Linear phase eq? Where? When?

Often on the 2 or drum buss, piano & other acoustic instruments, occasionally voice. Almost Never Electric guitars.

I’m using it less these days. If it’s something that’s got top end info in it, I’ll usually use linear for the over sampling. But I never use linear on stuff with 150hz and below because of pre-ringing. Kinda robs the initial transients.

I’ll give you another reason not to use linear phase on LF, take a look at the phase response of just about any speaker in LF range and you go “ why bother “😁

Minimum phase is infinite impulse response. The filter’s response decreases but is infinite! Linear phase is finite impulse response. The settling time is finite. Linear phase has the same delay at all frequencies. Minimum phase does not. Linear phase has pre ringing. Minimum phase does not. Both change the impulse response.

Now consider that Frequency is the time derivative of Phase. Frequency issues in the real, physical world of things are therefor phase issues too! Correcting them with minimum phase filters fixes both the frequency and phase. Floyd Toole’s book on loud speaker design covers this for eqing out resonances from speaker drivers. Frequency and phase can all be plotted on a Arcand graph with poles and zeroes. This means you can perfectly reverse a minimum phase filter too at the expense of running another filter!

Analog filters merely approximate this. This is how most old school digital eqs work with bilinear transforms. The problem is numerical errors for digital eqs so hardware got double precision number formats and and the programming gods discovered trapezoidal integration so new ones can run state variable filters exactly like ideal analog eqs. But most new eqs are made from older textbooks and white papers so they don’t.

For things that are not physical issues like aliasing, linear phage filters work better because the phase shift is distortion. Of course for things in the middle of the audible band, the pre ringing can sound unnatural. The fir filter also cannot be canceled out ny another fir filter because the zeroes are outside of the circle. Well you could use a non-causal iir filter to do so…

Oh and on a final note, some linear phase filters are not finite impulse response. Rather they truncate an infinite impulse response filter’s ringing and then run the filter in reverse. This cancels out the phase shift and makes the end result twice as tweep. This is what the Weiss EQ1-LP does.

I'm doing this too with TRD Infrasonic.  Wish it went up a bit higher but still useful.
The Elliptical filter they do is also great in Lin Phase mode on overheads or drum rooms, and the side channel high-pass can be turned into a shelf cut via the mix control. Great for tightening and centering lows if you need to. This works great in mastering too.

Otherwise I sometimes use it in mastering for small tweaks like 200-400Hz  cuts for revisions after a song is dialed in and printed from my analog chain. Same goes for small brightening adjustments, a wide bell or shelf filter can open up an analog master nicely without changing the tone much.

The only time I use linear phase is if I'm splitting one source into a high and low frequency component for separate processing. For example, I'll occasionally split a bass guitar this way so I can keep the bottom end consistent while performing fader rides on the higher part of the spectrum to bring out busier phrases or fills.

Otherwise, I generally don't prefer the sound of linear phase (nor the CPU hit!).

The only experience I have is with Logics and PRO Q3....

The difference to me is that linear phase sounds cleaner in the low end

cheers

Wiz

Well the sound of the records we all love and grew up with are from consoles and outboard EQ - all minimum phase.

It's "musical" analog and familiar to our ears.

Linear Phase EQ is a tool created in the digital age of DSP.

(IIRC Linear phase equalizers are impossible in the analog world)

There has been about 5 times in the last 15 years I've reached for a Linear Phase EQ and thought - yeah that's sounds better.

TESTIFY, brother svart