Why Do Similar Equalizer Settings Sound Different At times?

It's a situation that every sound engineer, musician and producer has faced. Why does the “sound" of one EQ sound better than the other, even though they are both set up in the same way. There's a way in which these seemingly intangible differences can be quantified and evaluated. We will be discussing that in this article.

To understand why equalizer settings can sound different even with the same settings, we first need to delve into the basics of the matter.

Equalizers have different frequency response curves because after all, EQ is about altering the frequency response. All equalizers have parameters for adjusting these response curves, and each parameter affects the sound in some way. There are three main equalizer filter designs: highpass/lowpass, shelving, and parametric.

One of the main reasons EQs with the same settings can sound different is because many modern EQs emulate the analog EQs from classic consoles and outboard gear. However, analog EQ design involves multiple tradeoffs. For example, the designer may have wanted a steeper slope, and was willing to trade off frequency response or phase anomalies. It’s also worth noting that analog EQ stages typically have some degree of phase shift. Combining these stages together, for example with a fourstage EQ, can produce subtle cancellations or additions at certain frequencies. This may seem undesirable, but it accounts for the “character” of many classic EQs.

A digital EQ that emulates one particular type of analog EQ can indeed sound “different” when compared to a digital EQ that emulates a different analog EQ design because these EQs will have different frequency response curves and slopes. Emulating a certain design doesn’t mean a particular EQ plug-in is inherently better; however, that particular plug-in might be better for a specific application.

For example, the SSL E Series EQ reduces Q as you increase a band’s level, so the bandwidth remains constant at different gain settings. With drums, that design can have a more “musical” result because it’s possible to combine higher Q with lower gain for affecting individual drums.

Another difference is that the emulated EQ may have a passive or active circuit design. Passive EQs don’t use gain in the filter sections themselves, so theoretically the filters can only cut, not boost. However, many passive designs include an output amplifier that adds makeup gain to all the filter sections, and the filters’ boost/ cut controls add a constant amount of attenuation at the “0” setting that offsets the amount of output boost. Therefore, when you’re boosting at a particular frequency, the filter circuit itself is simply reducing the amount of attenuation, which results in a “boost” by taking advantage of the gain provided by the output amplifier.

Active EQs are variations on amplifiers, so they can boost as well as cut and can add resonances that would be difficult to achieve with passive EQs. Many people consider passive EQs gentler and more “musical,” and active EQs better at problem-solving.

Trying to differentiate among EQ characteristics is difficult with program material because it’s a moving target — the distribution of energy at certain frequencies is always changing. Fortunately, there’s a simple way to evaluate the different tonal characteristics among different EQs: run pink noise through the EQ. Pink noise is a test signal with equal energy per octave, so it provides a constant, uniform way to make comparisons.

Lastly, as you adjust the settings for different EQs, you’ll hear tonal changes that highlight differences among an EQ’s characteristic curves. Monitoring the output visually through a spectrum analyzer (which shows the level of a signal at specific frequencies) further quantifies these differences and confirms what your ears are hearing.