Acoustic path testing

Abstract

An audio method, system, and computer readable medium for estimating an acoustic transfer function in an environment between a transducer and a microphone are provided. An audio test signal is generated in which an amplitude or energy of the audio test signal is selected at least in part across a plurality of frequency intervals to be masked at least in part by acoustic energy in the environment. The audio test signal is provided to a transducer to be translated into an acoustic signal in the environment. The microphone receives the acoustic signal and provides a microphone signal. The microphone signal is processed by a summing method over a predetermined duration of three (3) seconds or longer, and the acoustic transfer function is estimated based on the summing method.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 425,045, filed on November 14, 2022, the entire disclosure of which is incorporated herein by reference. Background Art

[0003] Various audio systems incorporate improvements to system performance, such as through the estimation of an acoustic transfer function via one or more acoustic paths. For example, in many applications (such as road noise cancellation (RNC) or engine harmonic cancellation (EHC) in the case of an automobile or a vehicle, to name just a few examples), the transfer of sound from a speaker to a microphone (usually an error microphone or a feedback microphone) can be referred to as a secondary path. The primary path is the path that road noise or engine harmonic sound takes from the source to the microphone (usually located near or as close as possible to the occupant's ear).

[0004] In many cases, an estimate of the acoustic transfer function can be pre - measured and stored in the system's memory. Such methods have some drawbacks, such as the fact that the pre - determined measurement represents the transfer function at only one point in time when the measurement was made and may represent the transfer function in only one configuration of the acoustic space. For example, in an automotive environment, the measured transfer function represents the internal configuration of the vehicle at that time, e.g., which and how many seats are occupied, the body type of the occupant, seat position, cargo loading, etc. Thus, various acoustic environments can have acoustic characteristics that vary greatly over time. Therefore, there is a need to actively estimate the acoustic transfer function in real - time under the current conditions that affect the acoustic environment. Summary of the Invention

[0005] Systems and methods are disclosed herein for estimating an acoustic transfer function by generating an audio test signal (or training signal) that is relatively low in energy such that the signal is relatively difficult to distinguish (for the human ear) from other sounds in the environment.

[0006] According to various aspects, provided is an audio method, system, and computer - readable medium for estimating an acoustic transfer function in an environment between a transducer and a microphone, comprising: generating an audio test signal, wherein the amplitude or energy of the audio test signal is at least partially selected across a plurality of frequency bins to be at least partially masked by acoustic energy in the environment; providing the audio test signal to the transducer to be transduced into an acoustic signal in the environment; receiving a microphone signal from the microphone based on the acoustic signal at the microphone in the environment; performing a summation method on the microphone signal over a predetermined duration of three (3) seconds or longer; and determining the estimated acoustic transfer function based on the summation method.

[0007] According to some examples, the predetermined duration may be at least one of five (5) seconds or longer, ten (10) seconds or longer, twenty (20) seconds or longer, or sixty (60) seconds or longer.

[0008] In various examples, the amplitude or energy of the audio test signal may be selected at least in part based on the acoustic energy content in the environment. In certain examples, additionally or alternatively, the amplitude or energy of the audio test signal may be selected at least in part based on the energy content of a playback signal that is also transduced into the environment.

[0009] In various examples, the summing method may include adding a first fractional value of the microphone signal to a second fractional value of the stored signal and saving the result as the next version of the stored signal. In certain examples, the first fractional value and the second fractional value add up to one.

[0010] In some examples, the summing method may further include repeatedly adding subsequent first fractional values of the microphone signal to subsequent second fractional values of the stored signal over the duration and saving the result as the next subsequent version of the stored signal. In various examples, the repeated summing method may be performed ten (10) times or more, twenty (20) times or more, one hundred (100) times or more, or two hundred (200) times or more during the duration.

[0011] In various examples, the summing method may be performed for each of a plurality of frequency bins of the microphone signal.

