Patent Description:
A vehicle may include an internal combustion engine for generating mechanical energy to drive the vehicle. The configuration of the engine, such as the arrangement of engine cylinders and valve timing for intake and exhaust valves, impacts the sound generated by the engine. For vehicles with different engine configurations, even with a same number of engine cylinders, the vehicles may sound substantially different. Some drivers may desire a certain engine sound. For example, some drivers may prefer a louder, raspier engine sound and thus may prefer to drive a sports car, while other drivers may prefer a smoother and quieter engine sound.

Various methods exist for enhancing the sound of an engine based on a desired engine sound. For example, an engine sound may be digitally synthesized based on current operating conditions, such as the revolution per minute (RPM) of the engine. However, for sporty engines with rapidly-changing RPM, such synthesis can sound artificial and unresponsive. Meanwhile, traditional acoustic sound synthesis requires a delicate tuning process to design layers of narrowband and broadband sound to be authentic.

<CIT> describes a vehicle sound synthesis system with a controller and a loudspeaker. The controller is programmed to receive an input indicative of at least one of a gear selection, an engine speed, and a pedal position and to generate an audio signal indicative of synthesized engine noise (SEN). The controller is further programmed to attenuate the audio signal at a first rate in response to at least one of the gear selection, the engine speed, and the pedal position indicating first vehicle conditions. The loudspeaker is adapted to project sound within a passenger compartment of a vehicle in response to receiving the attenuated audio signal.

<CIT> describes an active sound management system comprising a transducer that senses an actual sound or vibration from a sound generating source and generates a transducer signal in response to sensing the actual sound or vibration; a harmonic extractor device that extracts a plurality of harmonics from the transducer signal; and a harmonic modifier device that adjusts a feature of the extracted harmonic to be within a predetermined threshold with respect to a target harmonic corresponding to a desired sound.

<CIT> describes an automobile sound processing system having a detection device with which the automobile sound that is generated by the motive power section of an automobile is detected. The system also includes an input with which the automobile sound that has been detected by the detection means is input. The system further includes an effect imparting device with which an effect is imparted to the automobile sound that is input in conformance with the operating state of the motive power section of the automobile.

<CIT> describes an engine sound processing system. Microphones are provided to an intake port of an engine and a wall surface of an engine room on the interior side respectively to collect an engine sound. The engine sound is processed by a signal processing portion and output via a speaker provided to an interior of a vehicle. Filters for simulating the noise insulating characteristic in the interior of the vehicle and filters for processing the engine sound to emphasize the driving conditions are provided to the signal processing portion.

<CIT> describes a sound enhancement system of an engine of a vehicle including a vibration sensor disposed on the casing of the engine to generate an electrical signal indicative of the engine sound. A signal processor is connected to the vibration sensor to process the electrical signal-indicative of the engine sound and generate an output audio signal. A speaker is disposed in the vehicle compartment and connected to the signal processor to receive the output audio signal and generate an enhancement sound of the engine sound.

The dependent claims recite selected optional features.

In order to enhance the engine sound while maintaining authenticity, the original engine sound may be measured and the engine harmonics may be enhanced in real-time by filtering the spurious content. A more realistic sound enhancement in the vehicle cabin may thus be obtained by using the original engine sound as a source, instead of a synthesized signal. To capture the original engine sound, a sensor such as an accelerometer is installed directly onto the engine block, which captures the harmonic content originally generated by the engine, avoiding all other sound artifacts occurring close to the engine which would be captured by a sound pressure sensor such as a microphone.

Embodiments are disclosed for enhancing engine sound.

The disclosure may be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:.

<FIG> is a block diagram of an example system <NUM> within a vehicle <NUM> for enhanced vehicle sound synthesis. The system <NUM> may be located and/or integrated within the vehicle <NUM>. The system <NUM> includes one or more vehicle systems <NUM> such as an engine <NUM> of the vehicle <NUM>. The vehicle system <NUM> further includes a sensor <NUM>, such as an accelerometer, mounted to the engine <NUM> to measure the harmonic content generated by the engine <NUM>. By mounting the sensor <NUM> directly onto the engine <NUM>, the sensor <NUM> may avoid measuring or recording other sound artifacts occurring close to the engine <NUM>, which would be captured by an airborne sound-pressure sensor, such as a microphone.

