Filter Percussion



Creator's Website

Creator's description

A ringing filter
electronic drum

Picture (Click to enlarge)



DSP Usage:

Coming soon

Signal Flow:



Some new presets

Samples: Coming soon

This is one of the new patches released by Creamware for the launch of the new look website. 


It's a very simple patch, which uses a filter to create some percussive sounds. 

Thanks to Paul van der Valk for the Signal Flow diagram.


The DVC module triggers two AD Vintage envelope generators,  let's call them AD1 & AD2.

The output of AD1 is fed into the 24db Lowpass filter, and at the same time it is used to modulate the cutoff frequency of the filter. 

Meanwhile the AD2 is also used to modulate the cut off frequency of the filter.

The output of the filter is passed to a 6db Gain module, then to a Linear VCA and out to the Audio outs.


What is actually happening is that the envelope, even though it's not an Oscillator, generates a tiny Pulse when triggered. This is sufficient to 'kick start' the Filter into self-oscillation.  


The stock presets are for 'realistic' percussion sounds. Most of mine are far from realistic - watch your speakers with some of these!  If you listen to some of my presets, you'll hear much more clearly how the filter is self-oscillating.


By the way, this patch uses a DVC module - this means that it will only 'respond' if you hit Middle C. Don't be surprised if none of the other keys seem to work!




Below you'll find some more information about the 'theory' that makes this patch work (Thanks, again to my mentor Paul van der Valk for this info) :


This patch makes sound with a high resonant filter. It's resonance level is set to somewhere below self-oscillation level. This means that the filter can oscillate for a while, but only with the aid of an external impulse. So far so good.

This external impulse must consist of a sudden level change of the input signal a.k.a. steep slope. Feeding it just a DC offset or a gradually changing value is not sufficient to make it oscillate. This basically explains the entire behaviour of the patch.


Example 1: if you take a clave or bass drum patch, and change the attack slope to 1 second, the result is a clave/bd that plays 1 second too late! The attack slope is silent, but then at the decay stage there is a steep slope downwards wich counts as an 'energy pulse'.


Example 2: after selecting your first preset: 'blip', it does very little the first time you play it. The attack slope is silent. But once the envelope is loaded up and you trigger for a second time there is an energy pulse because the envelope gets reset from some level back to zero.


Such filter behaviour is natural and equal to analogue synths, and CW have managed to emulate the behaviour of 'real' analogue synths here.


Q: Shouldn't an envelope be 'silent'?

A: As for an envelope by itself being silent: this is not true. If the envelope has any steep slopes it will be audible as a (nasty) click.

The fact that 'anything below ~20Hz is inaudible' applies only to sine waves, which have no edges at all. Any waveform with some edge is audible as (a series of) click(s). So, an envelope (or any low frequency signal for that matter) with some edge in it, generates audible impulses. So again, the CW envelope implementation is very accurate


Actually, you can verify the energy-impulse-on-steep-slopes by feeding the filter input in the FilterPerc patch with a multi LFO. A saw wave generates 1 impulse every cycle. A block waves plays twice

as fast because is has 2 steep slopes (!) and the Sine wave is silent. The triangle wave is somewhat of an in-betweeny. It has strictly spoken no sudden changes in level: the deltas (current minus

previous value) are small. But the shape is sharpish when it goes from hi to low and vice versa. This counts as 'impact'. In the real world this can have a better effect than in a DSP implementation, because DSP code is likely to work with those delta values in filter code. (when using a triangle LFO on the filterperc patch it does nothing, but it may have some effect on an analogue synth).


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