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## Is there any equalizer with a zero delay feedback filters?

VST, AU, etc. plug-in Virtual Effects discussion
KVRist

253 posts since 3 May, 2007, from UK
Yo!

The new DMG EQ will have zero delay feedback filters. I spoke to Dave yesterday and this is just one of a ridiculous amount of features it will have.

Cheers

Scorb
KVRist

48 posts since 24 Mar, 2012

Because otherwise if it's linear I don't see a point in having a zero delay..
Correct me if I'm wrong here: to digitize a linear filter we have 2 options:
1. Use the Laplace transform (s-plane) followed by a bilinear transform (z-plane) with z^-1 being a unit delay - traditional method.
2. Use the voltage/current dependence of the energy-storing elements (capacitors and inductors) to come up with a differential equation (or a system) and solve it numerically. Numerical integration would involve using a previous output value as an independent variable which is equivalent to having a unit delay.

And in case we just approximate the derivative by a finite difference, it becomes a direct equivalent of the Laplace/bilinear combo.

Please correct me if I'm missing a point.

For nonlinear systems it's pretty obvious that it's tempting to introduce a unit delay into the feedback path to break it up into separate nonlinear and differential parts.
KVRian

810 posts since 9 Dec, 2011
djscorb wrote:Yo!

The new DMG EQ will have zero delay feedback filters. I spoke to Dave yesterday and this is just one of a ridiculous amount of features it will have.

Cheers

Scorb

A new DMG EQ?!?

KVRist

253 posts since 3 May, 2007, from UK
http://blog.dmgaudio.com/

It will be called Equilibrium and it's feature set is looking stunning.

I believe the beta is imminent.

There will be circuit models of many great analog EQs (API, SSL, Neve, Harrison, Focusrite, Pultec etc)

Multi channel support, flexible phase, low latency analog phase modes, parallel modes, every conceivable filter type and loads of awsome mouth wateringly cool mastering features. Dave hasn't even had enough space or time to let us testers know the full feature set yet!

Can't wait for this mutha!
KVRian

834 posts since 12 Jul, 2009, from Cornwall
Oi, Scorb, you forgot our discussion on 0df!

0df is a phrase which has come into kvr usage which has two meanings:

1. There is no artificially introduced delay in the signal path used to simplify calculation of a circuit model.

In a linear EQ (and, strangely, this is almost all EQs ever, even a Pultec is linear in its EQ stage), there is NO distortion in any feedback path to model, so no-one modelling EQs has been artificially adding delays in, because it'd break the response shape, and there's no need to anyway.

In this sense, ALL LINEAR EQS ARE DELAY FREE. Important point.

2. A particular filter structure that performs exceptionally well when modulated (typically now the Simper SVF model)

This filter structure appears to have excellent performance when modulated, and makes it almost a no-brainer for synth designers.

For EQ, audio-rate modulation would not just be unusual, it would simply not be EQ (at audio rate, it becomes its own kind of distortion).

So, when Scorb says that EQuilibrium has 0df, it's true- because ANY IIR filter is delay free. (As is any zero-latency FFT/FIR EQ)
By the same token, pretty much any EQ you can find is 0df, because using the phrase 0df applied to EQ is /basically/ taking it out of context. In synth filter design, however, it becomes a very meaningful and relevant term.

Dave.
[ DMGAudio ] | [ DMGAudio Blog ] | dave AT dmgaudio DOT com
KVRian

1016 posts since 12 Nov, 2012
KVRist

48 posts since 24 Mar, 2012
Dave, thank you very much for clarifying this. I couldn't understand what's this thing with 0-d linear eq's (I've posted my thoughts above in this thread) and now it all makes sense.
KVRist

253 posts since 3 May, 2007, from UK
Oops, My bad! In my defence I was a bit hungover when I was trying to recall our conversation but I do remember you explaining about 0df being unneccesary for a linear process. For some reason I assumed that you were referring to Linear Phase EQ which is rarely modulated (and doesn't seem to like being modulated ime).

Btw, I hope you included an all pass in the filter types for Equilibrium.

They can be very useful in EDM production when layering Kicks (sometimes they make stuff come together without having to nudge them back and forth in time, or when you want that phase shift but are already happy with the frequency balance. Also, an allpass can be awsome for creatively effecting bass and other elements. I currently turn to Tone2 Bifilter or DDMF for those duties but would welcome it in a DMG plugin, especially on a per band basis.

Sorry for the delay in my feedback arf arf
KVRist

485 posts since 1 Aug, 2006, from Italy
AXP wrote:Dave, thank you very much for clarifying this.

+1
Thank You Dave!
KVRian

1294 posts since 5 May, 2007, from Finland
I don't quite follow.. Wasn't the subject about zero feedback delay filters? Don't all IIR's by definition have a delay in their feedback structure?
www.mkdr.net

MophoEd - the BEST DSI Mopho Editor VSTi
u-he

16266 posts since 7 Aug, 2002, from Berlin
mkdr wrote:I don't quite follow.. Wasn't the subject about zero feedback delay filters? Don't all IIR's by definition have a delay in their feedback structure?

Yes, I'm a bit puzzled too (sorry Dave )

Anyhow, it's of course possible to eliminate the unit delay in EQ feedback paths too. Might make a difference at high q setting, but maybe not as big a difference as fast modulated synth filters.
KVRian

727 posts since 30 Oct, 2005
djscorb wrote:Btw, I hope you included an all pass in the filter types for Equilibrium.

+1
very useful and sametime the most overlooked filter by many eq devs like Fabfilter,Voxengo,Melda,IKM,PSP,Waves....almost all I know
KVRian

727 posts since 30 Oct, 2005
Urs wrote:
mkdr wrote:I don't quite follow.. Wasn't the subject about zero feedback delay filters? Don't all IIR's by definition have a delay in their feedback structure?

Yes, I'm a bit puzzled too (sorry Dave )

Anyhow, it's of course possible to eliminate the unit delay in EQ feedback paths too. Might make a difference at high q setting, but maybe not as big a difference as fast modulated synth filters.

now-its completely unclear to me,sorry...can you prove this unit delay???
for instance-I have a dirac/one sample/ and if I use any delay I can see it clearly...but if I use any LP filter all I can see is short preecho and postecho...or if I use any MP filter all I can see is long postecho...but still no delay at all
KVRAF

3749 posts since 16 Feb, 2005
So when did zero delay filters become about correcting some kind of time delay? All I know about it is the feedback is solved before anyone cares.
KVRian

727 posts since 30 Oct, 2005
camsr wrote:So when did zero delay filters become about correcting some kind of time delay? All I know about it is the feedback is solved before anyone cares.

again-can you show me this delay on dirac?
or...can you explain the details?
if not...I believe in Dave
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