[0012] These and other aspects, examples, and advantages of the exemplary aspects and examples are discussed in detail below. The 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 "example," "some examples," "alternative examples," "various examples," "one example," etc. are not necessarily mutually exclusive but are intended to indicate that the particular feature, structure, or characteristic described may be included in at least one example. The occurrence of such terms herein does not necessarily all refer to the same example. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Aspects of at least one example are discussed below with reference to the drawings, which are not necessarily drawn to scale. The drawings are included to provide illustration and further understanding of the aspects and examples, and the drawings are incorporated into and form a part of this specification but are not intended as a definition of the limits of the invention. In the drawings, the same or substantially the same components illustrated in the various figures may be represented by like reference numerals or numbers. For clarity, not every component is labeled in every figure. In the drawings:

[0014] Figure 1 is a schematic system diagram of an example noise cancellation system;

[0015] Figure 2 is associated with Figure 1 a schematic system diagram of an example acoustic path test system combined with the noise cancellation system; and

[0016] Figure 3 is a method diagram of an example method executable by Figure 2 the example acoustic path test system. DETAILED DESCRIPTION

[0017] Aspects of the present disclosure relate to systems and methods for estimating an acoustic transfer function by: generating an audio test signal (or training signal) of relatively low energy such that the signal will be relatively indistinguishable from other sounds in the environment (i.e., the test signal will be "masked" by other sounds in the environment) to the human ear; transducing the test signal into an acoustic signal; receiving the acoustic signal at a microphone; and processing the received microphone signal over a duration. At least some benefits of the method are: (a) the test signal generally will not be heard by most people and thus will not be noticed, (b) the test signal can be conducted substantially continuously since it will not be heard by the occupants of the environment, and (c) the system and method may benefit from processing gains achieved by processing the received microphone signal over a duration (e.g., rather than in a single test).

[0018] The innovations described herein can be understood as analogous to the processing of spread-spectrum radio signals and, more specifically, analogous to the processing of pilot signals in orthogonal frequency-division multiplexing (OFDM). However, unlike OFDM pilot signals, the systems and methods herein are applicable to testing an acoustic channel having acoustic energy at baseband audio frequencies rather than testing a radio channel at radio frequency (RF). In the RF analogy, testing the RF transfer function is referred to as channel estimation. Understanding RF channel characteristics (e.g., how a radio signal is affected by its propagation and reflection between a transmitter and a receiver) is useful for improving the performance of a receiver in interpreting the signal and demodulating the signal into a communication data stream.

[0019] As a further analogy to a radio system, which typically has multipath characteristics (due to reflections) and typically uses multiple transmit antennas and multiple receive antennas and is thus a multiple-input multiple-output (MIMO) system (with multiple paths from "transmit" to "receive" and thus a more complex effect of the channel characteristics on the received signal), many acoustic environments also have multiple sound sources (e.g., speakers), multiple paths to microphones, and multiple acoustic receivers (e.g., microphones). For example, an automotive audio system typically has multiple peripheral speakers and may have multiple microphones for monitoring the performance of noise cancellation, harmonic cancellation, or other active sound management subsystems. Accordingly, the systems and methods described herein are applicable to MIMO acoustic environments and perform acoustic channel estimation (acoustic transfer function estimation) in such environments.

[0020] Figure 1 Exemplified is an example noise cancellation system 100, which is an example of a system in which the acoustic path testing systems and methods described herein can be beneficially applied. The noise cancellation system 100 is one of a plurality of systems in which the system may benefit from determining the acoustic transfer function from one location to another location, and the noise cancellation system 100 is briefly described for reference. A noise source 110 may generate noise in the environment. For example, the noise source 110 may be the interaction between one or more wheels of a vehicle and the road for the example noise cancellation system 100, which may be a road noise cancellation (RNC) system. In another example, the noise source 110 may be an internal combustion engine (ICE), and the noise cancellation system 100 may be an engine harmonic cancellation (EHC) system. In any case, a sensor 120 may detect and provide a reference signal 122 indicative of the noise generated by the noise source 110. For example, a vibration signal from one or more accelerometers may indicate the vibration of the wheels on the road or may indicate the harmonic vibration of the engine. In another example, an RPM sensor may indicate the revolutions per minute (RPM) of the engine, and the harmonic frequencies may be calculated based on the RPM.

