Signal level standards

[jorgen.bergfors at idg.se]

I'm sure this has been discussed before, so I hope you don't mind that I bring 
it up again.
I need to set the standard for the signal levels in my synth.
Barry Klein's book suggests that audio signals are +/-5 volts peak to peak and 
control signals are 0 - 10 volts. But what about LFOs? They are control 
signals, but isn't it more practical to have them swing symmetrically (no DC 
offset)? Maybe it would be better to standardise on +/- 5V for all control 
signals? But then a VCA would be half on if you don't connect an EG to it. 
Maybe that isn't a bad thing? Then you could plug in an LFO and make tremolo 
without problems. But on the other hand it would mean that things start to make 
noise as soon as you unplug things. Not good, I suppose.
Another thing I'm pondering is how much headroom to provide. If the audio 
signals are +/- 5V p-p, I assume that the inputs ought to take some more than 
that before clipping. Is clipping at +/- 7,5 volts a good margin? I want to 
minimise noise, so I don't want more headroom than necessary.
Some synths (the Format for instance) seem to use 0 - 5 V for contol signals 
and +/- 2,5 V for audio. An advantage with this is that you can run 4066s on 
+/- 5 volts.
What do you say? What do the ASM-1 people use? Others?

/Jorgen