Patent Description:
An audio output apparatus can be configured to render sound for a user of the apparatus into different audio output channels using different associated transducers.

The different transducers can, for example, be used for different specific frequency ranges. A filter can be used to route audio signals below a cross-over frequency to a transducer optimised for lower frequency audio output and route audio signals above the cross-over frequency to a different transducer optimised for higher frequency audio output.

The cross-over frequency is fixed by the different specific frequency ranges of the transducers used.

If the transducers are replaced with transducers for use with different specific frequency ranges, then the filter is replaced with one that has a fixed cross-over frequency optimised for the new transducers.

<CIT> discloses (abstract) an apparatus including an air-conduction transducer and a bone conduction transducer. The air-conduction transducer is configured to convert a first frequency band component of an electrical audio signal into acoustic energy to be delivered to an ear canal of a user. The bone conduction transducer is configured to convert a second, at least partially different, frequency band component of the electrical audio signal into mechanical energy to be delivered to a skull of the user. The apparatus is configured to deliver both forms of the energies to the user at a substantially same time to provide a combined audio delivery result to the user.

In one aspect of the invention there is provided a head-mounted audio output apparatus as according to claim <NUM>.

In some but not necessarily all examples, the means for automatically changing a cut-off frequency of at least the first one of the audio output channels is configured to change the cut-off frequency of the first one of the audio output channels in dependence on at least a sensed environmental value at a position of the head-mounted audio output apparatus.

In some but not necessarily all examples, the means for automatically changing a cut-off frequency of at least the first one of the audio output channels is configured to increase the cross-over frequency between a lower frequency audio output channel and a higher frequency audio output channel such that a bandwidth of the lower frequency audio output channel increases and a bandwidth of the higher frequency audio output channel decreases. In some but not necessarily all examples, the hybrid audio system is configured to render sound for a left ear of the user into a first audio output channel using an associated first transducer and into a second audio output channel using an associated second transducer and is configured to render sound for a right ear of the user into a third audio output channel using an associated third transducer and into a fourth audio output channel using an associated fourth transducer.

In some but not necessarily all examples, a first set of different audio output channels comprising the first audio output channel and the second audio output channel and a second set of different audio output channels comprising the third audio output channel and the fourth audio output channel are controlled to render one or more audio objects.

In some but not necessarily all examples, the first audio output channel, the second audio output channel, the third audio output channel and the fourth audio output channel are controlled to render one or more audio objects.

In some but not necessarily all examples, the means for automatically changing a cut-off frequency of at least the first one of the audio output channels is configured to automatically change the cut-off frequency of the first one of the audio output channels in dependence upon a dynamic assessment of one or more of:.

In some but not necessarily all examples, the means for automatically changing a cut-off frequency of at least the first one of the audio output channels is configured to automatically change the cut-off frequency of the first one of the audio output channels to increase a bandwidth of the first one of the audio output channels, in dependence upon impairment of a second one of the audio output channels.

In some but not necessarily all examples, the means for automatically changing a cut-off frequency of at least the first one of the audio output channels is configured to automatically change the cut-off frequency of the first one of the audio output channels to optimize for hearability.

In some but not necessarily all examples, the means for automatically changing a cut-off frequency of at least the first one of the audio output channels is configured to automatically change the cut-off frequency of the first one of the audio output channels in dependence upon a dynamic assessment of one or more of sensor output; noise; content for rendering.

In some but not necessarily all examples, the means for automatically changing a cut-off frequency of at least the first one of the audio output channels is configured to automatically change the cut-off frequency of the first one of the audio output channels in dependence upon at least one of:.

According to a second aspect of the invention there is provided a computer program as according to claim <NUM>.

According to a third aspect of the invention there is provided a method as according to claim <NUM>.

According to various embodiments there is provided examples as claimed in the appended claims.

<FIG> illustrates an example of an audio output apparatus <NUM> comprising a hybrid audio system <NUM>.

The hybrid audio system <NUM> comprises multiple transducers <NUM>, including a first transducer <NUM>, and a second transducer <NUM><NUM>. The hybrid audio system <NUM> is configured to render sound for a user <NUM> of the apparatus <NUM> into different audio output channels <NUM> using different associated transducers <NUM>. The different audio output channels <NUM> include a first audio output channel <NUM><NUM> associated with the first transducer <NUM>, and a second audio output channel <NUM><NUM> associated with the second transducer <NUM><NUM>. The first transducer <NUM>, renders sound for the user <NUM> into the associated first audio output channel <NUM><NUM>. The second transducer <NUM><NUM> renders sound for the user <NUM> into the associated second audio output channel <NUM><NUM>.

