BACKGROUND OF THE INVENTION
1. Field of the invention
[0001] The present invention relates to protecting the hearing of users of communication
devices like a telephone and, more particularly, to methods and apparatus for monitoring
and limiting the sound pressure resulting both from ambient sound and sound generated
by the communication device, in particular for professional telephone users, e.g.
in a call centre.
2. Description of the related art
[0002] Users of telephones for business purposes especially when use is high undergo considerable
hazards of their hearing if the telephone does not provide means for hearing protection.
These hazard-potentials dramatically increase, if the person wears a headset, like
call centre agents usually do. Upon appearance of hazardous signals the user of a
conventional telephone can remove the handset from the ear very quickly, but a headset
user cannot. The headset is always tight to the ear and there is no possibility of
adjusting the sound pressure exposure of the ear by simply changing the distance to
the ear. Furthermore, one can assume that a headset is continuously used, while handset-use
is normally intermittent. Therefore, telephones and in particular a headset telephone
require means for adjusting the headset loudness over a wide range. In the business
environment it will shortly become mandatory to provide the telephone with intelligence
in order to protect the hearing of its user.
[0003] The sources of hazardous signals are manifold and can be divided into artificial
and human-made. Artificial signals are usual tone signals. The most prominent tone
hazards result from fax machines that are called by - or do call - a normal telephone,
be it intentional or not. Besides fax tones there are various other tones that are
liable to damage the hearing, like dial tones (DTMF) and some network control tones.
Loud bangs and noise termed 'Acoustic Shocks' can also occur on the telephone network
on occasions due to faults, lightning strikes and other reasons that are sufficiently
loud they can cause serious hearing problems even to the extent of permanent deafness.
Human-made hazards usually result from malignant users that shriek into the telephone,
blow a whistle or the like, with the sole purpose of bothering the call centre agent.
However, there are also unintended loud signals that can appear during normal speech,
like loud smack and pop sounds that especially appear when a microphone is too close
to the speaker's mouth.
[0004] But not only sudden loud signals, referred to as acoustic shocks are dangerous, also
comparably quiet but permanent background noise is more than just annoying if the
human ear is exposed to it for hours. Like shocks, such noise potentially has manifold
sources. An omnipresent but usually uncritical source is the network background noise;
however, the increasing use of IP telephony seems to considerably increase the importance
of this issue. Another noise source results from the usage of hands-free telephones,
especially in the car where there is permanent background noise caused by engine sound,
wind, and rough surface. Hands-free telephones used in an office environment also
produce more noise than a conventional telephone. Due to the greater distance between
microphone and speaker's mouth, environmental noise like that of a PC fan is amplified.
[0005] Presently, there are basically two directives that have to be taken into account
when designing a real-time noise-cancelling telephone. The first one is the recommendation
ITU-T P.360 of the International Telecommunication Union (ITU). This directive deals
with the
Efficiency of devices for preventing the occurrence of excessive acoustic pressure
by telephone receivers, i.e. it is specific for telephone-and headset design. The second one is the
Directive 2003/
10/
EC of the European Parliament and of the Council of 6 February 2003 on the minimum
health and safety requirements regarding the exposure of workers to the risk arising
from physical agents (noise). This directive becomes mandatory in April 2006 and is more general about hearing
protection of persons working in loud ambient conditions. Although a call centre agent
usually would not be suspected of working in loud ambient conditions, all criteria
of this directive apply to telephone users, with the only difference that it is primarily
not only ambient noise that jeopardizes the hearing, but also noise received from
the telephone.
[0006] ITU-T P.360 recommendation gives detailed rules of calculating the limits of acoustic
sound pressure levels. For the reasons explained above the limits applicable to headsets
are lower than those valid for handsets. The recommendation distinguishes between
short disturbances (referred to as shock signals in what follows) and longer disturbances.
The relevant physical measure is sound energy, i.e. if a disturbance is half as loud
as another one, its signal power may be twice for to reach the same limit as the first
disturbance. Longer disturbances are measured in the dBPa(A)-scale, while there is
no frequency weighting for short disturbances.
