The AE600 Active EQ builds on the design of the TEC Award nominated AE400 by adding more bands, more EQ and filter modes, independent operating of fixed and active bands, a larger UI display, and plenty of other features. This edition of Colin’s Corner focuses on the many EQ and filter modes found in the AE600.
Modes, Modes, Modes
The AE600 completely separates the active and fixed EQ control, for a total of 6 bands of fixed EQ and 6 bands of active EQ. But the AE600 offers much more than just increased band count (with no added latency by the way). A total of 13 EQ and filter modes are available on the AE600 – for both the active and fixed equalizer bands! Many of these modes are original McDSP designs and only available in the AE600. These EQ and filter modes operate like so…
Orig – Original mode – standard parametric EQ
Most active equalizers offer the parametric EQ option as this EQ shape lends itself well to most active EQ applications. The parametric EQ allows the user to select not just frequency and gain amounts, but also the range of frequencies over which the EQ operates (via the Q control). This is the original mode of the active EQ bands found in the AE400.
5x – Standard parametric EQ with five times the Q value
Sometimes parametric EQ is not narrow enough unless extremely tight bandwidth (1/Q) values can be selected. The 5x mode is offered for just such purposes, and alters the displayed Q range from 0.2 to 20.0, to an effective 1.0 to 100.0. When you need surgical precision in your active (or fixed) EQ, the 5x mode is a good choice.
Q+ – Proportional Q parametric EQ
A variation of the ‘original’ parametric EQ mode, with the exception that the actual Q value increases as gain increases (or decreases). For example, if the selected Q is 1.0, but the EQ gain is +6 dB (or -6 dB), the actual Q is higher than 1.0. An interesting trait for active EQ when in the Q+ mode, is the active response is equal to the selected Q initially, but as active equalization is triggered and EQ gain increases (or decreases) the Q value increases, and the bandwidth (1/Q) of the parametric bell shape narrows. Gentle EQ boosts and cuts become tighter as more gain is applied.
LS-BX, HS-BX – Baxandall shelving EQ
This style of EQ has had a resurgence in popularity in recent years, and it also lends itself well to the active EQ processing concept. The Baxandall shelving EQ is notorious for having an extremely gentle curve, and is useful for subtle EQ-ing – as an active or a fixed EQ band.
LS-V, HS-V – Vintage Styled shelving EQ
The LS-V and HS-V shelving EQ modes combine the gentle slope of a Baxandall with the classic undershoot characteristic similar to a Pultec EQ. The undershoot amount is controlled by adjusting the Q control. And unlike a Pultec, it’s available not only as a fixed band of EQ, but an active one as well!
LS-X, HS-X – X-Style EQ
The LS-X and HS-X EQ modes place two Baxandall shelving EQs at opposing frequencies and gains such that they create an ‘x-shape’ in their response. The amount of opposing EQ is controlled by the Q control. The opposing gain is useful as it counter-acts the primary gain of the shelf, creating some attenuation (or boost) as the user boosts (or attenuates) the shelving gain.
L-BXF – Baxandall low shelf with HPF
The gentle curve of the Baxandall is very useful, but like most shelving EQ, needs some roll off, particularly for a low shelf. This roll off is provided by an equally gentle first order high pass filter (HPF), placed approximately one octave below the shelving frequency. With the HPF in place, the low end does not get ‘muddy’ from too much low end boost.
H-BXF – Baxandall high shelf with LPF
Wanting to keep the ‘symmetry’ offered in the EQ/filter modes of the AE600, the H-BXF high shelf mode is the counterpart of the L-BXF mode. Like the L-BXF mode, the shelving EQ gets some roll off – this time approximately one octave above the shelving frequency, from a gentle first order low pass filter (LPF).
HPF, LPF – High Pass and Low Pass Filters
Active high pass filters? The guys in support said we should do it, so blame them! Imagine being able to turn on that crazy low end resonant peak of your high pass filter only when you need it. Or pull that LPF resonant peak back a bit when the signal level goes over the selected threshold (using inverse mode). You can do that and a lot more with the fixed (and active) high pass and low pass filters in the AE600.
The many EQ and filter modes in the AE600 are just the start. Within each active band there is control over the attack, release, and ratio of each active response. The inverse mode accessed by the ‘INV’ button next to each active threshold control can flip the response of the active EQ. Active and fixed bands can be locked together if desired. All six bands (or a subset therein) can be linked to any band as a master. Each band is completely overlapping (fixed and active). And lots more!
So check out the AE600 today! Demos can be access from the demo page at mcdsp.com.