[0021] A controller 130 receives the reference signal 122 and generates a command signal 132 at least in part based on the reference signal 122. The command signal 132 is transduced into an acoustic signal by an acoustic transducer 140 (such as, for example, a speaker, e.g., in the passenger compartment of a vehicle).

[0022] According to various systems, the feedback microphone 150 can be located in an environment where the noise reduction system 100 operates to reduce noise, such as in a vehicle cabin, or at one or more seat positions in such a vehicle cabin. The controller 130 can beneficially receive a feedback signal 152 from the feedback microphone 150 to improve the operation of the controller 130, for example, to determine an improved command signal 132 based on the reference signal 122. Thus, in many noise reduction systems, the controller 130 can generate the command signal 132 based on one or more reference signals 122 and one or more feedback signals 152.

[0023] In terms of terminology, the area in the environment where noise is to be reduced can be referred to as the cancellation zone or region. Noise is transmitted from the noise source 110 to the cancellation zone (and the feedback microphone 150) via the primary path 112. Mechanical and acoustic propagation - such as road noise sent from the suspension system into the vehicle cabin - defines the primary path 112. In the absence of any other sounds in the environment, the relationship between the feedback signal 152 representing the noise in the cancellation zone and the reference signal 122 representing the noise at the noise source 110 represents the transfer function of the primary path 112. Note that the controller 130 receives each of the reference signal 122 and the feedback signal 152, and can thus determine the transfer function of the primary path 112 at least in the absence of any other sounds (or if the controller 130 takes into account the presence of other sounds).

[0024] The acoustic transfer from the acoustic transducer 140 to the feedback microphone 150 is the secondary path 142. Many known noise reduction systems benefit from determining an estimate of the acoustic transfer function from the acoustic transducer 140 to the feedback microphone 150. The systems and methods described herein relate to determining an estimate of the transfer function of the secondary path 142.

[0025] The systems and methods herein generate a test (or training) audio signal by selecting the amount of signal energy to be sent (e.g., by a speaker) in respective frequency bins (e.g., in the frequency domain). The amount of signal energy to be placed in each frequency bin is based in part on other sounds in the environment, such that the test signal may be difficult (for the human ear) to distinguish from other sounds in the environment. Other sounds in the environment can be determined from playback signals processed by an audio system (which can be the same audio system as the systems and methods herein), or from various microphones in the environment (which can also be microphones used for the systems and methods herein), or a combination of the playback signal and the microphone signal, each of which can indicate other sounds in the environment.

[0026] The test signal is provided to one or more acoustic transducers (e.g., speakers) and transduced into an acoustic signal in the environment. The acoustic signal propagates to one or more microphones, which generate microphone signals representing the acoustic signals received by them.

[0027] The processor receives one or more microphone signals and may also receive a test signal from a generator and process these signals to estimate the acoustic transfer function from each of one or more acoustic transducers to each of one or more microphones. For simplicity, only a single transfer function (from one transducer to one microphone) is further described below.

[0028] The systems and methods herein can generate and process audio test signals (or training signals) over an extended duration. In various examples, the duration of test signal processing can be 3 seconds or longer, 5 seconds or longer, 10 seconds or longer, 20 seconds or longer, or 60 seconds or longer. This extended duration can allow for significant processing gain and can be beneficial, at least in part because the test signal has a low signal level (low energy) relative to other sounds in the environment. Thus, short duration signals may be difficult to detect and / or estimate the characteristics of the acoustic channel because there may be much more acoustic energy in the environment that is not associated with the test signal. However, the extended duration allows for processing gain because the (known) test signal is present in the environment while other sounds may be variable and changing. In at least one example, the received microphone signals can be continuously averaged (e.g., store a portion (such as a window length of the signal), and add the next portion, and so on, and divide by the total number of portions), such that other sounds can average to zero, or have a zero effect (e.g., other sounds can be considered random relative to the extended duration test / training signal and thus subtract as much from the average as they add to the average, resulting in a net zero or zero effect). Thus, the processing performed by the systems and methods herein can be considered a summation process or summation method applied to one or more microphone signals.

