Linear Phase EQ
I am not going to cover the basics of EQ in this article, I assume if you are ready to try your hand at mastering you are already familiar with the use of EQs, recording, mixing and the basic configurations like graphic versus parametric or peaking versus shelving response. Instead, I will focus more on the different types of EQs you might find, and the difference is an approach that I take in a mastering situation as opposed to recording and mixing use.
first off while there are dedicated mastering EQs out there, any EQ can be used for mastering purposes and since we're talking about mastering I'll break them down into three types of EQ plugins you're likely to come across:
- Standard EQs: like the kind that are included with every DAW - channel EQs. The standard type of EQ you will find and probably will get used the most is the typical channel EQ that comes with every DAW, by design; these are sometimes referred to as minimum phase EQs, these general-purpose designs are fine for any application from recording to mixing and mastering.
- Character EQs: which are designed to sound and behave like analog circuits, usually vintage analog designs like two based models or passive EQ designs. Character EQs are designed to capture the sound of analog circuit designs; this means that they will by design impart their own sonic character on any signals running through them, sometimes even when you do not dial up any booster cut. They are often based on classic analog EQ designs like the venerable PUL TEC EQP-1A; a passive design with tube circuitry known for its inherent analog warmth. A lot of the time in mastering you want your tweaks to have a subtle and affect as possible in the mix, but that does not mean you cannot use this kind of EQ to impart a little warmth. You do not have to dial up drastic settings; you do not even have to dial up as much of an obvious change, if the plug-in is well designed, the subtle flavor of a typical character EQ should come through even with minimal processing.
- Linear phase EQs: which are often bundled with mastering suites and targeted at applications where clarity of sound is prized. In a lot of mastering suites, you will often find a linear phase EQ; the idea is that this type of design will be more transparent than a standard minimum phase EQ. All analog EQ's and most digital EQ's produce phase shift when you dial up a booster cut. phase shift delays the frequencies just above and below the center frequency, affecting the harmonics in that range and subtly altering the tone over and above the intended tonal change you're trying to achieve with your EQ settings; this is normal it's not inherently good or bad. Moreover, we are all used to it from using traditional EQs, but some digital EQs employ extra processing to compensate for this artefact, eliminating the usual phase shift these are your linear phase EQs. without the usual phase shifts these EQs may in fact sound more transparent especially on already mixed material, like you'd be processing in a mastering session, in some cases they might allow you to dial up a subtle tonal change to part of the frequency spectrum with as little effect as possible on other areas of the mix. That is one reason they are often included with mastering bundles. However, they do come with some caveats; the extra processing to compensate for the phase shift, results in higher latencies and a side effect of that compensation is that a linear EQ may if used more heavily soften transients a little but with small tweaks, a most appropriate for mastering. The differences between regular minimum phase and linear phase EQ's are small and subtle, either can do a good job ultimately your ears will be your guide.
now none of these is necessarily the best in every situation, despite what marketing might sometimes suggest, they can all serve well for a mastering use, but they all will sound different even with identical settings dial-up. In fact, all EQs will sound different even if they are of the same type just due to specific differences in design, if you use EQ for recording and mixing then you already know that.