Patent Description:
Active acoustic noise cancellation systems generate anti-noise signals to be transduced into acoustic signals intended to destructively interfere with undesired acoustic noise such that the undesired noise is reduced. These systems can operate on a very personal level, such as in headphones, or in a broader noise reduction zone, such as a region near a user's head. Automotive systems may operate to reduce acoustic noise near one or more occupants' heads and/or more generally throughout the vehicle interior. Some such systems may include sensors to detect the source of the noise and provide a reference signal correlated to the undesired sound, as in feedforward systems. Various systems include error sensors, such as microphones, to detect the resulting acoustic sound in the zone of interest and provide error signals, as a feedback signal, such that the system may adjust. Various noise cancellation systems may use one or more reference signals and/or error signals to adjust one or more anti-noise signals, transduced by various loudspeakers, to optimize reduction of noise in the zone.

<CIT> discloses a method which reduces the number of instructions per second required to perform music compensation. <CIT> makes use of sample rate down conversion so as to reduce the processing bandwidth required to implement an ANC. <CIT> discloses reducing sound of the tire cavity resonance in a vehicle, by synthesizing frequencies of the tire cavity resonance according to the rotational speed of the tire.

The present invention relates to a method and a system for reducing noise and a noise cancellation system according to the independent claims. Advantageous embodiments are set forth in the dependent claims of the appended set of claims.

Systems and methods disclosed herein are directed to audio systems and methods that use one or more microphones to detect narrowband acoustic noise and to generate one or more driver signals to be transduced by one or more speakers to cause a reduction in the acoustic noise level in the region of the microphone(s). Narrowband noise is associated with a resonance of an acoustic region, such as a wheel cavity (e.g., a standing wave inside the wheel of an automobile) or a cabin of a vehicle.

Audio systems and methods herein select one or more frequency ranges in which to analyze microphone signal(s) to detect the presence of narrowband noise related to a resonance, and to identify the frequency phase, and width of the narrowband noise. Frequency ranges in which various resonances or other narrowband noise occur are known to the system a priori, and the system analyzes a spectrum of the microphone signal(s) to find a resonant peak within the frequency range. The system uses a portion of the signal around the peak as a feedback signal to actively generate one or more anti-noise signals.

According to the invention, noise cancellation systems and methods are provided that receive a signal representative of noise in a cancellation zone, identify a frequency within the signal to be reduced in the cancellation zone, down convert the signal to place the identified frequency component at baseband, generate a baseband anti-noise signal based upon the down converted signal, up convert the baseband anti-noise signal to the identified frequency to produce an anti-noise signal having components at the identified frequency, and provide the anti-noise signal to be transduced into an acoustic signal.

The signal representative of noise in the cancellation zone is a microphone signal.

According to the invention, identifying a frequency within the signal to be reduced in the cancellation zone includes analyzing the signal to identify a frequency having a peak in the spectrum of the signal. According to the invention, identifying a frequency within the signal to be reduced in the cancellation zone includes down converting the signal to baseband and analyzing the down converted signal to identify one or more peaks in the spectrum of the down converted signal.

According to the invention, identifying a frequency within the signal to be reduced in the cancellation zone includes analyzing the signal in a pre-selected range of frequencies. The pre-selected range of frequencies is associated with a cavity resonance. Further in particular examples, the cavity resonance may be associated with at least one of a wheel cavity and a vehicular cabin cavity.

In some examples, the anti-noise signal having components at the identified frequency is a narrowband anti-noise signal having components at and around the identified frequency. The components at and around the identified frequency may be limited to a range of frequencies <NUM> below the identified frequency and <NUM> above the identified frequency, in various examples. The components at and around the identified frequency is limited to a range of frequencies <NUM> below the identified frequency and <NUM> above the identified frequency, in certain examples.

The anti-noise signal includes frequency components having amplitude and phase characteristics to destructively interfere with narrowband noise at or around the identified frequency.

Noise cancellation systems include a sensor to provide the signal representative of noise in a cancellation zone. The sensor is a microphone.

Noise cancellation systems include a loudspeaker that receives the anti-noise signal and transduces the anti-noise signal into an acoustic signal.

Noise cancellation systems include a controller configured to perform the noise cancellation method. The controller may include a processor and a memory in various examples.

Still other aspects, examples, and advantages of these exemplary aspects and examples are discussed in detail below. Examples disclosed herein may be combined with other examples in any manner consistent with at least one of the principles disclosed herein, and references to "an example," "some examples," "an alternate example," "various examples," "one example" or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one example. The appearances of such terms herein are not necessarily all referring to the same example.

