User`s manual

109
4.5: BROADBAND FILTER CONTROL WINDOWS
4.5.1: Noise Reducer
Application:
The Noise Reducer is a frequency-domain spectral-subtraction filter that implements automatic noise
reduction over 512 separate frequency bands. It operates by continually measuring the spectrum of
the input signal and attempting to identify which portions of the signal are voice and which portions
are non-voice (or noise). All portions determined to be noise are used to continually update a noise
estimate calculation; this is used to calculate the equalization curve that needs to be applied to the
input signal to reduce each band’s energy by the amount of noise energy calculated to be in that
band.
The net result is an output signal that has all non-voice signals reduced in level as much as possible,
thereby “polishing” the enhanced voice signal as much as possible prior to final equalization and
AGC.
Operation of the Noise Reducer is governed by two primary controls: the Master Attenuation Control
and the Noise Smoothing button. Adjusting the Master Attenuation Control allows the user to
precisely control the amount of noise reduction being applied; the greater the value, the more
aggressive the operation of the Noise Reducer.
Because large amounts of noise reduction invariably create audible “birdy noise” artifacts in the
output audio due to the nature of adaptive frequency-domain processing, the user should always try
to minimize the amount of noise reduction being applied to achieve the best balance between maximal
noise reduction and minimal audible artifacts.
In cases where a large amount of noise reduction needs to be applied, but audible artifacts are
unacceptable, it is recommended that the Noise Smoothing feature be activated in order to try to
minimize the audible artifact as much as possible.
Finally, for convenience an Output Gain control and Output level bargraph are provided to enable
the user to adjust the processed output signal to maximum level for better listening and recording.