Acoustic Path Testing

Abstract

An audio method, system, and computer-readable medium are provided for estimating an acoustic transfer function in an environment between a transducer and a microphone. An audio test signal is generated, and the amplitude or energy of the audio test signal is selected to be at least partially masked by acoustic energy in the environment across a plurality of frequency bins. The audio test signal is provided to a transducer for conversion to an acoustic signal in the environment. A microphone receives the acoustic signal and provides a microphone signal. The microphone signal is processed via a summation method over a predetermined duration of 3 seconds or more, and the acoustic transfer function is estimated based on the summation method.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 425,045, filed November 4, 2022, which is incorporated by reference in its entirety. [Background technology]

[0002] Various audio systems incorporate estimates of acoustic transfer functions, for example, via one or more acoustic paths, to improve system performance. For example, the transmission of sound from a loudspeaker to a microphone (often an error microphone or a feedback microphone) is sometimes referred to as the secondary path in many applications, such as road noise cancellation (RNC) or engine harmonic cancellation (EHC), to name two, in an automotive or vehicle context. The primary path is the path that road noise or engine harmonic sounds take from the sound source to the microphone (usually located near, or as close as possible to, the occupant's ears).

[0003] In many cases, estimates of acoustic transfer functions can be measured in advance and stored in a system's memory. Such approaches have several drawbacks, such as the fact that a given 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 vehicle's internal configuration at that time, such as which seats are occupied and how many, the size of the occupants, their seat positions, the amount of luggage, etc. Therefore, various acoustic environments may have acoustic characteristics that change significantly over time. Therefore, there is a need to actively estimate the acoustic transfer function in real time based on the current conditions affecting the acoustic environment. Summary of the Invention

[0004] Disclosed herein are systems and methods for estimating an acoustic transfer function by generating a relatively low energy audio test signal (or training signal) that is relatively indistinguishable (to the human ear) from other sounds in the environment.

[0005] According to various aspects, an audio method, system, and computer-readable medium are provided for estimating an acoustic transfer function in an environment between a transducer and a microphone, the audio method, system, and computer-readable medium including: generating an audio test signal, the audio test signal being selected such that an amplitude or energy of the audio test signal is at least partially masked by acoustic energy in the environment across a plurality of frequency bins; providing the audio test signal to a transducer to convert the audio test signal 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 for a predetermined duration of 3 seconds or more; and determining an estimated acoustic transfer function based on the summation method.

[0006] According to some examples, the predetermined duration may be at least one of 5 seconds or more, 10 seconds or more, 20 seconds or more, or 60 seconds or more.

[0007] In various examples, the amplitude or energy of the audio test signal may be selected based at least in part on the acoustic energy content in the environment. In certain examples, the amplitude or energy of the audio test signal may also or alternatively be selected based at least in part on the energy content of the playback signal, which is also transformed into the environment.

[0008] 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 a new version of the stored signal. In particular examples, the first fractional value and the second fractional value sum to one.

[0009] 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 and saving the result as next subsequent versions of the stored signal multiple times over the duration. In various examples, the repeated summing method may be performed at least one of 10 or more times, 20 or more times, 100 or more times, or 200 or more times over the duration.

[0010] In various examples, the summation method may be performed for each of multiple frequency bins of the microphone signal.

[0011] Further aspects, embodiments, and advantages of these exemplary aspects and embodiments are discussed in detail below. The embodiments disclosed herein may be combined with other embodiments in a 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," etc. 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 embodiment. Appearances of such terms herein do not necessarily all refer to the same embodiment.

[0012] Various aspects of at least one embodiment are discussed below with reference to the accompanying drawings, which are not intended to be drawn to scale. These drawings are included to provide illustration and a further understanding of various aspects and embodiments, and are incorporated into and constitute a part of this specification, but are not intended to define the limitations of the invention. In the drawings, identical or nearly identical components shown in various figures may be represented by like reference characters or numerals. For clarity, not every component may be labeled in every figure. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic system diagram of an exemplary noise cancellation system. [Figure 2] FIG. 2 is a schematic system diagram of an exemplary acoustic path testing system incorporated into the noise cancellation system of FIG. 1. [Figure 3] 3 is a method diagram of an example method that may be performed by the example acoustic path testing system of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0014] Aspects of the present disclosure are directed to systems and methods for estimating an acoustic transfer function by generating a relatively low-energy audio test signal (or training signal) so that it is relatively indistinguishable (to the human ear) from other sounds in the environment (i.e., the test signal is "masked" by other sounds in the environment), converting the test signal to an acoustic signal, receiving the acoustic signal at a microphone, and processing the received microphone signal over a duration. At least some advantages of this approach are that (a) the test signal is generally inaudible and therefore unnoticed by most people, (b) the test signal can essentially continue without interruption because it is inaudible to occupants of the environment, and (c) the systems and methods can benefit from processing gains achieved by processing the received microphone signal over a duration (e.g., rather than at a single point in time during testing).