The method of transduction used by the first transducer <NUM>, and the second transducer <NUM><NUM> are different. The first transducer <NUM>, is configured to produce vibrations in bone that transfer sound via a bone-conduction audio output channel <NUM><NUM>. In this example, or other examples, the second transducer <NUM><NUM> is configured to produce pressure waves in air that transfer sound via an air-conduction audio output channel <NUM><NUM>.

The apparatus <NUM> comprises means for automatically changing a cut-off frequency of at least the first audio output channel <NUM><NUM> in dependence upon the transducer associated with the first audio output channel <NUM><NUM> (the first transducer <NUM><NUM>).

The apparatus <NUM> can also comprise means for automatically changing a cut-off frequency of the second audio output channel 30z in dependence upon the transducer associated with the second audio output channel <NUM><NUM> (the second transducer <NUM><NUM>).

The means for automatically changing a cut-off frequency of the first audio output channel <NUM><NUM> and a cut-off frequency of the second audio output channel <NUM><NUM> can comprise a filter <NUM> and a filter controller <NUM>. The filter <NUM> filters an audio signal <NUM> and produces a first audio signal <NUM><NUM> for driving the first transducer <NUM>, and produces a second audio signal <NUM><NUM> for driving the second transducer <NUM><NUM>. The filter characteristics of the filter <NUM> are controlled by control signal <NUM> provided by the filter controller <NUM>.

The filter controller <NUM> is configured to control the filter <NUM> to change a cut-off frequency of the first audio signal <NUM><NUM> and therefore control the cut-off frequency of the first audio output channel <NUM><NUM>.

The filter controller <NUM> is configured to control the filter <NUM> to change a cut-off frequency of the second audio signal <NUM><NUM> and therefore control the cut-off frequency of the second audio output channel <NUM><NUM>.

For example, if the first audio signal <NUM><NUM> is filtered to be a lower frequency signal, the filter controller <NUM> can control the filter <NUM> to change an upper cut-off frequency fuco of the first audio signal <NUM><NUM>.

For example, if the second audio signal <NUM><NUM> is filtered to be a higher frequency signal, the filter controller <NUM> can control the filter <NUM> to change a lower cut-off frequency flco of the second audio signal <NUM><NUM>.

In some but not necessarily all examples, the filter controller <NUM> is configured to automatically change a cut-off frequency of the first audio output channel <NUM><NUM> in dependence on a sensed environmental value <NUM> at a position of the audio output apparatus <NUM>. In some but not necessarily all examples, the filter controller <NUM> is configured to automatically change a cut-off frequency of the second audio output channel <NUM><NUM> in dependence on the or a sensed environmental value <NUM>.

In the illustrated example, the apparatus <NUM> optionally comprises a sensor <NUM> configured to sense a parameter <NUM> of an exterior environment <NUM>, at the position of the audio output apparatus <NUM>, and provide the sensed environmental value <NUM> to the filter controller <NUM>.

In some but not necessarily all examples, the apparatus <NUM> is a worn apparatus. In some but not necessarily all examples, the apparatus <NUM> is a head-mounted apparatus.

A head-mounted apparatus can, for example, be configured as an over-ear apparatus, an on-ear apparatus, an in-ear apparatus, or as a bud or pod.

One example of a head-mounted apparatus is headset. One example of a head-mounted apparatus is headphones. One example of a head-mounted apparatus is a head-worn mediated reality apparatus such as virtual reality (see-display) or augmented reality (see-through display) apparatus.

An example of a head-mounted audio output apparatus <NUM> is illustrated in FIG 10The first transducer <NUM>, is a bone-conduction transducer configured to render sound to a left ear <NUM>L of the user <NUM> of the apparatus <NUM> via a
bone-conduction audio output channel <NUM><NUM> (not illustrated in FIG <NUM>). The second transducer <NUM><NUM> is an air-conduction transducer configured to render sound to the left ear <NUM>L of the user <NUM> of the apparatus <NUM> via an air-conduction audio output channel <NUM><NUM> (not illustrated in FIG <NUM>).

As illustrated in <FIG>, in some but not necessarily all examples, the filter controller <NUM> is configured to automatically change, using control signal <NUM>, a cross-over frequency associated with the first audio output channel <NUM><NUM> and the second audio output channel <NUM><NUM>. For example, the filter <NUM> automatically adapts a cross-over frequency of the first audio output channel <NUM><NUM> and the second audio output channel <NUM><NUM> in response to the control signal <NUM>.

In some but not necessarily all examples, the control signal <NUM> is automatically changed in dependence on a sensed environmental value <NUM> at a position of the audio output apparatus <NUM>.

The filter <NUM> splits a bandwidth BW of the audio signal <NUM> into two contiguous, mostly nonoverlapping parts for the different audio output channels <NUM><NUM>, <NUM><NUM>. The two parts are a lower frequency part BWL. and a higher frequency part BWH.

