Linear phase equalizers have the most transparent sounding types of equalization. However, before delving into how they operate, we must understand its physics—which is where the name comes from. A linear phase is a property of a filter where the phase response of the filter is a linear function of frequency. As a result, the entire input signals of the frequency move at the same time and by the same constant amount, so there is no phase distortion. This is known as group delay.
Characteristics of Linear Phase EQs
A downgrade of linear phase equalizers is that they create unfavorable side effects. Some of these are pre-ringing and latency.
Pre-ringing
Pre-ringing is the biggest disadvantage with linear phase EQs. In simple terms, pre-ringing is a backward echo that sounds like a peculiar sucking. Technically, the only way to get a perfectly linear phase is to apply an EQ twice: forward and backwards in time. An identical backward in time EQ cancels out phase fluctuations.
This is to say that pre-ringing can be controlled by changing the EQ curve. This is possible because it is the EQ curve which determines its amount. Some plugins suppress pre-ringing, so the musician is not getting the exact curve or phase. In addition, there are some settings where linear phase equalization is not the best option because it generates an obvious latency. This is the case of live performances.
Latency
The other unfavorable side of linear phase equalizers is the latency. This is introduced in the linear phase EQ is the result of the backward in time portion of the EQ nullifying the phase. All equalizers have post-ringing, but we don’t always notice them. The longer the pre-ringing, the more perceptible it becomes. They are capable of reducing post-ringing as they offer an equal and opposite amount of pre-ringing.
Some Settings of Linear Phase Equalizers
Musicians can use linear phase equalizers in various settings. With acoustic instruments, the sound remains transparent with their assistance. They are ideal for stereo-correlated sources, since, by using regular EQ, the stereo coherence is likely to collapse. Also, they are the best for mastering without adding the parts that non-linear phase equalizers might add.
If you’re interested…
If you want to learn more on this topic, you can consult our entries on dynamic, shelving, and parametric equalizers.
