WO2008138349A2 - Enhanced management of sound provided via headphones - Google Patents

Enhanced management of sound provided via headphones Download PDF

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Publication number
WO2008138349A2
WO2008138349A2 PCT/DK2008/050106 DK2008050106W WO2008138349A2 WO 2008138349 A2 WO2008138349 A2 WO 2008138349A2 DK 2008050106 W DK2008050106 W DK 2008050106W WO 2008138349 A2 WO2008138349 A2 WO 2008138349A2
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WO
WIPO (PCT)
Prior art keywords
signals
estimate
sound
ambient sound
ambient
Prior art date
Application number
PCT/DK2008/050106
Other languages
French (fr)
Other versions
WO2008138349A3 (en
Inventor
Niels Farver
Original Assignee
Microsound A/S
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Microsound A/S filed Critical Microsound A/S
Publication of WO2008138349A2 publication Critical patent/WO2008138349A2/en
Publication of WO2008138349A3 publication Critical patent/WO2008138349A3/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R5/00—Stereophonic arrangements
    • H04R5/04—Circuit arrangements, e.g. for selective connection of amplifier inputs/outputs to loudspeakers, for loudspeaker detection, or for adaptation of settings to personal preferences or hearing impairments
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F11/00—Methods or devices for treatment of the ears or hearing sense; Non-electric hearing aids; Methods or devices for enabling ear patients to achieve auditory perception through physiological senses other than hearing sense; Protective devices for the ears, carried on the body or in the hand
    • A61F11/06—Protective devices for the ears
    • A61F11/14—Protective devices for the ears external, e.g. earcaps or earmuffs
    • A61F11/145—Protective devices for the ears external, e.g. earcaps or earmuffs electric, e.g. for active noise reduction
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
    • G10K11/17813—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms
    • G10K11/17815—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms between the reference signals and the error signals, i.e. primary path
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
    • G10K11/17813—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms
    • G10K11/17819—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms between the output signals and the reference signals, e.g. to prevent howling
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
    • G10K11/17821—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the input signals only
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
    • G10K11/17821—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the input signals only
    • G10K11/17823—Reference signals, e.g. ambient acoustic environment
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1783—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase handling or detecting of non-standard events or conditions, e.g. changing operating modes under specific operating conditions
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1787—General system configurations
    • G10K11/17873—General system configurations using a reference signal without an error signal, e.g. pure feedforward
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1787—General system configurations
    • G10K11/17885—General system configurations additionally using a desired external signal, e.g. pass-through audio such as music or speech
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/10—Earpieces; Attachments therefor ; Earphones; Monophonic headphones
    • H04R1/1083—Reduction of ambient noise
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/301—Computational
    • G10K2210/3055—Transfer function of the acoustic system

Definitions

  • the present invention relates to the usability and listening comfort for earphones and headsets.
  • Earphones and headsets are in widespread use for various purposes such as music reproduction, telephony, hearing protection or hearing enhancement.
  • Traditionally there are several inconveniencies associated with the use of an earphone, especially when used in environments with varying background noise.
  • loud sound levels and/or closed type earphones may shut off ambient sounds to the extent where even alert sounds are not audible and may cause increased danger for the wearer especially in the traffic.
  • Another annoyance factor occurs when the wearer needs to switch from e.g. listening to music or a podcast into active communication with persons in the environment.
  • the earphone masks the environmental sounds too effectively, it takes time before the wearer becomes aware that somebody is addressing him. Secondly, the earphones will have to be removed before communication can take place.
  • US patent no. 4,891,605 discloses an adaptive gain control amplifier for audio reproduction systems. The method involves automatically regulating the amplification level in accordance with the level of background noise determined by establishing a ratio between ambient sound comprising both background noise and utility audio obtained by a microphone and the output signal obtained from the amplifier.
  • a disadvantage of these methods when used in earphones or headsets is that they require a microphone to be located in the very limited space in the ear cavity together with the loudspeaker or other miniature sound transducer. Moreover these methods do not facilitate other operation, e.g. when the listener wants to hear all of the ambient sounds, e.g. in case of a relevant conversation, or some of the ambient sounds, e.g. in case of audible warnings for which an additional microphone would be required.
  • the possible uses of these headsets are also limited as they do not facilitate picking up the sounds outside the headset, e.g. as relevant when used as a cell phone headset where the user's voice needs to be picked up, or when certain ambient sounds should be conveyed unmasked or even cause a decrease of volume, e.g. warning sounds.
  • EP patent application publication no. EP 1 699 211 Al discloses an earphone for use as a communication device e.g. together with a cell phone, and thus incorporates a microphone on the outside of the earphone to pick up the user's voice, and to determine the type and level of background noise in order to facilitate noise reduction.
  • a problem with this headset is that the noise reduction algorithm does not know the amount of background noise actually slipping past the earphone and into the ear cavity, and thus the degree of amplification required to overcome a certain level of ambient noise. This depends very much on the type of earphone or headset, the physical fit of the specific earphone or headset to the shape of the user's ear, and the volume of the user's ear cavity.
  • the present invention relates to a method for use in an earphone or headset system, said system comprising at least one sound reproduction transducer 341, at least one microphone 101 arranged to pick up ambient sound signals, and a processor arranged to process at least one of at least one electronic sound signal obtained by an electronic source input 201 and/or said ambient sound signals, wherein said method employs an arrangement of said processor to process said signals so that time varying characteristics of one of said signals may modify a processing of an other of said signals prior to reproduction via said sound reproduction transducer 341, characterized in that said processor determines an estimate of an acoustic transfer function of a leakage path 510 between the environment and an ear cavity of a wearer of said system, employs said estimate of said acoustic transfer function to estimate a level of ambient sound reaching an eardrum of said wearer of said system, and establishes settings for said processing of said signals on the basis of said estimate of said level of ambient sound reaching said eardrum.
  • the present inventive method facilitates, without requiring a microphone located in the ear canal, estimation of the ambient sound that leaks past the earphones into the ear canal.
  • the method requires a microphone on the outside part of the earphone or otherwise located in the near vicinity of the earphone, but according to the present invention this microphone or microphones can serve other purposes as well, thus increasing the value of implementing the leakage estimation feature in the first place, and increasing the range of possible features in general.
