(19)
(11)EP 2 211 339 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
31.05.2017 Bulletin 2017/22

(21)Application number: 09151253.3

(22)Date of filing:  23.01.2009
(51)Int. Cl.: 
H04R 5/04  (2006.01)
G10L 21/038  (2013.01)
H04R 1/10  (2006.01)
H04R 25/00  (2006.01)
H04R 5/033  (2006.01)
G10L 21/06  (2013.01)

(54)

Listening system

Hörsystem

Système d'écoute


(84)Designated Contracting States:
AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO SE SI SK TR

(43)Date of publication of application:
28.07.2010 Bulletin 2010/30

(73)Proprietor: Oticon A/S
2765 Smørum (DK)

(72)Inventors:
  • Skovby, Lars
    DK-2765 Smørum (DK)
  • Kaulberg, Thomas
    DK-2765 Smørum (DK)

(74)Representative: Nielsen, Hans Jørgen Vind 
Oticon A/S IP Management Kongebakken 9
2765 Smørum
2765 Smørum (DK)


(56)References cited: : 
EP-B1- 1 367 566
US-A1- 2007 124 140
US-A- 5 812 598
US-A1- 2008 177 539
  
  • MURAKAMI T ET AL: "Speech enhancement based on a combined higher frequency regeneration technique and RBF networks" IEEE TENCON' 02. 2002 IEEE REGION 10 CONFERENCE ON COMPUTERS, COMMUNICATIONS, CONTROL AND POWER ENGINEERING PROCEEDINGS. BEIJING, CHINA, OCT. 28 - 31, 2002; [IEEE REGION 10 ANNUAL CONFERENCE], NEW YORK, NY : IEEE, US, vol. 1, 28 October 2002 (2002-10-28), pages 457-460, XP010628522 ISBN: 978-0-7803-7490-4
  • PUDER ET AL: "Adaptive signal processing for interference cancellation in hearing aids" SIGNAL PROCESSING, ELSEVIER SCIENCE PUBLISHERS B.V. AMSTERDAM, NL, vol. 86, no. 6, 1 June 2006 (2006-06-01), pages 1239-1253, XP024997675 ISSN: 0165-1684 [retrieved on 2006-06-01]
  • Michael L Seltzer ET AL: "Robust Bandwidth Extension of Noise-corrupted Narrowband Speech", Proc. Interspeech, 4 September 2005 (2005-09-04), pages 1509-1512, XP055279239, Lisbon, Portugal
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description

TECHNICAL FIELD



[0001] The invention relates to audio processing in portable devices with a view to keeping power consumption relatively low. The disclosure relates 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.

[0002] The invention relates to a listening system.

[0003] 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.

BACKGROUND ART



[0004] 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.

[0005] 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.

[0006] [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.

[0007] 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.

[0008] [Seltzer et al., 2005] deals with a bandwidth extension algorithm for converting narrowband telephone speech to wideband speech.

DISCLOSURE OF INVENTION



[0009] The present invention utilizes bandwidth extension techniques in signal processing of an audio signal to improve performance or save battery power in a portable.

[0010] The present invention relates to the processing and generation of an audio signal with a full bandwidth Δffull in a portable hearing aid, the audio signal comprising a low frequency part having an LF-bandwidth ΔfLF and a high-frequency part having a HF-bandwidth ΔfHF.

[0011] Typically signal processing in a listening device is carried out on a full bandwidth signal. In an aspect of this invention, the signal processing (e.g. 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 a receiver unit for presentation to a user, whereby power consumption is reduced.

[0012] 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.

[0013] Objects of the present invention are to improve performance or save power in a portable listening device.

[0014] 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:



[0015] In an aspect of the disclosure, 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 said audio output signal with a full bandwidth Δffull comprising said LF-bandwidth ΔfLF and said HF-bandwidth ΔfHF.

[0016] An advantage of this is that power consumption is reduced.

[0017] Bandwidth extension of band limited audio signals is e.g. discussed in EP 1 638 083 A1. In an example, 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 example, the listening device is adapted to use different bandwidth extension methods dependent upon characteristics of the acoustic input signal.

