Patent Grant
8929566
The invention relates to audio processing in portable devices with a view to keeping power consumption relatively low. The invention relates specifically to a method of processing an audio signal in a portable listening device, the audio signal comprising a low frequency part having an LF-bandwidth ΔfLF and a high-frequency part having a HF-bandwidth ΔfHF.
The invention furthermore relates to a portable listening device, a listening system and a method of operating a listening device.
The invention may e.g. be useful in applications such as portable communication device, mobile telephones or listening devices, such as a hearing aids, ear protection devices, headsets, head phones, etc.
The frequency resolution of the human auditory system is much less at high frequencies than at low frequencies due to the logarithmic nature of the human frequency resolution. This fact combined with the fact that most audio signals contain a lot of information redundancy across frequencies has led to a technique called bandwidth extension. With the use of this technique a signal missing some frequency ranges can be reconstructed. One example of this technique is called Spectral Band Replication (SBR) (see e.g. EP 1367566 B1 or WO 2007/006658 A1). Due to the logarithmic nature of the human frequency resolution it is less complicated to reconstruct higher frequencies from lower frequencies than vice versa without audible artefacts.
Bandwidth extension is a well known technique used in applications like audio coding and telecommunication systems. In audio coding the purpose of bandwidth extension is to improve the coding efficiency. In telecommunication systems the purpose of bandwidth extension is to artificially increase a limited signal bandwidth.
[Murakami et al., 2002] describes e.g. a method of noise reduction, where the noise reduction is performed on a down sampled input signal and where subsequently a bandwidth extension (BWX) technique using a ‘radial basis function’ (RBF) network is applied to the noise reduced signal.
US2007/0124140 A1 describes the use of BWX in a telecommunication system, wherein a transmitted signal representing a telephone conversation, which in the transmission channel is limited to low frequencies, on the receiver side is enhanced using BWX.
The present invention utilizes bandwidth extension techniques in signal processing of an audio signal to improve performance or save battery power in a portable listening device, such as a hearing aid, an ear protection device, a headset or a pair of head phones.
The present invention relates to the processing and generation of an audio signal with a full bandwidth Δffull in a portable listening device, the audio signal comprising a low frequency (LF) part having an LF-bandwidth ΔfLF and a high-frequency (HF) part having a HF-bandwidth ΔfHF, f denoting frequency.
Typically signal processing in a listening device is carried out on a full bandwidth signal. In an aspect of this invention, the bulk of the signal processing (e.g. analogue to digital (A/D-)conversion, time-frequency transformation, compression, noise reduction, feedback suppression, directionality, etc.) is carried out on a signal with a low frequency bandwidth (BW, e.g. BW=5 kHz). According to the Nyquist criterion a sample rate frequency (Fs) of twice the bandwidth is required (e.g. Fs=10 kHz). Signal components at higher frequencies (e.g. 5-10 kHz) are estimated from the lower frequencies with the use of bandwidth extension, e.g. just before the signal is fed to an output transducer (e.g. a receiver (speaker) unit) for presentation to a user, whereby power consumption is reduced.
In an aspect of this invention, an object is to reduce the load of a wireless link used for streaming audio to a listening device, whereby power consumption can be reduced or transmission range increased.
Objects of the present invention are to improve performance or save power in a portable listening device.
Objects of the invention are achieved by embodiments of the invention described in the accompanying claims and as described in the following.
A Method of Processing an Audio Signal:
In an aspect of the invention, there is provided a method of processing an audio signal in a portable listening device, the audio signal comprising a low frequency part having an LF-bandwidth ΔfLF and a high-frequency part having a HF-bandwidth ΔfHF. The method comprises a) providing an audio input signal consisting of said low frequency part having an LF-bandwidth ΔfLF; b) performing at least one signal processing step on the low frequency part of the audio signal; and c) performing a bandwidth extension process on said low frequency part of the audio signal to generate said high-frequency part of the audio signal, thereby generating or regenerating an audio output signal with a full bandwidth Δffull comprising said LF-bandwidth ΔfLF and said HF-bandwidth ΔfHF.
An advantage of this is that power consumption is reduced.
