Stereo Tool

Folks, I've heard from several pros and amateurs that "fully phase linear" is the big goal. It seams that the whole idea of audio processing and all it's aspects are inherently against that. I'll admit that my understanding of this concept is very limited. But I get that using Phase Rotation and Phase Delay and some other items in Band Pass can purposefully get you away from this goal. I've also heard differing opinions where fully phase linear is a silly goal and isn't that important, of course audio processing is a very subjective topic, but let's keep this thread focused on phase linear.

Can someone here please explain 2 things:

1) What is Phase Linear?

2) How can you, in the current 7.70 release, get "fully phase linear", if possible?

Thanks!

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America's Country
Totally RAD Radio

Hi. Phase linear as wikipedia defines it is
1) "Linear phase is a property of a filter, where the phase response of the filter is a linear function of frequency. The result is that all frequency components of the input signal are shifted in time (usually delayed) by the same constant amount, which is referred to as the phase delay. And consequently, there is no phase distortion due to the time delay of frequencies relative to one another".

Phase linear processing is usually used because you don't actually want different frequencies to be delayed by a different amount of samples (aka time); And the Phase Delay in st is exactly that. A non phase linear filter and you get that p-o-w-ing sound because lower frequencies are delayed by a different amount than the higher frequencies do.

2) I think that if you don't use any kind of phase delays in st you get a phase linear response (i say think because i don't know what happens in the clipper distortion protection part).

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Very proud user of Stereo Tool since 2010. Thanks Hans.

My radio station
http://amradio.ddns.net

Almost everything in ST is phase linear. Exceptions: Phase Rotation, Phase Delay, non-phase-linear HPF. I think that's it... one could debate about Stereo Image.

To add..
Since some phase non-linearity is needed atleast for tumpet and similar sounds Phase Rotator In st for a reason uses higher freq not lower so voices and bass stay "clean".

Minimum What you can you to even fully "fix" those sounds in higher freq is Phase rotator at '0' Rotations.

So if you want to fix this...


Then after Rotations to 1 (rest default)



What this exaple can cause is mostly to alter limiter to push it much down. Especially last band in MB. Compressor in same band is usually slow and does not go down much. So you get high IMD from limiter and also that part sounds much dull.

In every processor PhR is usually before AGC... but recently i again like it after MB.

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control point
control point2

Thank you all for the insight! So, like anything to do with processing audio, it's subjective. If you go 100% phase linear you get a clean and accurate sound. But, if you add some delay or rotations, you can get a punchier sound. Would you say I summed it up about right?

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America's Country
Totally RAD Radio

Yup. Check this video for a demo of what a bit of phase delay can do:
https://www.youtube.com/watch?v=PvH0AAkQMnk

Does anyone have an idea of the phase characteristics / linearity of some of the hardware processors?
I wonder how much is by design (aside from the phase rotation etc.) and how much is unintentional?