakers shown with reference to the speaker systems of, for example, FIG. 1 and FIG. 4. In particular, the speaker 5000 may be any of the left, right or surround speakers shown. Preferably, the speaker 5000 may be any high frequency speaker associated with either the left, right or surround speakers, such as, for example, the speakers (e.g. tweeters) 41, 42 and 43 shown in FIG. 1, since height cues are typically more prevalent in high frequency signals rather than in low frequency signals. The listening position 5100 may be the ear / head of a passenger or driver of the vehicle. The sound reproduced by the loudspeaker 5000 may be radiated along a reflected path 5300, shown in dashed lines in FIG. 5, and a direct path 5400, shown in solid lines in FIG. 5. The reflected path 5300 is an indirect path from the loudspeaker 5000 to the listening position 5100, formed by the sound being reflected from a surface 5500 located above the listening position 5100. In a vehicle, the surface 5500 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, or the upper inner part of a side window of the vehicle. In general, the surface 5500 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. To enhance the perception of the elevation of the sound, it is desirable for the sound to be radiated along the reflected path 5300. However, some of the sound from the speaker 5000 will travel along the direct path 5400, reducing the perception of sound coming from the location on the surface 5500 where the sound is reflected towards the listening position 5100. The amount of this undesirable direct sound compared to the desired reflected sound may be a function of the directional pattern of the speaker 5000. It has been found that a speaker positioned about halfway through the overall height of the interior of the vehicle (e.g., at about door mid-height) improves the perception of sound elevation.

[0036] It has been shown that incorporating signal processing to introduce perceptual height cues into the audio signal fed to the loudspeaker 5000 to compensate for undesired direct sounds improves the localization and perceived quality of the virtual height signal. For example, a directional hearing model has been developed to create a virtual height filter, which when used to process the audio being reproduced by the loudspeaker improves the perceived quality of the reproduction. In one embodiment, the virtual height filter is derived from both the physical speaker position relative to the listening position and the virtual speaker position (above the listening position). For the physical speaker position, a first directional filter is determined based on a model of the sound traveling directly from the speaker position to the ears of the listener at the listening position. Such a filter can be derived from a model of directional hearing, such as a database of HRTF (head related transfer function) measurements, a parametric binaural 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. The pinna model is one example of such a model of binaural hearing models that can be used, although other models can also be used.

[0037] The inverse of this filter is then determined and used to remove directional cues for audio traveling in a direct path from the physical speaker position to the listening position. A second directional filter is then determined for the virtual speaker position using the same model of directional hearing based on a model of sound traveling directly from the virtual speaker position to the ear of a listener at the same listening position. This filter is applied directly and gives the directional cues that the ear would receive if the sound emanated from the virtual speaker position above the listening position. In practice, the first and second directional filters may be combined to allow for a single filter that at least partially removes (attenuates) directional cues from the physical speaker positions and at least partially inserts (amplifies) directional cues from the virtual speaker positions. Such a single filter provides a frequency response curve that is referred to herein as a "height filter transfer function," "virtual height filter response curve," "desired frequency transfer function," "height cue response curve," or other terms that refer to a filter or filter response curve that filters (e.g., attenuates) direct sound components from height sound components in an audio speaker system.

[0038] With respect to the filter model, if P1 represents the frequency response in dB of the first filter that models the sound transmission from the physical speaker location, and P2 represents the frequency response in dB of the second filter that models the sound transmission from the virtual speaker 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 maximum, 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 direct sound increases compared to the reflected sound, α should also be higher to more fully impart the directional cues of the virtual speaker location to this undesirable direct sound path. However, α should not be so large as to impair the perceived timbre of the audio traveling down the reflected path, which already contains the appropriate directional cues. In general, the exact values ​​of the filters P1 and P2 will be a function of the azimuth of the physical speaker location relative to the listening position and the altitude of the reflected speaker location, which is in turn a function of the distance of the physical speaker location from the listening position and the difference between the height of the roof or near-roof area (surface 5500 in FIG. 5) and the height of the speaker.

