ART Pro Audio SGX LT - Guitar Preamp with F/X - Manual (Page 10)

Use this control to set low and high end frequency contours. With the control set
left of 12 o'clock, low frequencies are boosted and higher frequencies are cut.
At 12 o'clock, the control is "flat", no boost or cut to anything. To the right
of 12 o'clock, high frequencies are boosted and low frequencies are cut.
Frequency range is from 130Hz to 1.3KHz low to high.
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