[0007] In the view of Directive 2003/10/EC hearing protection denotes instruments (like
ear muffs) for the physical protection of the ears against ambient sound. When applying
the directive to telephony, hearing protection becomes signal processing that reduces
critical sound events in order to meet the limits of the directive. The directive
defines two different kinds of limits: peak level p
peak and daily exposure level L
Ex,8h; and three different sets of limit values for p
peak and L
Ex,8h: exposure limit values, upper exposure action values, lower exposure action values.
The Exposure limit values of p
peak and L
Ex,8h must not be exceeded. If the upper exposure action values are exceeded, one should
take action in order to reduce the exposure. In view of telephony, consequently output
volume of the headset or the handset of the telephone should be reduced. If one of
the lower exposure action values is exceeded, the directive says that means for hearing
protection shall be made available to a user. In the context of telephony one could
conclude that in this case a telephone with means for hearing protection should be
used. Whilst non-exceedance of the P
peak limits can be guaranteed quite easily by ensuring a sufficiently low volume of the
telephone, L
EX,8h monitoring is much more complex because it incorporates cumulative exposure calculations.
[0008] In regard of Directive 2003/10/EC it is worth mentioning that not only the sound
pressure that is produced by the telephone itself should be taken into consideration.
In the work environment there is a relevant amount of ambient noise caused by other
people working in the same room. This simplest but least satisfying method would be
to estimate or measure the typical ambient sound level of a work place and add it
as a constant to the output sound of the telephone. However, this approach makes it
impossible to take the real ambient noise into account.
[0009] The implementation of just a sound pressure limiter into the telephone may also not
cope with hazardous noise exposure in all cases.
[0010] Thus, there is a need for improved techniques for providing protection of the hearing
of users of communication devices.
SUMMARY OF THE INVENTION
[0011] It is therefore an object of the present invention to provide a method and a communication
device for protecting the hearing of a user having improved sound or noise exposure
monitoring and limiting properties.
[0012] This object is solved by a method for protecting the hearing of a user using a communication
device which comprises the steps of transforming an acoustic ambient signal into an
input signal, receiving a communication signal, updating a long-time noise signal
exposure for said input signal, updating a long-time sound signal exposure for said
communication signal, calculating a total sound exposure as the sum of said long-time
sound signal exposure and said long-time noise signal exposure, generating an output
signal from said communication signal, wherein the output signal level is attenuated
if said total sound exposure exceeds an upper action value, and transforming said
output signal into an acoustic sound signal.
[0013] The present invention further provides a communication device for protecting the
hearing of a user which comprises at least one first microphone adapted to transform
an acoustic ambient signal into an input signal, a speaker adapted to transform an
output signal into an acoustic sound pressure, a communication interface adapted to
receive a communication signal, and a processing unit operatively connected to said
first microphone and said communication interface for receiving said input signal
and said communication signal, adapted to calculate a total sound exposure as the
sum of the long-time sound signal exposure of said communication signal and the long-time
noise signal exposure of said input signal, and further operatively connected to said
speaker and adapted to generate said output signal from said communication signal,
wherein the output signal level is attenuated if said total sound exposure exceeds
an upper action value.
[0014] With the method and communication device according to the present invention it is
possible to monitor and eventually reduce the output sound pressure and thus the output
volume in case there is a danger for the hearing of the user according to the total
sound exposure to the user taking both the long-time noise signal exposure of ambient
signals from the environment of the user as well as the long-time sound signal exposure
of the communication signal like a telephone signal received over a telephone network
from a remote terminal into account.
[0015] Taking said directive 2003/10/EC into account, according to the present invention,
also the ambient noise level is monitored and added to the sound pressure produced
by the telephone headset/handset for calculating exposure action or limiting values.
According to the present invention, a kind of a measuring microphone, or at least
a setup option of the telephone defining a typical ambient noise exposure is provided.
