Simulated acoustics calibration system, method and applications

Abstract

The present embodiments relate generally to adjusting cancellation filters according to changing room conditions, including changing temperature and humidity. Some embodiments relate to adjusting the cancellation filters according to loudspeaker-microphone impulse response measurements made using imperceptible test signals, such as low-level maximal length sequences added to the augmented acoustics, or augmented acoustics with certain known or designed autocorrelation. Finally, in certain applications, some quiet sound sources would benefit from relatively louder reverberation. Also, some louder loudspeaker signals may cause unwanted feedback. To address these and other issues, some embodiments include adding a compressor and / or noise gate to the auralizer input so that quiet room sounds produce audible reverberation, and that low-frequency rumble and other low-level room sounds do not become auralized.

Description

SIMULATED ACOUSTICS CALIBRATION SYSTEM, METHOD AND APPLICATIONSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to United States Provisional Patent Appln. No. 63 / 701,461, filed September 30, 2024, the contents of which are incorporated herein by reference in their entirety.TECHNICAL FIELD

[0002] The present embodiments relate generally to audio, and more particularly to methods and systems for calibrating parameters for adjusting cancellation filters used for augmenting acoustics of a space.BACKGROUND

[0003] Acoustics are integral to a space, conveying its size, architecture, materials, even whether it's cluttered or empty. Acoustics also are important in conveying the "feel" of a space. In music performance, the performance space acoustics is vital: Performers adjust their phrasing, tempo, and aspects of pitch according to features of the room reverberation. In video game play, acoustics can be used to indicate the spaces occupied by the players and sound sources.

[0004] Techniques for augmenting the acoustics of a space can include playing - into the space over loudspeakers — simulated acoustics derived from estimates of sounds made by sources in the space, i.e. ’’dry” sounds, and picked up by microphones. Without the cancellation of the simulated acoustics from the microphone signals, problematic feedback could occur. If this cancellation is effective, the room acoustics may be enhanced, and room sounds without the enhanced acoustics could be made available.

[0005] In U.S. Patent No. 10,812,902 (“the ‘902 patent”), the contents of which are incorporated herein by reference, a calibration step is described for designing the cancellation filter based on impulse responses between each loudspeaker-microphone pair. Such impulse responses may be measured directly, for instance recording the microphone responses to swept sinusoids from each loudspeaker. However, there are circumstances in which the loudspeaker-1S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796microphone impulse responses change over time in ways that allow estimation of updated cancel er fdter designs without offline impulse response measurements.

[0006] It is against this technological backdrop that the present Applicant sought a technological solution to these and other problems rooted in this technology.SUMMARY

[0007] The present embodiments relate generally to audio, and more particularly to methods and systems for calibrating parameters for adjusting cancellation fdters used for augmenting acoustics of a space. Some embodiments relate to adjusting cancellation filters according to changing room conditions, including changing temperature and humidity. This can include recording the sound speed in the room at the time of initial calibration, and occasionally thereafter updating the cancellation filters by resampling them according to the ratio of initial and current sound speeds. Some embodiments relate to adjusting the cancellation filters according to loudspeaker-microphone impulse response measurements made using imperceptible test signals, such as low-level maximal length sequences added to the augmented acoustics, or augmented acoustics with certain known or designed autocorrelations.

[0008] Moreover, in certain applications, it is recognized that some quiet sound sources would benefit from relatively louder reverberation. Also, some louder loudspeaker signals may cause unwanted feedback. To address these and other issues, some embodiments include adding a compressor and / or noise gate to the auralizer input so that quiet room sounds produce audible reverberation, and that low-frequency rumble and other low-level room sounds do not become auralized. These and other embodiments may also include adding a frequency-dependent (e.g., multi-band) limiter or compressor before the loudspeaker output / canceler input, l(t), to limit the loudspeaker signal level to below a level at which unwanted feedback would occur.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] These and other aspects and features of the present embodiments will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures, wherein:2S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796

[0010] FIG. 1 is a diagram illustrating an example system for augmenting the acoustics of a space.

[0011] FIG. 2 is a diagram illustrating aspects of cancellation techniques that can be applied in a system such as that illustrated in FIG. 1.

[0012] FIGs. 3 A and 3B illustrates aspects of including canceler calibration updates according to an initial calibration and changing room temperature and humidity according to embodiments.

[0013] FIG. 4 is a diagram illustrating example aspects of additional embodiments for augmenting the acoustics of a space according to embodiments.