  • Such other purposes and features comprise e.g. picking up of ambient sound for performing active noise reduction or masking, for analysis and automatic change of operational mode, e.g. to let warning sounds or conversations pass through, for picking the user's voice up when the earphone is used for communication purposes, e.g. as a cell phone headset, etc.
  • an earphone or headset system may comprise any sound reproduction system involving sound reproducing transducers to be worn close to the ears, e.g. circumaural headphones with large pads that completely surround the outer ear, supra-aural headphones with smaller pads that sit on top of the ears rather than around them, earbuds or earphones that are located in the outer part of the ear canal and in-the-ear monitors or canalphones where the sound transducer is located inside the ear canal during use, etc.
  • both open earphones with vents or other similar features that facilitates ambient sound to enter the ear canal and closed earphones which are designed to block as much ambient sound out as possible, are within the scope of the present invention.
  • the method of the present invention facilitates picking up ambient sound, possibly including the user's voice, and receiving an electronic signal, e.g. from an MP3-player or cell phone, and establishing a mix of these to provide to the sound reproduction transducer, e.g. a miniature loudspeaker.
  • an electronic signal e.g. from an MP3-player or cell phone
  • the mixing settings may be based on a user-selected or automatically selected operational mode, e.g. comprising a block-all-ambient-sound mode for use when the ambient sounds are distracting or otherwise non-desirable, an amplify-ambient-sound mode for use when ambient sounds are desired, e.g. when a relevant conversation is going on, an block-most-ambient-sound mode for use when most background noise should be blocked but the existence of certain sounds, e.g. warning sounds or alerts, should be known, and a headset mode for use when the earphone is used for communication, and ambient sounds should therefore be attenuated while the user's voice is however picked up.
  • a user-selected or automatically selected operational mode e.g. comprising a block-all-ambient-sound mode for use when the ambient sounds are distracting or otherwise non-desirable, an amplify-ambient-sound mode for use when ambient sounds are desired, e.g. when a relevant conversation is going on, an block-most
  • the mix may comprise only the utility signal derived from an electronic source, only the ambient sounds, or a mix of both, where any of the two may be the most significant.
  • the inventor has realized that the sound reaching the user's ear is inherently a mix of the sound reproduced by the loudspeaker and the ambient sounds that leaks past the earphone, and it is therefore not acceptable to only consider the sound input signal and ambient sound outside the ear when establishing mixes according to the user's desires.
  • the present invention facilitates estimating the leakage path and use this information for various purposes. In the first place it is used to adapt the mix that is reproduced to the user, i.e. how much ambient sound should be mixed into the signal.
  • a special implementation of this is when the earphone is used as a cell phone headset, as a telephone user typically wants to hear his own voice to a certain level when speaking. Further uses comprise facilitating automatic operational mode changes, automatic enablement of noise reduction, masking, etc.
  • the processor may comprise any signal processing means suitable for carrying out the method of the present invention, for example digital signal processors with software memory and programmable gate arrays that are hard coded, but any suitable means are within the scope of the present invention.
  • the estimation of a level of ambient sound reaching an eardrum may according to the present invention comprise any representation of level, i.e. absolute or relative, DC or frequency dependent, or a function of other factors, e.g. time. It may be established and represented in the time domain, frequency domain or any other mathematically or logically suitable way.
  • the addition of a microphone for picking up ambient sound and the method of the present invention enables using the microphone signal and its characteristics for a number of purposes, including estimating a transfer function for the leakage path between the environment and the ear cavity and thereby enable knowing the level and characteristics of background sounds outside the earphone, background sounds inside the earphone, i.e. within the ear cavity and utility sounds inside the earphone.
  • various characteristics of the microphone signal and knowledge of the sound path for external sound to the wearer's ear drum may be used to adapt the parameters of a dynamic compression system acting on the desired music or telephone signal. This may be arranged so that soft parts of the desired signal are still audible even when the ambient noise level rises. The louder components of the desired signal need not be amplified to the same extent or maybe not at all.
  • a processed version of the ambient sound may be delivered to the ear of the wearer with the processing being simultaneously dependent on the current mode of usage, the characteristics of the connected signal (e.g. music or phone), and the characteristics of the leakage path. Such processing may involve expansion so that low level sounds are not conveyed at all.
  • the parameters of dynamic processing of the ambient signal may be varied according to the characteristics of the music or phone signal, thereby maintaining a suitable degree of awareness of the environment.
  • Processing of signals from both environment and other signal sources may according to the present invention optionally be adapted to the user preferences and hearing abilities.
  • the intervals may be regular or infrequent, e.g. triggered by other events, e.g. change of signal source, change of volume, significant pauses, significant change of background noise level or characteristics, etc.
  • additional information is used to improve the accuracy of the estimate of the acoustic transfer function of the leakage path 510.
  • Such additional information may e.g. comprise the actual input impedance represented by the loudspeaker.
  • the loudspeaker's inherent impedance can be measured at design time, any impedance changes measureable during use can be used to estimate the loudspeaker surrounding, e.g. the volume of the ear canal. Knowledge of this volume can be used to fine tune the estimated leakage path transfer function.
  • the impedance or other additional information is preferably determined and represented as frequency dependent information.
  • said settings for said processing of said signals comprise compressor characteristics for modifying the dynamic range of one or more of said signals prior to said reproduction, an advantageous embodiment of the present invention is obtained.
  • ⁇ modes are available, e.g. blocking of ambient sound, use as a cell phone headset, etc. Some of these modes may however not be possible to perform with certain earphone designs, certain ears, etc. For example, if the earphone is open, i.e. inherently comprises physical vents to facilitate background sounds to enter the ear canal, e.g. for warning purposes, the control logic will not be able to satisfactorily carry out a block-all-ambient-sound mode or an ear protection mode. This mode should therefore only be offered for use when the estimation of the leakage path indicates that a significant blocking is actually possible. Another example is to determine on the basis of the estimated transfer function whether or not noise cancellation is possible, and thereby only offer this option when possible. It is therefore a preferred embodiment of the present invention limit the options according to the actual circumstances, including the estimated leakage path transfer function.
  • an advantageous embodiment of the present invention is obtained.
