When the note gate is low, the filter resonance will be too low to support oscillation. When the gate goes high, the filter will begin to self-oscillate, but will take some time to reach its full amplitude. The patch shown below implements this idea. We use the E-filter, as this provides a control input for the resonance level. Resonant filter resonance controlled soft attack patch.
Resonant filters can also make good sources of drum sounds.
The following patch shows this. The resonance is set to a fairly high level and the filter input is connected to a pulse derived from the note gate. The pulse causes the filter to ring. The higher the resonance level, the longer the ringing period. The filter rings for longer times at low cutoff frequencies than at high, so we adjust the resonance level with the note output to compensate.