The system <NUM> further includes a computing system <NUM> comprising at least a processor <NUM> and a memory <NUM>. The processor <NUM> may comprise one or more central processing units (CPU), a graphics processing units (GPU), digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA), analog circuits, or combinations thereof. The memory <NUM> may include one or more of a main memory, a static memory, and a dynamic memory. The memory <NUM> may comprise a non-transitory memory device. The memory <NUM> may further comprise one or more volatile and/or non-volatile storage media including but not limited to random access memory, read-only memory, and the like. Executable instructions or software may be stored in the memory <NUM> that may be executed or processed by the processor <NUM>.

The computing system <NUM> may communicate with one or more elements within the vehicle, including but not limited to vehicle systems <NUM> such as the engine <NUM> connected via an in-vehicle interconnect, such as Controller-Area-Network (CAN) bus <NUM>. It should be understood that any suitable number and/or combination of interconnects may be used to permit communication between the computing system <NUM> and various in-vehicle components, including but not limited to CAN buses, Media Oriented Systems Transport (MOST) buses, Ethernet-based interconnects, and so on. Interconnects may communicate directly with in-vehicle components and/or may communicate with such components via intervening processors. In some embodiments, one or more in-vehicle components may communicate directly with the computing system <NUM> without or in addition to communicating with the computing system <NUM> via the CAN bus <NUM>. For example, a sensor <NUM> mounted on the engine <NUM> may directly communicate measurements to the computing system <NUM>. The sensor <NUM> may comprise an accelerometer configured to measure acceleration, for example by measuring vibrations of the engine <NUM>, as described hereinabove. Further, the computing system <NUM> may receive measurements of various operating parameters or operating conditions of the vehicle system <NUM> such as engine load or torque, engine RPM, gas pedal position, and so on, as CAN messages via the CAN bus <NUM>.

The computing system <NUM> is communicatively coupled to audio speakers <NUM> distributed throughout the vehicle <NUM> via an audio amplifier <NUM>. As described further herein, the computing system <NUM> is configured to perform digital signal processing of the signal from the sensor <NUM>, based on CAN messages from the CAN bus <NUM>, in order to enhance engine sounds. The enhanced engine sounds are output, via the audio amplifier <NUM>, to the plurality of audio speakers <NUM> in order to enhance the original engine sound of the engine <NUM> within the cabin of the vehicle <NUM>.

<FIG> is a block diagram illustrating an example method <NUM> for enhanced vehicle sound synthesis. A vehicle <NUM> may comprise a motor vehicle, for exampling, including drive wheels and an internal combustion engine. The vehicle <NUM> may comprise a road automobile, among other types of vehicles. In some examples, the vehicle <NUM> may include a hybrid propulsion system including an energy conversion device operable to absorb energy from vehicle motion and/or the engine and convert the absorbed energy to an energy form suitable for storage by an energy storage device. The vehicle <NUM> may comprise the vehicle <NUM> described hereinabove, for example.

The internal combustion engine of the vehicle <NUM> may include one or more combustion chambers which may receive intake air via an intake passage and exhaust combustion gases via an exhaust passage. The internal combustion engine, or simply the engine, may comprise a four-cycle engine, wherein power is obtained via an intake cycle, a compression cycle, an explosion/expansion cycle, and an exhaust cycle. The engine may comprise a plurality of combustion chambers or cylinders, which may be arranged in series, in a V shape, or in parallel, as illustrative examples. While the four cycles are performed in the engine, a piston of the engine is raised or lowered, thereby rotating a crankshaft mechanically connected to the piston. The rotation of the crankshaft is transferred to wheels of the vehicle <NUM>, thereby moving the vehicle <NUM> forward or backward. The crankshaft thus continuously rotates in accordance with repeated cycles of the engine, wherein the rate of rotations of the crankshaft or the revolutions per minute (RPM) of the crankshaft is referred to as the engine RPM. The engine RPM may vary by increasing or decreasing throughout the operation of the vehicle <NUM>.