  • a noise suppression algorithm such as spectral subtraction is applied to said ambient sound signal prior to said reproduction, an advantageous embodiment of the present invention is obtained.
  • the present invention further relates to an earphone or headset system comprising at least one sound reproduction transducer 341, at least one microphone 101 arranged to pick up ambient sound signals, and a processor arranged to process at least one of at least one electronic sound signal obtained by an electronic source input 201 and/or said ambient sound signals, wherein said processor is arranged to process said signals so that time varying characteristics of one of said signals may modify a processing of an other of said signals prior to reproduction via said sound reproduction transducer 341, characterized in that said processor is arranged to determine an estimate of an acoustic transfer function of a leakage path 510 between the environment and an ear cavity of a wearer of said system, employ said estimate of said acoustic transfer function to estimate a level of ambient sound reaching an eardrum of said wearer of said system, and establish settings for said processing of said signals on the basis of said estimate of said level of ambient sound reaching said eardrum.
  • a preferred embodiment of the present invention specifically relates to an arrangement of the elements so as to adapt the dynamics of said electronic source signal to the ambient sound levels so that the weaker parts of said electronic source signal are still audible above sound transmitted acoustically through leakage in the headset.
  • a preferred embodiment of the present invention is obtained when a processed version of the microphone signal is mixed with the electronic signal at a level which is low enough to be unobtrusive but still allowing the wearer to notice significant acoustical events in the environment.
  • a preferred embodiment is obtained when said mixing level depends on the level of the electronic source signal so that in soft passages of the electronic source signal, the mixing level of said ambient sound signal is attenuated and vice versa.
  • the mixing level is not only time varying but also frequency dependent so that a desired degree of masking may be obtained by employing a psychoacoustic model in the gain calculations.
  • Another preferred embodiment is obtained when the microphone signal is processed using a noise suppression scheme such as spectral subtraction.
  • the presence of changes to the modulation characteristics in one of the signals may in some operational modes be used to trigger a change in mixing levels and compression in order to attract the wearer's attention to this acoustic event.
  • the control logic may respond to the wearer's press on a button by changing focus to the changed source signal or by restoring processing to normal after a short time if the wearer does not take action.
  • a second button press may cancel the changed focus to normal.
  • the behavior may be reversed so that the wearer's first press on the button restores processing to normal.
  • fig. 1 illustrates a usage situation for a system according to the invention
  • fig. 2 illustrates a block diagram of an embodiment of the present invention
  • fig. 3 illustrates a simplified model of an earphone for simulation purposes
  • fig. 4 illustrates a simulation result.
  • the present invention relates to a method to be employed in a headset or earphone system in order to enhance the usability and comfort for the wearer.
  • the method comprises the steps of analyzing sound signals both from the environment and the signal from an electronic source to be reproduced and employ the obtained characteristics of these signals to establish parameters for dynamically processing said signals so that the stimuli available at the wearer's ear contains a suitable mixture of said signals.
  • the user may use a switch to select one of a number of different modes of operation. These may include a 'music listening mode' where music from the electronic source is the primary signal and only sudden changes in ambient sounds are made audible and that may even be at an attenuated level, a 'noise gate mode' in which background noise is greatly attenuated if below a certain threshold and in which music may or may not be used as a masker for residual environmental noise and a 'conversational mode', in which the sounds from the environment are presented to the ear, so that the wearer may participate in a conversation.
  • a 'music listening mode' where music from the electronic source is the primary signal and only sudden changes in ambient sounds are made audible and that may even be at an attenuated level
  • a 'noise gate mode' in which background noise is greatly attenuated if below a certain threshold and in which music may or may not be used as a masker for residual environmental noise
  • a 'conversational mode'
  • a mode may be included to use the headset as a phone headset in which case the microphone signal is used to pick up the wearers voice.
  • the present invention overcomes in a simple way many of the annoyance factors involved when using a headset, such as not being able to hear the music when background noise rises which in turn causes the wearer to turn up the volume to louder than safe or just uncomfortable levels. Further it decreases the sense of isolation by actually bringing in ambient sounds, but at tolerable levels. And finally it allows for quickly changing between music listening to music, conversation or simply full awareness of the environment without having to remove the headset.
  • Figure 1 illustrates a usage situation for a system according to this invention in which a user is wearing an earphone comprising a loudspeaker 341 for reproducing a utility signal and a microphone 101 arranged so that it may pick up sound from ambient sources 500 that may also enter the ear canal of the user through an acoustic leakage path 510 and interfere with signals from another source 200 such as an MP3 player or mobile phone.
  • a user is wearing an earphone comprising a loudspeaker 341 for reproducing a utility signal and a microphone 101 arranged so that it may pick up sound from ambient sources 500 that may also enter the ear canal of the user through an acoustic leakage path 510 and interfere with signals from another source 200 such as an MP3 player or mobile phone.
  • the level and spectrum of ambient sounds that pass through the acoustic leakage path and into the ear canal depends on several factors. For example is the acoustic leakage path for circumaural headphones having large pads completely surrounding the wearer's ear generally much less significant than it is for earbuds, i.e. small earphones resting in the outer part of the ear canal. But also the physical fit between a specific pair of headphones or earphones with a specific pair of ears has a great influence on the acoustic leakage path, and for some earphone designs it is very hard to achieve the same fit every time the earphones are put on.
  • a good estimate of the acoustic leakage path 510, and thereby the correspondence between ambient sounds outside the earphones and ambient sounds present in the ear canal, is therefore important in order to be able to establish and present the above mentioned desired mixture of signals to the user.
  • the present invention instead uses a measure of the amount and spectrum of sound escaping from the ear canal to the outside via the acoustic leakage path to establish the outbound transfer function of the acoustic leakage path.
  • This measure is enabled by the outside microphone 101 which is also used to pick up ambient sounds and/or the user's voice when the earphone is used for communication.
  • the acoustic leakage path 510 leaks both ways, elements of the signals that are reproduced by the loudspeaker inside the ear canal will also be present at the outside, where they can be picked up by the microphone 101.
  • the ambient sounds also comprised by the microphone signal can be filtered out and the remaining parts used to establish an outbound leakage path transfer function.
  • this outbound transfer function it is possible to estimate an inbound transfer function of the acoustic leakage path, i.e. a transfer function reflecting the level and spectrum of ambient sounds entering the ear canal via the acoustic leakage path 510.