Bandwidth extension of band limited audio signals is e.g. discussed in EP 1 638 083 A1. In an embodiment, the bandwidth extension method used is adapted to the characteristics of signals, which the listening device is expected to be exposed to (music, speech, speech and noise, signal level, signal energy, etc.). In an embodiment, the listening device is adapted to use different bandwidth extension methods dependent upon characteristics of the acoustic input signal.
In an embodiment, the frequency range Δf=[fmin; fmax] (where fmin is a minimum frequency and fmax is a maximum frequency) considered by the listening device (and thus of relevance to the audio signal comprising an LF-part of bandwidth ΔfLF and a HF-part of bandwidth ΔfHF) is limited to a part of the typical human audible frequency range (20 Hz≦f≦20 kHz) and is divided into a number K of frequency bands (FB), (FB1, FB2, . . . , FBK). In an embodiment, the number of bands K is larger than or equal to 2, e.g. K=8 or 16 or 32 or 64 or more.
In an embodiment, the audio signal is adapted to be arranged in time frames, each time frame comprising a predefined number N of digital time samples xn (n=1, 2, . . . , N), each time sample xn constituting a value of the signal (e.g. its amplitude) at a specific time tn, corresponding to a frame length in time of L=N/fs, where fs is a sampling frequency of an analog to digital conversion unit. In an embodiment, a time frame has a length in time of at least 8 ms, such as at least 24 ms, such as at least 50 ms, such as at least 80 ms. In an embodiment, the sampling frequency fs of an analog to digital conversion unit is larger than 1 kHz, such as larger than 4 kHz, such as larger than 8 kHz, such as larger than 16 kHz. In an embodiment, the sampling frequency is in the range between 1 kHz and 40 kHz, e.g. 10 kHz or 20 kHz. In an embodiment, the sampling frequency is different in different parts of the portable listening device. In an embodiment, time frames of the input signal are processed to a time-frequency representation by transforming the time frames on a frame by frame basis to provide corresponding spectra of frequency samples, the time frequency representation being constituted by TF-units each comprising a complex value (magnitude and phase) of the input signal at a particular unit in time and frequency. The frequency samples in a given time unit may be arranged in bands FBk (k=1, 2, . . . , K), each band comprising one or more frequency units (samples).
In an embodiment, one or more bands from the low-frequency part is/are used as donor band(s) and the spectral content of such donor band(s) is/are copied and possibly scaled to one or more target band(s) of the high-frequency part. A predefined scaling of the frequency content from the donor to the target band is e.g. determined to minimize artefacts in the signal. Such minimization may e.g. be achieved by means of a model of the human auditory system. The term ‘spectral content of a band’ is in the present context taken to mean the (complex) values of frequency components of a signal represented by the band in question. In general the spectral content at a given frequency comprises corresponding values of the magnitude and phase of the signal at that frequency at a given time (as e.g. determined by a time to frequency transformation of a time varying input signal at a given time or rather for a given time increment at that given time). In an embodiment, only the magnitude values of the signal are considered.
In a particular embodiment, the high-frequency part of the signal is reconstructed by spectral band replication. In an embodiment, one or more bands from a low-frequency part of the signal is/are used for reconstructing the high-frequency part of the signal. Details of spectral band replication in general are e.g. discussed in EP 1 367 566 B1 and in connection with application in a listening device, such as a hearing aid, in WO 2007/006658 A1.
In general, it is anticipated that the range constituted by Δffull is substantially equal to the sum of ΔfLF and ΔfHF. It is, however, intended that the ΔfLF and ΔfHF may constitute non-adjacent ranges of the audible frequency range (typically considered to be between 20 Hz and 20 kHz), ΔfLF defining a frequency range between a minimum LF-frequency fLF,min and a maximum LF-frequency fLF,max and ΔfHF defining a frequency range between a minimum HF-frequency fHF,min and a maximum HF-frequency fHF,max where fLF,max≦fHF,min.
