1n4148's istead of 1n34a's in "Flatline" will they work? ..how might they effect the sound?
Here is the layout http://aronnelson.com/gallery/bcreekmur/flatline_compressor (http://aronnelson.com/gallery/bcreekmur/flatline_compressor)
They will reduce the amount of "drive" to the LED, which will result in lower illumination and less change in the resistance of the LDR. On the other hand, it is a simple matter to get higher brightness LEDs that don't need quite so much drive to shine nice and bright.
I would think there's a bit of a thresholding problem as well. The LED will be dark until the output level of the first opamp and the output of the second opamp is different by .2x2 + LED drop. With 1n4148s this level is going to be .6x2 + LED drop. So the output level of the opamp will have to be run higher to compensate resulting in less headroom, less 'sustain' adjustment range.
--john