[sdiy] Roland TB-303 filter responses graphed
kmkennedy at gmail.com
Wed Oct 21 02:16:22 CEST 2015
Love the 303! Thanks for posting the info.
On Tuesday, October 20, 2015, Richie Burnett <rburnett at richieburnett.co.uk>
> For anyone interested, this graph shows the response of a real TB-303
> filter set at full resonance for a range of cutoff frequencies:
> There are lots of theoretical responses, mathematical transfer functions,
> and simulation results on the net, but i've never seen any real measured
> responses before.
> These responses were generated at the same drive level that the sawtooth
> VCO drives the filter in the TB-303. (The shape changes if the drive level
> is changed.)
> Notice how the resonance is much stronger at higher frequencies, and runs
> out of steam at low cutoff frequencies. The little peaks and dips to the
> right of the normal resonant peaks, are due to harmonic distortion in the
> filter and the VCA that follows it in the TB-303. Also notice how the
> actual resonant peak of the TB-303 has a steeper slope on the right side,
> than the left side when the Q is high. This "lop-sided" resonance is
> another artefact of the filter's non-linearity and occurs naturally in
> mechanical resonators as "hardening".
> Hopefully this is interesting to some TB-303 scrutinisers.
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