[0016] An advantage with respect to prior art technique may be seen by the fact that the
communication device may not only perform Noise-, Tone- and Shock-Elimination, but
also sound pressure monitoring, i.e. the telephone should calculate the L
Ex,8h during usage, and eventually reduce the output volume in case there is the danger
of exceeding the limit value of L
EX,8h. Since different headphones produce different sound pressure out of the same voltage
level, the user should not be totally free to use any headset he likes. Headsets should
be approved by the telephone manufacturer. According to an aspect of the present invention,
a calibration of the headphone volume of approved headsets is provided, since otherwise
compliance with the regulations cannot be guaranteed. For the same reason it is according
to the present invention mandatory to integrate the monitor into the communication
device like a telephone, the headset or a processing unit like a PC operatively linked
to the telephone and not into a black box between line and telephone. In the latter
approach besides the headset there is also the unknown telephone that would make it
very difficult to get reliable measures. Otherwise, to be safe, such a black box approach
would have to align with the loudest possible telephone and headset, with the consequence
that if equipment with lower volume is used the sound pressure measure might be dramatically
overestimated and the system would reduce the volume far too early resulting in an
unusable configuration.
[0017] According to further aspects of the present invention, there are also provided noise
reduction, shock and tone elimination from the received communication signal implemented
by respective method steps as defined by dependent claims 4 and 5 or respective signal
processing components of said communication device.
[0018] According to another aspect of the present invention, a warning indicator is provided
which is activated when said total sound exposure exceeds a lower action value which
is lower than the upper action value. The warning indicator may be implemented in
the telephone itself or as a software tool providing respective display messages like
"Attention: Sound or Noise Exposure!" on a computer (PC) of the user when activated.
In case the total sound exposure exceeds a limit value which is higher than the upper
action value, the transforming step or the speaker will be disabled.
[0019] The invention, according to further aspects, provides a computer program and a computer
program product as recited in claims 9 and 10.
[0020] The invention, in yet another aspect, provides a system for processing sound and/or
ambient noise signals as recited in claim 11.
[0021] Further specific variations of the invention are defined by the further dependent
claims.
[0022] Other aspects and advantages of the present invention will become more apparent from
the following detailed description taken in conjunction with the accompanying drawings
which illustrate, by way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention will be readily understood by the following detailed description in
conjunction with the accompanying drawings, wherein like reference numerals designate
like structural elements, and in which:
- Figure 1
- is a block diagram of a communication device according to an embodiment of the present
invention.
- Figure 2
- is a flow diagram of a method according to an embodiment of the present invention.
- Figure 3
- is a more detailed flow diagram of a part of the method as illustrated in Fig. 2.
- Figure 4
- is a flow diagram of a method for calculating long-time exposure according to an embodiment
of the present invention.
- Figure 5
- is a flow diagram of a method for calculating long-time exposure according to another
embodiment of the present invention.
- Figure 6
- is a flow diagram of a method for exposure monitoring and attenuating according to
an embodiment of the present invention.
- Figure 7
- is a combined block and flow diagram illustrating ambient sound signal measure according
to an embodiment of the present invention.
- Figure 8
- is a flow diagram of a method for ambient sound signal estimation according to an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The present invention relates to improved approaches to monitor and, if necessary,
attenuate or disable output signals of communication devices like telephones. In the
following telephones are described that are equipped with a headset worn by the user.
However, is it also within the scope of the present invention when the telephone is
equipped with a handset or itself functions as a handset like a mobile terminal or
a mobile phone.
[0025] Fig. 1 shows a block diagram of a first embodiment of a communication device according
to the present invention. According to Fig. 1, the communication device is a telephone
100 comprising the telephone terminal 10 and a headset 20 connected to the telephone
apparatus 10 via a cable 35. The Headset to be used by the user comprises a headset
microphone 25 and earphone or speaker 30 for outputting the output signal by means
of an acoustic sound pressure to the ear of the user. The telephone terminal comprises,
according to an embodiment, a microphone 15 for transforming the acoustic ambient
signals into input signals, a preferably battery powered real-time clock 40, a memory
60, a light emitting diode (LED) 70 as warning indicator and a communication interface
90 all operatively connected to a processing unit 50 implemented by a digital signal
processor (DSP) 50.The communication interface 90 may be implemented as a simple plug
or socket for the telephone line 95 connected to the telephone network, a radio interface
of a mobile network or the like.
