It's based on the implementation found in the The Art of VA Filter design by Vadim Zavalishin, a #DSP engineer of native instruments and creator of Reaktor.
I've uploaded a sample of what it sounds like when you use it to filter noise. Because it's only 1-pole, it sounds an awful lot like gain control.
1 1 sine 100 1000 biscale
"valp1.wav" wavout bdrop
sr 20 * _compute rep
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