I. Dynamics. My number one key production technique (especially for orchestral
mockups) is dynamics.
A) Timbre change vs. Decibel Change: If you want the most realistic
mockups it's vital to understand how to control timbre change and understand how it's sounding compared to real orchestra. If you aren't already using a sample library that allows you to
crossfade between different dynamics layers it's time to start.
VSL, Sonic Implants, project SAM are all excellent examples of sample libraries that utilize this function. This is especially important on sustain sounds and doesn't apply to staccato type patches. Using volume (decibel level) to change dynamics should be used exceedingly sparingly and only as means to realistically balance timbres.
B) Curve shapes: Parabolic Vs Straight lines. Better than even playing in dynamics is programing the curves properly. It's very important to be exacting. Again it's important to have the sound of the orchestra in your ear as you compare your dynamics to the real thing. Often times parabolic curves of varying degrees are more affective.
C) Timbrel balances vs Decibel balances. One of the worst things you can do is have
cuivre (brassy) brass that is mixed way too soft compared to the other no
cuivre sounds. To produce a brassy sound is synonymous with playing loudly (in all but the rarest of instances). This even applies to other instruments but it's most noticeable on the brass since they have the largest timbre change when they play louder.
D) Wrangling staccato patch problems: I hope most of you have discovered the joy of staccato patches, unfortunately, they are some of the most poorly programmed instruments in most libraries. In terms of dynamics there are often big gaps between different dynamic layers. There is no easy solution to this but being aware of the problem is part of the solution. What I usually do is test each layer and see what the different tonal characteristics are - often I'll stick between two layers that are close enough to not be noticeable and use DB volume often controlled in part by velocity (okay in this case) to create more dynamics. It's also very important that you are using alternation patches and/or using varied velocities to avoid the machine gun effect.