What is the difference in effects between “volume” and “expression” in Logic’s automation? When might I choose to use one over the other?
Thanks for your insights.
Chris
CC7 (volume) and CC11 (expression) is in most cases the exact same thing. I hardly ever use CC7 at all.
Unless Logic specifically is doing weird things, the definition of the MIDI CCs (7 and 11 in this case) depends entirely on the synth/instrument that is used. The DAW literally just sends the numbers into the plugin, or (in the case of hardware) out the MIDI wire.
Generally speaking, CC7 will effectively be a straight gain control in the final output stage of the plugin, much like the fader in the mixer. It should not affect timbre or anything like that. (Unless you use non-linear effects later in the chain, of course.)
CC11 will typically have the same effect as CC7; essentially an additional volume control, but implementations can vary. Generally, CC11 is intended for when the dynamic range of CC1 is not enough. Most orchestral sample libraries won’t do niente in actual samples, though some have a switch to “fake” it via CC1, but if you don’t have that, CC11 might work.
There is a big difference between volume and expression. Expression deals with the intensity played. More vibrato. Volume is the same expression only softer or louder. I use it a lot in my strings bundles like Hollywood en Native.
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That would be implementation dependent - as I mentioned. In most libraries I use (Spitfire, 8Dio etc), it’s CC1 (modwheel) that’s the actual expression control, whereas CC11 is basically just an extra volume control, which does not affect sample layers or anything like that.
So, in short, regardless of DAW, you need to find out how each instrument/library responds to the respective CCs. Unfortunately, there is only a partial de-facto standard for this.
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[Thread derailed slightly, but I’m leaving this part, as it’s a good example of how this differs between libraries/virtual instruments.]
From the Hollywood Strings manual:
EWQLSO responds to two different volume controllers: CC7 (volume) and CC11 (expression).
OTOH, it’s very unclear what CC11 is actually doing. On 'Niente" instruments:
For those in the Powerful System folders (2 and 8): As is described elsewhere, these patches
use CC 11 (Expression) to cross-fade dynamics and CC 1 (the Mod Wheel) to cross-fade
the depth of the vibrato. What is different about the “Niente” instruments is that CC 11
not only cross-fades the dynamic layers, but it can also bring the volume all the way to
zero when the value of CC 11 approaches zero.For instruments in other folders (1, 5, 6, and 7): Because these instruments are smaller, CC 1
(the Mod Wheel) controls the cross-fade of both vibrato and dynamics at the same time.
CC 11 (Expression) performs global volume control. What is different about the “Niente”
versions is that CC 1 can bring the volume all the way to zero in addition to cross-fading
dynamics and vibrato
So, I guess it’s even less standardized than most other sample libraries; here, it even varies between instruments. 
I withdraw my post because I did not realize that this is a technical discussion
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