Dr. David Berners (left) is the Universal Audio Director of Algorithm Development; Dr. Jonathan Abel is the co-founder and CTO

Ask the Doctors! Drs. David P. Berners and Jonathan S. Abel Answer Your Signal Processing Questions.

Q: Why is the new Pultec MEQ-5 combined with the EQP-1A? Wouldn't it be more flexible to have two separate plug-ins?

A: To answer this, let's go over some of the details of the Pultec EQ circuits. Both the EQP-1A and the MEQ-5 are passive equalizers, without any buffering between the (passive) EQ sections. This means that for both units, the different bands of EQ will interact, since there is nothing to provide a high-impedance input or low-impedance output for each stage. Partly because of this interaction, we at UA decided to implement both of these EQs using upsampling. This allows us to model the entire EQ circuits without having to compensate for warping caused by discretization of the filters (see Ask the Doctors, May, 2003 and June, 2003).

Given that we expect people to use these two EQs together much of the time, we wanted a way to run the plug-ins as efficiently as possible in that configuration.

The MEQ-5 circuit is similar to the circuit for the EQP-1A, but is a sixth order filter rather than fifth order. This allows for the three parametric filters available on the MEQ-5. These two circuits were designed to complement each other.

UA’s new Pultec-Pro

Given that we expect people to use these two EQs together much of the time, we wanted a way to run the plug-ins as efficiently as possible in that configuration. The best way to do that was to combine the two EQ sections within one up- and downsampling processor. This has the obvious advantage of saving the DSP cycles required to do an extra iteration of interpolation and decimation for the second EQ, but also has the benefit that the artifacts and latency caused by the up- and downsampling process are only incurred once. In terms of a real-world equivalent, this amounts to combining the passive EQ sections from the two equalizers into one unit with a single makeup-gain amplifier.

In terms of flexibility, since both sections of EQ are defeatable, users can run either of the two sections within the Pultec-Pro at about the same DSP cost that the plug-ins would have used separately. So the only real penalty for combining the plugs is the fact that if only one of the two sections is being used, the GUI is larger than necessary.

A few people have asked about switching the order of the MEQ-5 and EQP-1A1-A within the Pultec-Pro. As it turns out, the passive portions of these two EQ circuits are highly linear processes (very little distortion happens in the passive circuitry) so that switching the order of these two processes will make no audible difference.

-Dave Berners