In an embodiment, the frequency ranges ΔfLF and ΔfHF are separated by a predetermined LF-HF separation frequency fLF−HF. The term ‘separated by a predetermined LF-HF frequency fLF−HF can include the case where the LF-HF frequency is located in a frequency range between ΔfLF and ΔfHF (between fLF,max and fHF,min), and NOT being a common end-point of the ranges ΔfLF and ΔfHF (i.e. where the two ranges ΔfLF and ΔfHF are separated by an intermediate range). In an embodiment, fLF−HF=fLF,max=fHF,min. In an embodiment, the LF-bandwidth ΔfLF constitutes 0.7 times or less of the full bandwidth Δffull of the audio signal, such as 0.5 times or less, such as 0.4 times or less, such as 0.25 times or less of the full bandwidth of the audio signal. In an embodiment, the LF-bandwidth ΔfLF constitutes 0.5 times or more (such as 0.6 times or more, such as 0.7 times or more) of the full bandwidth Δffull of the audio signal considered by the listening device (e.g. as presented to a user via an output transducer).
In a particular embodiment, the predetermined separation frequency fLF−HF is in the range between 2 kHz and 8 kHz, such as between 3 kHz and 7 kHz, such as between 4 kHz and 6 kHz, e.g. around 5 kHz.
In a particular embodiment, the low-frequency part has a minimum frequency fLF,min in the range from 3 Hz to 300 Hz, such as from 5 Hz to 100 Hz, such as 20 Hz.
In a particular embodiment, the high-frequency part has a maximum frequency fHF,max in the range from 4 kHz to 20 kHz, such as from 7 kHz to 12 kHz, such as around 10 kHz.
Preferably, the at least one signal processing step performed on the low frequency part of the signal include(s) the more power consuming steps, such as one or more (such as a majority, or all) of wireless transmission/reception, A/D-conversion, time-frequency conversion, signal processing, such as extraction of directional information, providing an appropriate frequency dependent gain profile, compression, noise reduction, acoustic feedback suppression, etc.
In a particular embodiment, the low frequency part of the audio signal is picked up by an input transducer, e.g. a microphone, of the portable listening device. In an embodiment, the audio signal is converted to a digital signal by an analogue to digital (AD) converter. In an embodiment, the analogue to digital converter is sampled by a first sample rate Fs1 adapted to provide said low frequency part having an LF-bandwidth ΔfLF (whereby power is saved compared to using a higher sampling rate to provide a full bandwidth signal). In an embodiment, the audio signal is filtered to provide said low frequency part having an LF-bandwidth ΔfLF.
In a particular embodiment, the low frequency part of the audio signal (or a part thereof) is received by the portable listening device from another device, e.g. from an audio gateway or an entertainment device, e.g. a music player or a mobile telephone, via a wired or wireless connection. In a particular embodiment, the low frequency part of the audio signal is wirelessly transmitted to the portable listening device.
In a particular embodiment, the full bandwidth audio output signal is fed to a digital to analogue (DA) converter. In an embodiment, the digital to analogue converter is sampled by a second sample rate Fs2 (adapted to correspond to the full bandwidth signal reconstructed by bandwidth extension. In a particular embodiment, the full bandwidth audio output signal or the DA-converted full bandwidth audio output signal is fed to an output transducer, e.g. a receiver (speaker), for presentation to a wearer of the portable listening device. Alternatively, the output transducer can be electrodes of a cochlear implant or an electromechanical transducer of a bone conduction device.
In an embodiment, the first sample rate Fs1 is smaller than the second sample rate Fs2. In a particular embodiment, ratio of the first sample rate Fs1 to the second sample rate Fs2 is equal to the ratio of the bandwidth ΔfLF of the low frequency part to the full bandwidth Δffull of the audio signal, such as e.g. 0.7 or less 0.5 or less or 0.4 or less or 0.25 or less.
In a particular embodiment, the listening device comprises a hearing aid, an ear protection device, a headset, or a head phone or a combination thereof.
A tangible computer-readable medium storing a computer program comprising program code means for causing a data processing system to perform at least some (such as at least steps b) and c), such as all) of the steps of the method described above, in the detailed description of ‘mode(s) for carrying out the invention’ and in the claims, when said computer program is executed on the data processing system is furthermore provided by the present invention. In addition to being stored on a tangible medium such as diskettes, CD-ROM-, DVD-, or hard disk media, or any other machine readable medium, the computer program can also be transmitted via a transmission medium such as a wired or wireless link or a network, e.g. the Internet, and loaded into a data processing system for being executed at a location different from that of the tangible medium.