[0026] The hearing protection functionality of the communication device 100 will now be
described with reference to Fig. 2 illustrating a flow diagram of a method according
to embodiments of the present invention. In step 210, the communication signal which
is the receive signal from the telephone line is received over communication interface
90 by the telephone 10. According embodiments, noise reduction as well as tone and
shock elimination techniques are applied in steps 220 and 230 to the communication
signal as will be described in more detail with reference to Fig. 3. At the same time
when using the communication device by the user the acoustic ambient signal which
is also referred to as ambient noise signal is recorded and transformed into the input
signal by microphone 15 (also called measuring microphone) in step 250. For each the
input and the communication signal there is updated a long-time signal exposure in
steps 240 and 260 over a certain time window (long-time noise signal exposure for
the input signals and long-time sound signal exposure for the communication signal)
and preferably stored in a memory 60. These long-time signal exposures are then summed
in step 270 to a total sound exposure representing the total sound exposure acting
on the user's ear over the working hours using the real-time clock 40 of the telephone.
The total sound exposure is stored in the memory 60 as indicated by reference sign
65 and monitored by the DSP 50. The DSP 50 also generates the output signal from the
communication signal which is then transmitted to the earphone 30 for transforming
into an acoustic sound signal. If the DSP 50 detects that the total sound exposure
exceeds an upper action value, the level of the output signal is attenuated in order
to keep the total sound exposure possibly low and thus protecting the hearing of the
user.
[0027] Since most modern telephone workplaces are equipped with computers (PCs), according
to an embodiment of the present invention, an 8-hour total sound exposure is monitored
by a PC 80 that is linked to the telephone 10 e.g. via USB. In such an embodiment,
the telephone would need neither permanent power supply nor an own internal real-time
clock. Calculations are done on the PC, and naturally the PC offers good display options
(not shown), e.g., for displaying a sound pressure profile corresponding to the long-time
sound ands noise exposures. According to an embodiment, the PC also works as the warning
indicator and detailed warnings are issued by the PC either as sound warnings or as
visual warnings displayed on the screen of the PC before the system is forced to reduce
the output volume.
[0028] According to embodiments as now described with reference to Fig. 3, the communication
signal will be further subject to noise reduction (step 220 in Fig. 2; not shown in
Fig. 3) and tone and shock elimination (step 230 in Fig. 2) prior to the long-term
sound pressure monitoring.
[0029] The goal of shock elimination is the reduction of (sudden) loud signals in order
to prevent events that exceed the limit value and also the upper action value of p
peak. The simplest way of avoiding too loud signals is to physically limit the maximum
sound pressure output of a telephone handset and headset. In digital signal processing,
this is naturally the case, because the maximum voltage output level is restricted
by the properties of D/A-converters. Thus, one can easily guarantee that the limit
value of p
peak is never exceeded as the relation between voltage level produced by the D/A-converter
and corresponding sound pressure level in the used headset or headset is known an
which is a general requirement also for following discussions. Although such a simple
method may produce unwanted nonlinear effects (known as clipping) when the output
limit of the D/A-converter is reached, this is the easiest and safest way of assuring
compliance with the limit value p
peak. Making clipping "smoother" by means of a characteristic curve ("soft clipping")
is sometimes suggested as improvement in order to make clipping less annoying; however,
in practice the cost-value ratio of this method is poor. A shock-eliminator according
to the present invention is adapted to detect (step 330) and attenuate (step 340)
sudden loud acoustic events below the limit, i.e. signals that exceed the upper or
even the lower action value of p
peak. The shock eliminator does not require spectral domain processing and could, if there
is no need for other additional algorithmic components, run on a standard microcontroller;
or on the DSP 50 needed, for example, for the more complex noise reduction.