As shown, an accelerometer (ACC) <NUM> may be located or integrated into the vehicle <NUM>, for example by mounting the accelerometer <NUM> onto the engine of the vehicle <NUM>. The accelerometer <NUM> measures vibrations of the engine over time. The combustion cycles described hereinabove cause vibration of the engine, such that the engine vibrates with a variety of frequencies according to various factors including but not limited to engine RPM, torque, throttle position, vehicle velocity, amount of fuel injection, and so on. For example, as the engine RPM or simply RPM increases, the vibration frequency increases. As an illustrative and non-limiting example, a signal <NUM> acquired via the accelerometer <NUM> during operation of the engine of the vehicle <NUM> may comprise a measure of loudness (measured in decibels) as a function of frequency and RPM, wherein the intensity of vibrations in a given frequency band may be higher or lower than the intensity of vibrations in a different frequency band.

Further, engine sound is generated by the combustion within the engine as well as the vibration. While the engine generates a range of frequencies, especially under load, the root note of the engine sound is defined by a dominant frequency. As an illustrative example, for a six-cylinder engine operating at <NUM> RPM, which corresponds to a frequency of <NUM>, with a four-stroke cycle, each cylinder fires once every two crankshaft rotations. Therefore, as the number of ignition events per crankshaft revolution is three for a six-cylinder engine, the dominant frequency at <NUM> RPM is <NUM>. As the dominant frequency is three times the frequency of engine rotation, the dominant frequency is a third engine order or simply third order for a six-cylinder engine. Similarly, the dominant frequency for a two-cylinder engine is the first order, the dominant frequency for a four-cylinder engine is the second order, the dominant frequency for an eight-cylinder engine is the fourth order, the dominant frequency for a ten-cylinder engine is the fifth order, and so on.

In order to enhance the engine sound, the vibrations recorded by the accelerometer <NUM> may be filtered with a digital signal processing module <NUM> configured to enhance the engine sound. For example, as depicted by the graph <NUM> of <FIG>, a signal <NUM> acquired by the accelerometer <NUM> (e.g., the signal <NUM>) may be filtered with a plurality of bandpass filters <NUM> wherein the center frequency of the bandpass filters is guided by the RPM. In particular, each bandpass filter of the plurality of bandpass filters <NUM>, such as the bandpass filter <NUM>, the bandpass filter <NUM>, and the bandpass filter <NUM>, may be applied to a corresponding mode of the vibration signal to enhance the engine sound. Furthermore, the gain and the Q factor of the filters may be tuned based on operating conditions such as gas pedal position, engine load or engine torque, throttle position, and so on. Thus, the method <NUM> includes capturing the original engine sound <NUM>, or more specifically the harmonic content originally generated by the engine, with the accelerometer <NUM> and enhancing the engine sound with a bandpass filter for different modes of the original engine sound <NUM>. The enhanced engine sound <NUM> is then provided to one or more speakers <NUM> positioned within the vehicle <NUM> to play back the enhanced engine sound <NUM> to occupants of the vehicle <NUM>. The method <NUM> thus creates a realistic sound enhancement in the cabin of the vehicle <NUM> by using the original engine sound <NUM> as a source, rather than a synthesized signal such as oscillators or a stored sound bank.

<FIG> is a block diagram illustrating an example digital signal processing method <NUM> for enhanced vehicle sound synthesis. The digital signal processing method <NUM> may be implemented via the computing system <NUM> described hereinabove, for example, as the DSP module <NUM>.