  • this transfer function can be used to prepare the desired or relevant mixture for the user. If for example the acoustic leakage path is very limited, i.e.
  • the control logic should increase the amount of the microphone signal that is added to the mixture. If for example the acoustic leakage path is very significant, i.e. the earphones attenuates ambient sounds very little, and the user wants to use the music to disregard heavy background noise, or he wants to concentrate on a telephone conversation, the control logic should increase the volume of the utility signal or increase the effect of countermeasures such as e.g. active noise reduction or masking.
  • FIG. 2 illustrates a block diagram of a possible processing arrangement according to the present invention.
  • the elements are: Microphone(s) 101 , Adaptive Feedback Control / Estimation of feedback path 110, Analysis of ambient sound 111, Dynamic processing of ambient sound (compression / expansion) 121, Output mixer 321, Post processing / final signal conditioning 331, Loudspeaker 341, Electronic signal source / Utility signal 201, Analysis of utility signal 211, Dynamic processing of utility signal (compression / expansion) 221, User input / Mode selection / Volume control 301 and Central control logic 311 managing mode and settings of all other blocks according to pre-determined or adaptive rules.
  • the state -variables of the Adaptive Feedback Control 110 are used as an estimate of the feedback path which in turn may be used by the control logic 311 to estimate the inbound leakage and combine it with other information in order to derive appropriate settings for other blocks.
  • bounds may be imposed on the processing, so as to maintain reasonable localization and/or balance.
  • Figure 3 shows a simplified model of an earphone with a leakage path 512 for illustration of the principle of using an estimate of the feedback path for estimating the transfer of external sound 500 to the sound pressure at the wearer's eardrum 530.
  • An output stage 340 drives the earphone loudspeaker 341, which terminates into the ear canal.
  • a coupler 514 models the impedance of a typical occluded ear canal and has an output 530 for the sound pressure at the eardrum.
  • Capacitor 511 models additional volume for the sake of simulating variation among individual wearers.
  • the leakage that is part of both the feedback path to the microphone 101 as well as the inbound leakage path is modeled using tube 512.
  • the sound pressure 531 driving the feedback path is found at the output of the loudspeaker 341.
  • the tube terminates in the radiation impedance (combination of reactance and resistance) and the relative strength of the propagated wave appears at 520.
  • the sound pressure at the end of the tube appears at 521. Incident sound pressure from ambient sources is modeled by generator 500.
  • Figure 4 shows simulated curves for eardrum pressure due to the loudspeaker 601,602,603, eardrum pressure due to ambient sound 611,612,613 as well as a normalized feedback transfer function 621, 622, 623.
  • the curves are derived from the model in figure 3 in which the tube diameter has been set to lmm, see curves 601,611,621, 3mm, see curves 602,612,622 and 5mm, see curves 603,613,623 to illustrate how the various transfer functions change as the leakage changes.
  • the horizontal axis gives frequency from 100Hz to 10000 Hz, whereas the vertical scale is dB. Each curve group has been offset vertically for visual clarity.
  • the transfer function of the outbound feedback path from ear canal to the outside can actually provide cues for a system identification algorithm to derive a transfer function estimate for the inbound acoustic leakage path that leads external sound to the eardrum, the establishment of which in turn enables the control logic to prepare audio mixes that meet the user's different usage wishes because it can estimate to what extent the ambient sounds find way to the ear canal by itself, and to what extent their transportation have to be facilitated by mixing them into the utility signal.

Abstract

The present invention relates to a method for use in an earphone or headset system, said system comprising at least one sound reproduction transducer (341), at least one microphone (101) arranged to pick up ambient sound signals, and a processor arranged to process at least one of - at least one electronic sound signal obtained by an electronic source input (201) and/or - said ambient sound signals, wherein said method employs an arrangement of said processor to process said signals so that time varying characteristics of one of said signals may modify a processing of an other of said signals prior to reproduction via said sound reproduction transducer (341), characterized in that said processor - determines an estimate of an acoustic transfer function of a leakage path (510) between the environment and an ear cavity of a wearer of said system, - employs said estimate of said acoustic transfer function to estimate a level of ambient sound reaching an eardrum of said wearer of said system, and establishes settings for said processing of said signals on the basis of said estimate of said level of ambient sound reaching said eardrum.

Description

METHOD AND SYSTEM FOR ENHANCED MANAGEMENT OF SOUND PROVIDED VIA EARPHONES
Field of the invention
The present invention relates to the usability and listening comfort for earphones and headsets.
Background of the invention
Earphones and headsets are in widespread use for various purposes such as music reproduction, telephony, hearing protection or hearing enhancement. Traditionally, there are several inconveniencies associated with the use of an earphone, especially when used in environments with varying background noise.
Often people use headsets and MP3 players to relieve the stress factors stemming from ambient noise and other unwanted stimuli such as other people talking in public transportation, open office environments et cetera.
For once, when listening to music, varying levels of unwanted ambient sounds may require frequent use of the volume control often leading to the use of excessive sound levels, since once a loud level is set, turning it down leads to a dull impression.
Further, loud sound levels and/or closed type earphones may shut off ambient sounds to the extent where even alert sounds are not audible and may cause increased danger for the wearer especially in the traffic.
Another annoyance factor occurs when the wearer needs to switch from e.g. listening to music or a podcast into active communication with persons in the environment.
Firstly, if the earphone masks the environmental sounds too effectively, it takes time before the wearer becomes aware that somebody is addressing him. Secondly, the earphones will have to be removed before communication can take place.
US patent no. 4,891,605 discloses an adaptive gain control amplifier for audio reproduction systems. The method involves automatically regulating the amplification level in accordance with the level of background noise determined by establishing a ratio between ambient sound comprising both background noise and utility audio obtained by a microphone and the output signal obtained from the amplifier.
PCT patent application publication no. WO 2006/125061 Al expands the ideas of the above-mentioned US patent and discloses different headset processing methods that are possible when a microphone is provided for picking up ambient noise within the earphone, i.e. compression, masking and noise reduction.