[0039] 6 illustrates example curves 6200, 6300, and 6400 of a virtual height filter according to some embodiments of the present disclosure. Curves 6200, 6300, and 6400 are illustrated in a diagram showing the amplitude of the virtual height filter in decibels (dB) on the vertical axis and the frequency in Hertz (Hz) on the horizontal axis.

[0040] Curves 6200, 6300 and 6400 represent the filter transfer functions of three different virtual height filters. FIG. 6 shows that the filter transfer functions 6200, 6300 and 6400 of the three different filters have a peak at a first frequency of about 8000 Hertz and a notch at a second frequency of about 12000 Hertz, higher than the first frequency. 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 one embodiment, the gain may be user configurable, allowing the user to adjust the "strength" of the virtual height filter according to the particular implementation.

[0041] 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 identifying the filter transfer function. For example, the one or more parameters may indicate at least one 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 from the memory by the processing device, from which the processing device may reconstruct the virtual height filter. The reconstructed virtual height filter may be used and applied to the height channel. Identifying the filter transfer function with the one or more parameters simplifies the processing of the height channel, since the virtual height filter is described by a small number of parameters instead of being generated locally.

[0042] In one embodiment, as shown with reference to FIG. 2, the method of the present disclosure may further include determining 1850 a filter transfer function of the virtual height filter based on the relative distances of the at least two speakers from the listening position and the elevation of the roof or near-roof area relative to the listening position.

[0043] For example, in one embodiment, one or more sensors may be located at or near the listening position to measure the relative distance of at least two speakers from the listening position and the elevation of the roof or an area near the roof relative to the listening position. For example, in one embodiment, such sensors may be embedded in the head restraint of each seat in the vehicle at approximately the same height as the listener's head. The measurements may be performed during an initial calibration stage of the method or may be performed substantially in real time as the audio is played.

[0044] 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 at least two speakers, 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 seats 3110, 3120, 3130, or 3140 in FIG. 3) and the pair of stereo speakers, and the elevation of the roof may be determined / predetermined by environmental characteristics, such as the interior design of the vehicle, and the speaker installation. 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 include 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 a fleet of vehicles of the same type. Such offline calibration has the advantage that the vehicle does not need to be equipped with sensors to measure and obtain the filter transfer function online.

[0045] Alternatively, additionally, or optionally, in the embodiment 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 at least two speakers from the listening position and a range of altitudes of the roof or roof-near area relative to the listening position. For example, a range of speaker-listening position(s) distances may be measured, for example, during a calibration phase, for a plurality of different listening positions and / or speaker positions. Similarly, a range of altitudes of the roof (or its virtual speaker positions) may be measured, for example, during a calibration phase, for a plurality of different listening positions. The method 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 an average distance of at least two speakers from the listening position and an average altitude of the roof or roof-near area (or virtual speaker positions) relative to the listening position. In another embodiment, the (filter transfer function of) the selected virtual height filter 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 iteratively applied to each selected filter transfer function at each iteration, for example during a calibration phase, until the selected filter transfer function optimally (e.g., maximizes) provides a perception of height of sound at one or more listening positions, as shown in FIG. 2 by the dashed line connecting steps 1700 and 1900. In other words, the method 1000 including steps 1900 and 2000 may be iteratively applied until the (selected) filter transfer function provides a reproduction of at least two channels that maximizes the perception of height of sound.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 most of the listening positions / speaker positions and heights of the roof or near-roof area (or altitudes of virtual speaker positions). However, the filter transfer function may also be adaptively determined substantially in real time, for example by a sensor as described above. Adaptively determining the filter transfer function may allow a more accurate determination and improve the perception of the sound altitude.

[0046] In one embodiment, referring to Figure 2, each filter transfer function of the multiple transfer functions obtained in step 1900 may be determined from one or more parameters stored in memory, for example as a LUT or analytical function, as described above. The method may dynamically / adaptively select the parameters of the filter transfer functions for a particular vehicle type if sensors are used.

[0047] In one embodiment, referring to FIG. 2, step 1800 of determining the filter transfer function of the virtual height filter from one or more parameters (based on predetermined distance / altitude information or based on actual measurements) may be triggered upon detection of a movement of a listener 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 be located, for example, 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, thereby enabling the processing method to use the correct distance information to obtain the filter transfer function.

