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Patent Issued for Method for Improving the Comprehensibility of Speech with a Hearing Aid, Together with a Hearing Aid

February 19, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent by the inventors Pape, Sebastian (Erlangen, DE); Serman, Maja (Erlangen-Buckenhof, DE), filed on April 2, 2012, was published online on February 4, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8644538 is assigned to Siemens Medical Instruments Pte. Ltd. (Singapore, SG).

The following quote was obtained by the news editors from the background information supplied by the inventors: "The invention relates to a hearing aid together with a method for operating a hearing aid with an input transducer for receiving an input signal and converting it into an electrical input signal, a signal processing unit for processing the electrical input signal and effecting frequency-dependent amplification of it, and for generating an electrical output signal, and an output transducer for converting the electrical output signal into an output signal which the user can perceive as an acoustic output signal.

"Due to the required small size of the devices and the small distance between the input transducer (in particular a microphone) and the output transducer (in particular an earpiece), the maximum amplification which can be achieved with a hearing aid is generally subject to narrow limits. In particular, if the amplification is too high an extremely disturbing feedback whistle arises. The feedback susceptibility of a hearing aid is frequency-dependent, and mostly affects the upper end of the frequency range which a hearing aid can transmit.

"For many of those with damaged hearing, the problem thus arises that even when they are equipped with a hearing aid they can no longer adequately perceive certain frequency ranges. In the perception of speech this leads to certain sounds not being correctly understood, in particular consonants which in terms of speech have signal components which are in the high frequency signal spectrum. This particularly affects the so-called fricatives, which are named after the way they are articulated, for example 's', 'sh', 'v' or 'z'.

"A known way of compensating for the loss of hearing described is to transpose the frequency ranges affected into other frequency ranges, which can be better perceived. In performing a frequency transposition of this type, two main methods are distinguished: in the case of frequency displacement, a frequency range (e.g. 4 kHz-6 kHz) is shifted into another frequency range (e.g. 2 KHz-4 kHz). In contrast to this, in the case of frequency compression the frequency of the output signal is produced by multiplying the frequency of the input signal by a factor (e.g. 0.75). Often however, frequency compression is not effected with 0 Hz as the starting point, but only above a certain frequency (the knee point) e.g. 2 kHz.

"Methods for frequency transposition in a hearing aid, and a hearing aid for carrying out a frequency transposition, are known from the publication, European patent application EP 1 441 562 A2.

"Frequency transposition, in particular frequency shifting, has two main disadvantages: on the one hand in respect of the spectrum, corruption of the original spectral composition of certain consonants and other sounds and, on the other hand, the ability to distinguish different fricatives--which affects their perception--is significantly impaired.

"From the prior art, methods of speech signal processing are known by which the vowels or consonants can be recognized in a voice signal. For example, German utility model DE 691 05 154 T2 discloses a method of this type with which a voice signal spectrum is analyzed for the purpose of determining peak and average values, which are compared with certain threshold values to recognize vowels and consonants.

"Also, a method is known from U.S. patent publication No. 2009/0112594 A1 whereby pre-vowel consonants and post-vowel consonants are distinguished on the basis of acoustic models.

"U.S. Pat. No. 5,014,319 describes a hearing aid in which a frequency analysis device classifies sounds and, for a frequency transposition, determines a transposition factor appropriate for the frequencies occurring in the sounds. In order to avoid the frequency transposition suppressing individual speech sounds, so that useful information is then lost, a device for the reconstruction of speech components is provided in this hearing aid. For this purpose, the start of each individual speech sound which is recognized is stored, and the residue which remains is in each case discarded. The actual frequency transposition is then achieved by outputting these speech start-sounds over an extended time."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "It is the objective of the present invention to improve the comprehension of speech in the case of a hearing loss where certain frequency ranges can no longer be perceived even at high volumes.

