10 EQ Modes Explained:  Linear Phase and Minimal Phase EQ

The usefulness and creative options of an EQ include the ability to separate how one track stands against another and blending multiple sounds together. It defines whether there is a sonic issue that needs correcting, or whether you wish to breath new life into dull source material. We attach descriptions like “sweetening” and “silky” or “tight” and “punchy” when describing how an EQ affects the signal. When dealing with phase and EQ, considerations move beyond flexibility and layout, and into a scientific realm that some may not wish to concern themselves with. In audio, just like any other discipline, we find that the tools we choose to work with can free us, limit us, or even define our creative decisions. Therefore, we may think of a Mode as simply being determined by the shape of an EQ or the way that it is designed to handle a range of Frequencies or filtering, but Linear Phase and Minimal Phase act as Mode options for the same purposes.

Minimal Phase EQ is designed to provide a high quality filtering process that is capable of sounding pure and natural while doing very little to change the timing or cohesiveness of the timing elements of the Program Material. Phase issues can be the cause of many side effects, but it has become an increasingly small concern with professional gear. In software, phase cohesion takes the role not just of filtering and electronics, but in how sound is handled algorithmically. Therefore, the distinction between Minimal and Linear Phase can involve how an EQ handles actual processing, Gain structure, aliasing and sample rate, edge Frequency filtering, and numerous other issues.

Where Minimal Phase can provide natural and precise response, it can also lead to an increase in subtle coloration to the signal the more extreme, and numerous, the filtering options employed. With Linear Phase EQ, an extremely high fidelity process is used to keep the phase cohesion nearly perfect. The trade off can become more in favor of using less Gain and avoiding audible side effects, and in some cases, trading a bit of artistic musicality for the price of absolute unwavering and pristine timing elements. The choice to favor linearity over proven filtering options with Minimal Phase can lead to ringing and unusual overtones if extreme changes to Gain are attempted, so the choice to use Linear Phase should truly remain hand in hand with making very small, surgical and strategic changes to sound sources.

With Minimal Phase, or Minimum Phase as it is sometimes referred to, we have a trade off that finds a balance between the amount of phase a filter allows for, and how well it can provide the shape, slope, and Gain desired. In order to create truly Linear Phase, it has to be possible to adjust all timing elements to the longest potential timing change, which requires a great amount of processing. But, it also places crucial elemental changes to filtering and even can affect the amount of accuracy in actual Frequency and Gain that occur. The most important affect that Phase has on the audio signal is in the sharpness and speed of higher Frequencies, or transients. It is possible for small elements of coloration to occur with any Phase from any EQ that is not purely Linear. It is my personal opinion that an EQ that claims to be low in timing or Phase shift is generally preferable to Linear Phase, but many Mastering Engineers will disagree. I personally believe that if you listen for the changes that are made, it is much less prevalent to any overt changes in timing to use a Minimal Phase EQ in small amounts than it is to potentially change some of the slope shape and filtering and ripple effects of Linear Phase, at the benefit of near-perfect timing.

Whether you are mixing or mastering, the choice of EQ can include specific features like filter type, Gain range, or Frequency settings, and now we can see how the choice of phase cohesiveness can also determine the right choice.