ExpandBuf.sc (sc2)
arguments:
input, bufferDuration, playback rate (100% clean only with rate 1), recording gate

usage:

//strictly deflating - records when crossing center horiz of screen
Synth.scope({

var e, in, gate, scrub;
gate = Lag.kr(MouseY.kr(-1,1), 0.3);
in = SinOsc.ar(LFNoise0.kr(1, [10.0, 10.0],[252, 251]), 0, 0.1);

ExpandBuf.ar(in, 3, 1, gate);

});