Sensor input <NUM> comprises the signal from the sensor <NUM> or the accelerometer <NUM> as described hereinabove. That is, the sensor input <NUM> comprises measurements of the vibrations of the engine <NUM>. As the sensor <NUM> may sample the engine vibrations at a high rate, the sensor input <NUM> is downsampled <NUM> to a lower sampling rate by a factor M. The downsampled signal is then upmixed <NUM> from a single channel to a number of channels corresponding to a number of engine orders for enhancement. In an illustrative and non-limiting example, the downsampled signal is upmixed <NUM> or converted from a single channel to four channels of the same downsampled data. Each channel is then input to a corresponding order filter <NUM>. For example, as depicted, the order filters <NUM> may include four order filters (e.g., bandpass filters) for four different engine orders. The engine orders may correspond to whole orders, half orders (e.g., <NUM> order), and so on, depending on the particular configuration of the engine (e.g., the arrangement of the cylinders and the tuning of the various intake/exhaust valves) and thus the desired orders for enhancing. The orders are thus tuned to the firing order of the engine as described hereinabove. It should be appreciated that the method <NUM> may be adapted for a number of channels and a corresponding number of order filters other than four channels and four order filters. For example, the number of channels may be greater than or less than four in some examples, and so the number of engine orders and order filters may be greater than or less than four in such examples.

A plurality of CAN messages <NUM> or CAN signals, corresponding to measurements of RPM and torque, are also obtained via the CAN bus, as depicted, for the signal processing method <NUM>. The CAN signals <NUM> are used to adjust each order filter according to the current operating conditions of the engine. The gain, Q value, and center frequency (f) for each order are determined based on the CAN signals <NUM> to adjust the order filters <NUM>. In particular, the RPM and the torque are used to determine, via a three-dimensional gain lookup table <NUM> that returns a gain value for a pair of RPM and torque measurements, a gain value for each order filter. Further, the RPM and the torque are used to determine, via a three-dimensional Q value lookup table <NUM> that returns a Q value for a pair of RPM and torque measurements, a Q value for each order filter. Further, the RPM is used to determine, via an order lookup table <NUM>, a center frequency (f) for each order based on the RPM measurement. Thus, the order filters <NUM> are adapted, for each order, based on the current operating conditions. The lookup tables <NUM>, <NUM>, and <NUM> are tunable to provide desired enhancement of different orders for different combinations of operating conditions.

Thus, the order filters enhance the engine harmonics by filtering out spurious content. As the engine harmonics vary their frequencies proportionally with RPM, the filters should be reactive enough to filter precisely without stability issues when a new CAN parameter arrives. Therefore, state variable filters may be used for the order filters <NUM>. As another technique, filter coefficient morphing may be used to update the order filters as the operating conditions change. For example, to transition from an initial filter (based on a first set of operating conditions or a first set of RPM and torque measurements) to a target filter (based on a second set of operating conditions), the filter coefficients of the two filters may be blended according to a specified blend factor. Thus, the bandpass filters comprising the order filters shift in frequency, gain, and quality factor Q as a function of the RPM and torque measurements, wherein upon receiving the parameters (i.e., f, Q, and G), the filter coefficients are calculated via coefficient morphing.

As an illustrative and non-limiting example, <FIG> shows example spectrograms before and after filtering, including an original spectrogram <NUM> prior to filtering and a filtered spectrogram <NUM> after filtering, wherein the spectrograms <NUM> and <NUM> depict the spectrum of frequencies over time or samples. In particular, the original spectrogram <NUM> is obtained for a V8 engine during acceleration wherein RPM is ramping up. The spectrogram is analyzed to choose initial and target frequencies for the order filters to enhance only one harmonic (e.g., a single order), while maintaining the quality factor Q and the gain constant between the initial and target filters. The filtered spectrogram <NUM> depicts the signal after filtering according to the digital signal processing method <NUM> with coefficient morphing as mentioned hereinabove for every sample. Thus, as the frequency ramps up as depicted, the order filters may filter out a desired harmonic in real-time without audible transients or undesirable effects. The filters perform well even when changing parameters, such as RPM, rapidly.

