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 Forum index » Clavia Nord Modular » Nord Modular G2 Discussion
Good CEM filter simulation
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dorremifasol



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PostPosted: Thu Oct 18, 2007 8:15 am    Post subject: Good CEM filter simulation Reply with quote  Mark this post and the followings unread

I'm trying to build a classic synthesizer, based in the Nord lead 2 and others like the prophet or the matrix. The goal is to make it sound as "analog" as possible.

In order to do this I'm following Rob's and many other people tutorials and building blocks.

I also have recordings of various analog synthesizers, like the Matrix 1000 or the Cheetah MS6 (which sounds amazing for my taste).

What I'm missing is a good emulation of the classic filter found in those synthesizers, I think it's named CEM3396.

Now I'm using a ladder filter simulation but I think it's not appropriate.

Here is some work at progress..

the original sound:
http://www.synthmania.com/Synthesizers/Cheetah/MS6/Audio/4%20Sync%2073.mp3

Please let me know if you know how to simulate a CEM filter, thanks!


NL2 Moog2.pch2
 Description:
trying to make a G2 patch sound as analog as possible

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 Filename:  NL2 Moog2.pch2
 Filesize:  5.43 KB
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dasz



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PostPosted: Thu Oct 18, 2007 9:23 am    Post subject: Reply with quote  Mark this post and the followings unread

nice experiment. feedback loops and all. similar to my tricks re feedback.

One easy way to change the warmth of the filter is to add an eq before and/ or after the filter to boost certain frequencies.

/Dasz

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dorremifasol



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PostPosted: Thu Oct 18, 2007 10:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you master Very Happy

I think it would be very useful to have an audio library of sweeps of different filters, including variations with different resonance settings, just for reference.

Maybe there is already a site with those audio files? does anybody know?

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iPassenger



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PostPosted: Fri Oct 19, 2007 1:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Slightly OT:

When recording samples of my waldorf pulse to look at waveforms and see if could spot what made them sound different to the G2s...I spotted the shapes were quite uneven and rounded...even with no filter settings and no overdrive into the filter...Emulation of the Waldorf waves was made easier by placing a bass boosting EQ after each osc before mixing them into the filter. I am an EQ a phobe and tend to stay the hell away from it but it was the only way in this case.

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dasz



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PostPosted: Fri Oct 19, 2007 9:43 am    Post subject: Reply with quote  Mark this post and the followings unread

dorremifasol wrote:
Thank you master Very Happy


But I am not even a Jedi.

dorremifasol wrote:

I think it would be very useful to have an audio library of sweeps of different filters, including variations with different resonance settings, just for reference.


That would be a great idea. I can volunteer the waldorf xt sweeps. I recommend doing this all in one audio file (multiple sweeps) with a readme of the times and settings (with silence inbetween sweeps).

Actually, one could even create a g2 patch which will set (cutoff and res), and then sweep different filters, put silence between different filter settings and filters. All with sequencers.

Hmm, but I am not patching at the moment. Hands are recovering.
/Dasz

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doctorno



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PostPosted: Sat Oct 20, 2007 3:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

I am unable to give any advice how to improve it, but I love your work in progress, especially variations 1 and 5. Keep on this great work!
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Howard Scarr



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PostPosted: Sat Nov 03, 2007 7:05 pm    Post subject: Re: Good CEM filter simulation Reply with quote  Mark this post and the followings unread

dorremifasol wrote:
the original sound:
http://www.synthmania.com/Synthesizers/Cheetah/MS6/Audio/4%20Sync%2073.mp3


Sounds like sync sweeps only i.e. I don't hear a filter in there (or it's very subtle)
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3phase



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PostPosted: Sun Nov 11, 2007 1:09 am    Post subject: Reply with quote  Mark this post and the followings unread

i once tried to emulate a 101 and a pro one..booth eqipped with the same curtis 3320? filterchip...

i made a few observations...

the classic filter in the nm sounds fucking close to the sci prophet configuration...

in the 101 the same chip sounds very different..thinner but higher bandwith,

i would guess an sci style curtis filter was the model for the nm classic filter... its closer to this one than to any other classic analog filter i know... its so close that it cant be an accident.. i compared one to one with the pro one by having quite propper simulated waveforms as input..
when the sourve waveform is no mathematical correct saw and the level between waveforms are adjusted the same the classic nm filter started to sound pretty much the same as the one in the pro one.
But not quite wright...
what makes it impossible to simulate that very same sound from the 101 or pro one is an extremly high freq range digital systems cant really simulate..
a fast analog envelope on a resonant curtis filter is a real sharp transient... the classical short analog filtersnap cant be propperly simulated with just 96k... at least thats what i learned to belife..please proof me wrong Wink

