[PD] bandpass or resonant?

Scott R. Looney scottrlooney at gmail.com
Wed Jan 14 04:09:13 CET 2015

hey there - just to offer my armchair two cents on the subject...

i am definitely no electrical engineer  but to me Q, resonance and
bandwidth are basically the same thing. this is commonly found in
parametric EQs - there's not a lot of difference functionally between a
fully parametric one band EQ (with gain/cut, frequency center and Q) as
compared to something like a bandpass filter on a synth, although synth
filtering is generally covering a much wider range to achieve a lot more
sculpting possibilities, whereas mixer parametric bands are more limited in

the difference to me between a bandpass filter as traditionally applied in
synthesis and a resonant bandpass filter is the additional setting of
resonance basically. this acts as a bandwidth control which makes the peak
more and more pronounced. in a synth a standard bandpass filter would
usually have a single control for frequency, while the bandwidth and gain
would be preset. adding a resonance/bandwidth control narrows the range of
the band and eventually at high settings it can self oscillate. but the
main issue is i believe the same mathematical /signal principle is
involved, it's just that at low settings it sounds more subtle and high
settings more dramatic.

however since synth filter design is a bit of alchemy, i personally
wouldn't be surprised to see unusual methods applied in the process to
create a more robust sound, like ganging up bands, or possibly offsetting
the resonant peak as compared to the center frequency. i'm totally guessing
but i'm curious what things synth companies do or did to create their warm,
fat sounds that still sounded different from maker to maker - even later on
when they were using chips like the Curtis filters.


On Tue, Jan 13, 2015 at 3:02 PM, Tilo Kremer <pd at dadacafe.org> wrote:

> Hello,
> On 13.01.2015 04:20, Martin Peach wrote:
> > I was looking at circuit diagrams for analog synthesizers recently and
> > noticed that the "resonance" control is nothing more than feeding some
> > fraction of the output back to the input. With more feedback oscillation
> > occurs at the cutoff frequency for any type of filter, highpass, bandpass
> > or lowpass.
> >
> > Martin
> when i asked about the difference between the meaning of 'Q' in
> filters regarding a parametric EQ on a mixing console and the
> 'Q'/Resonance knob on [analogue synthesizer] filters, i was given an
> explanation along the lines of 'Q on a parametric eq will adjust the
> bandwith of the filter while the Q / resonance knob on the other one
> will adjust the amount of the feedback [back into its input]. Both
> however will have a similar impact:
> Reducing the available bandwith will lead to similar results as
> increasing the amount of "data" in the system.'
> hope that isn't too simplified, if it is, i recommend watching Aaron
> Lantermans lectures on filters on the web.
> hth,
> Tee
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