API 5500 - Peaking and Shelving EQ Modes; Boost and Cut Levels; Range Control Settings

5500 Dual Equalizer API
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frequencies. As mentioned before, the API equalizers have a Proportional Q that gets
larger as more amplitude change is selected.
On the LO and HI bands there is an option to select shelving response. When in shelving
mode, the equalizer reaches the indicated amplitude at the indicated frequency and
remains with that amplitude change for all frequencies to the edge of the audio
spectrum.
LO SHELF: When LO SHELF is engaged, the low-frequency band changes
from a peaking to a shelving EQ
Peaking is the default mode
Illuminates in blue when engaged
HI SHELF: When HI SHELF is engaged, the high-frequency band changes
from a peaking to a shelving EQ
Peaking is the default mode
Illuminates in blue when engaged
For frequencies towards the center of the spectrum the change is gradual, but the slope
differs slightly from the peaking mode. This can have important effects on the midrange
character of the sound, but that is not the typical reason to select shelving. The two
principal reasons for using a shelving response is either to eliminate noises like rumble
that are outside the frequency range of the desired sound, or to give a general “tilt” to
the tonal balance towards treble or bass. The API 5500 accomplishes both of these tasks
without sounding resonant.
2.2.4 Boost and Cut
Each band equipped with eleven (11) fixed boost and cut selections:
• -12dB
• -9dB
• -6dB
• -4dB
• -2dB
• 0dB
• +2dB
• +4dB
• +6dB
• +9dB
• +12dB
2.2.4.1 Range
The RANGE control is a unique and powerful addition to the traditional 550 circuit. It is a
formal implementation of a popular factory modification of the 550 EQ. The RANGE of
each channel can be set independently.
In x1 mode, the equalizer behaves
identically to the classic 550A and B.
In x.5 and x.25 modes, the amplitude
scale as shown on the front panel is
reduced proportionally.