Automatic attenuator

I have a lighting device, that reacts to sound (vulgarly called psichedelics). Now my biggest problem is that, from the preamp, not all songs come out at the same level. The light console has a pot (it is homemade) in series with the input, to attenuate the level. What i could use is some sorf of circuit, with a manually selectable threshold, that automatically starts attenuating the signal when this same signal goes above the threshold. I looked at limiters and compressors, but for what i understood these do not apply to my case: the compress the dynamic range, something i want to avoid. I want to apply the same attenuation to all the signal, just to maintan the same mean value. I hope i have stated it clearly enough. Anyone can help me? Thanks Claudio