_I have a friend; let's call him "Dave".  Dave has been engaged on a project to record and mix an album's worth of mostly vocal and acoustic-guitar songs for a client. The arrangements are very sparse and his client has been adamant that he doesn't want any additional parts added.

A couple or so weeks ago Dave dropped by and left 2 CDs with me, one is the collection of songs which he has recorded, mixed and pre-mastered using Izotope's Ozone; the other disc has a copy of one song recorded and mixed only.

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_I offered (begged really - it's a good song) to do a pre-master on the track. The track is acoustic guitar and vocal with a couple of very simple, neat guitar solos and it sounds great.  To my ears there was nothing much that needed to be done, a couple of points where a vocal resonance poked it's head out and the solos were just a little too far forward to me, but otherwise I'd list as "leave well alone".

With a spare hour that evening I added a little stereo widening, a little bit of band-specific compression to tame the resonances and push the solo back a dB or so, a tiny bit of EQ just to thicken a part of the acoustic guitar and an all-but-inaudible room reverb just to sweeten.  I then ran through Slate's FG-X to bring-up the levels and printed it.

When I came back the next morning and AB-d the new version with the original I felt that I'd massacred Dave's carefully crafted mix.  My ever-so-subtle adjustments had added up to a slight change in the sound that I just didn't feel was right.  I'd polished a little too hard and actually changed the shape of the track - not much but still too much to my fresh ears. 

So - I reduced the stereo widening, I still compressed to reduce the vocal resonance and pull back just the very peaks of the guitar solo, left the reverb as was (I could hear it only on headphones - just) and spent a while playing with the levels before settling for a very gentle treatment to gain a few dBs without bending the guitar transients. In the end I had a track that sounded like the raw mix but a little smoother and just a little bit "more" which was just what I was after.

Dave agreed about the solo being reigned-in (actually better done on the multitrack, let's face it) but otherwise didn't like the track at all - he felt that it was too narrow and too dry. At this point I fired-up the disc of mastered tracks that I had and found that every track was like a significantly more extreme version of my first attempt. With a new sense of freedom I've made my version wider and wetter but I can't bring myself to change the actual sound because I think it's nailed beautifully in the mix.

There's a lesson in here - probably.

• I had a whole album's worth of reference material that I didn't use.  In this case I chose not to because I saw little point in trying to reproduce someone else's work as this was an exercise for the love of the music, not a paid job, but it would be crazy to ignore a client's vision to this extent in a commercial situation where time is money.
• Perhaps one person recording and mixing and mastering really is a step too much.  I don't have all the original stereo mixes, but the one un-mastered track I have sounds significantly sweeter to me than any of the mastered tracks.
  
• I have very mixed feelings about all-in-one packages like Ozone; I think it is a very good product with some excellent processors and a world-class interface.  Unfortunately my brain can't deal with complex presets - I find something I like then feel a need to reverse-engineer it to see what component is doing what - at a time when my right-brain should be closing its eyes and listening my left-brain is taking notes and checking references. By the time It's done I'm so used to the sound that it tends to have become "right" just through familiarity. 
• Mixers often complain that Mastering Engineers ruin their carefully crafted mixes with heavy-handed processing, MEs often complain that they are asked to process tracks in a way that they don't feel is appropriate.  Just who do you complain to if you're both Mixer and ME?