[0048] In an embodiment, a new listening position, for example, a new position of the listener's head (or the listener's ear position), may be detected using one or more seat sensors or a different set of sensors. For example, the driver or passenger may adjust his / her seat horizontally and / or vertically for a more comfortable seating position in the vehicle. In this embodiment, the method may retrieve / obtain (a filter transfer function of) the virtual height filter according to the newly detected listening position. In this way, the correct information based on the correct set of predetermined listener-to-speaker distance information and predetermined roof altitude information (or based on actual measurements) may be used according to the new listening position. For example, when / when the predetermined 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.

[0049] As mentioned above, the immersive audio formats may be of different types as appropriate for a particular implementation.

[0050] For example, referring to FIG. 7, an immersive audio format of audio includes a single height channel 1010 and four non-height channels 1050, 1100, 1125, and 1150. The non-height channels 1050 and 1100 may be left (L) and right (R) channels, respectively. The non-height channels 1125 and 1150 may be left surround (L) and right surround (R) channels, respectively. S ) channel and right surround (R S ) channels. The non-height channels 1050 and 1100 can be front, middle or rear left and right channels, respectively. Similarly, the non-height channels 1125 and 1150 can be front, middle or rear left surround and right surround channels, respectively.

[0051] A virtual height filter 1300 is applied to the height channel 1010 to generate a virtual height filtered signal 1175. The virtual height filtered signal 1175 is mixed with each one of the non-height channels 1050, 1100, 1125 and 1150 to generate four channel signals 1008, 1016, 1032 and 1064. The channel signals 1008, 1016, 1032 and 1064 are fed to speakers 1, 2, 3 and 4 for playback. The use of a single virtual height filter (the filter transfer function of the filter) simplifies the conversion of audio in an immersive audio format into the channel feed signals 1008-1064 for speakers 1-4.

[0052] In another example, referring to FIG. 8, an immersive audio format of audio includes two height channels 1010 and 1020 and two non-height channels 1050 and 1100. For example, the height channels 1020 and 1010 may be top left (TL) and top right (TL) channels. The non-height channels 1050 and 1100 may be left (L) and right (R) channels, respectively. The channels 1020 and 1010 may be top front left, top middle / center left, or top rear left and right channels, respectively. Similarly, the channels 1050 and 1100 may be front left, middle / center left, or rear left and right channels, respectively.

[0053] A virtual height filter 1300 is applied to the height channel 1010 to generate a virtual height filtered signal 1175. A virtual height filter 1400 is applied to the height channel 1020 to generate a virtual height filtered signal 1200. The virtual height filter 1300 may be the same as the virtual height filter 1400. Using a single height filter for all height channels simplifies the audio processing and requires less processing power. However, in some embodiments, the virtual height filter 1300 may be different from the virtual height filter 1400. For example, the virtual height filter 1300 may be optimized for the right channel. For example, the filter transfer function of the virtual height filter 1300 may be selected to maximize the perception of height of sounds in the right channel. Similarly, the virtual height filter 1400 may be optimized for the left channel. For example, the filter transfer function of the virtual height filter 1400 may be selected to maximize the perception of height of sounds in the left channel. In general, adapting the virtual height filters to the different channels improves the perception of the height of the sound at the listening position associated with each (left and right in this example) channel.

[0054] The virtual height filtered signal 1175 is mixed with the non-height channel 1100 to generate the channel signal 1017 which is fed to speaker 2. The virtual height filtered signal 1200 is mixed with the non-height channel 1050 to generate the channel signal 1009 which is fed to speaker 1. Thus, by playing channels 1009 and 1017 on speakers 1 and 2 respectively, the perception of height of the sound can be improved.