However, a disadvantage of these methods when used in earphones or headsets is that they require a microphone to be located in the very limited space in the ear cavity together with the loudspeaker or other miniature sound transducer. Moreover these methods do not facilitate other operation, e.g. when the listener wants to hear all of the ambient sounds, e.g. in case of a relevant conversation, or some of the ambient sounds, e.g. in case of audible warnings for which an additional microphone would be required. The possible uses of these headsets are also limited as they do not facilitate picking up the sounds outside the headset, e.g. as relevant when used as a cell phone headset where the user's voice needs to be picked up, or when certain ambient sounds should be conveyed unmasked or even cause a decrease of volume, e.g. warning sounds.
EP patent application publication no. EP 1 699 211 Al discloses an earphone for use as a communication device e.g. together with a cell phone, and thus incorporates a microphone on the outside of the earphone to pick up the user's voice, and to determine the type and level of background noise in order to facilitate noise reduction. A problem with this headset is that the noise reduction algorithm does not know the amount of background noise actually slipping past the earphone and into the ear cavity, and thus the degree of amplification required to overcome a certain level of ambient noise. This depends very much on the type of earphone or headset, the physical fit of the specific earphone or headset to the shape of the user's ear, and the volume of the user's ear cavity. Hence, individual settings would have to be applied for each combination of earphone and ear. Some earphones and headsets also fit very differently to the ear each time an individual puts them on, e.g. due to bad design, and in such cases the automatic gain settings also have to be changed each time the headset is put on.
It is an object of the present invention to improve the usability of earphones and headsets by enabling monitoring of ambient sounds including the user's voice while also knowing the degree of ambient noise that slips into the ear cavity.
Summary of the invention
The present invention relates to a method for use in an earphone or headset system, said system comprising at least one sound reproduction transducer 341, at least one microphone 101 arranged to pick up ambient sound signals, and a processor arranged to process at least one of at least one electronic sound signal obtained by an electronic source input 201 and/or said ambient sound signals, wherein said method employs an arrangement of said processor to process said signals so that time varying characteristics of one of said signals may modify a processing of an other of said signals prior to reproduction via said sound reproduction transducer 341, characterized in that said processor determines an estimate of an acoustic transfer function of a leakage path 510 between the environment and an ear cavity of a wearer of said system, employs said estimate of said acoustic transfer function to estimate a level of ambient sound reaching an eardrum of said wearer of said system, and establishes settings for said processing of said signals on the basis of said estimate of said level of ambient sound reaching said eardrum.
According to the present invention an advantageous method of obtaining better control of the sound experience when using earphones is obtained. Among other things, the present inventive method facilitates, without requiring a microphone located in the ear canal, estimation of the ambient sound that leaks past the earphones into the ear canal. The method requires a microphone on the outside part of the earphone or otherwise located in the near vicinity of the earphone, but according to the present invention this microphone or microphones can serve other purposes as well, thus increasing the value of implementing the leakage estimation feature in the first place, and increasing the range of possible features in general. Such other purposes and features comprise e.g. picking up of ambient sound for performing active noise reduction or masking, for analysis and automatic change of operational mode, e.g. to let warning sounds or conversations pass through, for picking the user's voice up when the earphone is used for communication purposes, e.g. as a cell phone headset, etc.
According to the present invention, an earphone or headset system may comprise any sound reproduction system involving sound reproducing transducers to be worn close to the ears, e.g. circumaural headphones with large pads that completely surround the outer ear, supra-aural headphones with smaller pads that sit on top of the ears rather than around them, earbuds or earphones that are located in the outer part of the ear canal and in-the-ear monitors or canalphones where the sound transducer is located inside the ear canal during use, etc. Moreover, both open earphones with vents or other similar features that facilitates ambient sound to enter the ear canal and closed earphones which are designed to block as much ambient sound out as possible, are within the scope of the present invention. Simply put, the method of the present invention facilitates picking up ambient sound, possibly including the user's voice, and receiving an electronic signal, e.g. from an MP3-player or cell phone, and establishing a mix of these to provide to the sound reproduction transducer, e.g. a miniature loudspeaker.
The mixing settings may be based on a user-selected or automatically selected operational mode, e.g. comprising a block-all-ambient-sound mode for use when the ambient sounds are distracting or otherwise non-desirable, an amplify-ambient-sound mode for use when ambient sounds are desired, e.g. when a relevant conversation is going on, an block-most-ambient-sound mode for use when most background noise should be blocked but the existence of certain sounds, e.g. warning sounds or alerts, should be known, and a headset mode for use when the earphone is used for communication, and ambient sounds should therefore be attenuated while the user's voice is however picked up.
Hence, according to the present invention, the mix may comprise only the utility signal derived from an electronic source, only the ambient sounds, or a mix of both, where any of the two may be the most significant.
In order to enable these operational modes to work properly, i.e. to actually give the user the option of different experiences, the inventor has realized that the sound reaching the user's ear is inherently a mix of the sound reproduced by the loudspeaker and the ambient sounds that leaks past the earphone, and it is therefore not acceptable to only consider the sound input signal and ambient sound outside the ear when establishing mixes according to the user's desires. On the other hand it is also not desirable to implement an additional microphone inside the earphone due to space considerations. Instead the present invention facilitates estimating the leakage path and use this information for various purposes. In the first place it is used to adapt the mix that is reproduced to the user, i.e. how much ambient sound should be mixed into the signal. A special implementation of this is when the earphone is used as a cell phone headset, as a telephone user typically wants to hear his own voice to a certain level when speaking. Further uses comprise facilitating automatic operational mode changes, automatic enablement of noise reduction, masking, etc.
According to the present invention, the processor may comprise any signal processing means suitable for carrying out the method of the present invention, for example digital signal processors with software memory and programmable gate arrays that are hard coded, but any suitable means are within the scope of the present invention.
The estimation of a level of ambient sound reaching an eardrum may according to the present invention comprise any representation of level, i.e. absolute or relative, DC or frequency dependent, or a function of other factors, e.g. time. It may be established and represented in the time domain, frequency domain or any other mathematically or logically suitable way.
Put in another way, the addition of a microphone for picking up ambient sound and the method of the present invention enables using the microphone signal and its characteristics for a number of purposes, including estimating a transfer function for the leakage path between the environment and the ear cavity and thereby enable knowing the level and characteristics of background sounds outside the earphone, background sounds inside the earphone, i.e. within the ear cavity and utility sounds inside the earphone.
