How To Mix With Linear Phase & Minimum Phase EQ?

In today’s post, we’ll take a look at Linear and Minimum Phase EQs, their differences, and applicabilities. We’ll also give you some audio examples to help you hear the differences for yourself.

If you’re like me and you know nothing about the physics of audio processing, don’t worry. We’ve assembled a complete guide in a language close to English that won’t be hard to understand. Just grab your reading glasses and your headphones to embark with us on this journey to understand Linear and Minimum Phase EQs. Ready? Let’s roll!

When should you use Linear Phase EQ?

Some engineers sing Linear Phase’s praises for parallel processing or mastering situations. You can also use this technique to remove resonant frequencies from snare drums, high-pass vocals, filter multi-miked sources, etc. However, keep in mind Linear Phase is a highly CPU-consuming trick, so be judicious in its use.

During mixing, Linear Phase EQ is beneficial to maintain the phase coherence of a signal spread across multiple channels. That will ensure no phase cancellation happens due to extreme processing of any specific track.

A great example is multi-miked drums. Depending on your setup, there will be a lot of bleed between microphones. If you need to add a lot of EQ to any of the channels, it will create a phase imbalance that can thin out the sound. Linear Phase solves that problem by allowing you to EQ thoroughly without worrying about the phase.

The only thing to keep in mind here is how much latency is being applied to the signal. Too much can cause unwanted artifacts. That means it’s best to leave Linear Phase processing for the mixing stage rather than tracking or pre-mixing.

In this way, you can use this fantastic tool to improve already great results and minimize latency problems. Additionally, when using Linear Phase, consider printing the processed tracks once you’re satisfied with the results.

One of the major cons of Linear Phase EQ is the excessive CPU drain it can cause, so printing ensures you can bypass the plugin and ease the burden on the CPU.

What is Linear Phase EQ?

Linear Phase is an EQ technique that lets you change the frequencies’ magnitude without altering the phase response. Contrarily to regular EQ, Linear Phase helps avoid problems with transparency, especially when applying steep low- or high-cuts. However, this type of processing can add some issues that ask for moderate use.

Linear Phase EQing is an invention of the digital processing world. It was created to maintain phase coherence and avoid smearing when applying significant amounts of EQ change.

These results are impossible in the analog world due to signal delay and slight latency added by the components. To maintain phase linearity, a Linear Phase EQ delays all frequency segments of the audio by the same measure.

In higher processing resolutions, that will cause undesirable latency and the dreaded Pre-Ringing effect. This artifact is especially noticeable in transient-heavy low-frequency sounds, such as that of a kick drum.

When should you use Minimum Phase EQ?

You should use Minimum Phase EQ whenever you want to add coloration to your sound. Since this EQ topology adds some phase shifting, it is beneficial for creative applications rather than corrective processing. In short, you can use a Minimum Phase EQ for most of your equalizing tasks, and you’ll get great results.

Engineers have been using Minimum Phase EQ creatively and for corrections since the dawn of the recording industry. It’s a staple of audio processing in both the analog and digital domains and what most consumers identify as a “musical sound.”

To that effect, even with the advent of the Linear Phase, the good-old analog-like Minimum Phase hasn’t gone outdated. That means you can do your entire project using only Minimum Phase EQs if you don’t have access to a Linear topology.

Even so, the biggest con of Minimum Phase EQ comes when you have to apply extremely narrow cuts to remove ringing frequencies.

Not only will it add a great deal of phase-shifting in the frequencies surrounding the targeted cut, but it will also mess any previous EQ work you’ve already done. There are ways of countering that problem, but the best practice in the digital realm is to use Linear Phase EQ.

What is Minimum Phase EQ?

The minimum Phase is the structure behind every analog and most digital EQs. Even though they are designed to shift the phase as minor as possible, their components slightly delay the signal as it travels through the processor. This delay causes a phase shift that increases with the frequency value.

That means that every time you boost or cut a frequency, there is a slight phase shift being applied to the audio. It is not necessarily audible if you’re EQing an isolated track. However, if you’re processing a sound that’s spread across multiple channels, you might hear a phase difference when comparing it to another track containing the same audio.

The Neve 8803 is a Minimum Phase EQ. Source.

That phase difference is not necessarily bad, as it helps add color and depth to the sound. In a multi-channel recording of the same source, it can even help add separation to the sound. Too much of it will cause issues, of course. But still, the phase issues added by a Minimum Phase EQ are highly diminished with broader Qs. So, if you’re boosting or cutting a wide Q, say between 500 and 2000 Hz, the phasing will be very minimum. That’s why some hardware EQs have a fixed Q value to minimize phasing issues even further. However, if you do the same process with a narrow Q at any given frequency, the phasing will be much more apparent.

What’s the difference between Linear and Minimum Phase EQ?

When processing audio, Minimum Phase EQ imbues the sound with a slight delay and phase shifting, but only to the frequencies, it is manipulating. Linear Phase, however, delays the entire signal to avoid phase shifting. Also, Linear Phase is more transparent, while the Minimum Phase EQ adds some color to the sound.

The most significant difference between Linear and Minimum Phase EQs is the latency. However, in higher latency modes, Linear Phase also adds Pre-Ring to the sound, which precedes transients and makes them lose their punch. There is also a difference in function, as you will primarily use Linear Phase EQ in corrective situations.

Here’s a table with the main differences of each topology:

What is a Minimum Phase filter?

A Minimum Phase filter is a sound-modifying processor that matches the signal’s amplitude with the slightest delay. In other words, any equalizer, speaker crossover, mouth cavity, or bad-sounding room can be considered a Minimum Phase filter if it changes the sound with minimal delay.

It’s also worth mentioning that Linear Phase is not the opposite of the Minimum Phase. You’ll find equations for Linear, Minimum, and Maximum Phase filter topologies in mathematics, the latter being the direct opposite of Minimum Phase.

So, in audio processing, we’re mainly using the first two types of filter, which add zero and some phase shifting, respectively.

You can hear that the bass notes on the Linear Phase bass sound a lot less defined, while the Minimum Phase bass hits a lot harder. So in these extreme settings, Linear Phase would not necessarily be a good choice since your bass would lose a lot of the punch that makes it clicks with the kick drum.