RHYTHM R3110
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9
Adaptive Noise Reduction
The Adaptive Noise Reduction (ANR) algorithm deploys
a high resolution 32−band filter bank enabling precise
reduction of noise. The algorithm monitors the signal−to−
noise ratio activity in these bands, and calculates a separate
attenuation gain for each of the 32 bands. Noise reduction
has been included in the advanced hearing aid mode option
which can be obtaind either by using a momentary memory
select switch on MS1 (allowing the switching between
Basic, Advanced and telelcoil mode) or by hard wiring MS
to VB to automatically start in Advanced Mode.
Third Generation Adaptive Feedback Canceller
The third generation Adaptive Feedback Canceller (AFC)
reduces acoustic feedback by calculating an estimate of the
hearing aid feedback signal and then subtracting it from the
hearing aid input signal. The forward path of the hearing aid
is not affected. Unlike adaptive notch filter approaches, the
AFC in R3110 does not reduce the hearing aid’s gain. The
AFC is based on a time−domain model of the feedback path.
The AFC allows for an increase in the stable gain of the
hearing instrument while minimizing artefacts on music and
tonal input signals. The AFC is fully automatic and is
configured in R3110 to support all types of hearing aids,
allowing a distance from receiver to microphone as low as
2 centimeters. AFC is available in Advanced Mode and can
be selected via the MS pin with a push button or by hard
wiring MS to VB.
Analog Volume Control
The external analog volume control works with a
three−terminal 100 kW – 360 kW potentiometer connected
between ground (GND) and the regulated voltage (VREG).
The volume control shall have a linear taper. The
potentiometer must be connected to the VC pin. It allows
controlling the output attenuation from full scale down to
approximately 42 dB under full scale. This volume control
does not affect the tinnitus noise signal level when used.
Trimmers
R3110 is a pre-fit device for which all the
sound−processing algorithm parameters have been
preconfigured. Nonetheless, four parameters have been
assigned to four trimmer pins (referred to as “configuration
pins” throughout this document, allowing these parameters
to be adjusted externally. The four configuration pins are the
following:
• LC: Allows to configure the low−cut filter corner
frequency
• HC: Allows to configure the high−cut filter corner
frequency
• WG/NL: Allows adjusting either the wideband gain, or
the tinnitus noise level, depending on the state of the
TN−EN pin (enables the tinnitus noise generation
algorithm). When configured for its Wideband Gain
functionality (WG), this pin allows controlling the
overall gain of the device as per the 16 values defined
in Table 4. When used in its Noise Level (NL)
functionality, it only scales the level of the generated
tinnitus noise as per one of the 16 values also defined in
Table 4.
• AGCO: Allows to select the maximum output signals to
adjust to a particular receiver. The AGC−O module is
an output limiting circuit with a fixed compression ratio
of ∞ : 1. The limiting level is adjustable through the
AGCO pin as a level measured in dB from full scale.
The maximum output of the device is 0 dBFS. The
AGC−O module has its own level detector, with fixed
attack and release time constants.
Figure 1 shows the signal path and the relative position of
these filtering and amplification blocks in the audio path.
There are three possible ways to use these configuration
pins:
1. No configuration is performed; in this case, the
four configuration pins are connected to VREG.
R3110 will be using its predefined default values
for all four parameters. The default values are
defined by the configuration #16 in Table 4 below.
2. Resistive dividers are used to provide a fixed value
to any of the parameters controlled by the four
configuration pins. Table 4 shows parameter
values related to corresponding configuration
numbers (1 to 16). Figure 6 lists the corresponding
component values to use in the resistive divider
(R1 and R2).
3. A trimmer can be connected to any of the four
configuration pins, allowing the parameter to be
controlled by the audiologist or the end user. The
trimmer shall be a three−terminal 100 kW linear
taper. The range that the trimmer will offer is
defined in Table 4. Maximum gains and frequency
ranges are obtained with the default value set #16,
which also corresponds to the default position of
the trimmer, which is obtained when the trimmer
is turned to its end position, clock wise.