Referring again to <FIG>, after order filtering each channel based on the operating conditions, the filtered output is passed through corresponding equalization (EQ) filters <NUM> to further filter out or eliminate high-frequency content. The EQ filters <NUM> thus reinforce the order filters <NUM>. The EQ filters <NUM> are tunable, and up to ten EQ filters for each order may be provided, depending on the application. The EQ filters <NUM> may comprise low-pass filters.

After EQ filtering at <NUM>, the four filtered channels are then mixed via a tunable order mixer <NUM> into a single mono output. After summing the filtered signals into the mono signal, the gain of the mono signal is adjusted. For example, based on the RPM and torque measurements of the CAN signals <NUM>, a main gain is obtained from a three-dimensional main gain lookup table <NUM>, and the gain of the mono signal is adjusted according to the main gain. The gain-adjusted signal is then upsampled <NUM> to the original sampling rate of the sensor input <NUM>, for example by a factor L, and then upmixed <NUM> to a plurality of channels as depicted. For example, the signal may be upmixed <NUM> to four channels, with one channel for each speaker of the plurality of speakers <NUM> that will output the enhanced engine sound, though it should be appreciated that the method <NUM> may be adapted for a number of channels and respective speakers greater than four or less than four.

Delays <NUM> are applied to each channel based on the relative distribution of the speakers <NUM> throughout the cabin of the vehicle, such that enhanced engine sound is perceived as coming from the engine. For example, if the engine is positioned in the front of the vehicle, the signals may be delayed such that an occupant of the vehicle perceives the enhanced engine sound as coming from the front of the vehicle. Similarly, if the engine is positioned in the rear of the vehicle, the signals may be delayed such that the occupant perceives the enhanced engine sound as coming from the rear of the vehicle.

In addition, a limiter <NUM> may be applied to the signals, such that if one of the channel levels needs to be decreased, the other channels may be adjusted as well, thereby balancing the signals. After passing the signals through the limiter <NUM>, the signals are output to respective speakers <NUM> of the vehicle. The signals may be added to the normal audio content (e.g., radio or other musical playback, other audio playback such as navigation prompts, warning chimes, and so on) already being output to the speakers <NUM>. By delaying and limiting the signals as described hereinabove prior to mixing the signals into the pre-existing audio output of the speakers <NUM>, the enhanced engine sound comprising the signals may create the spatial image regardless of audio balancing for the audio system including the speakers <NUM>. For example, audio such as music may be played back through the speakers <NUM> with balanced levels and a stereo audio distribution, while the enhanced engine sound signals superimposed onto the musical audio is perceived with the spatial image or spatial effect such that the engine sound generated by the engine is enhanced with the enhanced engine sound.

As indicated by the legend, the delays <NUM> and the limiter <NUM> may also be tunable according to the desired application or configuration of the vehicle (e.g., the configuration of the engine, the configuration and number of the speakers, and so on). It should be appreciated that some parameters, such as the EQ filters <NUM>, the order mixer <NUM>, the delay <NUM>, and the limiter <NUM> may be tuned once based on the desired application or configuration of the vehicle, and do not change in real time. Other parameters change in real-time when a new CAN message arrives, for example, to change the harmonics filters. While the CAN protocol normally works at a rate of <NUM> or <NUM>, in order to avoid de-synchronization between the actual engine sound and the output of the signal processing, the CAN protocol preferably operates at <NUM>. The parameters that may be tuned in real-time are thus the order frequency, the 3D gain table, the 3D quality factor table, and the 3D main gain table.