[0014] FIG. 5 is a flowchart illustrating an example methodology for calibrating a canceler in a system for augmenting acoustics of a space according to embodiments.DETAILED DESCRIPTION

[0015] The present embodiments will now be described in detail with reference to the drawings, which are provided as illustrative examples of the embodiments so as to enable those skilled in the art to practice the embodiments and alternatives apparent to those skilled in the art. Notably, the figures and examples below are not meant to limit the scope of the present embodiments to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present embodiments can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present embodiments will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the present embodiments. Embodiments described as being implemented in software should not be limited thereto, but can include embodiments implemented in hardware, or combinations of software and hardware, and vice- versa, as will be apparent to those skilled in the art, unless otherwise specified herein. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the present disclosure is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an3S24-358 PCT.1. Abel et al. Atty. Dkt. 102354-796uncommon or special meaning unless explicitly set forth as such. Further, the present embodiments encompass present and future known equivalents to the known components referred to herein by way of illustration.

[0016] The present embodiments relate generally to audio, and more particularly to methods and systems for calibrating parameters for adjusting cancellation fdters used for augmenting acoustics of a space. According to certain aspects, the present embodiments can be used in conjunction with techniques described in the ‘902 patent, as well as in conjunction with other similar or alternative techniques.

[0017] FIG. l is a block diagram illustrating an example system having a cancelling auralizer according to embodiments.

[0018] As shown, example system 100 includes a microphone 102 and speaker 104 that are both connected to an audio interface 106. Audio interface 106 includes an input 108 connected to microphone 102 and an output 110 connected to speaker 104. Audio interface 106 can further include a port 112 (e.g., jack, slot, cable, etc.) connected to computer 114 (e.g. desktop or notebook computer, pad or tablet computer, smart phone, etc.). It should be noted that other embodiments of system 100 can include additional or fewer components than shown in the example of FIG. 1. For example, although FIG. 1 illustrates an example with one microphone 102 and one speaker 104, it should be apparent that there can by two or more microphones 102 and / or two or more speakers 104.

[0019] Moreover, although shown separately for ease of illustration, it should be noted that certain components of system 100 can be implemented together. For example, computer 114 can comprise digital audio workstation software (e.g. implementing auralization and cancelation processing according to embodiments) and be configured with an audio interface such as 106 connected to microphone preamps (e.g. input 108) and microphones (e.g. microphone 102) and a set of powered loudspeakers (e.g. speaker 104). In these and other embodiments, certain components can also be integrated into existing speaker arrays, and can be implemented using inexpensive and readily available software. For example, in virtual, augmented, and mixed reality scenarios, the system allows users to dispense with headphones for more immersive virtual acoustic experiences. Other hardware and software, including special-4S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796purpose hardware and custom software, may also be designed and used in accordance with the principles of the present embodiments.

[0020] In general operation according to aspects of embodiments, room sounds (e.g. a music performance, voices from a virtual reality game participant, etc.) are captured by microphone 102. The captured sounds (i.e. microphone signals) are provided via interface 106 to computer 114, which processes the signals in real time to perform artificial reverberation according to the acoustics of a desired target space (i.e. auralization). The processed sound signals are then presented via interface 106 over speaker 104, thereby augmenting the acoustics of the room and enriching the experience of performers, game players, etc. As should be apparent, the room microphone 102 will also capture sound from the speaker 104, which is playing the simulated acoustics. According to aspects of the present embodiments, and as will be described in more detail below, computer 114 further estimates and subtracts (e.g. cancels) the simulated acoustics in real time from the microphone signal, thereby eliminating feedback. It should be noted that the architecture of the system described can be modified to send desired sounds out the loudspeakers (and also to the canceler), either with or without auralization. Doing so would allow performers to hear backing tracks in a music recording scenario. It would also allow alerts, sounds, and voices to be heard in a game playing scenario, while making the "dried" microphone signal available for other listeners.

[0021] FIG. 2 is a signal flow diagram illustrating processing performed by node 100 (e g. computer 114) according to an example embodiment. As shown in FIG. 2, example computer 1 14 in embodiments includes a canceler 202 and an auralizer 204. In operation of node 100, a room microphone 102 captures contributions from room sound sources d(t) and synthetic acoustics produced by the loudspeaker 104 according to its applied signal l(t), t denoting time. Auralizer 204 imparts the sonic characteristic of a target space, embodied by the impulse response h(t), on the room sounds d(t) through convolution, l(t) = h(t) * d(t). (1)