[0018] In an example, the frequency range Δf = [fmin; fmax] 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 N of frequency bands (FB), (FB1, FB2, ...., FBN). In an example, the number of bands N is larger than or equal to 2, e.g. N=8 or 16 or 32 or 64 or more.

[0019] In an example, 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), 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 example, the sampling frequency 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 example, the sampling frequency is in the range between 1 kHz and 40 kHz, e.g. 10 kHz or 20 kHz. In an example, 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 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).

[0020] In an example, 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 example, only the magnitude values of the signal are considered.

[0021] In a particular example, the high-frequency part of the signal is reconstructed by spectral band replication. In an example, 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.

[0022] 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.

[0023] In an example, 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, 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 example, fLF-HF = fLF,max = fHF,min. In an example, the LF-bandwidth ΔfLF constitutes 0.7 times or less of the full bandwidth 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.

[0024] In a particular example, 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.

[0025] In a particular example, the low-frequency part has a minimum frequency fLF,min in the range from 5 Hz to 100 Hz, such as 20 Hz.

[0026] In a particular example, 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.

[0027] Preferably, the at least one signal processing performed on the low frequency part of the signal include the more power consuming steps, such as one or more 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.

[0028] In a particular example, 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 example, the audio signal is converted to a digital signal by an analogue to digital (AD) converter. In an example, 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. In an example, the audio signal is filtered to provide said low frequency part having an LF-bandwidth ΔfLF.

[0029] In a particular example, the low frequency part of the audio signal 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 example, the low frequency part of the audio signal is wirelessly transmitted to the portable listening device.

[0030] In a particular example, the full bandwidth audio output signal is fed to a digital to analogue (DA) converter. In an example, 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 example, 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, 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.

[0031] In an example, the first sample rate Fs1 is smaller than the second sample rate Fs2. In a particular example, 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.

[0032] In a particular example, the listening device comprises a hearing aid, an ear protection device, a headset, or a head phone.

[0033] A tangible computer-readable medium storing a computer program comprising program code means for causing a data processing system to perform at least some of the steps of the method described above, when said computer program is executed on the data processing system is furthermore provided by the present disclosure. 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.

[0034] A data processing system comprising a processor and program code means for causing the processor to perform at least some of the steps of the method described above is furthermore provided by the present disclosure.

A portable listening device:



[0035] 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.

[0036] It is intended that the process features of the method described above can be combined with the (portable listening) device, when appropriately substituted by a corresponding structural feature and vice versa. Examples of the device have the same advantages as the corresponding method.

[0037] In a particular example, the portable listening device further comprises a microphone and an A/D-converter for generating the low frequency bandwidth input audio signal (possibly using a filter, e.g. a low pass filter, e.g. a digital filter). In an example, the analogue to digital 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.

[0038] In a particular example, the signal processor is a digital signal processor.

[0039] In a particular example, the signal processor is adapted to process the low frequency bandwidth input signal in a number of separate frequency bands or ranges. In an example, the bandwidth extension unit is adapted to operate on each of the separate frequency bands or ranges (cf. e.g. FIG. 1 and 6 in WO 2007/006658 A1 and the corresponding description).

[0040] In a particular example, the bandwidth extension unit providing the full bandwidth output signal is sampled with a second sample rate Fs2. In a particular example, 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.

[0041] In a particular example, 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 example, the digital to analogue converter is sampled by a second sample rate Fs2. In a particular example, the portable listening device further comprises an output transducer, e.g. a receiver, 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.

[0042] In a particular example, the portable listening device further comprises a wireless interface adapted to receive said low frequency bandwidth input audio signal from another device via a wireless link.

[0043] In a particular example, the listening device is a hearing aid or a head set or an active ear plug or a headphone.

[0044] In a particular example, the portable listening device is adapted to provide a full bandwidth output signal according to the method described above.

A listening system:



[0045] In a further aspect, there is provided a listening system as defined in claim 1. It is intended that the process features of the method described above, 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.

