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 Forum index » Clavia Nord Modular » Nord Modular G2 Discussion
4LP Doped (AR) filter
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BobTheDog



Joined: Feb 28, 2005
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PostPosted: Tue Apr 18, 2006 12:08 pm    Post subject:  4LP Doped (AR) filter
Subject description: What exactly is one of these?
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Hi Everyone (especially filter gurus),

I don't know if any of you have the Photone synth that runs in Reaktor but it has a really nice sounding filter called "4LP Doped (AR)".

I have searched on the internet for Doped Filters and have not got very far (something to do with erbium maybe?), I have also looked at the internals of the filter in Reaktor but its all greek to me!

Is this a standard type of filter?

Cheers

Andy
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Blue Hell
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Joined: Apr 03, 2004
Posts: 20264
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PostPosted: Tue Apr 18, 2006 12:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm no filter guru, and to me it sounds more like some pothead said wOOw and then another decided to call the filter dOOped, you know, like grOOvy.

On the other hand, some virtualized Erbium or Iridium would be so cOOl Very Happy

Do you have a sound sample ? That might wake up some of the guru's here ...

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dasz



Joined: Oct 16, 2004
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PostPosted: Tue Apr 18, 2006 9:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

the filter stuff I do on the g2 has to do with augmening the resonance ... adding character at the cutoff ....

whoa never heard of a doped filter but I have heard some doped musicians ...

the waldorf filter are rich and warm as I recall ...
/Dasz

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BobTheDog



Joined: Feb 28, 2005
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PostPosted: Tue Apr 18, 2006 10:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Guys,

Here is a wav @ 24 bit 48K

Cheers

Andy


doped.wav
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 Filename:  doped.wav
 Filesize:  562.36 KB
 Downloaded:  561 Time(s)

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Rob



Joined: Mar 29, 2004
Posts: 578
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PostPosted: Wed Apr 19, 2006 1:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

BobTheDog wrote:
Hi Guys,

Here is a wav @ 24 bit 48K

Cheers

Andy


Sounds and looks (the waveforms) like a pretty standard 24dB ladder filter emulation to me.

/Rob

Btw, it made me change my avatar... Very Happy

(In fact, this little cactus that few of you might recognize as a Lophophora Williamsii decided to blossom again after twelve years, and as the flower lasts only one day it was especially special that this just happened on my birthday yesterday. A very special gift I would say and probably a sign that the great Mescalito will help patching quite a few doped filters the coming year.) Wink
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Blue Hell
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PostPosted: Wed Apr 19, 2006 1:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

Rob wrote:
probably a sign that the great Mescalito will help patching quite a few doped filters the coming year.) :wink:


Especially as Mescalito almost seems present in the flower. With a bit of zooming & color manipulation it gets a bit clearer.

And my congratulations !


001.jpg
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figure in flower
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001.jpg



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davep



Joined: Jul 05, 2004
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PostPosted: Wed Apr 19, 2006 4:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Rob wrote:


it was especially special that this just happened on my birthday yesterday. A very special gift I would say and probably a sign that the great Mescalito will help patching quite a few doped filters the coming year.) Wink



from one old fart to another, Hey! happy birthday!

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mosc
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PostPosted: Wed Apr 19, 2006 7:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

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Rob



Joined: Mar 29, 2004
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PostPosted: Thu Apr 20, 2006 5:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, thanks, though I don't really believe in birthdays. I'd rather celebrate everyday of everyone. Very Happy

Here is a fullsize picture of the flowering peyote:
http://www.xs4all.nl/~rhordijk/Images/RobsPeyote.jpg
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mother misty



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PostPosted: Thu Apr 20, 2006 5:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Rob wrote:
Lophophora Williamsii decided to blossom again after twelve years, and as the flower lasts only one day it was especially special that this just happened on my birthday yesterday. A very special gift I would say


What a coincidence that this just happens on your birthday!
Happy birthday by the way!!
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seraph
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PostPosted: Thu Apr 20, 2006 6:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Rob wrote:

Here is a fullsize picture of the flowering peyote:
http://www.xs4all.nl/~rhordijk/Images/RobsPeyote.jpg

I wish controllers were shaped like that Shocked
anyway... happy birthday

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dasz



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PostPosted: Thu Apr 20, 2006 7:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Rob,

Sto Lat! (transl.: "may you live a 100 years!") -- happy birthday in Polish

Now, don't you wish the G2 surface had a pot holder indent (for your potted flowers and other plants) Wink

/Dasz

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Afro88



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PostPosted: Thu Apr 20, 2006 5:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Rob wrote:
Well, thanks, though I don't really believe in birthdays. I'd rather celebrate everyday of everyone. Very Happy

Here is a fullsize picture of the flowering peyote:
http://www.xs4all.nl/~rhordijk/Images/RobsPeyote.jpg


Wow Rob, what a fantastic looking cactus. If flowering on the anniversary of your birth isn't a sure sign that it's ready to guide you, I don't know what is! Very Happy
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cebec



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PostPosted: Fri Apr 21, 2006 9:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Happy Birthday, Rob! What an awesome gift!

