Tonepad Ross Compressor question

[Barcode80]

so I was missing a few part values for the comp, but i got reasonably close by parallel resistors and such. all i have left to solder in is the diodes and i go to get them from my kit... OH NO! i'm all out of 4148's. so my question is, what function do the diodes serve in this circuit and could i possible sub in 4005 or 4007 or 4004 in the place of the 4148?

[Mark Hammer]

The diodes serve to separate the two half-waves of the input signal from each other.

If I was to take a sine-wave and invert it, the inverted version would have its positive peaks where the negative peaks occurred for the noninverted version, right? (Inverting makes everything the opposite).  If I used a diode to only let the positive peaks through for the two copies (inverted and noninverted) of the input signal, and combined those copies, then I would have twice as many positive peaks as I started out with, and NO negative peaks.  Voila!  Full-wave rectification.

The diodes in the rectifier circuit used by the Ross, MXR, CS-2, and so many other pedals essentially dumps one half cycle to ground.  In theory, the lower a forward voltage the diode has (e.g., schottky of GE diodes), the more of that unused half-cycle gets dumped, and the higher the forward voltage (e.g., LEDs), the less gets dumped.  Power diodes like the 1N4001-4007 will "work", though perhaps not exactly as well as the 4148 or 914, I gather.  The tiny glass silicon types typically have a forward voltage of 500-600mv, where the 1N40xx type can have forward voltages of up closer to 1V.