[0015] The innovations described herein can be understood as analogous to the processing of spread spectrum wireless signals, and more particularly, the processing of pilot signals in orthogonal frequency division multiplexing (OFDM). However, unlike OFDM pilot signals, the systems and methods herein apply not to testing wireless channels at radio frequencies (RF) but to testing acoustic channels using acoustic energy at baseband audio frequencies. In the radio frequency analogy, testing the RF transfer function is known as channel estimation. Understanding RF channel characteristics (e.g., how a wireless signal is affected by its propagation and reflections between a transmitter and a receiver) is useful for improving a receiver's performance in interpreting the signal and demodulating it into a communication data stream.

[0016] As a further analogy to wireless systems, which often have multipath characteristics (due to reflections), often use multiple transmit and receive antennas, and are therefore multiple-input, multiple-output (MIMO) systems (thereby having multiple paths from "transmit" to "receive," and therefore more complex effects of channel characteristics on the received signal), many acoustic environments also have multiple sound sources (e.g., loudspeakers), multiple paths to microphones, and multiple acoustic receivers (e.g., microphones). For example, an automobile audio system typically has multiple ambient loudspeakers and may have multiple microphones for monitoring the performance of noise cancellation, harmonic cancellation, or other active sound management subsystems. Thus, the systems and methods described herein are applicable to MIMO acoustic environments and perform acoustic channel estimation (acoustic transfer function estimation) in such environments.

[0017] FIG. 1 illustrates an exemplary noise abatement system 100, one example of a system to which the acoustic path testing systems and methods described herein can be beneficially applied. The noise abatement system 100 is one of several systems that can benefit from determining the acoustic transfer function from one location to another, and the noise abatement system 100 will be briefly described for reference. A noise source 110 may generate noise in an environment. For example, the noise source 110 may be the interaction between one or more wheels of a vehicle and the road, e.g., the noise abatement system 100 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 abatement system 100 may be an engine harmonic cancellation (EHC) system. In either 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 be indicative of wheel vibrations on the road or may be indicative of harmonic vibrations of the engine. In another example, an RPM sensor can indicate the engine's rotations per minute (RPM), from which harmonic frequencies can be calculated.

[0018] A controller 130 receives the reference signal 122 and generates a command signal 132 based at least in part on the reference signal 122. The command signal 132 is converted into an acoustic signal by an acoustic transducer 140 (e.g., a loudspeaker in the cabin of the automobile, etc.).

[0019] According to various systems, feedback microphone 150 may be located within the environment in which noise abatement system 100 operates to reduce noise, such as a vehicle cabin or one or more seating positions within such a vehicle cabin. Controller 130 may beneficially receive feedback signal 152 from feedback microphone 150 to improve operation of controller 130, for example, to determine an improved command signal 132 based on reference signal 122. Thus, in many noise abatement systems, controller 130 may generate command signal 132 based on one or more reference signals 122 and one or more feedback signals 152.

[0020] In terms of terminology, the area of ​​the environment where noise should be abated is sometimes referred to as the cancellation zone or region. Noise is transmitted from noise source 110 to the cancellation zone (and feedback microphone 150) via primary path 112. Mechanical and acoustic propagation, such as road noise transmitted from the suspension system into the vehicle cabin, defines primary path 112. In the absence of other sounds in the environment, the relationship between feedback signal 152, which represents the noise in the cancellation zone, and reference signal 122, which represents the noise at noise source 110, represents the transfer function of primary path 112. Note that controller 130 receives each of reference signal 122 and feedback signal 152 and is therefore able to determine the transfer function of primary path 112, at least in the absence of other sounds (or when controller 130 takes into account the presence of other sounds).

[0021] The acoustic transfer from the acoustic transducer 140 to the feedback microphone 150 is the secondary path 142. Many known noise abatement 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 are directed to determining an estimate of the transfer function of the secondary path 142.

