Sensory RSC-4 Series Quick Start Manual

I. Overview
Selecting a proper microphone and its source or biasing resistor are essential for achieving good recognition
results. This design guide describes the procedures for calculating the optimal resistor value, and provides
a list of recommended microphones and optimal resistor values for each one.
II. System Gain
A. Algorithm for determining the optimal overall system gain:
1. If the program source code is configured for "headset" microphone distance, where the
microphone
gain (G) should be -49 dB (0dB=1v/Pa@1KHz).
2. If the program source code is configured for "arms_length" microphone distance, where the
microphone distance is typically 2-3 feet from the user's mouth, then the overall system gain (G)
should be -44 dB.
3. If the program source code is configured for "far_mic" microphone distance, where the
microphone distance is up to 10 feet from the user's mouth, then the overall system gain (G)
should be -43 dB.
4. If MICIN2 is not connected to the microphone, then decrease the overall system gain (G) by 1 dB,
(G = G - 1).
5. Apply G to the following formula:
Where
G is the desired overall system gain,
Sensitivity is the sensitivity rating of the microphone you want to use, and it is specified in –dB
in the microphone's specification,
I is the impedance rating of the microphone,
RS is the optimal microphone bias
B. Example:
Assume a microphone with -42 dB sensitivity and 2.2 K ohms Impedance is used in an "arms_length"
design in which MICIN2 is connected to the microphone.
G = -44 dB; Sensitivity = -42 dB; I = 2200
Use the closest standard 5% resistor to Rs. In this example, it would be 1.8 K ohms.
© 2007 Sensory Inc.
distance is typically a few inches from the user's mouth, then the overall system
P/N 80-0259-H
Selecting a Microphone
DESIGN NOTE
1