[0046] The first device comprises a signal processor adapted for processing the low frequency signal and providing a processed low frequency signal to the bandwidth extension unit.

[0047] 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, for generating said low frequency signal having an LF-bandwidth ΔFLF for being wirelessly transmitted to the first device. In a particular example, the second device comprises an A/D-converter for generating the low frequency 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).

[0048] In a particular embodiment, the transmitter and receiver are adapted to provide an inductive coupling between 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.

[0049] A method of operating a listening system comprising wirelessly transferring an audio signal:

[0050] In a further aspect, a method of operating a listening system comprising a 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
  1. a) providing the following actions in the transmitting device
    • removing the high-frequency part of the first audio signal, thereby creating a reduced-bandwidth signal comprising the low-frequency part ΔfLF of the first audio signal;
    • reducing the sampling frequency to a reduced sampling frequency fs,red compared to the input sampling frequency fs,i of the first audio signal;
    • transmitting the reduced bandwidth signal ΔfLF to the receiving device; and
  2. b) providing the following actions in the receiving device:
    • receiving the reduced bandwidth signal ΔfLF;
    • resampling the received reduced bandwidth signal at a sampling rate fs,inc that is increased compared to the reduced sampling frequency fs,red; and
    • reconstructing the high-frequency part ΔfHF of the signal using a bandwidth extension technique.


[0051] In a particular example, a full bandwidth signal is generated or reconstructed based on the low-frequency part and the high-frequency part of the signal.

[0052] In a particular example, the high-frequency part of the signal is reconstructed by spectral band replication.

[0053] In a particular example, 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.

[0054] In a particular example, 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.

[0055] In a particular example, 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.

[0056] In a particular example, the input sampling frequency fs,i is reduced to a reduced sampling frequency fs,red with a predefined reduction factor Fred. In a particular embodiment, the predefined reduction factor Kred is in the range from 0.3 to 0.7, such as 0.5.

[0057] In a particular example, 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.

[0058] In a particular example, 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.

[0059] In a particular example, the listening device is a hearing aid.

[0060] In a particular example, the receiving device forms part of a hearing aid.

[0061] In a particular example, 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 example, the audio signal is selected among a multitude of audio signals.

[0062] Further objects of the invention are achieved by the preferred embodiment defined in the dependent claim and in the detailed description of the invention.

[0063] 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.

BRIEF DESCRIPTION OF DRAWINGS



[0064] The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which:

FIG. 1 shows a block diagram of a part of a listening system comprising a signal path from a microphone to a receiver,

FIG. 2 schematically illustrates steps of an embodiment of a method, the graphs indicating the bandwidth of frequency spectra of an audio signal in various steps of the method, fs denoting sampling frequency, SBR being short for Spectral Band Replication and DSP being short for Digital Signal Processing,

FIG. 3 shows a first example of a listening device according to the disclosure,

FIG. 4 shows a second example of a listening device according to the disclosure, and

FIG. 5 shows an example of a listening system according to the disclosure.



[0065] 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.

[0066] 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 are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.

MODE(S) FOR CARRYING OUT THE INVENTION



[0067] FIG. 1 shows a block diagram of a part of a listening system comprising a signal path from a microphone to a receiver. The listening system (e.g. a hearing aid) comprises a set of directional microphones for picking up sounds from the environment and converting them to an analogue electrical signal, which is fed to respective analogue-to-digital converters (A/D). The sampling frequency Fs1 of the A/D-converters is (here chosen to be) 10 kHz. The digitized output signals from the A/D-converters, having a bandwidth (ΔfLF) of 5 kHz, are fed to a digital signal processor (DSP) where they are processed to perform normal DSP-functions such as one or more of extraction of directional information, providing an appropriate gain profile, compression, feedback cancellation, noise reduction, etc., and providing a processed signal. The processed signal comprising 10 ksamples/s is fed to a bandwidth extension unit, here implemented as a unit adapted for performing Spectral Bandwidth Replication (indicated by SBR in FIG. 1). The bandwidth of the output signal from the SBR-unit is extended from 5 kHz (ΔfLF) to 10 kHz (ΔfFull) (the output signal comprising 20 ksamples/s, sampling frequency Fs2=20 kHz) and forwarded to a receiver for being presented to a wearer of the listening system as an acoustical signal (possibly via a digital to analogue converter). This has the advantage of saving power because the DSP-functionality is performed on the 'low bandwidth' signal.

