I'm not aware of any commercial opto compressors that actually use light bulbs, can you elaborate on that (just curious)?Edit: so yes, a slow lightbulb opto might superficially act RMS-ish, but it depends on how quick the light source is and what kind of photosensor it uses.
If you used a fast sensor and an optical fibre it would be as fast as peak.
The T4 cell in an LA-2A (and its variants) use an EL foil. That one is operated at high voltage (which is there anyway because of the tube circuitry for the drive/makeup amp and the metering). EL panels are what are also used as LCD backlights. Their response is instant.
[Their fist use was probably in military equipment (aircraft displays), as they're extremely consistent and durable. They don't erratically burn out like bulbs, they just get darker over time.]
In theory you could replace an EL foil with an LED and and the overall response won't be faster. The magic is in the LDR, which acts as program-dependent voltage divider. And which includes 'memory'. Unlike pure RMS math, the LDR can actually start reducing its resistance quite fast (as functional of photoconductance/(valence-electron flux if I recall correctly)). But once you keep on applying more and more light, flux saturation kicks in, creating inertia. Short transients can make it recover quickly (increase resistance), but prolonged exposure or - speaking of audio - especially ever-changing signals make use of the memory effect.
In contrast, RMS is a well-defined window that won't enlarge or collapse with varying load.
You can check that with an opto compressor (or emulations thereof) by applying burst signals of increasing length; program-dependency will reveal itself with a change in release time but also how the attack gets handled when it's not just a short spike, and also when such a sequence of burts is repeated multiple times in series.
Statistics: Posted by sascha — Wed Jul 10, 2024 2:27 pm
