Use The Random Function; Also Use Some Keytracking Modulation To The Vcos; Use Sample And Hold To Produce A Random Modulation On The Oscillator; Use A Slow Random Lfo Waveform - Alesis Andromeda A6 Tips And Tricks Manual

18.2 use the random function

The oscillators are the key places where you want a little " drift" to occur. Producing slight
detunes per note creates a feeling that the synthesizer is " a live" .
Usage: click one of the modulation buttons (such as Mod 1). Set the modulation source to
" Voice Random" . Set the modulation destination to " Frequency" . Adjust to taste.
On oscillators, I usually think – 0 .05 to 0.05 is good for moderate randomness; -0.20 to 0.20 is
a heftier range that is good for serious beef. If you aren' t using Sample and Hold, you may
want to consider the technique below – it works much better, especially in combinations.
If you are really picky, you might want to consider using random on other functions. Stick
voice randoms on any blank modulation you have to cream up the sound. 

18.3 also use some keytracking modulation to the vcos:

Colin suggested that a value of 0.01 for VCO 1, and – 0 .02 for VCO 2, might be nice to add
some warmth and " instability" to the pitch tightness at the top end. This should add a little
" cream" to the top, and perhaps eliminate some phase problems.
18.4 use sample and hold to produce a random modulation on the
oscillator.
A further way to get some great drifting noises was posted by Colin on the Andromeda mailing list:
I dunno if anyone has tried this but it works great -
Sample and Hold - input Voice random level 100 offset -50
Trig - Vox Key on Vel, enable, trigger sample on
Mods for VCO 1 - Sample and Hold +0.03 offset +0.01 to Frequency
Vox key Number +0.02 to Frequncy
Mods for VCO 2 - Sample and Hold -0.03 offset -0.01 to Frequency
Vox key Number -0.02
I have found that by using various combinations of these techniques, you get a real " 7 0 s
vintage" type of sound that doesn' t go out of tune. A combination I used was voice random
at 0.17 on one VCO and sample and hold at – 0 .05 on the other. This is a heavily detuned
patch with the two different techniques being played at once, but always is a recognizable
note.

18.5 use a slow random lfo waveform

This technique involves setting an LFO to the " Random" waveform, and then modulating
oscillators etc. with it.
From Brian Kehew:
Don't forget each LFO's Slow Random "waveform": It is very organic feeling (the rate actually affects
it, play with that) and that slide from step to step (instead of the jump on a S/Hold) is great for pitch
drift and acoustic character... AND you have a bunch of them, all different!
I like the Sample/Hold for stuff like Voice Pan or Filter settings that vary per key. I think the Slow
Random LFOs are better for simulating "old" and "organic". It's a very cool output on the eMu
modular Noise module, and I was OVERJOYED to find it on the A6's. These guys did their
homework.