[0068] The listening system of FIG. 1 may comprise a hearing instrument, a headset, an active ear protection device, a head phone, etc.

[0069] Instead of picking up an acoustical signal via one or more microphones (as shown in FIG. 1, a low bandwidth signal may be wirelessly transmitted to the listening system and received by a receiver and forwarded to the DSP (cf. FIG. 4, 5).

[0070] FIG. 2 shows steps of a method, the graphs indicating the bandwidth of frequency spectra of an audio signal in various steps of the method, fs denoting sampling frequency, SBR being short for Spectral Band Replication and DSP being short for Digital Signal Processing.

[0071] 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.

[0072] An example of a method comprises the following steps 1-6. Steps 1-2 are represented by the upper part of FIG. 2 (related to an audio source, e.g. a communication device), step 3 is represented by the arrow connecting the upper and lower parts of FIG. 2 (separated by the dotted line), and steps 4-6 are represented by the lower part of FIG. 2 (related to an audio processing (and/or presentation) device, e.g. a listening device):

[0073] Instead of transmitting a full-bandwidth audio at 20 kHz sampling frequency (bandwidth ΔfFull =10 kHz) do the following:
  1. 1. Reduce the bandwidth of the audio signal by low-pass filtering the signal to a low frequency part with an LF-bandwidth of 5 kHz (the audio signal being e.g. picked up by a (wireless) microphone or e.g. being based on an existing, e.g. stored, audio signal);
  2. 2. Reduce or set the sampling frequency fs=Fs1 to 10 kHz;
  3. 3. Transmit the low frequency part with an LF-bandwidth of 5 kHz to the audio processing device (the transmit-rate is half of a full-band audio signal), e.g. via a wireless link, e.g. an inductive link, the audio processing device being e.g. a part of a hearing aid;
  4. 4. Process the low frequency part of the signal by a digital signal processor (DSP) in a conventional manner.
  5. 5. Re-sample the received signal to a (full bandwidth) 20 ksample/s signal (ΔfFull=10 kHz, fs=Fs2=20 kHz);
  6. 6. Reconstruct the frequencies at 5-10 kHz (ΔfHF) with use of bandwidth extension techniques (here SBR is indicated).


[0074] 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.

[0075] 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 FIGs. 1-2 and corresponding parts of the description of preferred embodiments in EP 1 367 566.

[0076] FIG. 3 shows a first example of a listening device according to the disclosure. The listening device, e.g. a hearing instrument, comprises a microphone for converting an Acoustic input signal to an electric audio input signal, which is digitized by an analogue to digital converter (AD) sampled by a first sampling frequency Fs1. The bandwidth ΔfLF of the digitized signal I(ΔfLF) correspond to a low frequency part of a full bandwidth audio signal (here ~ Fs1/2). The digitized signal I(ΔfLF) is fed to a signal processing unit (DSP), where the signal is processed according to a users needs (e.g. including applying a frequency dependent gain to the signal). The processed signal P(ΔfLF) is fed to a bandwidth extension unit (BWX), where a high frequency part of the signal is synthesized based on the processed low frequency part and combined with the processed low frequency part to form a full bandwidth output signal Bx(ΔfLF+HF). The full bandwidth output signal B(dfΔLF+HF) is fed to a digital to analogue converter (DA), which is clocked by a second sampling frequency Fs2, converting the digital signal to an analogue full bandwidth output signal, which is fed to a receiver for being presented to a user. Preferably, Fs2 ≥ 2·Fs1.

[0077] Characteristics of the present example are that the listening device picks up 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) appropriate bandwidth extension method, presenting the full bandwidth signal for a user as an Acoustic output signal.