[0029] Successive summing and dividing by the number of signal portions may require a large amount of memory and processing power. Accordingly, various examples of the systems and methods herein may employ various techniques of summing methods that are designed to reduce the memory and processing (e.g., processor computations) required. For example, a summing method may receive a portion of a microphone signal and add a fractional value of the received portion to a previously stored partial accumulation, and then store the result as a newly stored partial accumulation. For example, if a summing method is designed to produce a result representing one hundred (100) samples (e.g., one hundred portions of a microphone signal or time-domain windows), the summing method may receive the next portion of the microphone signal and add 1 / 100 of the received portion to 99 / 100 of the previously stored partial accumulation, and store the result as the newly stored accumulation. This scheme produces a running average that essentially represents the average of the past one hundred (100) portions. Such a scheme or a similar scheme may only require storing a single representative (accumulated) portion in memory, and may not require a counter for the number of previous portions, and may only need to process relatively simple mathematical operations. Mathematically, the resulting output y(k) may be expressed as:

[0030] y(k) = αy(k - 1) + βx(k) (1)

[0031] where y(k - 1) is the previously stored partial accumulation, x(k) is the current portion of the microphone signal, and y(k) is the resulting output and newly stored accumulation. α and β are fractional values that, in some examples, may add up to 1 (one). Accordingly, in various examples, α + β = 1, but other examples may include fractional values that do not add up to one, or may include varying summing methods.

[0032] By accumulating (summing) the received microphone signal over a duration, a processor or processing method may determine an estimated transfer function (channel characteristics) relative to a known test signal that resulted in the received signal. Substantially, the ratio of the resulting output (the accumulated representative portion of the received signal at the microphone) to the test / training signal input produces the transfer function (also known as the impulse response) of the acoustic environment from the acoustic transducer to the microphone.

[0033] Figure 2An example test system 200 is illustrated for determining an estimated transfer function of, for example, a secondary path 142. The system 200 generates an audio test signal 210 having an amplitude and / or energy in various frequency bands selected based on other acoustic energy in the environment. The selection of the amplitude and / or energy of any given frequency band can be made such that the audio test signal 210 can be effectively masked in the environment, that is, when the audio test signal 210 is transduced into an acoustic signal by an acoustic transducer (such as the acoustic transducer 140 in this example), the audio test signal may not be distinguishable from other acoustic energy in the environment, i.e., an occupant in the environment is less likely to detect that the audio test signal 210 has been transduced into the environment. In various examples, the system 200 can determine other acoustic energy in the environment by receiving a microphone signal from the environment (such as from a microphone 150) or from other input 220, which can include an audio system accessible to other signals being played in the environment (e.g., music, radio, etc.). In some examples, other acoustic energy in the environment can include fan or wind noise, which may be particularly useful for masking the transduced audio test signal.

[0034] In various examples, the test system 200 can include various processors coupled to a memory, such as one or more general-purpose processors and / or digital signal processors, the memory can store instructions that cause the processors to behave as described above and further described below, and the test system 200 can include various input and output interfaces to, for example, receive one or more microphone signals and provide one or more audio test signals, as described herein.

[0035] Figure 3 An example acoustic path test method 300 is illustrated. The method 300 generates 310 an audio test signal to be masked in the environment. The amplitude or energy of the audio test signal is at least partially selected across multiple frequency bands to be at least partially masked by acoustic energy in the environment. The audio test signal is provided 320 to a transducer to be transduced into an acoustic signal in the environment. A microphone signal is received 330 from a microphone based on the acoustic signal at the microphone in the environment. A summing (or averaging) method is performed 340 on the microphone signal over a predetermined duration of three (3) seconds or longer, and an estimated acoustic transfer function is determined 350 based on the summing or averaging method.