[0055] In another example, referring to FIG. 9, an immersive audio format of audio includes four non-height channels 1050, 1100, 1125, and 1150, and four height channels 1010, 1020, 1030, and 1040. The non-height channels 1050 and 1100 may be left (L) and right (R) channels, respectively. The non-height channels 1125 and 1150 may be left surround (L) and right surround (R) channels, respectively. S ) channel and right surround (R S ) channels. The non-height channels 1050 and 1100 may be front left, middle / center left, or rear left and right channels, respectively. Similarly, the non-height channels 1125 and 1150 may be front surround left, middle / center surround left, or rear surround left and right channels, respectively. The height channels 1020 and 1010 may be top front left (TFL) and top front right (TFR) channels. The height channels 1040 and 1030 may be top rear right (TRR) and top rear left (TRL) channels. A virtual height filter 1300 is applied to the height channel 1010 to generate a virtual height filtered signal 1175. A virtual height filter 1400 is applied to the height channel 1020 to generate a virtual height filtered signal 1200. A virtual height filter 2500 is applied to the height channel 1030 to generate a virtual height filtered signal 1225. A virtual height filter 2600 is applied to the height channel 1040 to generate a virtual height filtered signal 1250. The virtual height filters 1300, 1400, 2500, 2600 may be the same or different, as described with reference to the example of FIG.

[0056] The virtual height filtered signal 1175 is mixed with the non-height channel 1100 to generate the channel signal 1018 that is fed to speaker 2. The virtual height filtered signal 1200 is mixed with the non-height channel 1050 to generate the channel signal 1011 that is fed to speaker 1. The virtual height filtered signal 1225 is mixed with the non-height channel 1125 to generate the channel signal 1033 that is fed to speaker 3. The virtual height filtered signal 1250 is mixed with the non-height channel 1150 to generate the channel signal 1063 that is fed to speaker 4.

[0057] Therefore, by reproducing channels (channel signals) 1011, 1018, 1033 and 1063 on speakers 1 to 4, respectively, the perception of the height of the sound can be improved.

[0058] As explained in the examples of Figures 2A, 7 to 9, the number of channels used for playback is generally less than the number of channels of the immersive audio format. Therefore, it can be said that the channels of the immersive audio format are downmixed in the channels for playback.

[0059] Any other suitable immersive audio formats and / or speaker configurations may be envisioned as appropriate for a particular implementation.

[0060] For example, in addition to the example channels shown with reference to Figures 7-9, the audio of the immersive audio format may also include a center (C) channel and / or a low frequency effects (LFE) channel (not shown in any of Figures 7-9). As mentioned above, height cues are typically more prevalent in high frequency signals rather than in low frequency signals, so the center channel and / or LFE channel, if present, are typically not mixed with the filtered height channel.

[0061] In some embodiments (not shown), if a center channel is present, the center channel may be mixed with the front left and front right channels. In such embodiments, mixing of the filtered height channel(s) with 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.

[0062] Similar considerations can be made for a speaker configuration including middle left (ML) and middle right (MR) speakers 4230 and 4240, as shown in Figure 4. Whatever speaker configuration is used, it is advantageous for all speakers in the system to remain active during playback of the generated channel.

[0063] FIG. 10 illustrates a schematic diagram of an example of a method for generating six audio channels (i.e., audio in a 5.1 audio format) from audio in an immersive audio format according to an embodiment of the present disclosure. The output of the 5.1 audio format is suitable for, for example, the speaker system shown in FIG. 1. The input audio format is, for example, 5.1.4. In this case, the front-left, front-right, and center channels may be mixed using the front-stage mixing 500 as described above. However, the front-stage mixing 500 may be enabled or disabled as appropriate depending on the particular implementation. When the front-stage mixing 500 is enabled, the four filtered height channels of the input audio 5.1.4 may be mixed with four non-height channels in block 600 as follows: The two non-height front-left and front-right channels mixed with the center channel are then mixed with the filtered, for example, TFL and TFR. The two non-height LS and RS are directly mixed with TRL and TRR. If pre-mixing 500 is disabled, then in block 600 the four filtered height channels may be mixed directly with the four input non-height channels (i.e., they are not mixed with the center channel). In this example, the center channel signal is not mixed and is fed directly to the center speaker 10 of FIG. 1. Similarly, in this example, the LFE channel is not mixed and is fed directly to the LFE speaker 11 of FIG. 1. The channels generated by mixing with the height channel are fed to the corresponding front and rear speakers as described with reference to the example of FIG. 9.

