Speck Electronics ASC - Manual (Page 20)

frequency range (4kHz to 25kHz), and is used in conjunction with the
high frequency sweep adjust. 0dB (flat) is obtained when this control
is set to its center detented position.
In addition to the ability to contour high band audio, the high band
controls can reduce hiss that is present on low frequency information.
If there is high frequency hiss or digital noise on a kick drum or bass
track, the high sweep control may be set to its higher clockwise setting
(16kHz-25kHz) and its associated boost/cut control "cut" a few dB's.
As long as you don't dramatically change the sound of the low
frequency audio, this could remove a little noise. Every little bit
improves the overall quality of your sound.
15. High boost/cut
16 Chapter 3 Operation Section