A data processing system comprising a processor and program code means for causing the processor to perform at least some (such as at least steps b) and c), such as all) of the steps of the method described above, in the detailed description of ‘mode(s) for carrying out the invention’ and in the claims is furthermore provided by the present invention.
A Portable Listening Device:
In a further aspect, there is provided a portable listening device comprising a signal processor adapted for processing a low frequency bandwidth input audio signal and providing a processed low bandwidth signal and a bandwidth extension unit adapted to provide a full bandwidth output signal based on the processed low bandwidth signal.
It is intended that the process features of the method described above, in the detailed description of ‘mode(s) for carrying out the invention’ and in the claims can be combined with the (portable listening) device, when appropriately substituted by a corresponding structural feature and vice versa. Embodiments of the device have the same advantages as the corresponding method.
In a particular embodiment, the portable listening device further comprises a microphone and an A/D-converter for generating the low frequency bandwidth input audio signal, or a part thereof (possibly using a filter, e.g. a low pass filter, e.g. a digital filter). In an embodiment, the analogue to digital (A/D) converter is sampled by a first sample rate Fs1. By using a relatively low sampling rate Fs1 in the A/D-converter corresponding to the LF-bandwidth of the low frequency bandwidth signal, power is saved (compared to converting a full-bandwidth signal) and a filter can be omitted.
In a particular embodiment, the signal processor is a digital signal processor.
In a particular embodiment, the portable listening device comprises a time to time-frequency conversion unit (and a corresponding time-frequency to time conversion unit) to provide a time-varying input signal in a number of frequency bands or ranges (and for synthesizing a time-varying output signal from a number of processed band specific signals). In a particular embodiment, the signal processor is adapted to process the low frequency bandwidth input signal in a number of separate frequency bands or ranges. In an embodiment, the bandwidth extension unit is adapted to operate on each of the separate frequency bands or ranges (cf. e.g. FIGS. 1 and 6 in WO 2007/006658 A1 and the corresponding description).
In a particular embodiment, the bandwidth extension unit providing the full bandwidth (Δffull) output signal is sampled with a second sample rate Fs2. In a particular embodiment, the ratio of the first sample rate Fs1 to the second sample rate Fs2 is equal to the ratio of the bandwidth ΔfLF of the low frequency part to the full bandwidth Δffull of the audio signal, such as e.g. 0.7 or less, 0.5 or less, or 0.4 or less, or 0.25 or less.
In a particular embodiment, the full bandwidth audio output signal is fed to a digital to analogue (DA) converter for converting a digital full bandwidth output signal to an analogue full bandwidth output signal. In an embodiment, the digital to analogue converter is sampled by a second sample rate Fs2. In a particular embodiment, the portable listening device further comprises an output transducer, e.g. a receiver (speaker), for presenting the full bandwidth output signal to a wearer of the listening device. Alternatively, the output transducer can be electrodes of a cochlear implant or an electromechanical transducer of a bone conduction device.
In a particular embodiment, the portable listening device further comprises a wireless interface adapted to receive said low frequency bandwidth input audio signal (or a part thereof) from another device via a wireless link. In an embodiment, the wireless interface comprises antenna and receiver or transceiver circuitry, the receiver or transceiver circuitry e.g. comprising an appropriate demodulation unit to extract an audio signal (e.g. including or constituted by a low frequency part of bandwidth ΔfLF) from the received wireless signal. In an embodiment, the antenna and receiver or transceiver circuitry comprises an induction coil and corresponding circuitry for receiving (and possibly transmitting) a signal from (to) another device via an inductive coupling to a corresponding induction coil in the other device. Alternatively, the antenna and the receiver or transceiver circuitry are adapted for far-field (radiated field) communication. In an embodiment, the listening device comprises a selector or mixing unit receiving inputs from the microphone and the wireless interface, the selector or mixing unit being adapted for providing as an output one of the inputs or a weighted mixture of the inputs. In an embodiment, a first sub-part of the low frequency part of the audio signal (comprising a first part ΔfLF-1 of the LF-bandwidth ΔfLF) is picked up by the microphone and fed to the selector or mixing unit as a first input and a second sub-part of the low frequency part of the audio signal (comprising a second part ΔfLF-2 of the LF-bandwidth ΔfLF) is received via the wireless interface and fed to the selector or mixing unit as a second input. In an embodiment, the selector or mixing unit is adapted to combine the first and second inputs to provide a combined low frequency part of the audio signal to the signal processing unit, the combined signal having an LF-bandwidth ΔfLF. This has the advantage that even less link-bandwidth is required (thereby saving power or enabling an increased transmission range).