[0030] With respect to tone elimination, tones like fax or DTMF tones are perhaps the most
annoying disturbances that appear in telephony, and since they are usually quite loud
they easily exceed the p
peak limits and thus could be seen as special sort of shock signal (although tones usually
are not short). However, from an algorithmic perspective they should be treated separately
from other shock signals because of their special properties. According to the present
invention, the approach of removing tones is spectral-domain processing, which is
more flexible and more tolerant compared to, for example, a time-domain approach using
notch filters, but naturally requires a Fourier-Transformation. This allocates considerable
resources of the processor and introduces a delay into the signal processing. Such
a delay may be handled by delaying the signal output itself by the time it takes to
detect the tone with the drawback is the additional latency. However, a latency of
10 ms is usually acceptable, but longer delays cause problems, especially with side
tone perception. If the latency is 20 ms or more the side tone appears echoic, which
is unacceptable. In spite of the latency effect the spectral domain processing is
favourable because it allows rather versatile handling of tones: if a tone with certain
frequency is detected (step 310), attenuation (step 320) is applied as long as the
tone is present. The attenuation value can be tone specific, if required, and frequency
tolerances can be easily taken into account. In case the signal contains simultaneous
speech, this will be attenuated, too. This fact can be seen as a drawback, but as
stated earlier speech and tones rarely appear simultaneously in normal telephony.
And since attenuation is only applied to the signal if a tone is present, the signal
is not modified at all during the absence of tones, because nothing influences the
frequency characteristic like notch filters do.
[0031] With respect to noise reduction, although also shock signals and tones can be seen
as noise, too, in the context of noise reduction one usually refers to noise as constant
and slowly varying background sound. The reduction of such background noise is more
than a convenience issue: Being continuously present even at low volumes background
noise considerably contributes to daily sound exposure L
Ex,8h, so its reduction is as important as the elimination of tones and shocks. According
to embodiments, there is provided noise reduction techniques to the communication
signal comprising an internal representation of the present noise by, e.g., some kind
of noise estimation. If the noise level is high (signal-to-noise ratio near 0 dB)
and noise reduction is set to be rather aggressive (e.g. 20 dB attenuation of white
noise), artefacts in the signal become unavoidable. There are two typical effects:
strange whistling sound appears (sometimes called "musical tones"), and the speech
signal itself degrades, the voice sounds "hollow" or "robotic". In a noise suppressor
implemented for example as software code portion executable by the DSP 50, both effects
can be kept at a low level and if there is no or only low noise, the speech signal
should remain completely unaltered. Examples for a suitable noise suppressor can be
found in
European patent No. 1091349 of the applicant which is hereby incorporated by reference. Noise reduction methods
require spectral domain processing and show the latency effects discussed earlier.
Since Noise Reduction is not only a simple attenuation of the signal but a sort of
subtraction of noise from speech, there is always some latency in the processed signal.
The latency of high quality noise reduction needs to be as low as 10 ms for the reasons
stated above, and there should be an integrated approach of noise reduction with tone-elimination
(and also shock-elimination), in order not to add the latencies of the single algorithms,
but to build a software tool with overall latency not more than 10 ms. Since noise
reduction requires spectral domain processing anyway, it is self-evident that also
tone-elimination operates in the spectral domain and share resources (like Fourier
Transforms) in an integrated approach.
[0032] According to an embodiment of the present invention, a telephone protecting the users
hearing by means of noise, tone and shock elimination as described herein even if
it works as a stand-alone telephone by using internal processing capabilities but
without an internal battery powered real-time clock is regarded as a good compromise.
If it is necessary to monitor 8 hour sound exposure (leading to a reduction of output
volume, if necessary), in this concept a link to a PC is required. The PC 80 linked
to the telephone 10 is a protection tool for the telephone user that can be used or
not. However, in the responsibility of the employee usage of the protection tool is
mandatory, and the PC demonstrates both to the telephone user and management that
compliance with the Noise Directive is being achieved. However, such an approach cannot
ensure compliance with the 8-hour exposure limit, because the communication device
is able to operate without the PC connected to the communication device.
[0033] Therefore, according to an embodiment, a real-time clock 40 is integrated into the
telephone 10. The real-time clock 40 and the DSP 50 are then adapted to perform the
total sound exposure calculations, update and monitor the exposure(s) and if necessary
adjust the level of the output acoustic sound signal by attenuating the output signal
in order to ensure the limits defined in the EU-Directive are not exceeded.