"With the foregoing and other objects in view there is provided, in accordance with the invention a hearing aid. The hearing aid includes an input transducer for receiving an input signal and converting the input signal into an electrical input signal, a signal processing unit for processing and frequency-dependent amplification of the electrical input signal and for generating an electrical output signal, an output transducer for converting the electrical output signal into an output signal which can be perceived by a user as an acoustic output signal, facilities for performing a frequency transposition and for generating a transposed signal, facilities for detecting specific features of the electrical input signal, and filtering facilities, for filtering the transposed signal, whereby the filtering is performed in dependence on the specific features which have been detected in the electrical input signal.

"A hearing aid in accordance with the invention is to be understood as any device which supplies an output signal which can be perceived by a user as an acoustic signal, or contributes to the supplying of such an output signal, and which provides facilities which act as or contribute towards compensation for an individual loss of hearing in the user. In particular, this will be a hearing aid which can be worn on, or can be wholly or partially implanted in, the body or the head, in particular on or in the ear. However, it also includes devices whose primary purpose is not to compensate for a hearing loss, for example electronic entertainment devices (TVs, hi-fi systems, MP3 players etc.), or communication devices (mobile telephones, PDAs, headsets etc.) which do however provide measures for compensating for an individual loss of hearing.

"In general, a hearing aid incorporates an input transducer for receiving an input signal. The input transducer will, for example, be in the form of a microphone which receives an acoustic signal and converts it into an electrical input signal. However, it is also possible to regard as the input transducer units which have a coil or an antenna and which receive an electromagnetic signal and convert it into an electrical input signal. Furthermore, a hearing aid conventionally incorporates a signal processing unit for processing and effecting frequency-dependent amplification of the electrical input signal. For the purpose of signal processing in the hearing aid, use will be made of a signal processor, preferably digital (a DSP), whose method of working can be influenced by programs or parameters which can be transmitted to the hearing aid. This enables the signal processing unit's way of working to be adapted, both for the individual loss of hearing of a hearing aid wearer and also for the current hearing situation in which the hearing aid is currently being operated. The electrical input signal which has been modified in this way is finally fed to an output transducer. This is generally in the form of an earpiece which converts the electrical output signal to an acoustic signal. However, here again other forms of embodiment are possible, e.g. an implantable output transducer which is directly linked to the auditory ossicles and which excites vibrations in them.

"The basic idea of the invention consists in detecting specific features of the electrical input signal and in filtering the transposed signal as a function of the specific features detected in the input signal. For this purpose, the inventive hearing aid provides appropriate facilities for detecting specific features of the electrical input signal, and filtering facilities for the purpose of filtering the transposed signal. The objective of this is to detect certain characteristics of the input signal which could be lost due to the frequency transposition and to restore them, at least partially, in the transposed signal.

"In the case of one preferred form of embodiment, the specific features of the electrical input signal which are detected are, in particular, characteristic features of a speech signal which the input signal includes. These are, in particular, characteristic features of certain speech components, such as for example characteristic features of certain sounds, consonants or fricatives. In addition, however, it is possible to detect specific features of other signals included in the input signal, for example of music, and for filtering to be effected as a function of these features. Quite generally, the objective of the invention is retrospectively to retrieve, at least partially, features of the input signal which are specific, i.e. particular or characteristic, which are lost as a result of the frequency transposition, by filtering facilities.

"In the case of one form of embodiment of the invention, the specific feature of an electrical input signal, in particular of a speech signal included in the electrical input signal, which is detected is the distribution of the input signal power against frequency. This can be based, for example, on a spectral analysis of the input signal, whereby the signal level is determined for each frequency in the input signal over a certain frequency range. The objective of the filtering of the transposed signal which follows is then to achieve a similar power distribution in the output signal, in which the corresponding power maxima and minima lie at an altered frequency, in accordance with a frequency transposition rule.

"Another form of embodiment of the invention provides for the detection of the maxima and/or minima of the electrical input signal, as a function of the frequency, as its specific features. Here too, the number and positions of the maxima and minima are then mapped onto the transposed frequency range by appropriate setting of the filtering facilities.

