Linear Phase Equalization

Robert Katz Leave a Comment

Dom wrote:

Can anyone point me to some papers or books so that I can understand Linear phase a bit better? I need to know what a linear phase eq does to sound and what a normal eq does to sound. I can hear it but I need to know why, how etc.

Dom, you’re right, you have to hear it. Words and mathematical explanations can only go so far. I cover the technical and subjective aspects of the subject in the second edition of my book. But here’s a summary: When you boost or cut a minimum phase equalizer band (standard equalizer, one that shifts phase), the instrument or instruments in that frequency range tend to move forward (or backward, respectively) in the soundstage at the same time you boost (or cut). The soundstage tends to “smear”. This can either be very useful, or else very distracting. The phase change is a very subtle time shift proportional to the boost or cut. Thus, minimum phase (abbreviated MP) tends to sound “more aggressive and more strongly effective”, perhaps also due to the phase distortion or other apparent distortion. Never underestimate the power of distortion to add a sense of clarity or even depth to the sound.

However, when you boost (or cut) a linear phase equalizer, the original depth is retained, nothing moves forward or backward in the soundstage, but the frequency range itself is emphasized or reduced. Linear phase tends to sound “smoother and rounder and subtler”, perhaps also because of a reduction in transient response (which reduction does not occur to the same extent
for all models of LP (linear phase) equalizers). In other words, regardless which model of equalizer you use, there is always a tradeoff. The tradeoff with the LP equalizer is also time-related, but instead of a time shift, it produces a dispersion of the signal in time, producing a subtly audible loss of transient response due to the addition of very low level echoes (not audible as echos per se). This dispersion is worse with a bell curve than with a shelf because the time dispersion is on both sides of the bell and only on one side of the shelf. The steeper the curve (higher the Q) the more the time dispersion.

There is no right or wrong. Linear phase is more significant with already-mixed material, and less important during mixing. If you are equalizing an individual instrument in a mixing situation I don’t think the differences or advantages/disadvantages of linear phase will be that obvious or even useful, but in mastering the differences are more obvious. Some people are entirely adverse to the linear phase and others like it a lot. It’s CPU-intensive to make a good-sounding linear phase and there may only be one plugin that I find transparent enough to recommend, the Algorithmix Red.

Hope this helps,


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