[0034] The calculation of the long-time sound and noise exposures will now be described
in more detail with reference to Figs. 4 and 5. Fig. 4 illustrates a method according
to an embodiment without the use of a PC 80. In this embodiment, the calculation is
preferably carried out by the DSP 50 of the telephone. First, the previous exposure
value is fetched from memory 60 in step 410 and the present time information is determined
in step 420 from real-time clock 40 in step 420. In step 430, the present signal energy
is calculated, each from the input signal to calculate the present noise signal exposure
value and from the communication signal to calculate the present sound signal exposure
value by using respective calibration data in step 440. Each of the long-term signal
exposure values are then updated by adding the respective previous and present exposure
values and storing the updated exposure value back in the memory.
[0035] Fig. 5 illustrates a method according to another embodiment calculating the long-term
signal exposure values by means of a PC linked to the telephone. The present signal
energy for both the input and the communication signal is calculated by the DSP 50
of the telephone and submitted to the PC 80 in step 510. The present noise signal
exposure value is then calculated by the processing unit of the PC from the input
signal energy and the present sound signal exposure value from the communication signal
energy by using respective calibration data in step 520. Similar to step 450, each
of the exposure values for noise and sound are then updated in step 530 and added
to get an updated total sound exposure value. This updated total sound exposure value
is then submitted back to the telephone in step 540 and preferably stored in memory
60 as indicated by reference sign 65.
[0036] The flow diagram as depicted in Fig. 6 illustrates a method according to the present
invention of how the sound exposure is monitored, displayed and attenuated either
by means of a PC or without PC. At first, it is determined in step 610 whether there
is a PC operatively connected to the telephone and prepared to carry out the monitoring
or not. Of course this option can also simply be disabled on the telephone so that
monitoring is always done by the telephone. However, according to a preferred embodiment,
as a default setup monitoring is done by the telephone and if it is detected by the
telephone that a PC is present and prepared to monitor the sound exposure monitoring
is taken over by the PC. If monitoring is done by the PC, the method branches to step
630 and the updated values for the long-time sound signal exposure and the long-time
noise signal exposure as well as the total sound exposure are displayed on the screen
of the PC. It is further preferred to display these values together with respective
limits, e.g. according to the EU Directive.
[0037] If the monitoring is done by the telephone itself, the method branches to step 620
and if a lower action value is exceeded the LED 70 as warning indicator is activated
by, e.g., flashing of the LED. Of course any other appropriate warning indicator may
be used instead of the LED.
[0038] In both scenarios with or without a PC, the telephone itself or the PC will attenuate
the output signal if a upper action value is exceeded in step 640 in order to lower
the sound pressure of the acoustic output signal produced by the earphone 30. The
upper action value is preferably a preset value that is selected to ensure that the
maximum allowable sound exposure over e.g. the 8 hour working time will expect-edly
not be reached. As a next step 650, the speaker or earphone will be disabled if despite
the attenuation is step 640 a limit value is reached or even exceeded. Of course,
for future processing the upper action value should then be lowered in order to avoid
the action in step 650 interrupting or even ending the use of the telephone at the
current working time. The disabling can be implemented by simply disabling the step
of generating the output signal or switching of the earphone itself.
[0039] Since it is not only the sound output of the earphone 30 into the user's ear that
contributes to the total 8-hour sound exposure, but also the ambient noise; it is
desirable to integrate this sound component into the monitoring.
[0040] According to an embodiment, an additional microphone 15 (also called ambient noise
measurement microphone) is integrated into the telephone that permanently measures
the ambient noise. According to this embodiment, the ambient sound level can be measured
directly, if one assumes that the ambient noise is a diffuse sound field. This assumption
is not completely correct, since at least one component of ambient sound is not diffuse,
but produced by a single distant but nearby source: the users own voice. It comes
close to a philosophical discussion whether or not the user's voice should count as
contribution to ambient sound exposure, so we will neglect this effect for the sake
of pragmatism. Under said assumption of background noise being a diffuse sound field
a calibration is required giving the relation between the signal level of the measuring
microphone and the sound pressure level caused by background noise being measured
in the users ear that is covered by a headset earphone. The difference between various
headsets in regard of the shielding effect against background noise is also an issue
that should be taken into account. In Fig. 7, the ambient noise signal measurement
by means of the microphone 15 is illustrated. A schematic circuit diagram 700 shows
microphone 15 coupled to the DSP 50 over an analogue-digital converter (ADC) 750.
