Understanding Filter "Character"—Why Noise Is Your Friend

Understanding Filter "Character"—Why Noise Is Your Friend

Yes, you can hear the difference between the "character" of different EQs

by Craig Anderton

You’ll often see posts in various forums from users who like the “sound” of one EQ more than another. that's not surprising; manufacturer's often tout how their particular EQ has some kind of "secret sauce" character. And while there can be times when an EQ aims for a specific character (like emulating the “ring” inherent in inductor-based units) and therefore does indeed have a different sound, I suspect that more often than not the difference relates more to the type of EQ curve chosen by the plug-in manufacturer.

Although digital technology allows for “surgical” EQ, analog EQs involved multiple design tradeoffs. For example, maybe you could obtain a steeper slope if you were willing to trade off passband ripple; constant-Q designs were different from non-constant Q; and so on. We don’t need to get bogged down in the technical details—suffice it to say a digital EQ that emulates one particular type of analog EQ curve is indeed going to sound “different” compared to a digital EQ that emulates a different type of analog EQ curve. But that doesn’t mean a particular EQ plug-in is inherently better. What it means is that a particular plug-in might be better for a specific application.

A PRACTICAL EXAMPLE

Some EQs offer multiple curves, which can be a source of confusion to end users trying to figure out which curve will work best for their application. I saw this confusion in discussions about Cakewalk SONAR’s QuadCurve EQ, so named because it has four different EQ curves. My sense was that many users chose a curve based on “Well I tried different ones, and this one sounds better.” But that doesn’t mean one of the other curves couldn’t have been optimized to provide something even more appropriate.

Filter plug-in documentation will often try to help; for example, SONAR’s description for the QuadCurve’s “G-Type” curve says: “Provides a curve that mimics a modern hardware equalizer. In this mode, the Q response is dynamic, meaning the Q is reduced as you increase the Level, and the effective bandwidth is increased for low gain settings. This is a musical EQ with a gentle Q curve.”

Okay, but what does that mean in terms of sound? Fortunately, there’s a simple way to really hear the differences among filter curves: noise! Here’s how to use noise to learn about your filter of choice.

MAKING NOISE WORK FOR YOU

To start, you need a pink noise source. If you don’t have an audio editor like Sound Forge or Wavelab, open your fave browser and search on “pink noise download”—you’ll find plenty of options. Then, load the noise sample into a track in your DAW.

Insert the filter into the track, adjust the settings, and sweep the frequency control—you’ll hear how the filter affects the noise. If you have more than one curve available, switch among curves and then sweep the frequency. You’ll likely hear a dramatic difference that really helps you zero in on what curve might be best for what you need. Make sure you also try out notch responses and different resonances, as they play into creating different curves as well.

If your filter has a spectrum analyzer so you can see as well as hear what’s happening, so much the better. For example, let’s consider SONAR’s QuadCurve.

 The four buttons circled in red select one of the QuadCurve’s four possible curves.

You’ll hear that the cut in the Hybrid is much sharper than the other curves, while the boost is fairly moderate—this would be the EQ to use on drums if you wanted to tame a resonance but also boost some frequencies. You’ll also hear that the Pure type is very broad and gentle, the E-Type sort of splits the difference, and the G-Type is like the Pure, but with a broader cut and narrower boost. These effects are far more obvious when listening with noise compared to listening with program material.

Play with your filter’s controls as you listen to noise, and you’ll really be able to understand the differences with how these curves affect sound—and ultimately, be able to choose the right curve for the right job instead of just clicking on buttons and hoping.  -HC-

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 Craig Anderton is Editorial Director of Harmony Central. He has played on, mixed, or produced over 20 major label releases (as well as mastered over a hundred tracks for various musicians), and written over a thousand articles for magazines like Guitar Player, Keyboard, Sound on Sound (UK), and Sound + Recording (Germany). He has also lectured on technology and the arts in 38 states, 10 countries, and three languages.