The nm with its 96k samplerate cant go much above 50k...and you have other intermodulations and control rate limits that makes it diffcult to get this very sharp filtersnaps.
actually i think its impossible...

however... when you just use the classic filter and apply analog saturation after the clean digital nm sound you get very close to prophet style filter sounds.. the nm is very good for beeing externaly proccesed...
when you just play it directly into the soundcard you miss some of the possible quality when going with the nm thru some preamping..
because the sound is so transparent any mudding up just adds colour without the loss of too much details...

a good preamp sometimes can be found for nothing in the mic inputs of a good 70-80 style tapedeck..as older as better...

with such real analog warming all the digital shaped sounds of the nm get
much closer to the analog originals.. exept the extrem freq ranges the nm can sound very close to a cem chip
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dorremifasol



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PostPosted: Sun Nov 11, 2007 5:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Although this is not a Curtis filter, I tried to simulate the behaviour of the Yamaha PLG150-AN card filter, which to my ears sounds very nice.

I couldn't get any closer to it, specially when the resonance and the cutoff are near the maximum level.

Anyway I'll post the filter sweep, may someone find it interesting.


plg150-an filter.mp3
 Description:
plg150-an filter sweep

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 Filename:  plg150-an filter.mp3
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katherine04



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PostPosted: Tue May 19, 2009 9:58 am    Post subject: Reply with quote  Mark this post and the followings unread

that is rather interesting. thank you for sharing. Very Happy
simulation rachat de credit
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Tim Kleinert



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PostPosted: Tue May 19, 2009 12:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh, I had overlooked this thread.

3phase wrote:

the classic filter in the nm sounds fucking close to the sci prophet configuration...

Hey yes, this was my observation too when comparing the G2 and a Rev3 Prophet5 side by side a while ago. The classic filter in conjunction with subtle pre-filter saturation sounded almost identical to the P5.

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dorremifasol



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PostPosted: Tue May 19, 2009 3:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

I own a DSI MoPho now, which has a curtis filter. I'm working (slowly I must say) on a G2 replica of the MoPho. I'll record some MoPho filter sweeps soon to post them here.

The problem with the G2 filters is that they lack high frequency detail. Basically, at high frequencies the resonance is lost or incomplete as if it was abruptly cut off. Also, at low frequencies the resonance doesn't give enough deep sound.

I have done some comparisons to the sounds. I can get the basic waveforms to sound pretty similar (after some EQ), but I noticed that when you play low frequencies in the MoPho, they tend to amplify and distort. However, the G2 always stays at the same level, at high and low frequencies, too perfect.

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fac



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PostPosted: Tue May 19, 2009 5:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

The CEM3396 is not just a filter, but a full synth-in-one chip with two oscillators, VCF and VCA. I know because I own a Matrix 6R which uses those chips.

Anyway... I can also record a few waveforms and filter sweeps with my M6R before I sell it. I just bought a Prophet 08 rack and I'm selling some stuff to finance it (and a Machinedrum). Too bad I already sold my ESQ-1 which is also CEM-based.

The Prophet 08 also uses CEM filters, but those are probably the same as your Mopho.

I also have a dotcom modular with the 12db/oct multimode filter and the 24 db/oct moog filter, and an Electrix Filter Factory. I can record sweeps with all of them.

Anyway, the trick I use to obtain a fuller, more analog sound is to place an overdrive module before and after the filter (besides the already suggested EQ). The Nord Lead 3 has this architecture and I found out it translated pretty well into G2 patches.

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cappy2112



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PostPosted: Tue May 19, 2009 9:36 pm    Post subject: Re: Good CEM filter simulation Reply with quote  Mark this post and the followings unread

dorremifasol wrote:
I'm trying to build a classic synthesizer, based in the Nord lead 2 and others like the prophet or the matrix. The goal is to make it sound as "analog" as possible.

In order to do this I'm following Rob's and many other people tutorials and building blocks.

I also have recordings of various analog synthesizers, like the Matrix 1000 or the Cheetah MS6 (which sounds amazing for my taste).

What I'm missing is a good emulation of the classic filter found in those synthesizers, I think it's named CEM3396.

Now I'm using a ladder filter simulation but I think it's not appropriate.

Here is some work at progress..

the original sound:
http://www.synthmania.com/Synthesizers/Cheetah/MS6/Audio/4%20Sync%2073.mp3

Please let me know if you know how to simulate a CEM filter, thanks!


Not sure if you saw these Albert
The website is acting up again tonight. It took me almost 5 minutes before I could copy that link.