That's a beautiful cactus, indeed.
salut silent Shocked puker shaking shakng2 compress cyclops
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Rob



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PostPosted: Sat Apr 22, 2006 12:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

BobTheDog wrote:
Hi Guys,

Here is a wav @ 24 bit 48K

Cheers

Andy


Bob, as it now looks like I hijacked your thread, which I suppose is not very gentlemen-like, I thought it proper to have another look at that wave file. Very Happy

There is definitely two resonances going on, which suggests some sort of filter with e.g. two second-order poles. The idea of such a filter is to create two or more slightly resonant and detuned filters, where the resonance peak of the higher tuned filter sort of sharpens the corner of the cutoff slope of the lower tuned filter at the cutoff point. Math geeks name these Chebyshev filters, btw. But in this case the second resonance is too high for emulating a Chebyshev filter, so there is something fishy going on here.

Another observation is that when a pure square wave is fed into a filter the resonance swings around the horizontal lines of the square wave. But here the flanks of the square wave seem to have been emphasised. This normally suggests AC coupling in an analog synth, which can be emulated by a highpass filter set lower than the fundamental of the wave to be filtered. But this might already be in the waveform before it is fed into the filter, so there is not much to say about this.

Anyway, I fiddled around a bit on the G2 and came up with two types of filters that are not really like what you are after, but that might still be of interest.

The first type is two state variable filters in series, which is similar to many of the analog filters used in Roland synths. On the first filter outputs is a mixer that mixes the LP and HP output in a way that it creates a notch at the third harmonic of the fundamental when the filter is tuned to the fundamental of the waveform to be filtered. This appears to make the cutoff slope sharper. But it also leaks a bit of the very high from the HP output, which is conveniently filtered away in the second filter. The filters are tuned in a way that they sort of create a "3-dB passband ripple" Chebyshev filter.

The second type is two detuned classic filters in parallel, but with a phase-shifting allpass filter set before the input of one of the filters. When the ouputs are mixed the result is better considered to be the interference between the two filters than just a sum of what they pass on. The phase shifting allpass filter can alter the interference by pushing the waveform harmonics forwards or backwards in time. Each harmonic will have its own amount of shift. This will shift harmonics in or out of phase with the output of the other classic filter, which sort of makes it between a lowpass filter or a bandpass filter. Changing the frequency parameter of the allpass filter (made with the simple and non-resonant 24 dB LP filter module) changes the character of the filter sound.

Have fun,
/Rob


DopeyFilters.pch2
 Description:
Just two more exotic types of resonant filters to sweep.

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BobTheDog



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PostPosted: Sun Apr 23, 2006 9:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Rob,

First of all there is no problem hijacking the thread and a happy birthday to you from me as well.

Thanks for the two filters, I particularly like the type I one.

I am just beginning to realise that the filters play a big part in the sound of different synths, do you have a recommendation of a book or good web site that would enable me to remove some of my ignorance surrounding the matter?

I have also included a pic of the Reaktor structure for you, I'm sure it will make a lot more sense to you than it does to me!

Once again thanks for your help

Andy


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Rob



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PostPosted: Sun Apr 23, 2006 4:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

BobTheDog wrote:

I have also included a pic of the Reaktor structure for you, I'm sure it will make a lot more sense to you than it does to me!

Andy


As I don't work with Reaktor I cannot say much about what is going on there. I don't know the peculiarities of those Reaktor modules, but next to a resonant LP filter an allpass filter and a 6dB LP filter seem to influence the sound.

Aah well, there is soo much variations one can try oneself by combining more than one filter that it seems more fun to just experiment and hear what comes out.

A book that tells a lot about filters is Don Lancaster's Active Filter Cookbook, already around for some thirty years and recently reprinted. It contains all the basics in accessible language. Regrettably it is all about actual analog circuit, so you would have to learn how to read analog opamp-based circuit diagrams. (Which isn't really that hard.)

Imho it is also very well possible to use a 'common sense approach' to filters, without having to use complex math. The important thing to realize is that filters also cause frequency-dependent phase shifts and both the cutoff and the phase shifts of a combination of filters act together to combine into a final 'sound' specific for that configuration. E.g. in that Type I filter I simply used a sinewave osc tuned three times higher as the cutoff frequency of the filter to set the balance of the mixer to get a notch at the 'third harmonic'. Simple to do and much quicker as calculating what that balance should be, which is actually quite complex math. A cheap trick that works like a charm on the G2. Wink

/Rob
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BobTheDog



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PostPosted: Sun Apr 23, 2006 11:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Rob,

Thanks for the info, I have ordered the book; I will hopefully be ok with the opamps as I studied electronics a bit in a dim and distant past.

I will also have a play.

All the best

Andy
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Afro88



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PostPosted: Tue Apr 25, 2006 2:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Really liking those dopeyfilters Rob. The first one sounds alot like the "phat" virtual analogue sound common in the nova/virus range. The second one without any resonance sounds really cool too - it's like the width of a 12db bandpass with the steepness on either side of a 24db one. They've given me some ideas for further experimentation Smile

Maybe this patch could be copied to the building blocks section? They both seem to have that "new" sound people search for when they first get their G2.
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