Various aspects of at least one example are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and examples, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the inventions. In the figures, identical or nearly identical components illustrated in various figures may be represented by a like reference character or numeral. In the figures:.

Aspects of the present disclosure are directed to noise cancellation systems and methods that use a microphone to provide a feedback signal and that analyze the feedback signal for the presence of narrowband noise in pre-selected frequency ranges. Such narrowband noise are associated with resonant noise sources. In some examples, the resonant noise sources are associated with an acoustic volume, or cavity, such as a wheel cavity (the air space inside a tire) or a cabin cavity. Such resonant cavities are pre-determined to produce narrowband resonant noise in one or more frequency ranges.

The systems and methods herein adapt to the feedback signal to provide anti-noise signals to be transduced by one or more loudspeakers to interfere with the narrowband noise and thereby reduce the level of narrowband noise in a listening region. In various examples, noise cancellation systems and methods herein may be integrated with various audio systems that also include audio for entertainment, communication, guidance, warning prompts, and the like. In various examples, noise cancellation systems and methods herein may provide the anti-noise signal(s) to a separate audio system to be included in various driver signals to loudspeakers, such as may also include other audio for entertainment, communication, guidance, warning prompts, and the like.

<FIG> is a schematic view of a noise-cancellation system <NUM>. Noise-cancellation system <NUM> is configured to destructively interfere with undesired sound in at least one cancellation zone <NUM> within a predefined volume <NUM> such as a vehicle cabin. At a high level, a noise-cancellation system <NUM> includes one or more microphones <NUM>, one or more loudspeakers <NUM>, and a controller <NUM>. Some examples may include a reference sensor, such as may sense a vibration of one or more components. Some examples may include other reference inputs, such as for receiving information about vehicle speed, engine RPM, torque, etc., such as information from which the controller <NUM> may determine a range of frequencies in which to analyze microphone signals for narrowband noise.

One or more anti-noise signals are generated by controller <NUM> and provided to the one or more loudspeakers <NUM> in the predefined volume, which transduce the anti-noise signal(s) into acoustic energy (i.e., sound waves). The acoustic energy produced as a result is approximately <NUM>° out of phase with-and thus destructively interferes with-the undesired sound within the cancellation zone <NUM>. The combination of sound waves generated from the anti-noise signal(s) and the undesired noise in the predefined volume results in a reduction of the undesired noise, as perceived by a listener in the cancellation zone <NUM>.

Microphone <NUM>, disposed within the predefined volume, generates an error signal based on detection of residual noise resulting from the combination of the sound waves in the cancellation zone, including the undesired noise. The error signal is provided to controller <NUM> as feedback, the error signal at least partially representing residual noise uncanceled by the anti-noise signal(s). Microphone <NUM> can be, for example, at least one microphone mounted within a vehicle cabin (e.g., in the roof, headrests, pillars, or elsewhere within the cabin).

It should be noted that the cancellation zone(s) can be positioned remotely from microphone <NUM>. In such case, the error signal may be filtered to represent an estimate of the residual noise in the cancellation zone(s). In either case, the error signal will be understood to represent residual undesired noise in the cancellation zone.

In various examples, controller <NUM> can comprise a non-transitory storage medium <NUM> and a processor <NUM>. In an example, non-transitory storage medium <NUM> can store program code that, when executed by processor <NUM>, implements the various filters and algorithms described below. Controller <NUM> can be implemented in hardware and/or software. For example, the controller can be implemented by a SHARC floating-point DSP processor, but it should be understood that controller <NUM> can be implemented by any other processor, FPGA, ASIC, or other suitable hardware.

<FIG> illustrates an example operation of the noise-cancellation system <NUM> including processes performed by the controller <NUM>. The physical plant <NUM> represents the physical transfer function of the anti-noise signal(s) through the loudspeakers <NUM>, the vehicle interior (e.g., the predefined volume <NUM>), and the response of the microphone(s) <NUM>. The microphone(s) <NUM> provide a residual signal <NUM> resulting from the anti-noise signal(s) and the undesired noise in the cancellation zone <NUM>. The residual signal <NUM> may also be referred to as a microphone signal. A frequency band selector <NUM> receives the microphone signal and analyzes it for narrowband noise in one or more selected frequency ranges. The frequency band selector <NUM> provides information to a control algorithm <NUM>, and such information identifies one or more frequencies at which narrowband noise exists in the microphone signal. The control algorithm <NUM> receives the microphone signal and generates the anti-noise signal(s) intended to reduce the narrowband noise at each of the one or more identified frequencies. In various examples, the anti-noise signal(s) reduce the narrowband noise within a range of frequencies around one or more of the identified frequencies.

