At 11:35 AM -0400 10/19/01, Tkacs, Ken wrote:
>
>A lot of early analog drum circuits used cheapie filters with high
>resonance. The effect you're describing is a damped oscillation caused by
>the filter 'ringing,' and by tweaking the filter component values, you can
>get all sorts of drum sounds.
>
>I think PAIA had/has a board that lets you play with this kind of thing.
Exactly :) Roland calls it a "periodic damping oscillation". The circuit
looks like a filter (in the more general sense of the word -- it's not a
VCF) as it has an RC network in the feedback path of an op-amp. It has two
parallel elements in the feedback path: a resistor; and a T-network
composed of two caps (parallel to the afformentioned resistor, and in
series to each other) with a second resistor between the two caps going to
ground.
I wouldn't want MOTM to make anything "cheapie"!! However, I'm thinking
this damped oscillation idea could be incorporated into a more
sophisticated "trigger to audio converter". Perhaps 1U, with trigger in,
audio out, and a couple of VC inputs.
I'm no EE, I'm just throwing around half-baked ideas :)
> For drums, the TR-808 uses a "bridged T-network" in order to create a
>waveform similar to an oscillator decaying in amplitude. Rather than using
>the trigger to trigger EG's controlling separate VCO's and VCA's as in the
>606 and 909, it seems the trigger itself is transformed into the sound. In
>my limited understanding, it's like a VCO that runs out of steam. Like the
>skin of a drum, it oscillates after being hit, then tapers off into
>silence. For the 808 toms, this circuit is modified with diodes such that
>the frequency decays as well. Perhaps this technology could be rolled into
>a MOTM module with increased flexibility such that it could produce more
>than just drum sounds.