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<h1>Soft Comfort Noise</h1>

<p>When discontinuous transmission is used in an uplink direction
and the subscriber is not speaking, the MS will stop transmitting and the
transcoder will generate soft comfort noise. When soft comfort noise is used,
the subscribers hear that the line is not cut. Soft comfort noise with DTX
will save the battery of the mobile.</p>


<p>In the basic approach presented in Recommendation 06.12,
the comfort noise and more specifically the gain and spectrum of the noise
are updated in the receive part only with 0.5 second intervals when the update
is received from the MS. As a result, the comfort noise generated in the transcoder
can have fast step-wise changes both in the spectrum and in the volume level.
This solution results in abnormal sound that does not resemble very much real
background noise. The solution is to interpolate the comfort noise parameters
obtained from the received updating SID-frame in order to smoothen the Comfort
Noise in the transcoder. This method results in very good comfort noise that
resembles very much the natural background noise.</p>
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