<FIG> illustrates an example frequency band selector <NUM>. The frequency band selector may convert a signal into a frequency domain representation, such as via an FFT <NUM>, and finds peaks in the spectrum at block <NUM>. The frequency band selector <NUM> identifies one or more identified frequencies <NUM> that have such peaks in the spectrum. In some examples, block <NUM> may look at only selected portions of the spectrum where narrowband noise may be expected, such as frequency ranges where a cavity resonance may be expected. In such examples, block <NUM> may analyze one or more pre-selected frequency ranges. In various examples, a down conversion may be performed prior to the FFT <NUM>, to shift one or more pre-selected frequency ranges to baseband, which may reduce computational resources required to perform the FFT <NUM> and to finds peaks in the spectrum at block <NUM>. Other examples may identify one or more frequencies <NUM> that have peaks in the spectrum from other narrowband sources, e.g., not necessarily related to cavity resonances. Accordingly, a frequency <NUM> may be identified for any narrowband noise based upon peaks in a signal spectrum.

In some examples, the frequency band selector <NUM> may operate to identify frequencies in the microphone signal. In other examples, the frequency band selector <NUM> may also receive speaker command signal(s), which represent the anti-noise signal(s) being transduced by the loudspeaker(s). In such examples, a block <NUM> may estimate an original signal at a location, e.g., an acoustic signal that would have existed at the location in the absence of the anti-noise signal, e.g., as if the noise cancellation system were not in operation. Such may be desirable, for example, if the noise cancellation system <NUM> is operating fairly well to reduce the narrowband noise and therefore the signals directly from the microphone(s) may not include peaks at the identified frequencies, e.g., because the noise cancellation system <NUM> is effectively reducing acoustic content at the identified frequencies.

<FIG> illustrates one example of the control algorithm <NUM>. The control algorithm <NUM> receives the identified frequencies <NUM> from the frequency band selector <NUM>. For each identified frequency, a downconverter <NUM> converts the spectrum of the microphone signal(s) and the speaker command signal(s) at (or around) the identified frequency down to baseband. An estimator <NUM> receives the baseband microphone and speaker command signal(s) and estimates a baseband version of the narrowband noise at the identified frequency (which may be an estimate at a particular location, such as at the location of an occupant's ears). The estimated baseband noise may be processed through an inverse <NUM> of physical plant (at baseband), also known in some cases as an inverse of the secondary path, to generate a baseband anti-noise signal, which is upconverted by an upconverter <NUM> to provide an anti-noise signal (which are speaker command signal(s)).

The example frequency band selector <NUM> and example control algorithm <NUM> of <FIG> and <FIG>, respectively, are each merely one example of their respective components of the noise cancellation system <NUM>, and other suitable arrangements exist. Some examples may include one or more adaptive algorithms to adjust an anti-noise signal in response to a feedback (residual) signal form a microphone. For example, the inverse <NUM> may be implemented as a fixed filter or may be adaptive and "learn" the relationship between the speaker commands and the resulting residual signal.

At least one benefit of the example noise cancellation system <NUM>, and the control algorithm <NUM>, is that the described down conversion to baseband may allow implementation of narrowband processing with a reduced requirement for number of filter taps. For example, the inverse <NUM> may be implemented by a filter at baseband with fewer taps to achieve the same narrowband operation as one that operates on signals at the identified frequency.

Any suitable hardware and/or software, including firmware and the like, may be configured to carry out or implement components of the aspects and examples disclosed herein, and various implementations of aspects and examples may include components and/or functionality in addition to those disclosed. Various implementations may include stored instructions for a digital signal processor and/or other processing circuitry to enable the circuitry, at least in part, to perform the functions described herein.

Examples disclosed herein may be combined with other examples in any manner consistent with at least one of the principles disclosed herein, and references to "an example," "some examples," "an alternate example," "various examples," "one example" or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one example. The appearances of such terms herein are not necessarily all referring to the same example.

Claim 1:
A method of reducing noise comprising:
receiving a signal representative of noise in a cancellation zone (<NUM>), wherein the signal representative of noise in the cancellation zone is a microphone signal;
identifying a frequency within the signal to be reduced in the cancellation zone, wherein said identifying includes analyzing the signal in a pre-selected range of frequencies for the presence of narrowband noise associated with a cavity resonance;
down converting the signal to place the identified frequency at baseband;
down converting a speaker command signal to place the identified frequency at baseband;
generating a baseband anti-noise signal based upon the down converted signal and the down converted speaker command signal;
up converting the baseband anti-noise signal to the identified frequency to produce an anti-noise signal having components at the identified frequency; and
providing the anti-noise signal to be transduced into an acoustic signal.