The first audio signal <NUM><NUM> has been filtered to be a lower frequency signal. It has a bandwidth corresponding to the lower frequency part BWL. The cross-over frequency fxo corresponds to an upper cut-off frequency fuco of the first audio signal <NUM><NUM>.

The second audio signal <NUM><NUM> has been filtered to be a higher frequency signal. It has a bandwidth corresponding to the higher frequency part BWH. The cross-over frequency fxo corresponds to a lower cut-off frequency flco of the second audio signal <NUM><NUM>.

The filter <NUM> filters the audio signal <NUM> and produces the first audio signal <NUM><NUM> for driving the first transducer <NUM>, and produces the second audio signal <NUM><NUM> for driving the second transducer <NUM><NUM>. The filter characteristics of the filter <NUM> are controlled by control signal <NUM> provided by the filter controller <NUM>.

The filter controller <NUM> is configured to control the filter <NUM> to change the cross-over frequency of the first audio signal <NUM><NUM> and the second audio signal <NUM><NUM>. This determines the cross-over frequency between the first audio output channel <NUM><NUM> and the second audio output channel <NUM><NUM>.

The cross-over frequency at time t1 (<FIG>) is increased at time t2 (<FIG>). This increases the bandwidth BWL of the lower frequency audio output channel <NUM><NUM>
and decreases the bandwidth BWH of the higher frequency audio output channel <NUM><NUM>.

<FIG> illustrate an example of a method. The method uses features described previously with reference to <FIG>. The method comprises, as illustrated in <FIG> at time t1, using a hybrid audio system <NUM> comprising multiple transducers <NUM> to render sound to a user <NUM> into different audio output channels <NUM>, wherein a first audio output channel <NUM><NUM>, associated with a first transducer <NUM><NUM>, has a first cut-off frequency (fuco) and wherein a second audio output channel <NUM><NUM>, associated with a second transducer <NUM><NUM>, different to the first transducer <NUM><NUM>, has a second cut-off frequency (flco).

In the transition from <FIG>, at time t1, to <FIG> at a later time t2, the method comprises changing the first cut-off frequency (fuco) to a different first cut-off frequency (f'uco) and changing the second cut-off frequency to a different second cut-off frequency (f'lco), wherein the change of the first cut-off frequency (fuco) to the different first cut-off frequency (f'uco) (e.g. increase in upper frequency of passband, extension of lower frequency passband) is different from the change of the second cut-off frequency (flco) to the different second cut-off frequency (f'uco) (e.g. increase in lower frequency of passband, contraction of higher frequency passband).

The method then comprises, as illustrated in <FIG> at time t2, using a hybrid audio system <NUM> comprising multiple transducers <NUM> to render sound to a user <NUM> into different audio output channels <NUM>, wherein the first audio output channel <NUM><NUM>, associated with the first transducer <NUM><NUM>, has the different first cut-off frequency (f'uco) and wherein the second audio output channel <NUM><NUM>, associated with the second transducer <NUM><NUM>, different to the first transducer <NUM><NUM>, has the different second cut-off frequency (f'lco).

As illustrated in <FIG>, in some examples, the hybrid audio system <NUM> is configured to render sound for a right ear <NUM>R of the user <NUM> into a first audio output channel <NUM><NUM> using an associated first transducer <NUM>, and into a second audio output channel <NUM><NUM> using an associated second transducer <NUM><NUM> and is configured to render sound for a left ear <NUM>L of the user <NUM> into a third audio output channel <NUM><NUM> using an associated third transducer <NUM><NUM> and into a fourth audio output channel <NUM><NUM> using an associated fourth transducer <NUM><NUM>.

There are two different hybrid transducers <NUM> per ear <NUM>. An equivalent pair of different hybrid transducers <NUM> can be used for each ear.

In the illustrated example, but not necessarily all examples:.

The first bone-conduction transducer <NUM>, and the third bone-conduction transducer <NUM><NUM> can be the same or similar. A bone-conduction transducer is configured to conduct energy representing the respective audio signal <NUM><NUM>, <NUM><NUM> to an ear <NUM> of the user <NUM> via the head bones of the user <NUM>. An example of a bone-conduction transducer <NUM><NUM>, <NUM><NUM> is an electromagnetically controlled mechanical vibrator.

The second air-conduction transducer <NUM><NUM> and the fourth air-conduction transducer <NUM><NUM> can be the same or similar. An air-conduction transducer is configured to conduct energy representing the respective audio signal <NUM><NUM>, <NUM><NUM> into an ear <NUM> of the user <NUM> via the open ear canal of the user <NUM>. An example of an air-conduction transducer <NUM><NUM>, <NUM><NUM> is an electromagnetically controlled diaphragm.

