Inverse env noise (bug?)

When setting an inverse envelope (on either layer, see images), when the envelope dips to it’s lowest point, there is a hissing noise and the envelope cuts out and back in pretty abruptly. Also the env led doesnt seem to show the env being generated.

Reproduce: Set an envelope as in my images, press a key and hold it until it happens, then release to let sound back in.

Edit: Im using headphones, it seems like maybe this is the noise floor being amplified at the quietest part of the env as it can be made to fade out with the decay. Does the SG have a compressor or something similar built in that could account for that? My power is not particularly clean (110v in US).

Lowering the filter completely still produce the hiss in the same manner.

Enabling binaural mode adds a distinct stereo quality to the hiss, Im guessing this is grounding noise.

@udo-audio does the env pause or something else when it hits the bottom? This noise is not present otherwise in the synth, it’s dead quiet the rest of the time, even with the master vol cranked theres barely a hiss.

Setting a high negative envelope that tries to force the cutoff freq to sub audio levels can push the bias control current of the SSI2144 analog filter below the threshold of stability and produce unpredictable results. This is a normal analog “quirk” of the filter IC described in the data sheet. By assuring the cutoff is never forced too low (generally only possible with negative envelope) you can avoid it.

Thank you for the quick and detailed answer! Im guessing using a negative envelope will have more of a learning curve.

Im going to assume its not a chip thats out of spec as each voice does this quite predictably in the same manner on the same setting.