As another illustrative and non-limiting example, <FIG> is a block diagram illustrating another example digital signal processing chain <NUM> for enhanced vehicle sound synthesis. A sensor input <NUM>, such as the signal from a sensor such as an accelerometer, is downsampled <NUM>, and then upmixed <NUM> to a desired number of channels. In the depicted example, the signal is upmixed to fourteen channels for fourteen orders. Selectively filtering such a number of filters for such a number of orders enables a more fine-tuned control over the enhancement of the engine sound. To that end, CAN signals such as the RPM measurement <NUM> and the throttle position <NUM> may be used to adjust the order filters <NUM> for each order based on a plurality of lookup tables <NUM>. For example, as depicted, the RPM <NUM> may be used to determine a center frequency (f) for each order. Further, the RPM <NUM> and the throttle position <NUM> may be used to determine a gain (G) for each order and a quality factor (Q) for each order. The lookup tables <NUM> may be tuned according to the desired enhancement of engine orders based on the RPM and the throttle position. Each order filter <NUM> is therefore adjusted to target a specific order. After order filtering at <NUM>, the fourteen filtered signals may be mixed or summed via the order mixer <NUM> into a mono output. The gain of the mono output is adjusted as desired at <NUM>, and then upmixed <NUM> into a desired number of channels. The signal for each channel is then filtered, for example with a tunable biquad filter <NUM>, prior to outputting the signals to speakers <NUM>.

To illustrate how the order filters are adjusted for each order, <FIG> depict different order filters for four different orders. In particular, <FIG> shows a set of graphs <NUM> illustrating example lookup tables for determining an example first order filter for a first order. The set of graphs <NUM> include a graph <NUM> illustrating a first order filter for the first order. An example three-dimensional gain lookup table that outputs a gain for a given RPM and torque measurement is depicted as two two-dimensional lookup tables, namely the gain-RPM lookup table <NUM> and the gain-torque lookup table <NUM>. Similarly, an example three-dimensional quality factor lookup table that outputs a quality factor Q for a given pair of RPM and torque measurements is depicted as two two-dimensional lookup tables, namely the Q-RPM lookup table <NUM> and the Q-torque lookup table <NUM>. The gain and Q factors for the first order filter depicted in graph <NUM> are thus determined based on the RPM measurement <NUM> and the torque measurement <NUM>. Further, the center frequency of the first order filter depicted in the graph <NUM> is determined based on the RPM measurement <NUM>.

Similarly, <FIG> shows a set of graphs <NUM> illustrating example lookup tables for determining an example second order filter for a second order. The set of graphs <NUM> include a graph <NUM> illustrating a second order filter for the second order, as well as a gain-RPM lookup table <NUM>, a gain-torque lookup table <NUM>, a Q-RPM lookup table <NUM>, and a Q-torque lookup table <NUM> for the second order. The gain and Q factors for the second order filter depicted in graph <NUM> are thus determined based on the RPM measurement <NUM> and the torque measurement <NUM>. Further, the center frequency of the second order filter depicted in the graph <NUM> is determined based on the RPM measurement <NUM>.

<FIG> shows a set of graphs <NUM> illustrating example lookup tables for determining an example third order filter for a third order. The set of graphs <NUM> include a graph <NUM> illustrating a third order filter for the third order, as well as a gain-RPM lookup table <NUM>, a gain-torque lookup table <NUM>, a Q-RPM lookup table <NUM>, and a Q-torque lookup table <NUM> for the third order. The gain and Q factors for the third order filter depicted in graph <NUM> are thus determined based on the RPM measurement <NUM> and the torque measurement <NUM>. Further, the center frequency of the third order filter depicted in the graph <NUM> is determined based on the RPM measurement <NUM>.

<FIG> shows a set of graphs <NUM> illustrating example lookup tables for determining an example fourth order filter for a fourth order. In particular, the set of graphs <NUM> include a graph <NUM> illustrating a fourth order filter for the fourth order, as well as a gain-RPM lookup table <NUM>, a gain-torque lookup table <NUM>, a Q-RPM lookup table <NUM>, and a Q-torque lookup table <NUM> for the fourth order. The gain and Q factors for the fourth order filter depicted in graph <NUM> are thus determined based on the RPM measurement <NUM> and the torque measurement <NUM>. Further, the center frequency of the fourth order filter depicted in the graph <NUM> is determined based on the RPM measurement <NUM>.