The apparatus <NUM> comprises a left part <NUM>L and a right part <NUM>R. The left part <NUM>L is positioned in, at or near a left ear <NUM>L of the user <NUM>. The right part <NUM>R is positioned in, at or near a right ear <NUM>R of the user <NUM>.

Operation of the left part <NUM>L of the apparatus <NUM> can be the same as operation of the apparatus <NUM> as described in relation to <FIG> and <FIG>.

Operation of the right part <NUM>R of the apparatus <NUM> can be the same as operation of the apparatus <NUM> as described in relation to <FIG> and <FIG>.

In the right part <NUM>R, the hybrid audio system <NUM> is configured to render sound for a right ear <NUM>R of the user <NUM> of the apparatus <NUM> into a first audio output channel <NUM><NUM> associated with the first transducer <NUM>, and a second audio output channel <NUM><NUM> associated with the second transducer <NUM><NUM>. The filter <NUM> filters a right-ear audio signal <NUM>R and produces a first audio signal <NUM><NUM> for driving the first transducer <NUM>, and produces a second audio signal <NUM><NUM> for driving the second transducer <NUM><NUM>. The filter characteristics of the filter <NUM> are controlled by control signal <NUM> provided by the filter controller <NUM>.

A sensor <NUM> can be configured to sense a parameter <NUM>, for example a parameter of an exterior environment <NUM> at the position of the right part <NUM>R of the audio output apparatus <NUM>, and provide the sensed parameter e.g. environmental value <NUM> to the filter controller <NUM>.

The filter controller <NUM> is configured to control the filter <NUM> to change a cross-over frequency fxo of the first audio signal <NUM><NUM> and the second audio signal <NUM><NUM>. The cross-over frequency fxo corresponds to an upper cut-off frequency fuco of the lower frequency first audio signal <NUM><NUM> and the lower cut-off frequency flco of the higher frequency second audio signal <NUM><NUM>. The change in the cross-over frequency is dependent on the sensed environmental value <NUM>.

In the left part <NUM>L, the hybrid audio system <NUM> is configured to render sound for a left ear <NUM>L of the user <NUM> of the apparatus <NUM> into a third audio output channel <NUM><NUM> associated with the third transducer <NUM><NUM> and a fourth audio output channel <NUM><NUM> associated with the fourth transducer <NUM><NUM>. The filter <NUM> filters a left-ear audio signal <NUM>L and produces a third audio signal <NUM><NUM> for driving the third transducer <NUM><NUM> and produces a fourth audio signal <NUM><NUM> for driving the fourth transducer <NUM><NUM>. The filter characteristics of the filter <NUM> are controlled by control signal <NUM> provided by the filter controller <NUM>.

A sensor <NUM> can be configured to sense a parameter <NUM>, for example a parameter of an exterior environment <NUM> at the position of the left part <NUM>L of the audio output apparatus <NUM>, and provide the sensed parameter e.g. environmental value <NUM> to the filter controller <NUM>.

The filter controller <NUM> is configured to control the filter <NUM> to change a cross-over frequency fxo of the third audio signal <NUM><NUM> and the fourth audio signal <NUM><NUM>. The cross-over frequency fxo corresponds to an upper cut-off frequency fuco of the lower frequency third audio signal <NUM><NUM> and the lower cut-off frequency flco of the higher frequency fourth audio signal <NUM><NUM>. The change in the cross-over frequency fxo is dependent on the sensed environmental value <NUM>.

In some examples, the filter controller <NUM> is configured to control the filter <NUM> to change a cross-over frequency fxo of the first audio signal <NUM><NUM> (first audio output channel <NUM><NUM>) and the second audio signal <NUM><NUM> (second audio output channel <NUM><NUM>) in dependence upon on the sensed environmental value <NUM> at the left part <NUM>L and the right part <NUM>R.

In some examples, the filter controller <NUM> is configured to control the filter <NUM> to change a cross-over frequency fxo of the third audio signal <NUM><NUM> (third audio output channel <NUM><NUM>) and the fourth audio signal <NUM><NUM> (fourth audio output channel <NUM><NUM>) in dependence upon on the sensed environmental value <NUM> at the right part <NUM>R and the left part <NUM>L.

In some examples, a separate filter controller <NUM> is provided in the left part <NUM>L and also in the right part <NUM>R. The separate filter controllers <NUM>, can for example, communicate.

In some examples, a single filter controller <NUM> is provided for controlling separately filters <NUM> in the left part <NUM>L and in the right part <NUM>R.

An audio content controller <NUM> processes an audio signal <NUM> to produce the left-ear audio signal <NUM>L and the right-ear audio signal <NUM>R. In some but not necessarily all examples, the audio content controller <NUM> is comprised in the apparatus <NUM>. In other examples, the audio content controller <NUM> is not comprised in the apparatus <NUM>.