[0022] The systems and methods herein generate a test (or training) audio signal by selecting an amount of signal energy to be transmitted in each frequency bin, e.g., in the frequency domain (e.g., by a loudspeaker). The amount of signal energy placed in each frequency bin is based in part on other sounds in the environment, such that the test signal is indistinguishable (to the human ear) from other sounds in the environment. The other sounds in the environment may be determined from a playback signal processed by an audio system (which may be the same audio system as the systems and methods herein), or from various microphones in the environment (which may also be microphones used in the systems and methods herein), or from a combination of playback and microphone signals, each of which may be indicative of other sounds in the environment.

[0023] The test signal is provided to one or more acoustic transducers (e.g., loudspeakers) and converted into an acoustic signal in the environment. The acoustic signal propagates to one or more microphones, which generate microphone signals representative of the acoustic signal received by them.

[0024] The processor receives one or more microphone signals, and may also receive a test signal from the generator, and processes these signals to estimate an acoustic transfer function from each of the one or more acoustic transducers to each of the one or more microphones. For simplicity, only a single transfer function (from one transducer to one microphone) is described further below.

[0025] The systems and methods herein may generate and process audio test signals (or training signals) over long durations. In various examples, the duration of test signal processing may be 3 seconds or more, 5 seconds or more, 10 seconds or more, 20 seconds or more, or 60 seconds or more. Such long durations may enable significant processing gain and may be beneficial, at least in part, because the test signal has a low signal level (low energy) compared to other sounds in the environment. Thus, signals of short duration may be difficult to detect and / or estimate characteristics of the acoustic channel, since there may be much more acoustic energy in the environment that is not related to the test signal. However, long durations enable processing gain because the (known) test signal is present in the environment, while other sounds are variable and may constantly change. In at least one example, the received microphone signal may be continuously averaged (e.g., store a portion, such as a window length of the signal, add the next portion, etc., and divide by the total number of portions), so that other sounds may average out to a zero or null effect (e.g., other sounds may be considered random to the long duration test / training signal, and therefore subtract from the average as much as they add to it, resulting in a net zero or null effect). Thus, such processing by the systems and methods herein may be considered a summation process or method applied to one or more microphone signals.

[0026] Successive additions and divisions by the number of signal portions can require significant memory and processing power. Therefore, various examples of the systems and methods herein can employ various techniques for summation methods intended to reduce memory and processing (e.g., processor operations) requirements. For example, a summation method may receive one portion of a microphone signal, add a fractional value of the received portion to an accumulation of previously stored portions, and then store the result as a new accumulation of stored portions. For example, if a summation method is intended to generate a result representing 100 samples (e.g., 100 portions or a time-domain window of a microphone signal), the summation method may receive the next portion of the microphone signal, add 1 / 100 of the received portion to 99 / 100 of the accumulation of previously stored portions, and store the result as a new stored accumulation. Such a scheme generates a moving average that essentially represents the average of the past 100 portions. Such a scheme, or a similar scheme, may require storing only a single representative (accumulated) portion in memory, may not require a counter of the number of previous portions, and may require only relatively simple mathematical operations. Mathematically, the resulting output y(k) can be expressed as: y(k)=αy(k-1)+βx(k) (1) where y(k-1) is the accumulation of the previously stored portion, x(k) is the current portion of the microphone signal, and y(k) is the resulting output and the newly stored accumulation. α and β are fractional values ​​that, in some examples, may sum to 1 (unity). Thus, in various examples, α+β=1, but other examples may include fractional values ​​that do not sum to 1 or may include various summation methods.

[0027] By accumulating (adding) the received microphone signals over a duration, a processor or processing method can determine an estimated transfer function (channel characteristics) for a known test signal that caused the resulting received signal. Essentially, the ratio of the resulting output (cumulative representative portion of the signal received at the microphone) to the test / training signal input yields the transfer function (also known as the impulse response) of the acoustic environment from the acoustic transducer to the microphone.

[0028] 2 illustrates an exemplary test system 200 that operates to determine, for example, an estimated transfer function of secondary path 142. System 200 generates audio test signal 210 having amplitudes and / or energies in various frequency bins that are selected based on other acoustic energy in the environment. The selection of the amplitude and / or energy of any given frequency bin may be selected such that audio test signal 210 can be effectively masked in the environment, i.e., such that when audio test signal 210 is converted into an acoustic signal by an acoustic transducer, such as acoustic transducer 140 in this example, it is indistinguishable from other acoustic energy in the environment, i.e., such that an occupant in the environment may be unlikely to detect that audio test signal 210 has been converted into the environment. In various examples, system 200 can determine other acoustic energy in the environment by receiving a microphone signal from the environment, such as from microphone 150, or from other inputs 220, which may include an audio system having access to other signals being played in the environment, e.g., music, radio, etc. In some instances, other acoustic energy in the environment may include fan noise or wind noise, which may be particularly useful for masking the converted audio test signal.