<FIG> shows a high-level flow chart illustrating an example method <NUM> for enhanced vehicle sound synthesis. The method <NUM> may be implemented, for example, as the digital signal processing method <NUM> in the computing system <NUM>, as a non-limiting example.

Method <NUM> begins at <NUM>. At <NUM>, method <NUM> receives a sensor signal, such as the sensor input <NUM> from the sensor <NUM>. Further, at <NUM>, method <NUM> receives measurements of RPM and torque, for example via the CAN bus <NUM>. At <NUM>, method <NUM> downsamples the sensor signal. At <NUM>, method <NUM> upmixes the downsampled sensor signal into a number of channels according to a number of orders. At <NUM>, method <NUM> determines a gain value and a Q value for each order based on the RPM and torque, for example by retrieving the gain values and Q values from the lookup tables <NUM> and <NUM>. Further, at <NUM>, method <NUM> determines a center frequency for each order based on the RPM, for example by retrieving center frequencies for each order from the order lookup table <NUM>.

At <NUM>, method <NUM> determines an order filter for each order based on the gain, Q value, and center frequency. Each order filter is different, as described hereinabove with regard to <FIG>. Further, the filter coefficients may also be determined according to filter coefficient morphing in order to maintain stability and prevent transient frequencies from passing through. At <NUM>, method <NUM> applies each order filter to a corresponding channel of the downsampled sensor signal. Further, at <NUM>, method <NUM> applies an equalization filter to each order filtered channel to filter out high-frequency content. After filtering each channel, method <NUM> continues to <NUM>. At <NUM>, method <NUM> mixes the equalized signals into a single channel output. At <NUM>, method <NUM> determines a main gain based on the RPM and torque. At <NUM>, method <NUM> adjusts the gain of the single channel output based on the main gain. At <NUM>, method <NUM> upsamples the gain-adjusted single channel output. At <NUM>, method <NUM> upmixes the upsampled signal into a plurality of channels, including one channel for each speaker. At <NUM>, method <NUM> adjusts a delay for each channel based on speaker position. At <NUM>, method <NUM> applies a limiter to the signals to balance the levels. At <NUM>, method <NUM> outputs the signals to a plurality of speakers. Method <NUM> then returns.

The description of embodiments has been presented for purposes of illustration and description. Suitable modifications and variations to the embodiments may be performed in light of the above description or may be acquired from practicing the methods. For example, unless otherwise noted, one or more of the described methods may be performed by a suitable device and/or combination of devices, such as the vehicle systems described above with respect to <FIG> and <FIG>. The methods may be performed by executing stored instructions with one or more logic devices (e.g., processors) in combination with one or more hardware elements, such as storage devices, memory, hardware network interfaces/antennas, switches, actuators, clock circuits, and so on. The described methods and associated actions may also be performed in various orders in addition to the order described in this application, in parallel, and/or simultaneously. The described systems are exemplary in nature, and may include additional elements and/or omit elements.

Claim 1:
A method (<NUM>) for a vehicle, comprising:
acquiring (<NUM>) a signal including harmonic content generated by an engine of the vehicle;
upmixing (<NUM>) the signal into a plurality of channels for a given number of engine orders, the engine orders corresponding to multiples of a frequency of rotations of a crankshaft of the engine multiplied by a number of ignition events per rotation of the crankshaft of the engine;
adjusting (<NUM>) an order filter for each engine order of the given number of engine orders based on operating conditions of the engine;
filtering (<NUM>) each channel of the plurality of channels with the corresponding order filter;
mixing (<NUM>) the filtered channels into a mono output; and
outputting (<NUM>) the mono output to at least one speaker in the vehicle,
characterized in that adjusting the order filter for each engine order based on the operating conditions of the engine comprises adjusting a gain and a quality factor for each order filter based on measurements of revolutions per minute, RPM, of the engine and torque of the engine, and further adjusting a center frequency for each order filter based on the RPM.