The ambient noise microphone signal is transformed into the input signal and measured
by the ADC 750 as voltage U
N in step 710. The DSP 50 then calculates a resulting sound level for the input signal
produced by the earphone 30 using calibration data in step 720.
[0041] According to another embodiment, instead of integrating a dedicated measuring microphone
into the telephone, one could use the microphone of the headset (headset microphone)
25 itself for the measurement of the ambient noise. This approach has the advantage
that no additional ambient noise measurement microphone is needed. However, it then
has to be taken into account that the microphone gain of the used headset is not a
priori know, resulting in a calibration need for the microphone gain of the approved
headsets (in addition to the independent calibration of the earphone volume calibration
discussed above). This approach further requires distinction between speech signals
and background noise, because the speaker's mouth is so close to the microphone that
the user's speech would otherwise be dramatically overestimated in its contribution
to the total ambient sound exposure. Said distinction is made by means of an approach
according to an embodiment as illustrated in the flow diagram of Fig. 8. In step 810
first the headset microphone signal is used as input signal. Human speech is not completely
continuous; there are short breaks where only background sound is present, so the
minima of the microphone signal is tracked being a good estimate of the background
sound (or ambient noise signal) level in step 820. In contrast to the alternative
approach of integrating a measurement microphone into the telephone, according to
this embodiment, the method would define the user's own voice not to be a contribution
to ambient noise exposure. As stated before, whether to do so or not is not really
relevant; none of the regulations attribute any importance to this detail. In step
830 again it is then calculated the resulting sound level for the input signal produced
by the earphone 30 using calibration data.
[0042] According to preferred embodiments of the present invention, methods, systems and
hearing aid devices described herein are implemented in a telephone or on any other
signal processing devices suitable for the same, such as, e.g., digital signal processors,
analogue/digital signal processing systems including field programmable gate arrays
(FPGA), standard processors, or application specific signal processors (ASSP or ASIC).
[0043] According to a further embodiment, the invention is implemented in a computer program
containing executable program code. The program code may be stored in a memory of
a telephone or any other telecommunication terminal or a computer memory of a PC operatively
connected to a telephone and executed by the telephone itself or any processing unit
like the CPU of the PC or by any other suitable processor, DSP or computing element
executing a method according to the described embodiments. The computer program may
be embodied by a computer program product like a floppy disk, a CD-ROM, a memory stick
or any other suitable memory medium for storing program code.
[0044] All appropriate combinations of features described above are to be considered as
belonging to the invention, even if they have not been explicitly described in their
combination.
[0045] Having described and illustrated their principles of the present invention in embodiments
thereof, it should be apparent to those skilled in the art that the present invention
may be modified in arrangement and detail without departing from such principles.
Changes and modifications within the scope of the present invention may be made without
departing from the spirit thereof, and the present invention includes all such changes
and modifications.
1. A method for protecting the hearing of a user using a communication device, comprising
the steps of:
- transforming an acoustic ambient signal into an input signal;
- receiving a communication signal;
- updating a long-time noise signal exposure for said input signal;
- updating a long-time sound signal exposure for said communication signal;
- calculating a total sound exposure as the sum of said long-time sound signal exposure
and said long-time noise signal exposure;
- generating an output signal from said communication signal, wherein the output signal
level is attenuated if said total sound exposure exceeds an upper action value; and
- transforming said output signal into an acoustic sound signal.
2. The method according to claim 1, further comprising the step of:
- activating a warning indicator when said total sound exposure exceeds a lower action
value which is lower than said upper action value.
3. The method according to claim 1 or 2, further comprising the step of:
- disabling said transforming step when said total sound exposure exceeds a limit
value which is higher than said upper action value.
4. The method according to one of the preceding claims, further comprising the step of
applying noise reduction to said communication signal prior to said updating of said
long-time sound signal exposure.
5. The method according to one of the preceding claims, further comprising the step of
applying tone or shock elimination to said communication signal prior to said updating
of said long-time sound signal exposure.
