Making the assumption that you’re already familiar with what an equalizer is, basic EQ parameters, and how EQs work, let’s explore some of the various types of EQ and when you might use them.
PARAMETRIC EQ
With dedicated controls for frequency, bandwidth (Q), and gain, fully-parametric EQs are the most widely used and most flexible type of equalizers. These versatile EQs can do everything from extreme surgical boosts/cuts to broad shelves and filters. Parametric EQs that don’t offer full control are referred to as semi-parametric EQs, which often have a fixed Q bandwidth and are found in many studio and live sound consoles.
Fabfilter’s Pro-Q 3 is a great example of a fully-parametric EQ that offers almost-unlimited control, while the Waves API 550A is a popular example of a semi-parametric EQ.
The 550A has 3 bands with 7 fixed frequencies per band, which were all carefully selected for their musicality. For beginner engineers, it can be helpful to use an EQ with fixed bands in order to become familiar with the frequency spectrum and how the frequencies interact with each other.
GRAPHIC EQ
Like a 550A, graphic equalizers have fixed frequencies with bands that are chosen for their musical significance. Often having a minimum of 7 bands, and sometimes over 30 bands, graphic EQs are great at notching out problem frequencies and are a go-to for live sound engineers trying to tame pesky feedback at a venue.
Many of these types of EQs have what is called ‘proportional Q design,’ meaning that the bandwidth of the filters become more narrow when the gain of the filter increases or decreases. For instance, the more you boost/cut the more narrow the Q.
SHELVING EQ
As the name suggests, Shelving EQ is based on ‘shelves’ that boost or attenuate frequencies above or below a cutoff point. Dedicated shelving EQs generally come with two main parameters: boost/cut amount and frequency selection. One of the most popular shelving EQs is the Dangerous BAX EQ, which uses a gentle slope to create a musically-rich curve when boosting or cutting.
DYNAMIC EQ
Working in a similar way to multi-band compression, Dynamic EQ uses a threshold control to trigger the gain or attenuation of a specific EQ band once the threshold is reached.
Let’s say you apply a high frequency notch on a singer, who’s falsetto in the chorus is resonating uncomfortably, but that same EQ makes the verse’s sound dull and un-energetic. Using a Dynamic EQ ensures that the cut only engages once the threshold is passed on the high notes in the chorus.
MINIMUM-PHASE VS. LINEAR-PHASE EQ
All analog EQs, and many digital EQs, are what we call ‘minimum phase’ equalizers — EQs that introduce a tiny amount of latency when manipulating different frequencies, which in turn affects the phase of the signal.
Often the phase shifts caused by minimum-phase EQ aren’t problematic and can be musically pleasing to our ears. However, an instance where phase shifts might cause an issue is when applying EQ to a parallel processed track and small differences in the phase relationship could add up to unwanted signal filtering. This is where linear-phase EQ could be your best bet. Linear-phase EQs work by delaying the entire signal, ensuring that the phase relationship stays intact once EQ changes are made to specific frequencies.
Linear-phase EQ isn’t without some issues of its own, though. Due to the computational demand of these plugins they often use quite a bit more CPU than their minimum-phase counterparts. The biggest potential issue of linear-phase EQs is “pre-ringing”. Pre-ringing is an artifact caused by the delay that linear-phase EQs introduce to curb phase issues. This pre-ringing can cause havoc on transients and suck the punch out of your track if used incorrectly.
This video might help with avoiding some of the potential pitfalls of linear-phase EQ:
While there is much more nuance and depth to the topics mentioned above, you should walk away from this article with a better understanding of these EQs and hopefully some newly found curiosity around EQ types and their many uses! Happy EQing, everyone!