[0064] 10A illustrates a schematic diagram of an example of a method for generating eight audio channels (i.e., 7.1 audio format audio) from an immersive audio format audio according to an embodiment of the present disclosure. The 7.1 audio format output is suitable for, for example, a speaker system as shown in FIG.

[0065] In this example, in order to keep all speakers of the speaker system of FIG. 4 active, an additional mid-stage mixing 700 may be used to obtain an audio output in a 7.1 audio format.

[0066] This process is the same as that described with reference to Figure 10 and will not be repeated here. At the output of block 600, the audio output is in 5.1 audio format as described with reference to Figure 10. An additional mid-stage mixing block 700 converts the audio from 5.1 to 7.1 audio format to feed all speakers of the speaker system shown in Figure 4. In a practical implementation, the pre-stage mixing 500 and the mid-stage mixing 700 are always implemented in the vehicle / processor or device and may be enabled / disabled as required by the particular speaker system configuration and / or pre-stage mixing requirements.

[0067] 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 height channels. 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 the passenger(s) / driver in the vehicle. Compensation for off-center listening positions can be performed with the algorithm described in EP1994795B1, which is incorporated herein by reference in its entirety. In EP1994795B1, it is shown that it is possible to simultaneously "virtual center" two off-center symmetric listening positions from the same pair of (stereo) speakers. This is the same principle as reducing the interaural phase difference (IDP) of one listening position. In the case of two listening positions, the phase difference of the IDPs obtained for each of the two listening positions is simultaneously reduced so that each IDP at each listening position has a value in the desired frequency range between -90 degrees and 90 degrees. By compensating for off-center listening positions and mixing the filtered height channels with the corresponding compensated front and / or rear non-height channels, panning of the height channel content across the front and / or rear speakers can be prevented.

[0068] (Example of a computing device) Methods for generating at least two audio channels from audio in an immersive audio format and generating said at least two audio channels using a non-immersive speaker system of at least two audio speakers have been described. Additionally, the present disclosure also relates to an apparatus for implementing these methods. Additionally, the present disclosure relates to a vehicle that may include an apparatus for implementing these methods. An example of such an apparatus 1440 is shown diagrammatically in FIG. 11. The apparatus 1440 may include 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, one (or a set of) analysis function(s) or one (or a set of) look-up table(s) 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. The processor may be configured to perform some or all of the methodologies described throughout this disclosure, for example, by retrieving the set of analysis functions and / or LTUs from the memory 1420. To perform the method of generating at least two audio channels, the device 1440 may receive as input a channel of (e.g., rendered) audio in an immersive audio format, for example 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 a non-immersive speaker system.

[0069] 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 mobile phone, a smart phone, a web appliance, a network router, a switch, a bridge, or any device capable of executing instructions (sequential or otherwise) that specify actions to be performed by the device. Additionally, although only a single device 1440 is illustrated in Figure 11, the present disclosure relates to any collection of devices that individually or jointly execute instructions to perform any one or more of the methodologies discussed herein.

[0070] The present disclosure further relates to a program (eg, a computer program) comprising instructions that, when executed by a processor, cause the processor to perform some or all of the methods described herein.

[0071] Furthermore, the present disclosure relates to a computer-readable (or machine-readable) storage medium having stored thereon the aforementioned program, 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.

[0072] The embodiments described herein may be implemented in hardware, software, firmware, and combinations thereof. For example, the embodiments may be implemented on a system composed of 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 be composed of at least one of, for example, 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).

[0073] 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 comprise a non-transitory medium having said instructions stored thereon, such as a physical medium, e.g., a magnetic data storage medium including a floppy disk or a hard disk drive, an optical data storage medium including a CD ROM or a DVD, an electronic data storage medium including a ROM, or a flash memory including a flash RAM or a USB flash drive. In another example, the computer program product comprises a data stream including said instructions, or a file including said instructions stored in a distributed computing system, e.g., in one or more data centers.

[0074] The present disclosure is not limited to the above-described embodiments and examples: many modifications and variations are possible without departing from the scope of the present disclosure, which is defined by the appended claims.