6. The method according to one of the proceeding claims, wherein said updating steps
of said long-time signal exposures each comprising:
- providing said long-time signal exposure as a previous exposure value;
- determining a present time information;
- calculating a present signal energy from said present time information and a respective
signal level of said input or communication signal;
- calculating a present exposure value from said present signal energy by using calibration
data;
- updating said respective long-time signal exposure by summing said respective present
and previous exposure values.
7. The method according to one of the preceding claims, wherein said communication device
is a telephone comprising a headset worn by said user and wherein said input signal
is transformed by a headset microphone and said acoustic sound pressure is transformed
by an earphone of said headset, and wherein said step of updating said long-time noise
signal exposure further comprises tracking minima of said input signal as ambient
noise signal and calculating said long-time noise exposure by calculating an input
signal level based on said ambient noise signal and calibration data.
8. The method according to one of claims 1 to 6, wherein said communication device is
a telephone comprising a headset worn by said user, and wherein said input signal
is transformed by a microphone disposed at a distance from a headset microphone and
said acoustic sound pressure is transformed by an earphone of said headset, and wherein
said step of updating said long-time noise signal exposure further comprises calculating
said long-time noise exposure by calculating an input signal level based on said input
signal and calibration data.
9. Computer program containing executable program code which, when executed on a computer,
executes a method according to any one of Claims 1 to 8.
10. Computer program product, containing executable program code which, when executed
on a computer, executes a method according to any one of Claims 1 to 8.
11. A system for processing sound or ambient noise signals comprising means configured
to carry out a method according to one of Claims 1 to 8.
12. A communication device for protecting the hearing of a user, comprising:
- at least one first microphone adapted to transform an acoustic ambient signal into
an input signal;
- a speaker adapted to transform an output signal into an acoustic sound pressure;
- a communication interface adapted to receive a communication signal;
- a processing unit operatively connected to said first microphone and said communication
interface for receiving said input signal and said communication signal, adapted to
calculate a total sound exposure as the sum of the long-time sound signal exposure
of said communication signal and the long-time noise signal exposure of said input
signal, and further operatively connected to said speaker and adapted to generate
said output signal from said communication signal, wherein the output signal level
is attenuated if said total sound exposure exceeds an upper action value.
13. The communication device according to claim 12, further comprising a clock unit which
is adapted to measure a use time of said communication device by said user, and wherein
said total sound exposure is calculated over said use time.
14. The communication device according to claim 12 or 13, further comprising a memory
unit operatively connected to said processing device, and wherein said memory unit
is further adapted to store said total sound exposure for every user over said use
time.
15. The communication device according to any of claims 12 to 14, further comprising a
warning indicator operatively connected to said processing unit or said memory unit,
and wherein said warning indicator is activated when said total sound exposure exceeds
a lower action value which is lower than said upper action value.
16. The communication device according to any of claims 12 to 15,wherein said processing
unit is further adapted to disable said speaker when said total sound exposure exceeds
a limit value which is higher than said upper action value.
17. The communication device according to any of claims 12 to 16, wherein said communication
device is a telephone comprising a headset worn by said user and wherein said first
microphone is a headset microphone and said speaker is a earphone of said headset,
and wherein said processing unit is further adapted to calculate said long-time noise
signal exposure of said input signal by tracking minima of said input signal as ambient
noise signal and calculating said long-time noise exposure by calculating an input
signal level based on said ambient noise signal and calibration data.
18. The communication device according to any of claims 12 to 16, wherein said communication
device is a telephone comprising a headset worn by said user, wherein a headset microphone
is a second microphone, said first microphone is disposed at a distance from said
second microphone and said speaker is an earphone of said headset and wherein said
processing unit is further adapted to calculate said long-time noise signal exposure
by calculating an input signal level based on said input signal and calibration data.
19. A communication system comprising said communication device according claims 12 to
18 and a computer connectable to said communication device via a data interface, wherein
said communication device is further adapted to calculate a signal energy from said
input signal and said communication signal and to transmit said signal energy to said
computer, and wherein said computer is adapted to calculate and monitor said total
sound exposure from said signal energy by using calibration data and to transmit an
updated total sound exposure to said communication device.