In a particular embodiment, the portable listening device comprises an analyzing unit for determining a type of input signal and for providing a control signal indicative of the type. In a particular embodiment, the bandwidth extension unit comprises several different schemes for providing bandwidth extension depending on a control signal.
In a particular embodiment, the listening device comprises a hearing aid or a head set or an active ear plug or a headphone or a combination thereof.
In a particular embodiment, the portable listening device is adapted to provide a full bandwidth output signal according to the method described above, in the section on ‘Mode(s) for carrying out the invention’, in the drawings or in the claims.
A Listening System:
In a further aspect, there is provided a listening system comprising first and second devices, the first device being a portable listening device adapted for presenting an electrical output audio signal to a wearer of the first listening device, the electrical output audio signal having a full bandwidth Δffull comprising a low frequency part and a high frequency part, wherein the second device comprises a wireless transmitter for wirelessly transmitting the low frequency signal and the first device comprises a) a wireless receiver for receiving said low frequency signal and b) a bandwidth extension unit for constructing or (re-)generating a high-frequency part of the electrical output audio signal, the high-frequency part having a HF-bandwidth ΔfHF, and for forming the electrical output audio signal having a full bandwidth Δffull based on or comprising said low frequency signal having an LF-bandwidth ΔfLF and said high frequency signal having a HF-bandwidth ΔfHF.
It is intended that the process features of the method described above, in the detailed description of ‘mode(s) for carrying out the invention’ and in the claims can be combined with the system, when appropriately substituted by a corresponding structural feature and vice versa. Embodiments of the system have the same advantages as the corresponding method.
In a particular embodiment, the first device comprises a signal processor adapted for processing the low frequency input signal and providing a processed low frequency output signal to the bandwidth extension unit.
In an embodiment, the second device comprises an input transducer for converting an input sound to an electric input signal and a frequency limiting unit, e.g. a low pass filter and/or an A/D converter unit, for generating said low frequency part of a signal having an LF-bandwidth ΔfLF (or at least a part thereof) for being wirelessly transmitted to the first device. In a particular embodiment, the second device is a portable device. In a particular embodiment, the (first) portable listening device comprises an input transducer for converting an input sound to an electric input signal and an A/D-converter for generating the low frequency bandwidth input audio signal sampled by a first sample rate Fs1. By using a relatively low sampling rate Fs1 in the A/D-converter corresponding to the LF-bandwidth of the low frequency bandwidth signal, power is saved (compared to converting a full-bandwidth signal).
In a particular embodiment, the wireless transmitter and receiver are adapted to provide a near-field communication system, e.g. based on an inductive coupling between (antenna coils located in, respectively) the first and second devices on which said transmission of said low frequency signal can be based, when said first and second devices are located in an operational distance from each other. Such system is e.g. described in US 2005/0255843 A1. Alternatively, the wireless transmission link established by the wireless transmitter and receiver may be based on radiated fields. The wireless link may be adapted to use analogue (e.g. FM or AM) or digital modulation, e.g. according to the Bluetooth or DECT standard.
In an embodiment, the second device comprises an electric interface for receiving a signal comprising an audio signal (e.g. from a mobile telephone or an entertainment device) and providing an electric input signal based thereon (e.g. comprising or consisting of the audio signal), and a frequency limiting unit, e.g. low pass filter and/or an A/D conversion unit, for generating said low frequency part of a signal having an LF-bandwidth ΔfLF (or a part thereof) for being wirelessly transmitted to the first device from said electric input signal.
