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Threshold control for simple compressor?

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Hello all! I am planning on at least trying out this circuit:

Opto-electric compression circuit

Having tried a similar basic optical compressor in the past I realise I quite like thier sound (mainly for drums), more than my VST effect compressors anyhow! Even if they arn't very "Hi-Fi", or perhaps it is, afterall it only goes through a low distortion volume element and a few good quality op-amps?

Anyhow, I got thinking about an effective threshold control which the circuit currently lacks. I post my musings here!

My additions can be seen at the bottom, ignore the indicator (red) LED for now! My thinking is that the diode string (and inherent LED voltage drop) require a fixed level to overcome. The resistor chain at the buffer op-amp's input provides a means to add a DC offset up to the point of overcoming this overall drop. This will allow threshold levels to be changed from very high threshold (only compression of large transients) down to low threshold (compression of nearly everything!).

Any thoughts? I was concerned the circuit would add a lot of distortion but then I don't see why as the LED won't suddenly kick in after the threshold level, it will just begin lighting at that point. Asymmetric signals will suffer worse but this shouldn't be a problem. Is the 4.5v or so drop excessive for audio signals? I am fairly certain this control has a different effect to that of the compressor circuit's gain control (R11)?
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