When listening to music or a telephone signal, various characteristics of the microphone signal and knowledge of the sound path for external sound to the wearer's ear drum, i.e. the inbound leakage path, may be used to adapt the parameters of a dynamic compression system acting on the desired music or telephone signal. This may be arranged so that soft parts of the desired signal are still audible even when the ambient noise level rises. The louder components of the desired signal need not be amplified to the same extent or maybe not at all. Moreover, a processed version of the ambient sound may be delivered to the ear of the wearer with the processing being simultaneously dependent on the current mode of usage, the characteristics of the connected signal (e.g. music or phone), and the characteristics of the leakage path. Such processing may involve expansion so that low level sounds are not conveyed at all. Further, the parameters of dynamic processing of the ambient signal may be varied according to the characteristics of the music or phone signal, thereby maintaining a suitable degree of awareness of the environment.
Processing of signals from both environment and other signal sources may according to the present invention optionally be adapted to the user preferences and hearing abilities.
When said estimate of said acoustic transfer function of said leakage path 510 is updated continuously or at intervals using an estimate of a feedback path from said sound reproduction transducer 341 to said microphone 101, an advantageous embodiment of the present invention is obtained.
According to the present invention, the intervals may be regular or infrequent, e.g. triggered by other events, e.g. change of signal source, change of volume, significant pauses, significant change of background noise level or characteristics, etc.
When said estimate of said feedback path is established at least partly on the basis of a determination of correlation between a signal being reproduced by said sound reproduction transducer 341 and said ambient sound signals picked up by said microphone 101, an advantageous embodiment of the present invention is obtained.
In other words, the greater the leakage, the greater the amount of utility signal being picked up by the microphone.
When said establishment of said estimate of said acoustic transfer function of said leakage path 510 and/or said settings for said processing of said signals is at least partially based on further cues such as for instance electrical impedance measured at the terminals of said sound reproduction transducer 341, an advantageous embodiment of the present invention is obtained.
According to the present invention, additional information is used to improve the accuracy of the estimate of the acoustic transfer function of the leakage path 510. Such additional information may e.g. comprise the actual input impedance represented by the loudspeaker. As the loudspeaker's inherent impedance can be measured at design time, any impedance changes measureable during use can be used to estimate the loudspeaker surrounding, e.g. the volume of the ear canal. Knowledge of this volume can be used to fine tune the estimated leakage path transfer function. It is noted that the impedance or other additional information is preferably determined and represented as frequency dependent information.
When said settings for said processing of said signals comprise compressor characteristics for modifying the dynamic range of one or more of said signals prior to said reproduction, an advantageous embodiment of the present invention is obtained.
When one or more user inputs 301 such as a push button, touch sensor, voice control or similar are employed to allow a user to quickly change an operational mode, an advantageous embodiment of the present invention is obtained.
When automatic operational mode changes are triggered by changes in characteristics of said sound signals, an advantageous embodiment of the present invention is obtained.
When self-learning mechanisms such as a neural network are employed to adapt criteria for said automatic operational mode changes based on a user's previous operational mode changes or reactions to previous automatic operational mode changes so as to only invoke such changes when they are likely to be accepted, an advantageous embodiment of the present invention is obtained. When a psychoacoustic model is employed to establish absolute and relative presentation levels of said signals so as to achieve masking characteristics suitable for the currently selected operational mode, an advantageous embodiment of the present invention is obtained.
When a selection of operational modes is constrained by estimated characteristics of said leakage path 510, an advantageous embodiment of the present invention is obtained.
According to a preferred embodiment of the present invention several operational modes are available, e.g. blocking of ambient sound, use as a cell phone headset, etc. Some of these modes may however not be possible to perform with certain earphone designs, certain ears, etc. For example, if the earphone is open, i.e. inherently comprises physical vents to facilitate background sounds to enter the ear canal, e.g. for warning purposes, the control logic will not be able to satisfactorily carry out a block-all-ambient-sound mode or an ear protection mode. This mode should therefore only be offered for use when the estimation of the leakage path indicates that a significant blocking is actually possible. Another example is to determine on the basis of the estimated transfer function whether or not noise cancellation is possible, and thereby only offer this option when possible. It is therefore a preferred embodiment of the present invention limit the options according to the actual circumstances, including the estimated leakage path transfer function.
When the present invention is implemented as a stereophonic system, an advantageous embodiment of the present invention is obtained.
When the present invention is implemented as a monophonic system, an advantageous embodiment of the present invention is obtained. When a noise suppression algorithm such as spectral subtraction is applied to said ambient sound signal prior to said reproduction, an advantageous embodiment of the present invention is obtained.
When a noise suppression algorithm such as spectral subtraction is applied to any of said signals to facilitate the task of making operational mode changes and/or said establishment of settings for said processing, e.g. compression characteristics, an advantageous embodiment of the present invention is obtained.
When said system comprises an electronic signal source 200 as an integral part, an advantageous embodiment of the present invention is obtained.
The present invention further relates to an earphone or headset system comprising at least one sound reproduction transducer 341, at least one microphone 101 arranged to pick up ambient sound signals, and a processor arranged to process at least one of at least one electronic sound signal obtained by an electronic source input 201 and/or said ambient sound signals, wherein said processor is arranged to process said signals so that time varying characteristics of one of said signals may modify a processing of an other of said signals prior to reproduction via said sound reproduction transducer 341, characterized in that said processor is arranged to determine an estimate of an acoustic transfer function of a leakage path 510 between the environment and an ear cavity of a wearer of said system, employ said estimate of said acoustic transfer function to estimate a level of ambient sound reaching an eardrum of said wearer of said system, and establish settings for said processing of said signals on the basis of said estimate of said level of ambient sound reaching said eardrum.
When said system is arranged to carry out a method according to any of the above, an advantageous embodiment of the present invention is obtained. A preferred embodiment of the present invention specifically relates to an arrangement of the elements so as to adapt the dynamics of said electronic source signal to the ambient sound levels so that the weaker parts of said electronic source signal are still audible above sound transmitted acoustically through leakage in the headset.
A preferred embodiment of the present invention is obtained when a processed version of the microphone signal is mixed with the electronic signal at a level which is low enough to be unobtrusive but still allowing the wearer to notice significant acoustical events in the environment.
