How can I sonically get the most out of Sigma?
As with all SSL consoles, Sigma has a sweet spot where the SSL sonic character is most pronounced. This is achieved by pushing the mix bus, or buses, slightly hotter than usual such that a small amount of harmonic distortion and compression is introduced into your mix. This sonic character is a subjective matter that may not be to everybody's taste so these are guidelines only for experimentation purposes.
To hit the sweet spot of Sigma it is recommended to:
1 - Keep your DAW outputs as high as possible before clipping. This is recommended to keep your signal to noise ratio at its optimum anyway. Using DAs which operate at +24dBu as Sigma does will yield the best results here.
Tip: Using a small amount of brick wall limiting on your DAW output buses on transient signals can allow you to achieve higher output levels.
2 - Keep the Sigma faders at 0dB or above.
3 - Reduce the level of the mix bus, or buses, to avoid clipping your ADs on the way back into the DAW for printing your mix.
This way of operating sends a high signal level into the Sigma mix buses where there is a large amount of available headroom, and subsequently attenuates the mix bus to bring the mix back into a normal operating range.
You could, for example, use this technique on only mix bus B which is subsequently feeding mix bus A, so you can select which signals you would like to benefit from this effect by routing them to mix bus B. By keeping the master mix bus A in a more conservative operating range you can route signals that you wish to remain 'clean' directly to mix bus A.