[0078] FIG. 4 shows a second example of a listening device according to the disclosure. The example of FIG. 4 comprises the same elements as then example shown in FIG. 3 and mentioned above. Additionally, the listening device comprises a wireless interface (at least) for receiving an audio signal from another device via a Wireless link. The transceiver (Rx-circuitry in FIG. 4) comprises an Antenna (adapted to the frequency, bandwidth and modulation of the transmitted signal W(ΔfLF) for receiving a signal W(ΔfLF) comprising a low frequency part of an audio signal (having an LF-bandwidth ΔfLF) and receiver and demodulation circuitry (RF and AD-units in FIG. 4) for extracting the low frequency part I'(ΔfLF) of the audio signal. The low frequency part I'(ΔfLF) of the audio signal is fed to a selector unit (SEL) together with the digitized signal I(ΔfLF) based on the Acoustic input signal picked up by the microphone of the listening device. The selector unit (SEL) selects one of the two inputs based on a select input signal (SL). Alternatively, 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 unit as a first input and 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 link and fed to the selector unit as a second input. In this case, the selector unit (SEL) 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 (DSP), the combined signal having an LF-bandwidth ΔfLF. The latter has the advantage that even less link-bandwidth is required (thereby saving power or enabling an increased transmission range).

[0079] The received signal W(ΔfLF) from the Wireless link is in an example 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 example, 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 example, 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.

[0080] FIG. 5 shows an example of a listening system according to the invention. The listening system of FIG. 5 comprises the same elements as the example of the listening device shown in FIG. 4 and mentioned above. The system of FIG. 5 comprises first 51 and second 52 devices. The first device 51 is a portable listening device, e.g. comprising a part of a hearing instrument, adapted for presenting an electrical output audio signal to a wearer of the first listening device 51, the electrical output audio signal having a full bandwidth Δffull comprising a low frequency part and a high frequency part. The second device 52 comprises a transceiver comprising a transmitter for wirelessly transmitting the low frequency signal W(ΔfLF) to the first device 51 via a Wireless link. The first device 51 comprises a transceiver comprising an antenna and a receiver (Rx) for receiving and demodulating the received signal an providing a digitized low frequency signal I(ΔfLF), which is fed to the signal processing unit (DSP), possibly comprising t->f capability. The system shown in FIG. 5 can be an example of a listening device as e.g. shown in FIG. 3 or 4 where the microphone is located in a first physical device while other functional blocks of the listening device (e.g. processing and bandwidth extension) are located in a second physical device, and where the two devices are connected via a Wireless link. The first device 51 may in an example be a listening device as shown in FIG. 4, were the microphone of the second device 52 is an additional microphone to the one present in the (first) listening device 51, and where the signal used for processing in the digital signal processing unit (DSP) is selectable via control signal SL. Alternatively, the signal used for processing in the digital signal processing unit (DSP) is a combination (e.g. a sum) of the two input signals (I, I').

[0081] The invention is defined by the features of the independent claim. A preferred embodiment is defined in the dependent claim. Any reference numerals in the claims are intended to be non-limiting for their scope.

REFERENCES



[0082] 


Claims

1. A listening system comprising first and second devices, the first device being a portable hearing aid adapted for presenting an electrical output audio signal to a wearer of the first 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 transmitter for wirelessly transmitting a low frequency signal and the first device comprises a) a receiver for receiving said low frequency signal and b) a bandwidth extension unit for constructing or generating the high-frequency part of the output audio signal having a HF-bandwidth ΔfHF and forming the electrical output audio signal having a full bandwidth Δffull based on said low frequency signal having an LF-bandwidth ΔfLF and said high frequency part having a HF-bandwidth ΔfHF, and c) a signal processor adapted for processing the low frequency signal and providing a processed low frequency signal to the bandwidth extension unit, and wherein the second device further comprises an input transducer for converting an input sound to an electric input signal and a frequency limiting unit for generating said low frequency signal having an LF-bandwidth ΔfLF for being wirelessly transmitted to the first device.
 
