User`s manual

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4.5.2: NoiseEQ™
Application:
Like the Noise Reducer tool, the NoiseEQ™ 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 NoiseEQ is governed by two primary controls: the Frequency Specific Noise
Reduction (FSNR) control group and the Noise Smoothing button. Adjusting the control sliders within
the FSNR section allows the user to precisely control the amount of noise reduction being applied
within each of 20 distinct groups of frequency bands, offering much more precise control of the
spectral subtraction than is available in the Noise Reducer tool, though it does take more time to
setup.
The idea is to tailor the FSNR controls to minimize the amount of noise reduction applied within the
speech frequency groups while maximizing it in other frequency groups. For each slider control, the
greater the value, the more aggressive the operation of the NoiseEQ will be within that group of
frequencies. 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 in each band to achieve
the best balance between maximal noise reduction and minimal audible artifacts.
In cases where large amounts of noise reduction need 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.