EQ 301- Digital Equalization

In Uncategorizedby tfwm

So what I want to know is: how many of you still have a graphic equalizer that is either smiling or frowning at you? If that describes your EQ curve, I would suggest you hire a good contractor to come and help you properly EQ your system, or you may think about fixing some serious room problems. It has been awhile since the last writing in EQ 201 (March 2002 Issue- KRC) but I hope you have been experimenting and having some fun learning about your gear.

In our last discussion we focused in on the 1/3 octave graphic EQ and the parametric EQ, those being in the analog domain. This time, we will look at the same equalizers in digital. Again, we will focus in on the 1/3 octave graphic and the parametric equalizers only, in the digital domain there will be other functions available to explore.

First lets look at one I am familiar with, the Ashly Protea 4.24G graphic equalizer. See below.

As you can see, there are some obvious differences between this and analog graphic equalizers. This particular unit has four channels of 1/3 octave graphic EQ’s in one small package. Instead of the slide faders we expect to see, this unit has up and down touch buttons for each filter with the corresponding frequencies printed above the buttons. On the display screen there are little faders that move with the touch of the buttons so you can still see the EQ curve as you make your adjustments. This particular unit also has the option of controlling other 4 channel slave units for total control of 16 channels of graphic EQ from one front panel or from a remote control panel.

In addition to being a multi-channel graphic EQ, this unit also includes digital delay, high and low pass filters, and compressor/limiters on each channel of graphic EQ. So when I said we will explore other functions as well, here they are. Once an analog signal is converted to digital it then becomes much easier to do other types of processing in the same box. We will see many boxes that have graphic EQ and parametric EQ in the same box. And some have graphic, parametric, and notch filtering all combined.

All of this is just another way of doing what we have already discussed doing in the analog domain. One of the great advantages of doing it digitally is being able to get more out of single boxes.

There are many wonderful things about using digital. To name a few: more accurate filtering, precisely choosing at what frequency we want to put a parametric filter, storing information that can be retrieved easily, user interface i.e. a computer that allows us to see more accurately the effect our EQ has on the overall signal and one of my favorite things; locking out unwanted users. Most of the digital units I have used either with a computer or with front panel controls have some type of password security. This allows you, the “pro”, to make adjustments to the system without having the usher “fix” the sound.

Below is a picture of a four channel parametric equalizer. You will notice there are no front panel controls on this unit at all, making it only controllable via computer. This too, helps to keep unwanted users from “fixing” the sound where you are not around.

Because all the controls for the digital processors are internal, it is much easier and more cost effective for the manufacturers to not use buttons and knobs for control. This creates a bit of a learning curve for some of us old-timers who were brought up on buttons and knobs, but it is worth the time it takes to learn.

I mentioned that the units I have pictured have “high and low pass filters” as do most good digital processors. It just occurred to me that the last time we discussed pass filters was in the discussion of EQ on the channel strip of your console and some about high pass filters in analog graphic EQs. In the digital realm, it is quite simple to put a 24dB per octave filter on either end of the audio band. These filters are floating and can be moved to whatever frequency you decide. It was a bit confusing for me at first when I would use a high pass filter at the low end of the audio spectrum. For me it was easier to think in terms of the audio signal I wanted to pass through the system. A ‘high pass’ filter would let audio higher than the frequency where I set the filter, pass through the system. A ‘low pass’ filter would do the opposite, letting frequencies lower than where I set the filter pass through the system.

These filters can be very helpful when equalizing your monitor speakers. Most often the problems we get on stage are high levels of bass frequencies going everywhere; remember, they are omni-directional. So if we put a ‘high pass’ filter at say, 150Hz we can keep frequencies below that from causing problems on stage and we wouldn’t be working those small drivers in those floor wedges beyond what we should – or the amps either, for that matter. Low pass filters also work great in monitors to stop some of the really annoying high frequency feedback that happens when the vocalist insists on pointing the mic at the floor wedge.

Okay, so now that you are more confused than ever, don’t lose heart. The world of digital is really not too frightening; you learned how to use a computer didn’t you? As always, there are those ready to help. You can email me anytime at jawisler@cs.com and I will be happy to take you further into the exciting world of digital EQ.