What is Linear Phase EQ?
Introduction
Before we dive into linear phase EQ, let’s first go over the basics of standard equalization and how it relates to phase. Understanding this foundation will help you see just how powerful linear phase EQ can be.
A minimum phase EQ is simply another name for your typical, everyday equalizer. With these common equalizers, we often encounter phase shifts because of the latency that occurs when we adjust the amplitude of certain frequency bands. This latency—or delay—of specific frequencies leads to what’s called phase smear.
Phase smearing can introduce audible artifacts into the signal that might be unwanted. Sometimes, you won’t even notice the smearing. Other times, you might actually like the effect it creates. However, in some situations, you’ll want an equalizer that keeps the phase consistent.
Equalization, or EQ, is one of the trickiest aspects of mixing and mastering to get right. Even small changes to frequencies can drastically alter the character of a track or an entire song.
If you’re not careful with your EQ settings, it’s easy to go too far and end up in a difficult spot. Still, EQ is essential in both mixing and mastering. When working on these processes, there’s a specific type of EQ that can be incredibly useful: linear phase EQ.
What is a Linear Phase EQ?
Linear phase EQ also changes the phase of your signal, but instead of only affecting the frequencies you boost or cut, it shifts the phase of the entire signal evenly. This means you can make the frequency adjustments you need without messing up the phase relationship between different parts of your audio.
Linear phase EQ is only possible because of digital technology. Digital recording has made things much easier for us, but it’s still new compared to the long history of recording. For years, music was made with consoles and tape machines—that’s the sound people are used to. When working digitally, we often use analog emulation plugins to bring back some of that classic warmth into our clean recordings.
Linear phase EQ can’t be done with analog gear. That’s one of the big advantages of digital. With linear phase equalization, the phase of your sound source isn’t affected. The phase relationship stays constant across the spectrum, so you can boost or cut frequencies without any unwanted side effects.
The main point of linear phase EQ is to let engineers avoid phase smearing altogether. But, like most things in audio, there are tradeoffs. The biggest downside of using linear phase EQ is something called pre-ringing. To keep everything in time, these EQs analyze the frequency signal and shift the processed audio.
During this process, you might hear a slight echo just before a strong transient, called pre-ringing. This can be noticeable and might negatively affect the punch of your transients.
What’s Pre-Ringing
To keep the phase relationship intact, linear phase EQs add a small delay to your signal. Your DAW usually compensates for this latency by shifting the audio back so everything stays in time. However, this process can cause pre-ringing.
Pre-ringing happens because the signal is processed both forwards and backwards, creating an effect that sounds like a reversed echo at the start of the transient. You can control pre-ringing by adjusting your EQ settings carefully, which helps you avoid this issue.
Should we use Linear EQ all the time?
Most of the time, using a minimum phase EQ won’t make a noticeable difference because any audible artifacts it might add are unlikely to be heard in your track. It’s not really an “everyday tool”—think of it more as a specialty option that works alongside your other production gear.
In fact, many minimum phase EQs can easily be switched to linear phase mode with just one click.
Linear-phase equalizers are mostly used in mastering, and you’ll often find a Weiss EQ1-LP or something similar in most mastering studios. That doesn’t mean linear-phase EQs are only for mastering, but in general, they’re used sparingly rather than on every single track that needs EQ.
Personally, we don’t reach for linear-phase EQs very often. However, we do sometimes use them to handle subfrequencies on tracks we’re asked to mix.
Sometimes, we come across muddy low-end in mixes—frequencies so low the client couldn’t even hear them on their system—that need to be cleaned up. In these cases, a linear-phase EQ is exactly the right tool for the job.
When should you use the Linear Phase EQ?
Using linear phase EQ can be really helpful when you’re working with an audio source that has multiple microphones on it. Drums are a great example of this. Even if you use gating and other plugins to try to isolate each drum, you’ll still get some bleed from other drums in each microphone.
For example, the kick drum will bleed into the snare mic, the snare will bleed into the tom mics, and so on. Adjusting the phase relationships between all these microphones with a regular EQ can change the sound of the drum kit quite a lot.
This is where linear phase EQ comes in handy. It lets you make EQ adjustments without causing any phase smearing between the different drum mics.
Linear phase EQ is also useful for instruments recorded in stereo, like acoustic guitars. When recording, these mics are placed carefully to stay in phase and capture the most accurate stereo image possible. Using a regular EQ can change the phase relationship and affect the tone of the guitars in ways you may not want.
Linear phase EQ can also help in parallel processing setups, such as parallel compression or distortion. Changing the phase relationship between the original audio and the parallel processed audio can alter the tone of the track in unintended ways. Using linear phase EQ ensures this doesn’t happen.
Conclusion
We’ve broken down what a linear phase EQ is, how to use it, and when you might want to avoid it. Linear phase EQ can be especially helpful if you’re dealing with phase issues while EQing low frequencies—which is where we tend to use it most.
Don’t be afraid to experiment with it, even if you don’t immediately notice any audible artifacts before applying it. Every test helps train your ears and makes you more comfortable with this tool in your production toolkit.
If you have any questions about using linear phase EQ, feel free to ask in the comment section below. We’ll be more than happy to help!