[0022] Many known auralization techniques can be used to implement auralizer 204, such as those using fast, low-latency convolution methods to save computation (e.g., William G.5S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796Gardner, “Efficient convolution without latency,” Journal of the Audio Engineering Society, vol. 43, pp. 2, 1993; Guillermo Garcia, “Optimal filter partition for efficient convolution with short in-put / output delay,” in Proceedings of the 113th Audio Engineering Society Convention, 2002; and Frank Wefers and Michael Vorlander, “Optimal filter partitions for real-time fir filtering using uniformly-partitioned fft-based convolution in the frequency-domain,” in Proceedings of the 14th International Conference on Digital Audio Effects, 2011, pp. 155-61). Another “modal reverberator” approach is disclosed in U.S. Patent No. 9,805,704, the contents of which are incorporated herein by reference in their entirety. Although these known techniques can provide a form of impulse response h(t) used by auralizer 204, the difficulty is that the room source signals d(t) are not directly available: As described above, the room microphones also pick up the synthesized acoustics, and would cause feedback if the room microphone signal m(t) were reverberated without additional processing.

[0023] According to certain aspects, the present embodiments auralize (e.g. using known techniques such as those mentioned above) an estimate of the room source signals d'ft), formed by subtracting from the microphone signal m(t) an estimate of the synthesized acoustics (e.g. the output of speaker 104). Assuming the geometry between the loudspeaker and microphone is unchanging, the actual “dry” signal d(t) is determined by: d(t) = m(t) - g(t) * l(t), (2) where g(t) is the impulse response between the loudspeaker and microphone. Embodiments design an impulse response c(t), which approximates the loudspeaker-microphone response, and use it to form an estimate of the “dry” signal, d'(t), which is determined by: d'(t) = m(t) - c(t) * l(t). (3) as shown in the signal flow diagram FIG. 2. The synthetic acoustics are canceled from the microphone signal m(t) by canceler 202 and subtractor 206 to estimate the room signal d'(t), which signal is reverberated by auralizer 204.6S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796

[0024] As should be apparent, without the cancellation of the simulated acoustics l(t) from the microphone signals m(t), problematic feedback could occur. If this cancellation is effective, the room acoustics may be enhanced, and room sounds without the enhanced acoustics could be made available. Accordingly, it is desired to ensure that the canceler 202 and its transfer function c(t) are kept as accurate as possible.

[0025] According to some aspects of embodiments, new calibrations for canceler 202 and / or transfer function c(t) are often run when the current cancelation is no longer performing as well as desired. This may be due to changes in microphone or loudspeaker placement, or repositioning of objects in the room. Even rooms with unchanging geometry can fall out of calibration with changes in the environment that affect sound propagation.

[0026] Note that the speed of sound in air depends on temperature T and relative humidity H, and as a result, any canceler fdter design based on calibration measurements at one temperature-humidity pair (TO, HO) might not be as effective at another temperature-humidity pair (Tl, Hl). When the speed of sound is faster, the impulse response between the loudspeaker and microphone takes on the same shape, but over a shorter time scale. Accordingly, the desired calibration filter is simply a resampled version of the one at the slower sound speed.

[0027] In the embodiment shown in FIGs. 3 A, a room acoustics enhancement system 300 according to embodiments is shown, using an adapted canceler filter 302 implemented as a convolution with an adapted canceler impulse response Cr,H(t). As further shown, similar to previous embodiments, the system includes an auralizer 304 for providing desired acoustic effects, which can be implemented as described in the ‘902 patent.

[0028] According to the present embodiments, as shown in FIG. 3B, the canceler impulse response is found by forming an initial canceler filter Co(t) at a known, initial temperature and relative humidity (TO, HO). The current temperature and relative humidity (T, H) is then used by adaptor 306 to form the ratio p of the current and initial sound speeds, and the current canceler filter computed as a resampled version of the initial impulse response, c(t) = co(p x t). (4)7S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796

[0029] The adaptor 306 of FIG. 3B can be used to occasionally, periodically, or even continuously update the canceler filter design according to changing temperature and humidity. Should only one of temperature and relative humidity be available, the other may be assumed constant or assumed to change in some known fashion, say relative to the one. It should be apparent that there are many ways that temperature and humidity information can be obtained such as by including and / or integrating temperature and humidity sensors in a cancellation / auralization system such as shown in FIG. 1 (e.g. computer 114).

[0030] In these and other embodiments, cancellation filters (e.g. initial canceler Co(t)) are formed by making impulse response measurements while the acoustics augmentation system is operating. The idea is to add to the auralization signal a test signal that is sufficiently quiet (as a function of frequency and time) that the sum would sound like the auralization signal, but is sufficiently long that the energy added would allow accurate measurement of the loudspeakermicrophone impulse response.