2. A listening system according to claim 1 wherein said transmitter and receiver are adapted to provide an inductive coupling between the first and second device 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.
 


Ansprüche

1. Hörsystem mit ersten und zweiten Geräten, von denen das erste Gerät ein tragbares Hörgerät ist, das zum Präsentieren eines elektrischen Ausgangsaudiosignals für einen Träger des ersten Gerätes ausgebildet ist, wobei das elektrische Ausgangsaudiosignal eine volle Bandbreite Δffull besitzt, die einen niederfrequenten Anteil und einen höherfrequenten Anteil umfasst, wobei das zweite Gerät einen Sender zum drahtlosen Übertragen eines niederfrequenten Signals aufweist und das erste Gerät

a) einen Empfänger zum Empfangen des niederfrequenten Signals und

b) eine Bandbreitenerweiterungseinheit zum

- Konstruieren und Generieren des höherfrequenten Teils des Ausgangsaudiosignals mit einer Hochfrequenzbandbreite ΔfHF und

- Bilden des elektrischen Audioausgangssignals mit einer vollen Bandbreite Δffull auf Basis des niederfrequenten Signals mit einer LF-Bandbreite ΔfLF und des höherfrequenten Teils mit einer HF-Bandbreite ΔfHF, und

c) einen Signalprozessor, der zum Verarbeiten des niederfrequenten Signals und Bereitstellen eines verarbeiteten niederfrequenten Signals für die Bandbreitenerweiterungseinheit ausgebildet ist,

aufweist und wobei das zweite Gerät weiterhin einen Eingangswandler zum Umwandeln eines Eingangsschalls in ein elektrisches Eingangssignal und eine Frequenzbegrenzungseinheit zum Generieren des drahtlos zu dem ersten Gerät zu übertragenden niederfrequenten Signals mit einer LF-Bandbreite ΔfLF aufweist.
 
2. Hörgerät gemäß Anspruch 1, bei dem der Sender und der Empfänger zum Bereitstellen einer induktiven Kopplung zwischen dem ersten und dem zweiten Gerät ausgebildet sind, auf welcher die Übertragung des niederfrequenten Signals basieren kann, wenn das erste und zweite Gerät in einer Betriebsentfernung voneinander angeordnet sind.
 


Revendications

1. Système d'écoute comprenant des premier et second dispositifs, le premier dispositif étant un appareil auditif portable adapté pour présenter un signal audio de sortie électrique à un porteur du premier dispositif, le signal audio de sortie électrique présentant une bande passante pleine Δffull comprenant une partie basse fréquence et une partie haute fréquence, où le second dispositif comprend un émetteur destiné à émettre sans fil un signal basse fréquence et le premier dispositif comprend a) un récepteur destiné à recevoir ledit signal basse fréquence et b) une unité d'extension de bande passante destinée à construire ou générer la partie haute fréquence du signal audio de sortie présentant une bande passante haute fréquence ΔfHF et à former le signal audio de sortie électrique présentant une bande passante pleine Δffull sur la base dudit signal basse fréquence présentant une bande passante basse fréquence ΔfLF et de ladite partie haute fréquence présentant une bande passante haute fréquence ΔfHF, et c) un processeur de signal adapté pour traiter le signal basse fréquence et émettre un signal basse fréquence traité à l'unité d'extension de bande passante, et où le second dispositif comprend en outre un transducteur d'entrée destiné à convertir un son d'entrée en un signal d'entrée électrique et une unité de limitation de fréquence destinée à générer ledit signal basse fréquence présentant une bande passante basse fréquence ΔfLF destinée à être transmise sans fil au premier dispositif.
 
2. Système d'écoute selon la revendication 1, où ledit émetteur et ledit récepteur sont adaptés pour fournir un couplage inductif entre les premier et second dispositifs sur lesquels ladite émission dudit signal basse fréquence peut être basée, lorsque lesdits premier et second dispositifs sont situés à une distance opérationnelle l'un de l'autre.
 




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REFERENCES CITED IN THE DESCRIPTION



This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description




Non-patent literature cited in the description