A first set of different audio output channels <NUM><NUM>, <NUM><NUM> are rendered using different associated transducers <NUM><NUM>, <NUM><NUM> to provide sound to the right ear <NUM>R. A second set of different audio output channels <NUM><NUM>, <NUM><NUM> are rendered using different associated transducers <NUM><NUM>, <NUM><NUM> to provide sound to the left ear <NUM>L.

As illustrated in <FIG> &4B and <FIG>, in some but not necessarily all examples, the different audio output channels <NUM><NUM>, <NUM><NUM> of the first set are controlled to represent a first spatial audio object <NUM>R, <NUM><NUM> and the different audio output channels <NUM><NUM>, <NUM><NUM> of the second set are controlled to represent a second spatial audio object <NUM>L, <NUM><NUM>.

Each set of audio output channels comprises a bone-conduction audio output channel and an air-conduction audio output channel.

In the example, illustrated in <FIG> &4B, the first set of audio output channels provides stereo output for the right ear and the second set of audio output channels provides stereo output for the left ear. The first audio object <NUM>R is the right-ear stereo loudspeaker located adjacent the right-ear <NUM>R. The second audio object <NUM>L is the left-ear stereo loudspeaker located adjacent the left-ear <NUM>L. <FIG> illustrates a front perspective and <FIG> illustrates a top perspective.

In the example, illustrated in <FIG> &5B, the first set of audio output channels provides binaural output for the right ear and the second set of audio output channels provides binaural output for the left ear. The combination of the first set of audio output channels and the second set of audio output channels locates a first spatial audio object <NUM>, at a distance and bearing from the user <NUM>. Optionally, the combination of the first set of audio output channels and the second set of audio output channels locates a second spatial audio object <NUM><NUM> at a distance and bearing from the user <NUM>. <FIG> illustrates a front perspective and <FIG> illustrates a top perspective. The first spatial audio object <NUM>, can be a virtual loudspeaker (sound source). The second spatial audio object <NUM><NUM> can be a virtual loudspeaker (sound source).

In other examples the set of audio output channels may provide, mono, stereo or any other type of audio that can be used with the apparatus <NUM>.

In at least some examples, the filter controller <NUM> of the apparatus <NUM> is configured to automatically change the cut-off frequencies of audio output channels <NUM> in dependence upon a dynamic assessment of parameters that relate to impairment of the audio output channels <NUM>.

For example, the filter controller <NUM> is configured to automatically change the cut-off frequency of a lower frequency audio output channel <NUM><NUM> /<NUM><NUM> for an ear to increase a bandwidth (increase the upper cut-off frequency fuco) of that lower frequency audio output channel <NUM><NUM> /<NUM><NUM>, in dependence upon impairment of the higher frequency audio output channels <NUM><NUM>/<NUM><NUM> for the same ear.

For example, the filter controller <NUM> is configured to automatically change the cross-over frequency fxo between a lower frequency audio output channel <NUM><NUM> /<NUM><NUM> and a higher frequency audio output channel <NUM><NUM>/<NUM><NUM> for the same ear, in dependence upon impairment of the respective higher frequency audio output channel <NUM><NUM>/<NUM><NUM> for the same ear.

Thus, more information (larger bandwidth) can be used for a less impaired audio channel.

The impairment can, for example, be based on hearability. The automatic change in a cut-off frequency (or cross-over frequency) optimizes or improves hearability.

In the example illustrated in <FIG>, an exterior noise <NUM> in the exterior environment <NUM> reduces hearability to the user <NUM> via an air-conduction audio output channel and causes an impairment to the user <NUM>. The exterior noise can for example be wind, machinery or other noises. The impairment can be detected by using a sensor <NUM> (not illustrated) to sense the environment <NUM>. For example, a microphone can listen to sounds in the exterior environment <NUM> and an impairment can be detected when the energy density per Hz exceeds a threshold within a defined spectral range. Thus, an impairment can be detected when the exterior noise is a loud higher frequency noise, for example, such as wind.

The apparatus <NUM> responds to detection of the impairment by automatically changing the cut-off (cross-over) frequency so that higher frequency audio signals are provided via the bone-conduction audio output channel rather than the air-conduction audio output channel. The threshold used to detect impairment can, for example, be based on one or more properties of the audio output channels <NUM> such as energy spectrum and/or audio content (e.g. speech, private,.

Thus, the apparatus <NUM> can be configured to automatically change the cut-off frequency of an audio output channel in dependence upon a dynamic assessment of one or more of: one or more properties of the audio output channels;
audio content; and/or an environment of the user.