[0031] In a related embodiment, the cancellation filter is designed by comparing the loudspeaker and microphone signals to estimate or update the needed microphone-loudspeaker impulse responses, for instance via cross correlation and related methods as described in Widrow and S. D. Steams. Adaptive Signal Processing. Prentice-Hall, Englewood Cliffs, NJ, 1985, and in Torsten Soderstrom and Petre Stoica, System identification. New York: Prentice Hall, 1989.

[0032] In a further related embodiment, a moving microphone, such as a boom microphone or lavalier microphone following or attached to an actor on a sound stage, may be incorporated into the augmented acoustics system to produce a ’’dried” output by subtracting outputs of time-varying cancellation filters applied to the respective loudspeaker signals. In this case, the time-varying filters are updated continuously to account for the motion of the microphone. This can be done off line or in real time by least-squares techniques fitting the loudspeaker outputs to the microphone signals via correlation.

[0033] In other embodiments, automatic gain control processors are placed on the ’’dried” microphone outputs and the auralizer outputs, as shown in FIG. 4. In the illustrated example, a processor 402 including a compressor is added to the auralizer 304 input so that quiet room sounds are made louder at the auralizer input, thereby producing more audible reverberation.8S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796Additionally or alternatively, processor 402 can include a noise gate (or downward expander) so that low-frequency rumble and other low-level room sounds do not become auralized.

[0034] In these and other embodiments, a frequency-dependent (e.g., multi-band) limiter 404 is added before the loudspeaker 104 input to limit the loudspeaker signal level to below that at which unwanted feedback would occur. It should be noted that although a frequencydependent (multi-band) limiter might be preferred in some cases, a multi-band compressor would work as well. Note that the multi -band limiter (or compressor) would be preferred over a standard wide-band limiter (or compressor), as feedback tends to take place in certain frequency bands. That said, a wide-band limiter (or compressor) would also be effective.

[0035] FIG. 5 is a flowchart illustrating an example methodology according to embodiments. This method can be implemented in many ways, for example using a computer (e.g. 114 in FIG. 1, digital audio workstation, etc.) executing software and / or interacting with a user in a manner to become apparent from the descriptions below.

[0036] As shown in FIG. 5, first an initial cancellation function c(t) and / or canceler filter is obtained. This can include performing initial measurements in block 502 for initializing the filter. For example, the canceler impulse response is found by forming an initial canceler filter Co(t) at a known, initial temperature and relative humidity (TO, HO).

[0037] Using this and other information, block 504 can include preparing the initial canceler co(t) by making impulse response measurements while the acoustics augmentation system is operating. The idea is to add to the auralization signal a test signal that is sufficiently quiet (as a function of frequency and time) that the sum would sound like the auralization signal, but is sufficiently long that the energy added would allow accurate measurement of the loudspeaker-microphone impulse response. Additionally or alternatively, the cancellation filter can be designed by comparing the loudspeaker and microphone signals to estimate or update the needed microphone-loudspeaker impulse responses, for instance via cross correlation and related methods as described above.

[0038] The initially prepared cancellation filter can be used as described above, for example in an auralization system as described in connection with the system of FIG. 1 and the block diagram of FIG. 2. According to some aspects of embodiments, new calibrations for canceler and / or transfer function c(t) can be obtained, as determined in block 506. This can9S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796include determining when the current cancelation is no longer performing as well as desired. This may be due to changes in microphone or loudspeaker placement, or repositioning of objects in the room. Even rooms with unchanging geometry can fall out of calibration with changes in the environment that affect sound propagation. Other possibilities for determining whether to initiate a new calibration can be based on a timer, and / or may be done continuously.

[0039] The determination of when the current cancellation is not performing well can be made in many ways. For example, a user of the system can audibly perceive that unwanted feedback is occurring and can manually initiate a new calibration. Alternatively, block 506 can include implementing a regular schedule for performing calibration, for example after a predetermined amount of time, or predetermined number of cancellation operations performed. The determination of when the current cancellation is not performing well can be made in many ways. For example, a user of the system can audibly perceive that unwanted feedback is occurring and can manually initiate a new calibration. Similarly, the microphone and loudspeaker signals may be monitored to determine if feedback is about to occur (for instance, looking for pure tones with growing amplitude), and initiate a calibration. Alternatively, block 506 can include implementing a regular schedule for performing calibration, for example after a predetermined amount of time.

[0040] If calibration is needed, block 508 can includes performing a new calibration. As described above, this can include updating an temperature-humidity pair (TO, HO) to a new temperature-humidity pair (Tl, Hl).

