(...) So, when a piano is by itself there's isn't much to mix.(...)
Can’t agree wit that. Mixing a solo piano track — or what has to sound as if it were a solo piano track — is often incredibly difficult, at least as difficult as mixing a band or orchestral track, particularly if you’re working with a virtual piano, all specimens of which, when exposed, are prone to show their many weaknesses much more than their rare qualities.
It requires your complete attention regarding things like weight of the sound (having it consistent across all dynamic layers), timbral sculpting, stereo imaging, the inevitable weak-sounding note(s), cumulating frequency clusters (an unpleasant phenomenon in nearly all virtual pianos), convincing dynamic behaviour, finding a virtual space that’s sympathetic to both the instrument and the music, … and several more considerations that just can be ignored.
(...) I doubt anyone can hear what's been done here in terms of mastering (...).
Don’t agree with this either. Listening to this track for example, I would think it impossible *not* to notice that the dynamics of the audio don’t sound quite right. The middle section, where the piano part is denser and happening in a higher dynamic range, sounds compressed — quite heavily compressed in fact, to my ears — resulting in evened-out levels that are quite unrealistic. To my ears anyway.
Can’t tell whether it is Pianoteq’s built-in compressor or some plug-in in the audio chain that’s causing this dynamic flatness, but whatever it is, I would definitely suggest to make sure its presence is a lot more subtle than it currently is.
A good trick, in my experience, is to mix occasionally at really low levels. I mean: really *very* low levels. For some reason, that brings out any dynamic inconsistencies and/or other flaws in a mix that much clearer, I find.
I also often uses several instances of the same instrument in order to have more control over specific problem areas in a virtual piano. (Not a rarity for me to use up to five instances of the same piano.) With the added bonus that I can place the left hand range ever so slightly further away from the listener than the right hand. (Anything to increase the illusion of depth in a recording of a virtual instrument in a virtual space, is always welcome, in my opinion.)
In this case, I would definitely load up at least one more instance of the Pianoteq instrument to take care of the somewhat problematic midrange of the piano: the tone there is borderline congested and some careful EQ’ing might open things up a little. (You also might want to consider fractionally lowering the Impedance-parameter as well as raising the ‘Direct sound duration’ of the notes in the midrange — only possible if you have the Pro version of Pianoteq — for a less dense sound.)
For my taste, the chosen space in your recording sounds perfectly OK.
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