Linear phase EQ - pros & cons

Hey hey!

So this is my first post here, although I've been a visitor for quite a while now (great job David and mods!).

I interested in people's thoughts about linear phase EQ vs. channel EQ. It seems using the linear phase would be the best option on a channel strip to avoid EQ smearing, but I've read several posts now hinting otherwise.

I know EQ artifacts can often be sonically desirable (one of the reasons some manufacturers have a good reputation over others), but I'm really interested in understanding why else one might choose a regular EQ plugin over the linear phase?

Thanks for your thoughts everyone!

Olisidecar.

MacBook 2.1GHz 4Gb RAM

OS X 10.5.8

Logic Pro 8

Part of what makes minimum phase filters add character to a signal is their attribute of group delay, ie a twisting of the signal phase relative to frequency. The smearing you're referring to can be noticeable with transients as signals of various frequencies that may have previously been concurrent, are now sequential. For more steady-state signals, it can effect how simultaneous frequencies, (like a chord) intermodulate. This can either be a good or a bad thing for the music. A matter of taste, really.

Additionally, the impulse response of the filter may cause an audible, short ringing, sometimes called filter echo, depending on how severe the filter settings are.

Linear phase filtering only corrects the group delay element. It does nothing for the ringing or echo imparted by the filters impulse response. In fact, to achieve linear phase, the signal must be run backwards though the filter to normalize the phase, which means there will now be a mirror of the echo before the signal, aka filter pre-echo. This can be very disturbing on certain material.

Linear phase is certainly not better than a minimum phase EQ like the channel EQ, just different. Deliberately so. Knowing when and how to use both is the important thing.

Thanks for your response fader8!

I had been wondering about this ever since watching the Freemasons' video (somewhere in this forum). Your comment about the effects on transients is exactly what they were describing.

Again, thanks!

Olisidecar

I had been wondering about this ever since watching the Freemasons' video (somewhere in this forum). Your comment about the effects on transients is exactly what they were describing.

You should note that these are characteristics of ALL filters. It's inescapable. Some may report, like in that video you referred to, that replacing the EQ with a different manufacturer's solved the problem. It didn't. It can sometimes appear that way because even if you try to duplicate settings, it's really not the same setting. There are way too many variations of how Q is interpreted, gain-Q coupling, filter symmetry, overshoot, the list goes on. So, just a heads up on that.

Unless I know I have to use linear phase for some specific reason (i..e processing an already heavily processed file etc.) I usually go for minimum phase, especially in mixing.

When mastering I sometimes compare identical or near identical settings in minmum/linear EQs and select what I think works best, but usually I simply go with minimum phase if it sounds good. The exception being when a minimum phase HPF changes the peak value of the mix radically due to a phase shift - then I almost always go with the linear phase version, at least for the HPF.

Thank you both

This is all really helpful, in what I expect is an often overlooked or misunderstood area!

Regarding various EQs, you will probably be happy using just the Logic Channel EQ.

Most other digital EQs are identical or near identical in sound, as you can find out for yourself or by searching Google "digital eq myth".

If you want to go splashing on plug-ins then buy more compressors or reverbs Or a good analog EQ.

Absolutely!

Now I just need to get back to actually writing some music!

How would one know when to pull Linear Phase Eq instead of Channel Eq ?.

The answer is already in these posts

If you want to go splashing on plug-ins then buy more compressors or reverbs Or a good analog EQ.

Absolutely!

That's not to say that you may find EQ's that fit your particular workflow better. Even at that, Logic provides a good selection. For example, I like the Fat EQ as it provides shelving filters for any band, not just the lowest and highest bands. Also, if you happen to need more bands for some reason, running two EQ's in series is the same as having twice as many bans for your EQ.

Most of Logic's filters are IIR filter implementations, with the exception of the Match EQ, which is a decent FIR filter set and doesn't have to be used just for "matching" purposes. It's a nice linear phase filter set in itself, particularly when you need to do something surgical. Worth trying for some things.

As for 3rd party filters, I like the UAD Cambridge and the SSL X-EQ for their excellent selection of low and high pass filters, or the RNDigital FirEQ which allows automated morphing between 50 different states for each instance. The UAD Helios 69 offers very unique filter asymmetry and a few other useful details. The DDMF Leq Pro offers continuous adjustment between minimum and linear phase for each band, etc., etc., etc. Eiosis AirEQ is another with unique features. There are even some EQs that add noise or graininess or even an allpass filter, either optional or always there, to make them sound unique. The point is that certain filter sets can offer additional features that could be useful to you, or not. But that's how you should shop. Since Logic Pro comes with such a large collection of decent filters, it means you should be all the more picky when selecting alternative tools. Too many me-too EQs are just going to be redundant.

I like the M/S of the Flux. and though I do not own the Eiosis it looks smart since it has lots of flexible curves.

The rest of the time I use either my Summit EQ-200 or Gyraf G14, if I'm not using the Logic Channel EQ.

Thanks for the advice on the 3rd Partys...

I don't think I'll be buying anything new until I've got to grips with the full functionality and applications of Logic's own EQs. If I can confidently apply any one of Logic's plug-ins and understand why I did so, then maybe I can branch out and explore new things.