In a particular embodiment, the first (portable listening) device comprises a portable listening device as described above, in the section on ‘Mode(s) for carrying out the invention’, in the drawings or in the claims.
In a particular embodiment, the second device is selected from the group comprising a listening device (e.g. a hearing aid of a binaural system), a mobile telephone, an audio selection device (e.g. an audio gateway adapted for receiving a number of audio signals and for transmitting a selected one to the first device), a TV-set, a PC, an audio-player (e.g. a portable music player) and combinations thereof.
In a particular embodiment, the second device comprises an audio gateway comprising a number of interfaces adapted for receiving a number of audio signals and for transmitting a selected one to the first device. In an embodiment, the audio gateway comprises an interface (such as a wireless interface, e.g. a Bluetooth or DECT interface) to a mobile telephone. In an embodiment, the audio gateway comprises an interface to an audio entertainment device, e.g. a player of music, e.g. recorded or streamed music. In an embodiment, the audio gateway comprises a user operable activation element adapted for selecting one of the audio signals received by the audio gateway for being transmitted to the first listening device (e.g. a hearing aid).
Typically, the first and/or second devices comprise(s) a local source of energy, e.g. a battery, such as a rechargeable battery.
A Method of Operating a Listening System Comprising Wirelessly Transferring an Audio Signal:
In a further aspect, a method of operating a listening system comprising wirelessly transferring a first audio signal between a transmitting device and a receiving device is provided, at least one of the transmitting and receiving devices forming part of a listening device, the first audio signal comprising a low-frequency part having an LF-bandwidth ΔfLF and a high-frequency part having a HF-bandwidth ΔfHF, the first audio signal having an input bandwidth Δfi and being sampled at an input sampling frequency fs,i. The method comprises
In a particular embodiment, a full bandwidth signal is generated or reconstructed based on the low-frequency part and the (reconstructed) high-frequency part of the signal.
In a particular embodiment, the high-frequency part of the signal is reconstructed by spectral band replication.
In a particular embodiment, the low frequency part of the first audio signal has a maximum frequency fLF,max in the range between 3 kHz and 7 kHz, such as between 4 kHz and 6 kHz, e.g. 5 kHz.
In a particular embodiment, the low-frequency part of the first audio signal has a minimum frequency fLF,min in the range from 5 Hz to 100 Hz, such as 20 Hz.
In a particular embodiment, the high-frequency part of the first audio signal has a maximum frequency fHF,max in the range from 7 kHz to 20 kHz, e.g. from 8 kHz to 12 kHz, such as 10 kHz.
In a particular embodiment, the input sampling frequency fs,i is reduced to a reduced sampling frequency fs,red with a predefined reduction factor Kred. In a particular embodiment, the predefined reduction factor Kred is in the range from 0.3 to 0.7, such as 0.5.
In a particular embodiment, the reduced sampling frequency fs,red is increased to fs,inc with a predefined increase factor Kinc. In a particular embodiment, the predefined increase factor Kinc is in the range from 1.5 to 2.5, such as 2.
In a particular embodiment, signal processing of the low frequency part of the first audio signal is provided in the receiving device prior to reconstructing the high-frequency part.
In a particular embodiment, the listening device comprises a hearing aid, an ear protection device, a headset or a pair of head phones or a combination thereof.
In a particular embodiment, the receiving device forms part of the listening device, e.g. comprising a hearing aid.
In a particular embodiment, the transmitting device forms part of a communication device, e.g. a mobile telephone, portable entertainment device, e.g. a music player, or an audio gateway for forwarding an audio signal to a receiving device. In a particular embodiment, the audio signal is selected among a multitude of audio signals.
Further objects of the invention are achieved by the embodiments defined in the dependent claims and in the detailed description of the invention.
As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes,” “comprises,” “including,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements maybe present. Furthermore, “connected” or “coupled” as used herein may include wirelessly connected or coupled. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which:
The figures are schematic and simplified for clarity, and they just show details which are essential to the understanding of the invention, while other details are left out.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The listening device of
Instead of picking up an acoustical signal via one or more microphones (as shown in
By reducing the bandwidth of the transmitted audio signal, the range of the transmitter can be increased or power in the transmitter and receiver can be saved.
