An Introduction to Zero-Phase Filters
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- เผยแพร่เมื่อ 8 ก.พ. 2025
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An introduction and technical video on zero-phase filters.
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Hey guys, this is Eric Tarr for theproaudiofiles.com.
I've got a video for all of the audio nerds out there. The guys that like to geek out on anything and everything related to audio, how stuff works, all of the details, all of the subtle nuanced things.
So this video is really just about different kinds of filters, or different kinds of equalizers. We'll call them basically the same thing.
These tools that we use to process our signal in a frequency dependent manner. There are different categories of these things. If you've been around audio for awhile, you've probably come across and notice that there are some equalizers, or filters, that are called “Linear Phase.” Right?
And then that opens up the possibility that there must be another category of equalizers that are non-linear phase. So here's one from Waves, and it's even - you know, branded, marketed as “This is a linear phase equalizer.”
I'm going to pull up another one here so we can look at it. This is one from Ozone. This is their equalizer that's part of the Ozone Advanced, and you can see on this plot that there is a line. That's the main one we used. The white line that tells us the amplitude response of this filter. This equalizer.
But behind that, there's another line. This is the phase response that's going to happen, and it's based on units of degrees. What kind of phase shift is going to occur for this equalizer. We can see right around this frequency of interest, there's this phase warping that occurs where there's some kind of phase shift that happens in a quick transition, and a little bit more of a phase shift right around there.
So you know, this would be considered then a non-linear phase. So it's not just a straight line here when it comes to the phase shift that occurs. If we were to analyze a linear phase one, it would be a straight line that we could work with.
Now, most of the time, our ears could care less about the phase shift. Our ears are not very good at picking up on a phase shift that occurs in a signal if we send it through an equalizer.
So that's good. We're much better as listeners at picking up the amplitude change. However, there are some situations if you're doing stuff in parallel or complicated kinds of routing, and you're doing equalization, where it's appropriate to use linear phase.
So what happens with linear phase? We're going to have this constant delay that happens to all of the frequencies together. So in audio, we could call that some small amount of latency, or electrical engineers call that group delay. Some kind of short delay that happens to all of the frequencies evenly.
Well, that doesn't occur when we've got it going on over here, like we have this group delay. We can see that. Right? That's not happening evenly to all frequencies. Some amount of milliseconds now over here that we can see that some of these frequencies are getting offset.
So if we're trying to do things in parallel and blend stuff together, this could cause some weird interaction where there might be some constructive and destructive interferences going on right around this frequency of interest.
So those are kind of some things to understand just about linear phase and non-linear phase forms of filtering and equalization.
However, there is a whole other category. A third type of filter to know about. They are less common. We don't really have plug-ins that are branded as this kind of thing, because it's going to require some finesse. Some ways of working with the signal.
This is called “Zero Phase Filters.” These are filters that have no frequency phase change. No phase distortion, no phase offset.
Now, to accomplish this is very possible for us as audio engineers to do it in our digital audio workstation. So what I'm going to show you here is some information.
This is up on a video online. Some of the stuff that you'll come across if you Google search zero phase filtering. It can be pretty complicated as far as the math goes. If you're really interested in getting into it, it might take some time to understand really how you can prove that these things work, but I'm going to show you mainly how do you use it. How could you possibly create it.
So zero phase filtering, what's the idea? You're going to end up with no phase distortion. No warping or anything like that. We don't even have a time delay, which is the case in the linear phase kinds of filters.
So I'm going to jump ahead down here, and let's talk about how does this actually occur? How can we implement this ourselves in our digital audio workstation, where we could do some spectral processing where we changed the amplitude with zero phase shift? Zero phase change?
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Quality content as always. Thank you.
Amazing intuitive explanation without all the DSP maths!
thanks for your splendid explanation.
Wow - that is very cool.
Interesting video! Keep it up!
WOW IF THIS IS GOING TO ACCOMPLISH THE WHAT IVE BEEN TRYING TO DO FOR A MOTHER FUCKING MONO SYSTEM PLAYBACK I FUCKING LOVE YOU BOY.
amazing video....
how much is the difference in the sound with and without zero phase distortion ? is it worth going through all these steps practically ?
Ok, i can understand the process, but can anybody say a situation where You can apply it? Very usefull vídeo :)
That would be very good for mastering equalization. Am i right ?
Honestly - first time listening to you/your clip, but this is an Awesome explanation, thank you very much :)
But i have a question, like man from above, what are the consequences of phase problem? Thanks in advance, and keep it with these awesome tutorials :)
As he said in the video, if you have to eq a track that's part of a parallel chain or a multi mic setup, Snare up and down for example, the switched phase will mess the sound around the area where the EQ was applied. If you are eqing a soloist track this is not relevant.
Could you please tell me if this zero latency technique will work with a low pass filter?
I want to hear a before and after
You will hear it like a normal -12 cut at 500hz unless the processed track is part of a multi mic setup. As he said, our ears are not good a hearing phase distortion on single mic sources.
Doesn't reversing it again at the last step bring back the original phase difference or does it get cancelled out by the phase shift caused by the second EQ?
The phase is cancelled, the track remains the same plus the clean EQ cut.
we always use equalizer in live sound to illuminate feedback. How can we avoid phase cancelation in live sound ?
The best you can do is linear phase
Interesting
unique
Two words: doesn't work... try with a simple sine wave to test if it works
bk8biokiller8 After lots of experimenting with more complex sounds , I found that sometimes it made it sound better and some times worse . Linear phase Ewing seems to be like that in general . But I got really interesting results by bouncing the same sound backwards and forwards with a phaser