A preferred embodiment is obtained when said mixing level depends on the level of the electronic source signal so that in soft passages of the electronic source signal, the mixing level of said ambient sound signal is attenuated and vice versa.
In another preferred embodiment of the present invention the mixing level is not only time varying but also frequency dependent so that a desired degree of masking may be obtained by employing a psychoacoustic model in the gain calculations.
Another preferred embodiment is obtained when the microphone signal is processed using a noise suppression scheme such as spectral subtraction.
Further, in yet another embodiment, the presence of changes to the modulation characteristics in one of the signals may in some operational modes be used to trigger a change in mixing levels and compression in order to attract the wearer's attention to this acoustic event. In such cases, the control logic may respond to the wearer's press on a button by changing focus to the changed source signal or by restoring processing to normal after a short time if the wearer does not take action. A second button press may cancel the changed focus to normal. In another mode of operation the behavior may be reversed so that the wearer's first press on the button restores processing to normal. The drawings
The invention will in the following be described with reference to the drawings where
fig. 1 illustrates a usage situation for a system according to the invention, fig. 2 illustrates a block diagram of an embodiment of the present invention, fig. 3 illustrates a simplified model of an earphone for simulation purposes, and fig. 4 illustrates a simulation result.
Detailed description
The present invention relates to a method to be employed in a headset or earphone system in order to enhance the usability and comfort for the wearer. The method comprises the steps of analyzing sound signals both from the environment and the signal from an electronic source to be reproduced and employ the obtained characteristics of these signals to establish parameters for dynamically processing said signals so that the stimuli available at the wearer's ear contains a suitable mixture of said signals.
The mixture thus presented can be varied according to both usage situation and general user preferences. In a preferred embodiment, the user may use a switch to select one of a number of different modes of operation. These may include a 'music listening mode' where music from the electronic source is the primary signal and only sudden changes in ambient sounds are made audible and that may even be at an attenuated level, a 'noise gate mode' in which background noise is greatly attenuated if below a certain threshold and in which music may or may not be used as a masker for residual environmental noise and a 'conversational mode', in which the sounds from the environment are presented to the ear, so that the wearer may participate in a conversation. Further, a mode may be included to use the headset as a phone headset in which case the microphone signal is used to pick up the wearers voice. The present invention overcomes in a simple way many of the annoyance factors involved when using a headset, such as not being able to hear the music when background noise rises which in turn causes the wearer to turn up the volume to louder than safe or just uncomfortable levels. Further it decreases the sense of isolation by actually bringing in ambient sounds, but at tolerable levels. And finally it allows for quickly changing between music listening to music, conversation or simply full awareness of the environment without having to remove the headset.
Figure 1 illustrates a usage situation for a system according to this invention in which a user is wearing an earphone comprising a loudspeaker 341 for reproducing a utility signal and a microphone 101 arranged so that it may pick up sound from ambient sources 500 that may also enter the ear canal of the user through an acoustic leakage path 510 and interfere with signals from another source 200 such as an MP3 player or mobile phone.
The level and spectrum of ambient sounds that pass through the acoustic leakage path and into the ear canal depends on several factors. For example is the acoustic leakage path for circumaural headphones having large pads completely surrounding the wearer's ear generally much less significant than it is for earbuds, i.e. small earphones resting in the outer part of the ear canal. But also the physical fit between a specific pair of headphones or earphones with a specific pair of ears has a great influence on the acoustic leakage path, and for some earphone designs it is very hard to achieve the same fit every time the earphones are put on.
A good estimate of the acoustic leakage path 510, and thereby the correspondence between ambient sounds outside the earphones and ambient sounds present in the ear canal, is therefore important in order to be able to establish and present the above mentioned desired mixture of signals to the user.
Instead of locating a microphone at the ear-side of the earphone or headphone to measure the ambient sounds entering the ear canal as seen in the prior art, the present invention instead uses a measure of the amount and spectrum of sound escaping from the ear canal to the outside via the acoustic leakage path to establish the outbound transfer function of the acoustic leakage path. This measure is enabled by the outside microphone 101 which is also used to pick up ambient sounds and/or the user's voice when the earphone is used for communication. In other words because the acoustic leakage path 510 leaks both ways, elements of the signals that are reproduced by the loudspeaker inside the ear canal will also be present at the outside, where they can be picked up by the microphone 101. As the utility signal and the microphone signal is known by the control logic the ambient sounds also comprised by the microphone signal can be filtered out and the remaining parts used to establish an outbound leakage path transfer function. On the basis of this outbound transfer function, it is possible to estimate an inbound transfer function of the acoustic leakage path, i.e. a transfer function reflecting the level and spectrum of ambient sounds entering the ear canal via the acoustic leakage path 510. When this transfer function is known, it can be used to prepare the desired or relevant mixture for the user. If for example the acoustic leakage path is very limited, i.e. the headphones attenuates ambient sounds very well, and the user wants to listen to a conversation or be able to hear warning sounds, the control logic should increase the amount of the microphone signal that is added to the mixture. If for example the acoustic leakage path is very significant, i.e. the earphones attenuates ambient sounds very little, and the user wants to use the music to disregard heavy background noise, or he wants to concentrate on a telephone conversation, the control logic should increase the volume of the utility signal or increase the effect of countermeasures such as e.g. active noise reduction or masking.
Figure 2 illustrates a block diagram of a possible processing arrangement according to the present invention. The elements are: Microphone(s) 101 , Adaptive Feedback Control / Estimation of feedback path 110, Analysis of ambient sound 111, Dynamic processing of ambient sound (compression / expansion) 121, Output mixer 321, Post processing / final signal conditioning 331, Loudspeaker 341, Electronic signal source / Utility signal 201, Analysis of utility signal 211, Dynamic processing of utility signal (compression / expansion) 221, User input / Mode selection / Volume control 301 and Central control logic 311 managing mode and settings of all other blocks according to pre-determined or adaptive rules.
The state -variables of the Adaptive Feedback Control 110 are used as an estimate of the feedback path which in turn may be used by the control logic 311 to estimate the inbound leakage and combine it with other information in order to derive appropriate settings for other blocks. In a stereophonic arrangement, bounds may be imposed on the processing, so as to maintain reasonable localization and/or balance.