An example of a method according to an embodiment of the invention comprises the following steps 1-6. Steps 1-2 are represented by the upper part of
Instead of transmitting a full-bandwidth audio at 20 kHz sampling frequency (bandwidth ΔfFull=10 kHz) do the following:
Alternatively, step 4 and 5 could be reversed so that the high frequency part of the signal is reconstructed before signal processing and the combined, full bandwidth signal is processed by a digital signal processor (DSP) in a conventional manner. Alternatively, step 4 could be omitted altogether, if no processing (in excess of the reconstruction of the high frequency part of the signal) is needed.
A bandwidth extension technique denoted Spectral Band Replication (SBR) can advantageously be used, as e.g. described in EP 1 367 566, cf. in particular section [0007] and
Characteristics of the present embodiment of the invention are that the listening device picks up (or filters the input signal to provide) only an LF-part of an Acoustic input signal (thereby saving power in the A/D-conversion etc.), processes only this LF-part of the signal (thereby saving power compared to the processing of a full bandwidth signal), generates a full bandwidth signal by an (possibly selectable according to the type of input signal) appropriate bandwidth extension method, presenting the full bandwidth signal for a user as an Acoustic output signal. In an embodiment, the listening device comprises an analyzing unit for determining a type of input signal and for providing a control output indicative of the type. In an embodiment, the bandwidth extension unit comprises several different schemes for providing bandwidth extension depending on a control input from an input signal analyzing unit.
The received signal W(ΔfLF) from the Wireless link is in an embodiment based on a signal from a communication device, e.g. an entertainment device, a mobile telephone or an audio selection device for selecting an audio signal among a multitude audio signals and transmitting the selected one to the listening device. In an embodiment, the communication device streams an LF signal part of an audio signal to the listening device (e.g. a hearing aid), where it is processed and the full-bandwidth signal subsequently created, whereby power or bandwidth is saved (or transmission-range can be increased). In an embodiment, the electric input signal I(ΔfLF) (I′(ΔfLF)) is split into frequency bands (in a separate time-to-frequency (t->f) conversion unit or in the signal processing unit (DSP)), which together constitute the low frequency part of the audio signal, and the frequency bands are individually processed in the DSP and then bandwidth-extended.
a shows a user U wearing the listening device LD (the listening device LD e.g. implementing a hearing aid comprising a behind the ear (BTE) part located behind the ear of the user U). The listening instrument LD is adapted to receive an audio signal from the audio gateway (2nd Device) as a direct electric input, here a wireless input received via a wireless link WLS2. The audio gateway is adapted for receiving a number of audio signals from a number of audio sources, here (1) a mobile telephone MT (e.g. a cellular telephone) via wireless link WLS1, and (2) an audio entertainment device MP (e.g. a music player) via wired connection WIS1, and for transmitting a selected one of the audio signals to the listening device LD via wireless link WLS2. The audio gateway comprises a microphone M for picking up sounds in its environment, e.g. the user U's own voice OV in connection with a telephone conversation. The audio gateway further comprises a user interface UI (comprising activation elements or zones, e.g. in the form of a touch sensitive display and/or a number of push buttons or selection wheels) for allowing a user U to influence the functioning of the system, e.g. a volume setting, a program selection, the selection of an input to be transmitted to the listening device, etc. The listening device LD may e.g.—in addition to the direct electric input—comprise an input transducer (e.g. a microphone system) for picking up sounds from the environment of the user and converting the input sound signal to an electric microphone signal (cf. e.g.
b shows a (partial) block diagram of the audio gateway device (2nd Device). The audio gateway comprises an input transducer M (here a microphone) for converting a Sound in the local environment (e.g. comprising a user's own voice, cf. OV in
c illustrates a special use or mode of the setup of a listening system as shown in
An audio selection device (audio gateway device), which may be modified and used according to the present invention is e.g. described in EP 1 460 769 A1 and in EP 1 981 253 A1.
The invention is defined by the features of the independent claim(s). Preferred embodiments are defined in the dependent claims. Any reference numerals in the claims are intended to be non-limiting for their scope.
Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject-matter defined in the following claims.
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| 20110019838 A1 | Jan 2011 | US |