[0036] Examples of the methods and apparatuses discussed herein are not limited to applications to the construction details and component arrangements listed in the above description or illustrated in the drawings. These methods and apparatuses can be implemented in other examples and can be operated or executed in various ways. The specific implementation examples provided herein are for illustrative purposes only and are not intended to be limiting. Specifically, the functions, components, elements, and features discussed in connection with any one or more examples are not intended to be excluded from similar roles in any other example.

[0037] Furthermore, the language and terminology used herein are for descriptive purposes and should not be regarded as limiting. Any reference in the singular to an example, component, element, action, or function of the systems and methods herein may also cover embodiments including the plural, and any reference in the plural to any example, component, element, action, or function herein may also cover examples including only the singular. Thus, references in the singular or plural form are not intended to limit the systems or methods, their components, actions, or elements disclosed herein. The use of "including," "comprising," "having," "containing," "involving," and their variants herein is intended to cover the items listed thereafter and their equivalents as well as additional items. References to "or" may be understood to be inclusive, such that any term described using "or" may indicate any one of the single, more than one, and all of the stated terms. Any reference to front and back, left and right, top and bottom, upper and lower, and vertical and horizontal is intended to facilitate description unless the context reasonably implies otherwise, rather than to limit the systems and methods herein or their components to any one position or spatial orientation.

[0038] Having described several aspects of at least one example above, it should be understood that various changes, modifications, and improvements will readily occur to those skilled in the art. Such changes, modifications, and improvements are intended to be part of this disclosure and are intended to fall within the scope of the invention. Accordingly, the above specification and drawings are exemplary only, and the scope of the invention should be determined by the proper construction of the appended claims and their equivalents.

Claims

1. A method for estimating an acoustic transfer function in an environment between a transducer and a microphone, the method comprising: generating an audio test signal, wherein the amplitude or energy of the audio test signal is at least partially selected across a plurality of frequency intervals to be at least partially masked by acoustic energy in the environment; providing the audio test signal to the transducer to be transduced into an acoustic signal in the environment; receiving a microphone signal from the microphone based on the acoustic signal at the microphone in the environment; performing a summation method on the microphone signal over a predetermined duration of three (3) seconds or longer; and determining the estimated acoustic transfer function based on the summation method.

2. The method according to claim 1, wherein the predetermined duration is at least one of five (5) seconds or longer, ten (10) seconds or longer, twenty (20) seconds or longer, or sixty (60) seconds or longer.

3. The method according to claim 1, wherein the amplitude or energy of the audio test signal is selected at least partially based on the acoustic energy content in the environment.

4. The method according to claim 1, wherein the amplitude or energy of the audio test signal is selected at least partially based on the energy content of a playback signal that is also transduced into the environment.

5. The method according to claim 1, wherein the summation method comprises: adding a first fractional value of the microphone signal to a second fractional value of a stored signal; and saving the result as a new version of the stored signal.

6. The method according to claim 5, wherein the first fractional value and the second fractional value add up to one.

7. The method according to claim 5, wherein the summation method further comprises repeatedly adding subsequent first fractional values of the microphone signal to subsequent second fractional values of the stored signal multiple times over the duration and saving the result as the next subsequent version of the stored signal.

8. The method according to claim 7, wherein the repeated summation method is performed ten (10) times or more, twenty (20) times or more, one hundred (100) times or more, or two hundred (200) times or more at least one of during the duration.

9. The method according to claim 1, wherein the summation method is performed on each of a plurality of frequency intervals of the microphone signal.

10. An audio system, the audio system comprising: a transducer; a microphone; and a processor coupled to the transducer and the microphone and configured to perform the method according to any one of claims 1 to 9.

11. A non-transitory computer-readable medium having instructions stored thereon, the instructions when executed by a suitable processor coupled to a transducer and a microphone, perform the method according to any one of claims 1 to 9.

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