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 you 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!
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 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:
– Analog Design
– Digital Design
– Adds Phase Shifting
– No Phase Shifting
– Usable in every situation
– Usable in some situations
– Adds color and depth to the sound
– Transparent, artifact-free processing
– Delays only the frequencies being processed
– Delays all frequencies simultaneously
– Narrow Qs enhance phasing issues
– Creates latency and pre-ring
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 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 with 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 Minimum Phase EQ?
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.
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 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.
What is Linear Phase Pre-Ring?
Linear Phase Pre-Ring is the addition of a backward tail before the transient. The DAW causes it as it tries to put the delayed signal in time for playback. The artifact is more prominent with high latency and will cause the transient to lose punch. The resulting sound is a reversed hit followed by a thump with short decay.
This image clearly shows how the Pre-Ring effect, present in the bottom graph before the transient, differs from how the transient looks in the Minimum Phase. And even though the peak has greater amplitude in the chart, the transient sounds a lot duller when you listen to the effect in action.
Using FabFilter’s Pro Q3, I’ll show you the sonic differences between topologies with a few audio examples.
Here’s a bass line processed with extreme settings with Minimum Phase. The image shows the plugin’s settings used to shape the sound.
Here’s the same track, with the same settings, only now processed with Linear Phase.
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.
Now let’s hear an acoustic guitar and repeat the process.
Here’s the guitar with extreme settings in Minimum Phase mode. The image shows the plugin’s settings used to achieve the sound.
Here’s the same guitar with the same settings but in Linear Phase mode.
Again, the sound is a lot less transient-heavy. However, in this case, if you have a strong hi-hat or shaker holding the rhythm, you could use this processing to cut out the excessive transients of the guitar.
Finally, let’s listen to the kick drum and redo the process.
Again, this is the kick drum in Minimum Phase mode and extreme settings.
And this is Linear Phase mode:
In this example, you can clearly hear the pre-ringing effect preceding the kick’s initial attack and killing a bit of the transient. That is totally undesirable on a mix unless you’re looking for a different approach to the reverse hit effect.
How do you use Linear Phase EQ in mastering?
To use Linear Phase EQ in mastering, first, you must set your plugin to the lowest latency possible to avoid too much pre-ringing. If, after checking, you’re not noticing anything out of place, all you have to do is use it as a regular EQ. The greatest benefit will be the transparency and lack of phase smearing.
Other than that, using Linear Phase EQing during mastering can be excellent for corrective approaches. So, if you have to master a bad-sounding mix and believe that EQ can do the trick, try out first with a Linear Phase processor. You can later add a Minimum Phase EQ for coloration in case it’s necessary. However, Linear Phase EQs don’t tend to be very popular among most mastering engineers. This tool is used mainly in parallel and aux track applications.
Does Ableton EQ offer Linear Phase Mode?
Unfortunately, Ableton Live does not offer a Linear Phase EQ. Both of its stock EQs, EQ3 and EQ8, are multiband Minimum Phase equalizers. If you want to use a Linear Phase EQ in Ableton, you’ll have to check out some third-party options, such as Waves’ creatively named Linear Phase EQ and FabFilter’s Pro Q3.
Minimum and Linear Phase EQs have been a source of debate for some time in the audio community. While some people vouch for Linear Phase’s transparency, others say it actually sounds too digital and lifeless. Whatever the case, both have situations in which they shine best, and it’s up to you to decide which you’ll use and when.
Minimum Phase EQ is the Swiss-Army knife of equalization. It’s been around for decades, and it will continue in use for as long as they’re counting time. You can use it for everything in subtle or extreme settings. It’s a reliable tool, and its best attribute is that every model sounds different, so if you collect multiple models from different manufacturers, you’ll have an arsenal of sonic capabilities.
On the other hand, Linear Phase EQ is not as versatile as its analog-like counterpart, but it does a great job at delivering precise fixes that most Minimum Phase EQs can’t. You’ll use it mostly in parallel applications, adding just a bit of processing to change some details here and there. Its best attribute is being a transparent tool, so you can silently sneak into a track and fix it without having to worry about messing with the phase.
Pedro Nascente is an artist, record producer, and mix engineer, currently operating his own studio and working with his band, Yellow Boulevard. Believing that music should convey experiences and feelings, Pedro is known for applying design thinking to his workflow to achieve different sounds and deliver the right messages.