[0075] Various aspects of the present invention can be understood from the following enumerated example details (A-EEE and B-EEE):

[0076] A method for generating discrete channels from an immersive bitstream, comprising: identifying one or more height channels and one or more non-height channels of the immersive bitstream; processing the one or more height channels using a virtual height filter and a non-standard mixing technique; mixing the processed one or more height channels with the one or more non-height channels; A method comprising:

[0077] 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) and playing the at least two audio channels using a non-immersive speaker system of at least two audio speakers (1, 2) in a vehicle, comprising: - applying (1500) a virtual height filter (1300) to the at least one height channel (1010) such that, when the at least one audio height channel is reproduced by one of the at least two speakers, the virtual height filter (1300) generates at least one virtual height filtered audio signal (1175) by at least partially attenuating spectral components of the at least one height channel (1010) that emanate directly from the speakers (1, 2) and at least partially amplifying spectral components of the at least one height channel that are reflected from a roof or an area close to the roof of the vehicle; - generating the at least two audio channels (1008, 1016) by mixing (1700) the at least one virtual height filtered audio signal (1175) with at least one of the two non-height audio channels; A method comprising:

[0078] 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 one of the non-height audio channels (1050, 1100, 1125, 1150) to generate four audio channels (1008, 1016, 1032, 1064).

[0079] B-EEE3. A method according to any preceding B-EEE, wherein the audio in the immersive audio format comprises at least two height audio channels (1010, 1020), and wherein the virtual height filter (1300, 1400) is applied to each one of the at least two height audio channels (1010, 1020) to generate at least two virtual height filtered audio signals (1175, 1200), each one of the virtual height filtered audio signals (1175, 1200) being mixed with one of the at least two non-height channels (1100, 1050).

[0080] B-EEE4. The audio of the immersive audio format includes four height audio channels (1010, 1020, 1030, 1040) and four non-height audio channels (1050, 1100, 1125, 1150), and the virtual height filters (1300, 1400, 2500, 2600) filter the four height audio channels (1010, 1020, 1030, 1040). A method as described in any one of the preceding B-EEE, wherein a respective one of the virtual height filtered audio signals (1175, 1200, 1225, 1250) is mixed with a respective one of the four non-height channels (1100, 1050, 1125, 1150).

[0081] B-EEE5. A method according to any one of the preceding B-EEE, wherein said non-immersive speaker system is a stereo or surround speaker system.

[0082] B-EEE6. A method according to any one of the preceding B-EEE, 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.

[0083] B-EEE7. A method as claimed in any one of the preceding B-EEE, 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.

[0084] B-EEE8. The method of B-EEE6 and 7, wherein the one or more parameters are indicative of at least one of a peak, a first frequency, a notch, and a second frequency of the filter transfer function.

[0085] B-EEE9. A method according to any one of the preceding B-EEE, wherein said at least two audio speakers (1, 2) are laterally spaced apart relative to a listening position.

[0086] B-EEE10. The method of B-EEE9, further comprising determining (1800) a filter transfer function for the virtual height filter based on a relative distance of the at least two speakers from the listening position and an elevation of the roof or an area near the roof relative to the listening position.

[0087] B-EEE11. 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 speakers from the listening position and a range of elevations of the roof or an area near the roof relative to the listening position; The method according to claim 9, further comprising: selecting (2000) a filter transfer function from the plurality of filter transfer functions.

[0088] B-EEE12. The method of B-EEE11, wherein the selected filter transfer function is an average of the plurality of filter transfer functions.

[0089] B-EEE13. A method according to B-EEE11 dependent on any of E-EEE6 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 speakers from the listening position and an average elevation of the roof or an area close to the roof relative to the listening position.

[0090] B-EEE14. 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 that maximizes the perception of sonic height.

[0091] B-EEE15. The method of any one of B-EEE6-14, further comprising storing said one or more parameters in a processor as a look-up table or an analytical function.

[0092] B-EEE16. The method of any one of the preceding B-EEE further comprising applying a gain to said virtual height filter.

[0093] B-EEE17. The method of B-EEE16, wherein said gain is user configurable.

[0094] B-EEE18. A method according to any one of the preceding B-EEE, wherein said audio in said immersive audio format is audio rendered in said immersive audio format, and / or said 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 or subwoofer audio channel, if present, and Z≧1 is said at least one height audio channel.

