What is Linear Phase EQ? And Why It’s Great for Mastering

Equalization, or EQ, is undoubtedly one of the most difficult aspects of mixing and mastering to get the hang of. Even the smallest changes in frequencies can drastically alter the character of a track or entire song. If you’re not prudent with your EQing, you can go beyond the point of no return and wind up in a perilous position. Still, it’s necessary to use EQ in both the mixing and mastering processes. And when it comes to mastering, there’s a special kind of EQ that can really come in handy: linear phase EQ.

Linear phase EQ vs. regular EQ

Describing linear phase EQ without getting too technical is somewhat difficult. It helps, however, to first draw a distinction between «regular» EQ and linear phase EQ.

Regular EQ is the tool that alters the frequencies present in any given track. When these frequencies are manipulated, something called «phase shifting» occurs. In the old days of analog EQing, this shifting was an electrical response involving capacitors and inductors. The digital EQ of today simply mimics this physical alteration. A good way to understand phase shifting is to imagine a simple sine wave.

Regular EQ works by shifting this initial wave a certain amount, then combining this duplicated shifted wave with the original. The result is a change in frequencies. This happens because certain frequencies are being reduced, enhanced, or muted entirely depending on where these waves are colliding. For instance, when two identical sine waves are separated by 180 degrees, they cancel each other out (known as destructive interference). Each peak is met with a valley, resulting in almost no sound at all.

What is linear phase EQ, then, and why use it?

Of course, EQing doesn’t mute the sound altogether, just certain frequencies of that sound. By shifting phases, however, the sound can become «smeared» due to a slight delay of frequency ranges. Additionally, overall gain, or level, often fluctuates with regular EQ due to this phase shifting.

Linear phase EQ, on the other hand, does not involve phase-shifting like regular EQ. The sine wave mentioned earlier is never moved left or right. Instead, it stays in place while digital technology handles the EQing. In the simplest terms, this means there is far less smearing when using linear phase EQ.

Why is linear phase EQ great for mastering?

When it comes to mixing with EQ, phase shifting isn’t necessarily the worst thing. There will be several tracks to deal with, after all, and each one will likely be sitting at different frequencies. However, the song as a whole might present some phasing problems. Some frequencies might be missing or too pronounced. By using Linear Phase EQ for mastering, you can reduce or remove these phase collision issues while also not introducing them anymore.

Conclusion

Linear phase EQ can be difficult to grasp at a deep level. At the very least, however, it’s good to know that it’s available to use as a mastering tool. There are many Linear Phase EQ plugins for Windows and Mac, but keep in mind that most often carry with them a good amount of latency. This is yet another reason to use it when mastering, not when mixing.