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Tim Kleinert



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PostPosted: Wed May 20, 2009 1:32 am    Post subject: Reply with quote  Mark this post and the followings unread

dorremifasol wrote:

The problem with the G2 filters is that they lack high frequency detail. Basically, at high frequencies the resonance is lost or incomplete as if it was abruptly cut off.

Yes, this is unfortunately inherent in the design. Discrete time feedback loops (like filter resonance) become unstable as they approach ca. 1/8 of the system frequency. On the G2, this would equal 12kHz, which is still within the limit of human hearing. The only solution is either to perform oversampling on the filter algorithm (the G2 filters don't), or to roll off the feedback amount as the filter frequency approaches this limit. Which is what most digital filters in synths do.

Remember that most digital synths run on 44.1 or 48kHz. They all have to oversample the critical processes. Compared to those, the G2 actually oversamples 2x all the time.

One of the simplest things to get a more authentic (I hate to use the word "analogue" anymore) feel of the G2 filters is to turn gain compensation (GC) off. You get a more satisfying tactile feedback (pun? Laughing) when tweaking resonance, and the filter also performs more authentically when it sweeps over harmonics, as there isn't any of that artificial-sounding GC-compression going on. Obviously you then have to be more careful with overloading the circuits. But that's one basic thing that makes alot of difference IMHO. They should have left GC off as a default IMO. YMMV.

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dorremifasol



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PostPosted: Wed May 20, 2009 6:05 am    Post subject: Re: Good CEM filter simulation Reply with quote  Mark this post and the followings unread

cappy2112 wrote:

Not sure if you saw these Albert


Yes I know this excellent patch. It has a very good CEM filter emulation! This topic is much older than the patch from FlowerP.

tim wrote:

Yes, this is unfortunately inherent in the design. Discrete time feedback loops (like filter resonance) become unstable as they approach ca. 1/8 of the system frequency. On the G2, this would equal 12kHz, which is still within the limit of human hearing. The only solution is either to perform oversampling on the filter algorithm (the G2 filters don't), or to roll off the feedback amount as the filter frequency approaches this limit. Which is what most digital filters in synths do.


What a good explanation! Now I understand completely. I also noticed that the SAW harmonics are cut somewhat abruptly at the high register. I suppose it's for the same reason. The Nord Lead 3 sounds much more natural and has a better high register, despite its lower output frequency.

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dasz



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PostPosted: Thu May 28, 2009 10:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
One of the simplest things to get a more authentic (I hate to use the word "analogue" anymore) feel of the G2 filters is to turn gain compensation (GC) off. You get a more satisfying tactile feedback (pun? Laughing) when tweaking resonance, and the filter also performs more authentically when it sweeps over harmonics, as there isn't any of that artificial-sounding GC-compression going on. Obviously you then have to be more careful with overloading the circuits. But that's one basic thing that makes alot of difference IMHO. They should have left GC off as a default IMO. YMMV.


Tim, I wholeheartedly agree about this point. I have barely used GC, only for bleeps and spacy sounds, but not for bass or pads ... I am so used to to overdriven filter sound, it in fact I have become used to it.

Having said that, I'd be curious about how we could keep GC off, having a conistent input going into the filter, with no distortion at high resonance settings?

---

Perhaps if I put a Band reject filter before it .. and fade between a normal and bandpassed signal if the resonance is high ... hmmm

I just went off and patched this all and attached the patch (which works in the demo too).

...

I noticed that playing with the resonance of the bandpass either dulls the low pass's resonance or makes it bigger, whereas if I turn the xfade mod (essentially deciding how much bandpass I want to use gives you more spikes and essentially distorts the resonance) ...

I'm pretty happy with the results ...

I also added some dithering when the osc is near it's peak (this may be wrong) ...

Your thoughts?
/Dasz


auth_filter.jpg
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auth_filter.jpg



Auth_Filter_DZ.pch2
 Description:
"authentic" filter ... NO built in Gain Comp, just a more frequency based one (using bandpass) ... enjoy!

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 Filename:  Auth_Filter_DZ.pch2
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dasz



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PostPosted: Thu May 28, 2009 3:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

and I just added the same sequence to control my x0xb0x and blofeld.

so here is an mp3 of the 3 playing. they are playing in the following order,

g2 synth with filter, x0xb0x, blofeld.

It is interesting, but I am really fond of the g2 filter, when run side by side with the x0xb0x or blofeld, bot which sound a bit thinner (but this could the AD converters in the g2 since this patch is also mixing the x0x0, and blofeld + internal sound)

the bd is g2
/Dasz


g2 diy cg bandpass, x0xb0x, and blofeld 303 Filters.mp3
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 Filename:  g2 diy cg bandpass, x0xb0x, and blofeld 303 Filters.mp3
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