In the example illustrated in <FIG>, noise <NUM> leaking from the apparatus <NUM> via an air-conduction audio output channel increasing hearability to a potential eavesdropper nearby (not illustrated) and causes an impairment. The impairment can be detected by using a sensor <NUM> (not illustrated) to sense a nearby potential eavesdropper or to sense that the apparatus <NUM> is in a public environment <NUM> (rather than a private environment).

The apparatus <NUM> responds to detection of the impairment by automatically changing the cut-off (cross-over) frequency so that higher frequency audio signals are provided via the bone-conduction audio output channel rather than the air-conduction audio output channel to improve privacy and reduce the likelihood of being overheard. The
detection of such a privacy impairment can be activated when the audio signals rendered to the user comprise speech or other private content and/or when the energy spectrum of the audio signal exceeds a threshold value.

Thus, the assessment of impairment is dynamic and can be based upon:
one or more properties of the audio output channels <NUM> such as energy spectrum and/or audio content (e.g. speech, private,. ) and/or an environment <NUM> of the user <NUM>.

In one use case, the cut-off frequency of a first audio output channel <NUM> is automatically changed in dependence upon a dynamic assessment of
content for rendering as private content and a local environment as a public environment. More information can be transferred to the less leaky channel. For example, by increasing the upper cut-off frequency for the bone conduction channel and the lower cut-off frequency for the air conduction channel.

In one use case, the cut-off frequency of a first audio output channel <NUM> is automatically changed in dependence upon a dynamic assessment of content for rendering as comprising speech and a local environment as a noisy environment.

More information can be transferred to the less noisy channel. For example, by increasing the upper cut-off frequency for the bone conduction channel and optionally the lower cut-off frequency for air conduction channel.

In one use case, the cut-off frequency of a first audio output channel <NUM> is automatically changed in dependence upon a dynamic assessment of a local environment <NUM> as an environment subject to wind noise. More information can be transferred to the less noisy channel. For example, by increasing the upper cut-off frequency for the bone conduction channel and optionally the lower cut-off frequency for the air conduction channel.

In one use case, the cut-off frequency of a first audio output channel <NUM> is automatically changed in dependence upon a dynamic assessment of content for rendering as spatial audio content to be rendered from different directions and assessment of a local environment as a noisy environment in some but not all directions. More information can be transferred to the less noisy conduction channel. For example, by increasing the upper cut-off frequency (or cross-over frequency) for the bone-conduction channel(s) associated with the spatial audio channel with noise.

Thus, the apparatus <NUM> can be configured to automatically change the cut-off frequency of an audio output channel in dependence upon a dynamic assessment of one or more of: sensor output; noise; content for rendering.

<FIG> illustrates an example of an apparatus <NUM> previously described, with both a bone-conduction transducer <NUM>, and an air-conduction transducer <NUM><NUM>. Similar references are used for similar features.

The apparatus <NUM> can be a headset for example as illustrated in FIG <NUM>.

A filtered part <NUM><NUM> of the audio signal <NUM> is routed to the bone-conduction transducer <NUM>, and a differently filtered part <NUM><NUM> of the audio signal <NUM> is routed to the air-conduction transducer <NUM><NUM>. This can be done, for example, by applying a low-pass filter <NUM>LP to the audio signal <NUM> to produce the audio signal <NUM><NUM> going to the bone-conduction transducer <NUM>, and by applying a high-pass filter <NUM>HP to the audio signal <NUM> to produce the audio signal <NUM><NUM> going to the air-conduction transducer <NUM><NUM>. Frequencies above a certain threshold (fuco) are filtered from the audio signals <NUM><NUM> going to the bone-conduction transducer <NUM>, and frequencies below a certain threshold (flco) are filtered from the audio signals <NUM><NUM> going into the air-conduction transducer <NUM><NUM>. The filters <NUM>LP, <NUM>HP can be designed so that frequencies below a certain threshold (the cross-over frequency fxo) are filtered from the audio signals <NUM><NUM> going into the air-conduction transducer <NUM><NUM> and frequencies above this same threshold fxo are filtered from the audio signal <NUM><NUM> going to the bone-conduction transducer <NUM><NUM>.

The apparatus <NUM> can be used in different environments <NUM> and the audio signals <NUM> can be used to render various kinds of different content.

The apparatus <NUM> does not use a fixed cut-off frequency (or cross-over frequency), and therefore mitigates a sub-optimal user experience.

The cut-off/cross-over frequency can be set low such that a user <NUM>, listening to audio in a quiet environment <NUM>, hears high bandwidth audio via the air-conduction audio output channel <NUM><NUM> and can be set higher in a noisy environment <NUM> (e.g. wind noise, construction noise, engine noise. ) such that a user <NUM> listening hears a higher bandwidth via the bone-conduction audio output channel <NUM><NUM>.

