Electrical audio signal processing systems and devices – Hearing aids – electrical – Directional
Reexamination Certificate
1998-09-03
2004-07-20
Harvey, Minsun Oh (Department: 2644)
Electrical audio signal processing systems and devices
Hearing aids, electrical
Directional
C381S092000
Reexamination Certificate
active
06766029
ABSTRACT:
The present invention is generically directed on a technique according to which acoustical signals are received by at least two acoustical/electrical converters as e.g. by multidirectional microphones, respective output signals of such converters are electronically computed by an electronic transducer unit so as to generate an output signal which represents the acoustical signals weighted by a spatial characteristic of amplification. Thus, the output signal represents the received acoustical signal weighted by the spatial amplification characteristic as if reception of the acoustical signals had been done by means of e.g. an antenna with an according reception lobe or beam. Thus, the present invention is generically directed on an electronically preset, possibly electronically adjusted and tailored reception “lobe”.
FIG. 1
most generically shows such known technique for such “beam forming” on acoustical signals. Thereby, at least two multidirectional acoustical/electrical converters
2
a
and
2
b
are provided, which both—per se—convert acoustical signal irrespective of their impinging direction &thgr; and thus substantially unweighted with respect to impinging direction &thgr; into first and second electrical output signals A
1
and A2. The output signals A
1
and A
2
are fed to an electronic transducer unit
3
which generates from the input signals A
1
, A
2
an output signal A
r
. As shown within the block of unit
3
the signals A
1,2
are treated to result in the result signal A
r
which represents either of A
1
or A
2
, but additionally weighted by the spatial amplification function F
1
(&thgr;). Thus, acoustic signals may selectively be amplified dependent from the fact under which spatial angle &thgr; they impinge, i.e. under which spatial angle the transducer arrangement
2
a
,
2
b
“sees” an acoustical source. Thereby, such known approach is strictly bound to the physical location and intrinsic “lobe” of the converters as provided.
One approach to perform signal processing within transducer unit
3
shall be exemplified with the help of FIG.
2
. Thereby, all such approaches are based on the fact that due to a predetermined mutual physical distance p
p
, of the two converters
2
a
and
2
b
, there occurs a time-lag dt between reception of an acoustical signal at the converters
2
a
,
2
b
.
Considering a single frequency—&ohgr;—acoustical signal, received by the converter
2
a
, this converter will generate an output signal
A
1
=A
·sin &ohgr;
t,
(1)
whereas the second transducer
2
b
will generate an output signal according to
A
2
=A
·sin &ohgr;(
t+dt
), (2)
whereat dt is given by
dt
=
p
p
sin
θ
c
(
3
)
therein, c is the sound velocity.
By time-delaying e.g. A
1
by an amount
&tgr;=
p
p
/c
(4)
and forming the result signal A
r
from the difference of time-delayed signal A
1
′—as a third signal—namely from
A
1
′=A
·sin &ohgr;(
t
+&tgr;), and (5)
A
2
=A
·sin &ohgr;(
t+dt
), (2),
there results, considered at the frequency &ohgr;, a spatially cardoid weighted output signal A
r
as shown in the block of transducer unit
3
:
|
A
r
|=|A
1
′−A
2
|=2
A
sin(&ohgr;(&tgr;−
dt
)/2)=2
A
sin(&ohgr;(&tgr;−
p
p
*sin &thgr;/
c
)/2). (6)
At &thgr;=90° A
r
becomes zero and
at &thgr;=−90° A
r
becomes
A
rmax
=2
A
sin &ohgr;
p
p
/c.
(7)
Such processing of the output signals of two omnidirectional order converters leads to a first order cardoid weighing function F
1
(&thgr;) as shown in FIG.
3
. By respectively selecting converters with higher order acoustical to electrical conversion characteristic i.e. “lobe” and/or by using more than two converters, higher order—m—weighing functions F
m
(&thgr;) may be realised.
In
FIG. 4
there is shown the amplitude A
rmax
-characteristic, resulting from first order cardoid weighing as a function of frequency f=&ohgr;/2&pgr;. Additionally, the respective function for a second order cardoid weighing function F
2
(&thgr;) is shown. Thereby, there is selected a physical distance p
p
of the two converters
2
a
and
2
b
of
FIG. 1
to be 12 mm.
As may clearly be seen at a frequency f
r
which is
f
r
=c
/(4
p
p
) (8)
maximum amplification occurs of +6 dB at the first order cardoid and of +12 dB at a second order cardoid. For p
p
=12 mm, f
r
is about 7 kHz.
From
FIG. 4
a significant roll-off for low and high frequencies with respect to f
r
is recognised, i.e. a significant decrease of amplification.
Techniques for such or similar type of beam forming are e.g. known from the U.S. Pat. No. 4,333,170—acoustical source detection—, from the European patent application 0 381 498 directional microphone—or from Norio Koike et al., “Verification of the Possibility of Separation of Sound Source Direction via a Pair of Pressure Microphones”, Electronics and Communications in Japan, Part 3, Vol. 77, No. 5, 1994, page 68 to 75.
Irrespective of the prior art techniques used for such beam forming with at least two converters, the distance p
p
is an important entity as may be seen e.g. from formula (8) and directly determines the resulting amplification/angle dependency.
Formula (8) may be of no special handicap if such a technique is used for narrow band signal detection or if no serious limits are encountered for geometrically providing the at least two converters at a large mutual physical distance p
p
.
Nevertheless, and especially for hearing aid applications, the fact that f
r
is inversely proportional to the physical distance p
p
of the transducers is a serious drawback, due to the fact that for hearing aid applications the audio frequency band up to about 4 kHz for speech recognition should be detectable by the at least two transducers which further should be mounted with the shortest possible mutual distance p
p
. These two requirements are in contradiction: The lower f
r
shall be realised, the larger will be the distance p
p
required.
It is thus a first object of the present invention to remedy the drawbacks encountered with respect to p
p
-dependency of known acoustical “beam forming”.
The first object of the present invention is reached by providing a method for electronically selecting the dependency of an electric output signal of an electronic transducer unit from spatial direction wherefrom acoustical signals impinge on at least a first and a second acoustical/electrical converter, connected to the inputs of said transducer unit, thereby inputting first and second electric signals thereto, which comprises the steps of
generating at least one third electric signal in dependency from mutual phasing of the first and the second electric signals, said phasing being multiplied by a constant or a frequency-dependent factor and further from a fourth electric signal which depends from at least one of the first and the second electric signals;
generating the output signals of the transducer unit in dependency of the third signal and further from a fifth electric signal which is dependent from at least one of the first and the second electric signals.
Thereby, it becomes possible, irrespective of the actual physical mutual distance of the two converters, to select said dependency, thereby pre-selecting same and possibly tuning and adjusting same, to result in a dependency as if the at least two converters were physically arranged at completely different physical positions than they really are.
In a first preferred manner of realising the inventive method the fourth electric signal is selected to be linearly dependent only from one of the first and second electric signals, thereby being preferably directly formed by such first or second electric signal.
Nevertheless, in a today's more preferred manner of realising the inventive method, the fourth electric signal is dependent on both first and second electric signals. In a preferred
Harvey Minsun Oh
Pendleton Brian
Phonak AG
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