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 Forum index » Instruments and Equipment » General Discussion
Filter FM
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JovianPyx



Joined: Nov 20, 2007
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PostPosted: Wed May 25, 2011 11:54 am    Post subject: Filter FM
Subject description: What is it?
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I hope this is the appropriate forum to ask this question:

First, I develop FPGA (hardware, digital) synthesizers as an avocation using various DSP techniques.

I am always looking for new and interesting ways to make sound and recently on another forum I read about "Filter FM".

I've used oscillator FM (for bells mainly) and I would like to know exactly what is Filter FM? I can see that it might take various forms such as using a filter as a sine wave oscillator and FM-ing it like any other oscillator. Or one could feed an oscillator like sawtooth into a filter (used say as a bandpass) and modulate the filter's frequency input with a second oscillator. There are probably other ways I'm not thinking about, so if someone(s) can enlighten me, I'd be grateful.

I'm also interested in what kinds of sounds can be made with filter FM?

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Wout Blommers



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PostPosted: Thu May 26, 2011 1:21 am    Post subject: Re: Filter FM
Subject description: What is it?
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JovianPyx wrote:
... I'm also interested in what kinds of sounds can be made with filter FM?
If you like to experiment the effect of Filter FM, download the free software version of the G2 Demo at Clavia's site:
http://www.nordkeyboards.com/main.asp?tm=Products&clpm=Nord_Modular_G2&clnmm=Information
In the Filter section there is the NordFilter capable of FM linear.

Try it out Smile

Wout
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Wout Blommers



Joined: Sep 07, 2003
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Location: The Hague - The Netherlands
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PostPosted: Thu May 26, 2011 1:38 am    Post subject: Reply with quote  Mark this post and the followings unread

An example...


FilterFM.jpg
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FilterFM.jpg



FilterFM.pch2
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JovianPyx



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PostPosted: Thu May 26, 2011 1:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, thanks Wout ... as you will no doubt see from my reply, I am not a G2 guy... I will see if I can try the demo anyway to hear what this does, but I may or may not understand what this patch is doing... Here is what I see:

OscA2 out feeds a saw wave to the filter input which is set to lowpass 24 dB per oct, so it's a pretty steep falloff filter (4 pole).

keyboard triggers EnvD1 which controls the level of saw OscA1 the output of which feeds filter modulation inputs FM Lin and Res. "FM Lin" I assume to be Fc without Expo prescale or linear and "Res" would be the filter's Q.

Both OscA1 and OscA2 track the keyboard, but I can't really tell whether they are related harmonically or not.

The filter output is amplitude modulated by EnvADSR1 which is sent to both stereo R and L channels (mono).


It's important that I understand the structure or I won't be able to create this in an FPGA.

I also assume that one can mess with things like the waveform, harmonic relationship between the oscillators, levels of modulation et al.

How close am I?

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Blue Hell
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PostPosted: Thu May 26, 2011 1:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
Both OscA1 and OscA2 track the keyboard, but I can't really tell whether they are related harmonically or not.


12 semitones apart.

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Jan
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JovianPyx



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PostPosted: Thu May 26, 2011 1:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

OH! Thanks Jan, now I see on #2 is 0 and #1 is -12 in the little box. Got it. But the pitch knobs are different... does the pitch knob do anything with this config?

Also, does the demo work for Win XP?

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FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.
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Blue Hell
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Joined: Apr 03, 2004
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PostPosted: Thu May 26, 2011 1:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
does the pitch knob do anything with this config?


no, its an attenuater for the unconnected input to its left.

Quote:
Also, does the demo work for Win XP?


Yes.

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