The adaptive cut-off/cross-over frequency can be used for:.

An optimal cut-off/cross-over frequency can be selected based on the user's environment <NUM> and/or the content (or content type) of the audio signals <NUM> rendered to the user <NUM>. The cut-off/cross-over frequency can be determined based on the type of content rendered and/or the environment <NUM>.

When spatial audio content is being rendered to the user <NUM> via audio signals <NUM>, the cut-off/cross-over frequency can be applied in a direction specific manner. The cut-off/cross-over frequency for a particular direction can be dependent upon the environment <NUM> (e.g. noise) in that direction and/or the content (or content type) rendered to the user <NUM> from that direction based on the audio signals <NUM>.

The directionality of the cut-off/cross-over frequency can be dependent on which audio sources are heard from which direction and from which direction environmental sounds (noise) is heard by the user. The directionality can be taken into account by applying:.

Adaptation may be done based on both, the spatial content directions and direction of the potentially disturbing environmental noises.

The cut-off/cross-over frequencies for different parts <NUM>L, <NUM>R can be set separately.

In some examples, optimal cut-off/cross-over frequencies for different environments <NUM> and/or content (or content type) of the audio signals <NUM> rendered to the user <NUM> are predetermined and stored in a database in a memory. During operation of the apparatus <NUM>, the cut-off/cross-over frequency is read from the database based on combinations of parameters representing different combinations of environments <NUM> and/or content of the audio signals <NUM>.

The automatic changing of a cut-off/cross-over frequency can therefore be based on pre-stored characteristics. Pre-stored characteristics can be combined by maximizing the cross-over frequency.

Environment detection can use environmental values <NUM> from various sensors <NUM> such as, for example, noise sensors 50B. The sensors <NUM> can use sensing hardware such as, for example, a microphone <NUM>, gyroscope, accelerometer, proximity detector, a location detector etc. One example of environment detection is noise sensing 50B (e.g. wind noise detection) using a microphone or microphones <NUM>.

Content detection can use environmental values <NUM> from various sensors <NUM> such as speech sensors 50A. The sensors <NUM> can process data, for example, the audio signals <NUM> or metadata associated with the audio signals <NUM>. Content type determination can use the metadata associated with the audio signals <NUM> (if available) or can process the audio signals <NUM> to determine content or content type algorithmically. For example, speech or music can be disambiguated. For example, the content type can be determined to be stereophonic or binaural spatial audio.

In one use case, content (or content type) of the audio signals <NUM> rendered to the user <NUM> is spatial audio content. The user <NUM> is listening to spatial audio content using the head-mounted audio output apparatus <NUM>. The spatial audio content comprises audio sources/objects that have been placed in different directions around the user <NUM>. The user <NUM> hears music content from the left and speech content from the right (a phone call with a friend). In this case, the cut-off/cross-over frequency is set separately for the different content types. That is, the cut-off/cross-over frequency for the music content is set according to what is optimal for music listening and the cross-over frequency for the speech is set according to what is optimal for the speech signal.

In another use case, the user is in a noisy environment <NUM>. The noise source is to the right of the user <NUM> and impacts mainly how the user <NUM> hears speech content. The noise may be, for example, wind noise that is affecting only the right air-conduction transducer <NUM><NUM> (see <FIG>). In this case, the cut-off/cross-over frequency is adjusted (made higher) due to the noise only for the right transducers <NUM><NUM> , <NUM><NUM> (see <FIG>). The cut-off/cross-over frequency is not adjusted for the left transducers <NUM><NUM> , <NUM><NUM> (see <FIG>).

<FIG> shows a block diagram for an example use case. Here the cut-off/cross-over frequency is adjusted based on the presence of speech content in the content of the audio signals <NUM> rendered to the user <NUM>.

Content sensing block 50A implements speech sensing and detection using speech detection methods. One example is to extract features, such as mel-frequency cepstral coefficients (MFCCs), from the content of the audio signal <NUM> and feed these into a classifier (Gaussian Mixture Model (GMM) classifier, for example) for classification to speech and non-speech parts. The GMM classifier is prior-trained on a large database of speech/non-speech data. Neural networks could also be used to build a classifier.

The cut-off/cross-over frequency determination block <NUM> (this corresponds to the filter controller <NUM>) looks at the classifier output and sets the cut-off frequency (cross-over frequency in this example) to the value that is determined in a stored database. For this example, the cut-off frequencies may be set to <NUM> for no speech and <NUM> for speech.

<FIG> shows a block diagram for another example use case. Here the cut-off/cross-over frequency is adjusted based on the presence of wind noise in the environment <NUM>.