[0041] Next, block 510 can include preparing an updated cancelation filter with an adapted canceler impulse response CT,n(t). For example, the current temperature and relative humidity (T, H) is then used by an adaptor to form the ratio p of the current and initial sound speeds, and the current canceler filter computed as a resampled version of the initial impulse response, c(t) = co(p x t). (4)10S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796

[0042] As set forth above, should only one of temperature and relative humidity be available, the other may be assumed constant or assumed to change in some known fashion, say relative to the one.

[0043] An aspect of embodiments includes improving on previous work for artificially enhancing the acoustics of a room by keeping the system in calibration under changing conditions, limiting the possibility of feedback when simulating extremely reverberant spaces, and by enhancing the simulated acoustics for quiet sound sources. The simulated acoustics system with the inventive improvements can - provide specific acoustics for music performance, recording, and production; - synthesize changing acoustics for gaming and VR applications; and - generate acoustics to produce a subtle, but desired psychological state when used in architectural settings.

[0044] Embodiments provide improvements to previous work, such as the ‘902 patent, for artificially enhancing the acoustics of a room by keeping the system in calibration under changing conditions, limiting the possibility of feedback when simulating extremely reverberant spaces, and by enhancing the simulated acoustics for quiet sound sources.

[0045] The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are illustrative, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being "operably coupleable," to each other to achieve the desired functionality. Specific examples of operably coupleable include but are not limited to physically mateable and / or physically interacting components and / or wirelessly interactable and / or wirelessly interacting components and / or logically interacting and / or logically interactable components.11S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796

[0046] With respect to the use of plural and / or singular terms herein, those having skill in the art can translate from the plural to the singular and / or from the singular to the plural as is appropriate to the context and / or application. The various singular / plural permutations may be expressly set forth herein for sake of clarity.

[0047] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.).

[0048] Although the figures and description may illustrate a specific order of method steps, the order of such steps may differ from what is depicted and described, unless specified differently above. Also, two or more steps may be performed concurrently or with partial concurrence, unless specified differently above. Such variation may depend, for example, on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations of the described methods could be accomplished with standard programming techniques with rule-based logic and other logic to accomplish the various connection steps, processing steps, comparison steps, and decision steps.

[0049] It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation, no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and / or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the12S24-358 PCT.1. Abel et al. Atty. Dkt. 102354-796recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations).

[0050] Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general, such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and / or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0051] Further, unless otherwise noted, the use of the words “approximate,” “about,” “around,” “substantially,” etc., mean plus or minus ten percent.

[0052] Although the present embodiments have been particularly described with reference to preferred examples thereof, it should be readily apparent to those of ordinary skill in the art that changes and modifications in the form and details may be made without departing from the spirit and scope of the present disclosure. It is intended that the appended claims encompass such changes and modifications.13S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796

Claims

WHAT IS CLAIMED IS:

1. A method for calibrating parameters for adjusting cancellation filters used for estimating sounds produced in space in the presence of known other sounds played over loudspeakers, comprising: adjusting cancellation filters according to changing room conditions, including changing temperature and humidity.

2. The method of claim 1, further comprising: recording the sound speed in the room at the time of initial calibration, and occasionally thereafter; updating the cancellation filters by resampling them according to the ratio of initial and current sound speeds.

3. A method for calibrating parameters for adjusting cancellation filters used for estimating sounds produced in space in the presence of known other sounds played over loudspeakers, comprising: adjusting the cancellation filters according to loudspeaker-microphone impulse response measurements made using imperceptible test signals, such as low-level maximal length sequences added to the augmented acoustics, or augmented acoustics with certain known or designed autocorrelations.

4. A method for calibrating parameters for adjusting cancellation filters used for estimating sounds produced in space in the presence of known other sounds played over loudspeakers, comprising: adjusting cancellation filters according to changing room conditions, including identifying quiet sound sources that would benefit from relatively louder reverberation or identifying louder loudspeaker signals that cause unwanted feedback.14S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-7965. The method of claim 4, further comprising: adding a noise gate or downward expander to the auralization process so that low- frequency rumble and other low-level room sounds are to an extent suppressed in the auralization.

6. A method for calibrating parameters for adjusting cancellation filters used for estimating sounds produced in space in the presence of known other sounds played over loudspeakers, comprising: adjusting cancellation filters according to changing room conditions; and adding a compressor to the auralizer input so that quiet room sounds produce audible reverberation than they would otherwise.

7. The method of claim 4, 5 or 6, further comprising: adding a limiter or compressor before the loudspeaker output / canceler input, l(t), to limit the loudspeaker signal level to below a level at which unwanted feedback would occur.15S24-358 PCTJ. Abel et al. Atty. Dkt. 102354-796

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