[0095] B-EEE19. Apparatus configured to perform the methods of B-EEE1 to B-EEE18.

[0096] B-EEE20. A vehicle having a speaker system of at least two audio speakers (1, 2), further comprising an apparatus as described in B-EEE19.

[0097] B-EEE21. A program comprising instructions which, when executed by a processor, cause the processor to perform a method according to any one of B-EEE1 to B-EEE18.

[0098] A computer-readable storage medium storing the program described in B-EEE22.B-EEE21.

Claims

1. 1. A method for generating at least two audio channels from audio in an immersive audio format including at least one height audio channel and at least two non-height audio channels, and playing the at least two audio channels using a non-immersive speaker system of at least two audio speakers in a vehicle, comprising: applying a virtual height filter to the at least one height channel such that, when the at least one audio height channel is reproduced by one of the at least two speakers, the virtual height filter generates at least one virtual height filtered audio signal by at least partially attenuating spectral components of the at least one height channel that emanate directly from the speaker and at least partially amplifying spectral components of the at least one height channel that are reflected from a roof or an area close to the roof of the vehicle; - generating said at least two audio channels by mixing said at least one virtual height filtered audio signal with at least one of said two non-height audio channels; A method comprising:

2. 2. The method of claim 1, wherein the audio in the immersive audio format further includes at least two additional non-height audio channels, and the virtual height filtered audio signal is mixed with each one of the non-height audio channels to generate four audio channels.

3. 10. The method of claim 1, wherein the audio in the immersive audio format includes at least two height audio channels, and the virtual height filter is applied to each one of the at least two height audio channels to generate at least two virtual height filtered audio signals, each one of the virtual height filtered audio signals being mixed with one of the at least two non-height channels.

4. the audio in the immersive audio format includes four height audio channels and four non-height audio channels, the virtual height filter being applied to each one of the four height audio channels to generate four virtual height filtered audio signals, each one of the virtual height filtered audio signals being mixed with one of the four non-height channels; 13. A method according to any one of the preceding claims.

5. 10. The method of any one of the preceding claims, wherein the non-immersive speaker system is a stereo or surround speaker system.

6. 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.

7. 10. A method according to any one of the preceding claims, 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.

8. The method of claims 6 and 7, wherein the one or more parameters are indicative of at least one of a peak, a first frequency, a notch, and a second frequency of the filter transfer function.

9. 2. A method according to any one of the preceding claims, wherein the at least two audio speakers are laterally spaced apart relative to a listening position.

10. 10. The method of claim 9, further comprising determining a filter transfer function for the virtual height filter based on a relative distance of the at least two speakers from the listening position and an elevation of the roof or an area near the roof with respect to the listening position.

11. 10. The method of claim 9, further comprising: obtaining 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 speakers from the listening position and a range of elevations of the roof or an area near the roof relative to the listening position; and selecting one filter transfer function from the plurality of filter transfer functions.

12. The method of claim 11 , wherein the selected filter transfer function is an average of the multiple filter transfer functions.

13. 12. The method of claim 11 when dependent on any 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 speakers from the listening position and an average altitude of the roof or an area close to the roof relative to the listening position.

14. 14. A method according to any of claims 11 to 13, wherein the steps of obtaining, selecting, applying and mixing are applied iteratively for each selected filter transfer function until the filter transfer function provides a reproduction of the at least two channels that maximizes the perception of sonic sonic height.

15. 15. The method of claim 6, further comprising storing the one or more parameters in a processor as a look-up table or an analytical function.

16. 10. The method of any one of the preceding claims, further comprising applying a gain or a user configurable gain to the virtual height filter.

17. 10. The method of any one of the preceding claims, wherein the audio in the immersive audio format is audio rendered in the immersive audio format, and / or the immersive audio format is Dolby Atmos or any X.Y.Z 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 at least one height audio channel.

18. Apparatus configured to carry out a method according to any one of the preceding claims.

19. 20. A vehicle having a speaker system of at least two audio speakers, further comprising the apparatus of claim 18.

20. 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 17.

21. A computer-readable storage medium storing the program according to claim 20.

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