[0029] In various examples, test system 200 may include various processors, such as one or more general-purpose processors and / or digital signal processors, coupled to a memory that may store instructions that cause the processors to operate as described above and further below, and may include various input / output interfaces, for example, for receiving one or more microphone signals and providing one or more audio test signals, as described herein.

[0030] 3 illustrates an exemplary acoustic path testing method 300. The method 300 generates an audio test signal to be masked in an environment (310). The amplitude or energy of the audio test signal is selected across multiple frequency bins to be at least partially masked by acoustic energy in the environment. The audio test signal is provided to a transducer (320) for conversion to an acoustic signal in the environment. A microphone signal is received from a microphone based on the acoustic signal at the microphone in the environment (330). A summing (or averaging) method is performed on the microphone signal over a predetermined duration of 3 seconds or more (340), and an estimated acoustic transfer function is determined based on the summing or averaging method (350).

[0031] The method and apparatus embodiments discussed herein are not limited in their application to the details of construction and the arrangement of components set forth in the above description or illustrated in the accompanying drawings. The methods and apparatus of the present invention may be implemented in other embodiments and may be practiced or carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, functions, components, elements, and features discussed in connection with any one or more embodiments are not intended to be excluded from a similar role in any other embodiments.

[0032] Additionally, the phraseology and terminology used herein are for descriptive purposes and should not be considered limiting. Any reference herein to system and method examples, components, elements, acts, or functions in the singular may also encompass embodiments that include the plural, and any reference herein to any example, component, element, act, or function in the plural may also encompass examples that include only the singular. Thus, singular or plural references are not intended to limit the disclosed systems or methods, their components, acts, or elements. The use herein of "including," "comprising," "having," "containing," "involving," and variations thereof, is meant to encompass the items listed below and equivalents thereof, as well as additional items. References to "or" may be interpreted as inclusive, such that any term described with "or" may refer to either one, more than one, or all of the listed terms. Unless the context reasonably suggests otherwise, references to front, back, left, right, up, down, top, bottom, and length and width are for convenience of description and are not intended to limit the present systems and methods, or components thereof, to any one positional or spatial orientation.

[0033] Having described several aspects of at least one embodiment, it will be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only, with the scope of the invention to be determined from proper construction of the appended claims and their equivalents. [Explanation of symbols]

[0034] 100 Noise Reduction System 110 Noise Source 112 Primary Pathway 120 sensors 122 Reference Signal 130 Controller 132 Command Signal 140 Acoustic Transducer 142 Secondary Pathway 150 Feedback Microphone 152 Feedback Signal 200 systems 210 Audio Test Signal 220 Input 300 Acoustic Path Test Method

Claims

1. 1. A method for estimating an acoustic transfer function in an environment between a transducer and a microphone, comprising: generating an audio test signal, the amplitude or energy of the audio test signal being selected such that it is at least partially masked by acoustic energy in the environment across a plurality of frequency bins; providing the audio test signal to the transducer for conversion 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 summing method on the microphone signals for a predetermined duration of at least 3 seconds; determining the estimated acoustic transfer function based on the summation method; A method comprising:

2. The method of claim 1 , wherein the predetermined duration is at least one of 5 seconds or more, 10 seconds or more, 20 seconds or more, or 60 seconds or more.

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

4. 10. The method of claim 1, wherein the amplitude or the energy of the audio test signal is selected based at least in part on the energy content of a reproduced signal, the reproduced signal also being transformed into the environment.

5. The addition method is adding a first fractional value of the microphone signal to a second fractional value of the stored signal; saving the result as a new version of the stored signal; The method of claim 1 , comprising:

6. The method of claim 5 , wherein the first fractional value and the second fractional value sum to one.

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

8. The method of claim 7 , wherein the repeated summing method is performed at least one of 10 or more times, 20 or more times, 100 or more times, or 200 or more times over the duration.

9. The method of claim 1 , wherein the summing method is performed for each of a plurality of frequency bins of the microphone signal.

10. A transducer; A microphone and a processor coupled to the transducer and the microphone and configured to perform the method of any one of claims 1 to 9; An audio system equipped with.

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

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