Adjusting The Equalizer; Graphic 1/3 Octave Equalizer - HELIX PP50DSP Operating Instructions Manual

Adjusting the equalizer

Graphic 1/3 octave equalizer

Each of the DSP channels has its own equalizer which affects the frequency response in high
resolution 1/3-octave increments. The front and rear channels therefore have 30 slide controls
for the bands between 25 Hz and 20 kHz. The subwoofer channel has 10 bands from 25 Hz to
200 Hz. The curve displayed above the slide control indicates the function of the equalizer.
The frequency bands have been subdivided into 1/3 octave internals because this is particularly
suited to human hearing and makes it easy to adjust the equalizer if the frequency response is
also measured in the same 1/3 octave resolution (please also refer to the chapter "Measuring fre-
quency responses").
Each band of the equalizer allows a maximum boost of "+6 dB" and a maximum cut of "-18 dB".
This asymmetrical design was chosen because
boost levels of more than "+6 dB" are rarely required. Any stronger, narrow band frequency dips
measured in the frequency response are usually due to signal cancellations caused by the
phase shifts which may not be eliminated by the equalizer, even with greater boost levels. Expe-
rience shows that attention should be paid to the elimination of excess gain in the frequency res-
ponse when adjusting it. Hearing is considerably more sensitive to narrow band excess gain than
to narrow band frequency dips. You can read more about adjusting the equalizer in the chapter
entitled "Measuring frequency responses".
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