ExtensionBand limited impulse generator based on B-Spline interpolation of order 3, integrated to create a sawtooth waveform.
| freq | 
 Maximum frequency is a period of 4 samples, so a quarter of the sampling rate. You may start to hear aliasing over 5000 Hz or so, otherwise perceptually indistinguishable from an analog waveform.  | 
| leak | 
 leaky coefficient. 0 would give back the impulses, higher numbers (up to near 1.0) fill out the inter-impulse space, integrating the waveform.  |