User`s manual

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7.9 20-Band Graphic Equalizer
Application:
The 20-band Graphic Equalizer is an easy-to-use linear-phase FIR digital filter that is used to
reshape the spectrum of the final output signal. Reshaping is accomplished with twenty vertical
scroll bars (also called "slider" controls) which adjust the attenuation of each frequency band.
These controls are very similar to the slider controls found on analog graphic equalizers found on
many consumer stereo systems, and thus should be very familiar to even the novice user.
Figure 7-16: 20-Band Graphic Equalizer Control Window
Description of controls/indicators is as follows:
Slider controls: The twenty vertical scroll bar "slider" controls are used to set the frequency
response of the equalizer. Each slider can set the gain of its frequency band
to any value between 0dB and -40 dB in 1dB steps.
Center Frequency: Note that the Center Frequency of each band is labelled underneath each
slider, and that bands are more closely spaced at low frequencies.
Gain Indication: Above each slider control, the gain for that frequency band is given. The
gain can also be visualized graphically by the position of the slider control.
Normalize Button: This button instantly shifts all slider controls up together until the top slider is
at 0dB. After normalization, the relative positioning of the sliders remains the
same. This allows the digital equalizer to implement the desired equalization
curve with minimum signal loss.
Make All 0dB This button instantly moves the slider
Button: controls for all bands to 0dB, defeating the entire equalizer. This is a useful
feature when it is desired to reset all sliders from scratch.
All Down 1dB This button shifts all sliders down by 1dB
Button: from their current positions; no slider, however, will be allowed to go below -
40dB. This button allows the user to shift the entire equalizer curve down so
that there will be room to move one or more sliders up relative to the others.
7.10 Spectral Graphic Equalizer
Application:
In some applications, it may be necessary to precisely reshape the spectrum of input audio prior
to passing it through successive DSP filter stages. For example, if the audio is from a
microphone which has an unusual frequency response curve (for example, a microphone
acoustically modified as a result of concealment), a compensation filter that reshapes the audio to
a normal spectral shape might be desirable.