Figure 3 shows a simplified model of an earphone with a leakage path 512 for illustration of the principle of using an estimate of the feedback path for estimating the transfer of external sound 500 to the sound pressure at the wearer's eardrum 530. An output stage 340 drives the earphone loudspeaker 341, which terminates into the ear canal. A coupler 514 models the impedance of a typical occluded ear canal and has an output 530 for the sound pressure at the eardrum. Capacitor 511 models additional volume for the sake of simulating variation among individual wearers. The leakage that is part of both the feedback path to the microphone 101 as well as the inbound leakage path is modeled using tube 512. The sound pressure 531 driving the feedback path is found at the output of the loudspeaker 341. The tube terminates in the radiation impedance (combination of reactance and resistance) and the relative strength of the propagated wave appears at 520. The sound pressure at the end of the tube (close to the microphone 101) appears at 521. Incident sound pressure from ambient sources is modeled by generator 500.
Figure 4 shows simulated curves for eardrum pressure due to the loudspeaker 601,602,603, eardrum pressure due to ambient sound 611,612,613 as well as a normalized feedback transfer function 621, 622, 623. The curves are derived from the model in figure 3 in which the tube diameter has been set to lmm, see curves 601,611,621, 3mm, see curves 602,612,622 and 5mm, see curves 603,613,623 to illustrate how the various transfer functions change as the leakage changes. The horizontal axis gives frequency from 100Hz to 10000 Hz, whereas the vertical scale is dB. Each curve group has been offset vertically for visual clarity. Hence, given prior knowledge, which can be established at design time, the transfer function of the outbound feedback path from ear canal to the outside can actually provide cues for a system identification algorithm to derive a transfer function estimate for the inbound acoustic leakage path that leads external sound to the eardrum, the establishment of which in turn enables the control logic to prepare audio mixes that meet the user's different usage wishes because it can estimate to what extent the ambient sounds find way to the ear canal by itself, and to what extent their transportation have to be facilitated by mixing them into the utility signal.
It must be understood that the above model and curves are merely for illustrational purposes and should not be seen as limiting for the scope of this invention.

Claims

Patent Claims
1. Method for use in an earphone or headset system, said system comprising at least one sound reproduction transducer (341), at least one microphone (101) arranged to pick up ambient sound signals, and a processor arranged to process at least one of at least one electronic sound signal obtained by an electronic source input (201) and/or said ambient sound signals, wherein said method employs an arrangement of said processor to process said signals so that time varying characteristics of one of said signals may modify a processing of an other of said signals prior to reproduction via said sound reproduction transducer (341), characterized in that said processor - determines an estimate of an acoustic transfer function of a leakage path (510) between the environment and an ear cavity of a wearer of said system, employs said estimate of said acoustic transfer function to estimate a level of ambient sound reaching an eardrum of said wearer of said system, and establishes settings for said processing of said signals on the basis of said estimate of said level of ambient sound reaching said eardrum.
2. Method according to claim 1 whereby said estimate of said acoustic transfer function of said leakage path (510) is updated continuously or at intervals using an estimate of a feedback path from said sound reproduction transducer (341) to said microphone (101).
3. Method according to claim 2 whereby said estimate of said feedback path is established at least partly on the basis of a determination of correlation between a signal being reproduced by said sound reproduction transducer (341) and said ambient sound signals picked up by said microphone (101).
4. Method according to any of the preceding claims whereby said establishment of said estimate of said acoustic transfer function of said leakage path (510) and/or said settings for said processing of said signals is at least partially based on further cues such as for instance electrical impedance measured at the terminals of said sound reproduction transducer (341).
5. Method according to any of the preceding claims whereby said settings for said processing of said signals comprise compressor characteristics for modifying the dynamic range of one or more of said signals prior to said reproduction.
6. Method according to any of the preceding claims whereby one or more user inputs (301) such as a push button, touch sensor, voice control or similar are employed to allow a user to quickly change an operational mode.
7. Method according to any of the preceding claims, whereby automatic operational mode changes are triggered by changes in characteristics of said sound signals.
8. Method according to claim 7 whereby self-learning mechanisms such as a neural network are employed to adapt criteria for said automatic operational mode changes based on a user's previous operational mode changes or reactions to previous automatic operational mode changes so as to only invoke such changes when they are likely to be accepted.
9. Method according to any of the preceding claims whereby a psychoacoustic model is employed to establish absolute and relative presentation levels of said signals so as to achieve masking characteristics suitable for the currently selected operational mode.
10. Method according to any of the preceding claims whereby a selection of operational modes is constrained according to estimated characteristics of said leakage path (510).
11. Method according to any of the preceding claims working as a stereophonic system.
12. Method according to any of the claims 1 to 10 working as a monophonic system.
13. Method according to any of the preceding claims whereby a noise suppression algorithm such as spectral subtraction is applied to said ambient sound signal prior to said reproduction.
14. Method according to any of the preceding claims whereby a noise suppression algorithm such as spectral subtraction is applied to any of said signals to facilitate the task of making operational mode changes and/or said establishment of settings for said processing, e.g. compression characteristics.
15. Method according to any of the preceding claims wherein said system comprises an electronic signal source (200) as an integral part.
16. Earphone or headset system comprising at least one sound reproduction transducer (341), at least one microphone (101) arranged to pick up ambient sound signals, and a processor arranged to process at least one of at least one electronic sound signal obtained by an electronic source input (201) and/or said ambient sound signals, wherein said processor is arranged to process said signals so that time varying characteristics of one of said signals may modify a processing of an other of said signals prior to reproduction via said sound reproduction transducer (341), characterized in that said processor is arranged to determine an estimate of an acoustic transfer function of a leakage path (510) between the environment and an ear cavity of a wearer of said system, employ said estimate of said acoustic transfer function to estimate a level of ambient sound reaching an eardrum of said wearer of said system, and establish settings for said processing of said signals on the basis of said estimate of said level of ambient sound reaching said eardrum.
17. Earphone or headset system according to claim 16, wherein said system is arranged to carry out a method according to any of the claims 1 to 15.
PCT/DK2008/050106 2007-05-10 2008-05-13 Enhanced management of sound provided via headphones WO2008138349A2 (en)

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