Re: [music-dsp] SVF and SKF with input mixing

[Vadim Zavalishin]

The SVF transposition can be done in continuous-time domain (where the 
filter is basically two integrators in series, both feeding back to the 
input). Then, applying the trapezoidal integration/ZDF techniques we 
obtain a multi-input 2-pole SVF.


Obviously, the same technique can be applied to any other linear 
multi-output filter, where in principle the transposition doesn't need 
to be applied on all levels of the filter. E.g. for a multimode 
transistor ladder we could handle the underlying 1-pole lowpasses as 
atomic blocks and not transpose them internally (although I'm not sure, 
whether their transposed version is not identical to the original ;-) ).


Things can get less straightforward, once nonlinearities are involved.

Regards,
Vadim

On 06-Jan-15 14:30, STEFFAN DIEDRICHSEN wrote:

Actually, it’s an interesting filter.
BTW, if you transpose Chamberlin’s SVF, you get a similar filter with HP/BP/LP 
inputs and a common output:

Out = HP + f * (BP + Z1)
Z1 +=  BP  - Out * q + f * (Z2 + LP - Out)
Z2 +=  LP - Out

f: frequency  coefficient
q: Q factor coefficient
Out: output
Z1, Z2: state variables
HP, BP, LP: filter inputs

HNY!

Steffan


On 05.01.2015|KW2, at 14:19, Andrew Simper a...@cytomic.com wrote:

Thanks to the ARP engineers for the original circuit and Sam
HOSHUYAMA's great work for outlining the theory and designing a
schematic for an input mixing SVF.

Sam's articles-
Theory: http://houshu.at.webry.info/200602/article_1.html
Schematic: http://houshu.at.webry.info/201202/article_2.html

I have taken Sam's design and written a technical paper on
discretizing this form of the SVF. I also took the chance to update
the SKF (Sallen Key Filter) paper to more explicitly deal with input
mixing of different signals, here they are in as similar form as
possible:

http://cytomic.com/files/dsp/SvfInputMixing.pdf
http://cytomic.com/files/dsp/SkfInputMixing.pdf

As always all the technical papers I've done can be accessed from this page:



--
dupswapdrop -- the music-dsp mailing list and website:
subscription info, FAQ, source code archive, list archive, book reviews, dsp 
links
http://music.columbia.edu/cmc/music-dsp
http://music.columbia.edu/mailman/listinfo/music-dsp



--
Vadim Zavalishin
Reaktor Application Architect
Native Instruments GmbH
+49-30-611035-0

www.native-instruments.com
--
dupswapdrop -- the music-dsp mailing list and website:
subscription info, FAQ, source code archive, list archive, book reviews, dsp 
links
http://music.columbia.edu/cmc/music-dsp
http://music.columbia.edu/mailman/listinfo/music-dsp

Re: [music-dsp] SVF and SKF with input mixing

[STEFFAN DIEDRICHSEN]

Transposed filters have identical transfer functions, but differ in terms of 
rounding noise and coefficient quantization. 

In case of nonlinearities, it’s difficult. A typical non-linearity is the Diode 
circuitry to “un-damp” the filter, which can be seen as a voltage dependent 
voltage divider. In the original arrangement, like the SEM filter, it depends 
on the BP out, but if you transpose it, this output is lost. I’m not sure, if 
you get the same properties distortion wise after transposition. However, the 
analog input mixing filters will sound differently from  a standard SVF, too. 


Steffan 


 On 06.01.2015|KW2, at 14:40, Vadim Zavalishin 
 vadim.zavalis...@native-instruments.de wrote:
 
 (although I'm not sure, whether their transposed version is not identical to 
 the original ;-) ).
 
 Things can get less straightforward, once nonlinearities are involved.

--
dupswapdrop -- the music-dsp mailing list and website:
subscription info, FAQ, source code archive, list archive, book reviews, dsp 
links
http://music.columbia.edu/cmc/music-dsp
http://music.columbia.edu/mailman/listinfo/music-dsp