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Microphone Information Page

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Microphone considerations:

Most speech recognition engine vendors recommend a that the application developer use the microphone specifed for the specific engine, and that the end user use an equivalent microphone. In choosing a microphone, care should be used since the choice of a microphone can influence speech recognition accuracy. An alternative microphone should be very high quality and designed for close range pickup to reduce background noise. The microphone must have a flat audio response range.

A typical microphone would have the following characteristics:

•Type: Electret •DC Input Voltage: 2.5 to 5 V DC •Frequency response: 50 to 15,000 Hz •Polar pattern: Bi-directional, with opposing lobes added with a 180 degree relative phase shift for noise cancellation •Impedance: 2.2 Kohms (with 2.2 Kohm collector resistor) •Output level: 20 mVp-p @ 2.5 V DC Input
40 mVp-p @ 5.0 V DC Input
(@ 104 dB SPL, 0.5 inches from sound source) •Sensitivity: -63 +3 dB (0 dB = 1 V/ubar at 1 KHz)

Checking your microphone

If you haven't already, you should make sure that your microphone is:

  1. Plugged in correctly.
  2. Compatible with your sound card.
  3. And that the record volume on the sound card is at a good level.

If you don't do this, speech recognition might not work properly.

One of the best ways to check your microphone is to run the Microphone Setup Wizard which is included with the Microsoft Speech API SDK. The registered version of DTalk includes a component which wraps this wizard.

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Last updated October 20, 2005
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