The environment noise sensing block 50B processes sound recorded by an environmental microphone <NUM> and determines in which (if any) parts of the frequency spectrum wind noise is present. This may be done by comparing, frequency band-wise, level differences in microphone signals captured by spatially separated the microphones <NUM>, for example, microphones <NUM> on the different left and right parts <NUM>L, <NUM>R. If the level difference in a frequency band is over a threshold e.g. 6dB, this band is considered to contain wind noise.

The cut-off/cross-over frequency is set by the cut-off/cross-over frequency determination block <NUM> (this corresponds to the filter controller <NUM>) so that the highest frequency band that contains wind noise is 'covered' by the bone-conduction channel. For example, if a frequency band, let's say <NUM>-<NUM> is the highest which contains wind noise, the cut-off/cross-over frequency is increased to <NUM>. If no wind-noise is present the cut-off frequency is maintained at <NUM>.

<FIG> shows a block diagram for another example use case where the cut-off/cross-over frequency is adjusted based on both the presence of speech content in the content of the audio signals <NUM> rendered to the user <NUM> and also the presence of wind noise in the environment <NUM>.

The cut-off/cross-over frequency is set to the highest one of the two values determined by the two separate use cases described above for <FIG>. That is, both the wind-noise dependent cut-off/cross-over frequency and the speech content dependent cut-off/cross-over frequency are determined as in the previous examples at cut-off/cross-over frequency determination block <NUM> and the highest one of these is used as the cut-off/cross-over frequency of the filter.

It will therefore be appreciated that the apparatus <NUM> comprises means for:
adaptively filtering audio output channels <NUM> for rendering separately via a head-positioned audio output device comprising automatically changing a cut-off frequency of at least a first filter <NUM> of a first audio output channel <NUM>.

<FIG> illustrates an example of a controller <NUM>. Implementation of a controller <NUM> may be as controller circuitry. The controller <NUM> may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware).

The memory <NUM> stores a computer program <NUM> comprising computer program instructions (computer program code) that controls the operation of the apparatus <NUM> when loaded into the processor <NUM>. The computer program instructions, of the computer program <NUM>, provide the logic and routines that enables the apparatus to perform the methods illustrated and described. The processor <NUM> by reading the memory <NUM> is able to load and execute the computer program <NUM>.

As illustrated in <FIG>, the computer program <NUM> may arrive at the apparatus <NUM> via any suitable delivery mechanism <NUM>. The delivery mechanism <NUM> may be, for example, a machine readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid state memory, an article of manufacture that comprises or tangibly embodies the computer program <NUM>. The delivery mechanism may be a signal configured to reliably transfer the computer program <NUM>. The apparatus <NUM> may propagate or transmit the computer program <NUM> as a computer data signal.

Computer program instructions for causing an apparatus to perform at least the following or for performing at least the following:
The computer program <NUM> that when run on at least one processor of an audio output apparatus <NUM> comprising a hybrid audio system <NUM> comprising multiple transducers <NUM> configured to render sound for a user <NUM> of the apparatus <NUM> into different audio output channels <NUM>, causes an automatic change of a cut-off frequency of one or more audio output channels <NUM> in dependence upon the one or more transducers <NUM> associated with the respective one or more audio output channels <NUM>.

The blocks illustrated in the FIGs may represent steps in a method and/or sections of code in the computer program <NUM>. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

As used here 'module' refers to a unit or apparatus that excludes certain parts/components that would be added by an end manufacturer or a user. The apparatus <NUM> can be a module.

The above described examples find application as enabling components of:.

The term 'a' or 'the' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use 'a' or 'the' with an exclusive meaning then it will be made clear in the context. In some circumstances the use of 'at least one' or `one or more' may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

Claim 1:
A head-mounted audio output apparatus (<NUM>) comprising:
at least one hybrid audio system (<NUM>) comprising multiple transducers (<NUM>), wherein the hybrid audio system (<NUM>) is configured to render sound for a user (<NUM>) of the head-mounted audio output apparatus (<NUM>) into different audio output channels (<NUM>) using different associated transducers of the multiple transducers (<NUM>) , wherein the hybrid audio system is configured to render sound for the user of the apparatus into a bone-conduction audio output channel using an associated bone-conduction transducer and an air-conduction audio output channel using an associated air-conduction transducer;
means for changing a cut-off frequency of at least a first one of the audio output channels (<NUM>) in dependence upon the transducer associated with the first one of the audio output channels, wherein the first one of the audio output channels is the bone-conduction audio output channel, and
wherein the means for changing a cut-off frequency of at least the first one of the audio output channels is configured to:
automatically change a cross-over frequency of the first one of the audio output channels and a second one of the audio output channels; and
automatically change the cut-off frequency of the first one of the audio output channels in dependence upon spectral analysis of exterior noise.