"The advantages of the invention are shown particularly clearly in the case of a hearing aid with filtering facilities for distributing the electrical input signal into several frequency bands (channels), in which the processing and the frequency-dependent amplification of the electrical input signal are effected at least partially in parallel in the individual frequency bands, and with facilities for the transference of at least one signal which is present in a first frequency band into a second frequency band in the course of the frequency transposition. In particular in the case of this channel-dependent or channel-by-channel frequency shift, as applicable, which in practice represents the method used for preference rather than frequency compression, the resulting power distribution or the distribution of the maxima and minima in the output signal, as appropriate, can deviate greatly from that of these variables in the original signal. As a result--if the invention is not used--when the input signal contains a speech signal the comprehension of this speech is in particular made significantly more difficult.

"In the case of one particularly preferred form of embodiment of the invention, a hearing aid in accordance with the invention incorporates a sound detection device for the purpose of detecting specific features of the electrical input signal, by which sounds, in particular consonants or fricatives, can be recognized in the electrical input signal and the filtering can be effected as a function of a sound which has been recognized. The specific features of the electrical input signal which are detected in accordance with the invention are then characteristic features of these sounds, in particular a characteristic shape of the frequency spectrum, the power distribution etc.

"In general terms, a sound is a noise or tone produced by a human or animal voice. In general speech science, a sound in the more narrow sense is a defined sound wave produced by a flow of breath (phonation airstream) with a particular adjustment of the speech organs. The generation and perception of sounds is the subject of phonetics. A speech sound, or phone, is here regarded as the smallest phonetic unit of spoken language.

"In the sense of the invention, a consonant is to be understood generally as a sound, the articulation of which includes a narrowing of the vocal passage, so that the airstream from the breath is totally or partially blocked and audible turbulences (air eddies) are produced. Consonants are sounds which overcome a hindrance. In particular, in the sense of the invention consonants are not restricted to the consonant letters (B, C, D, F etc.).

"Because the invention is intended, in particular, to contribute to improving the comprehensibility of speech, it is possible to restrict the application of the invention to periods of time in which there is a speech signal. The invention then detects the spectral power distribution of a recognized sound, or the distribution of the maxima and minima in the signal level, as applicable, and maps this onto the appropriate distribution in the transposed signal.

"With one preferred form of embodiment of the invention, the inventive hearing aid incorporates facilities for the transformation of the input signal, or of a signal derived from this, into the frequency domain, whereby the signal processing takes place at least partially in the frequency domain. In the frequency domain it is more easily possible, in particular, to recognize sounds, in particular consonants or fricatives, than when the signal processing is in the time domain. Also, some specific features of the input signal can be detected more easily in the frequency domain than in the time domain.

"Further, with one preferred form of embodiment of the invention, the filtering facilities effect the filtering in the time domain. In particular, narrow-band filters at the end of the signal processing performed by a relevant hearing aid can contribute to the mapping of a spectral distribution characteristic of certain sounds or fricatives, as applicable, into the restricted frequency range of the output signal.

"Other features which are considered as characteristic for the invention are set forth in the appended claims.

"Although the invention is illustrated and described herein as embodied in a method for improving the comprehensibility of speech with a hearing aid, together with a hearing aid, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

"The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings."

URL and more information on this patent, see: Pape, Sebastian; Serman, Maja. Method for Improving the Comprehensibility of Speech with a Hearing Aid, Together with a Hearing Aid. U.S. Patent Number 8644538, filed April 2, 2012, and published online on February 4, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=42&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=2085&f=G&l=50&co1=AND&d=PTXT&s1=20140204.PD.&OS=ISD/20140204&RS=ISD/20140204

Keywords for this news article include: Electronics, Signal Processing, Siemens Medical Instruments Pte. Ltd..

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Source: Electronics Newsweekly


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