Hello all,
 
      I'm working on a mid-tempo piano based pop tune, but I'm having quite the issue getting the bass part to fit with the left hand of the piano.  I'm using Addictive Keys for the piano and a Dim Pro bass patch for the bass.  They just don't... "fit".  I don't think it's a timing issue, maybe more of a frequency overlap problem.  If I remove either the bass track or the LH of the piano, it seems too empty.  Is there a tried and true method for dealing with this, perhaps just EQ-ing the low end out of the piano track?  Making sure the piano LH and the bass are lined up to the exact tick?  I don't want it to sound too "perfect".  Or any other tricks I should be aware of?  Thanks in advance for any suggestions!

The first question that comes to mind is;

Are the left hand and bass playing the same notes? If they are then don't. Have them play complementary notes and give the rhythm part to the bass, let the piano left hand accompany the melody which I assume is the pianos right hand.

+ 1 to Mike's suggestion. 
You can open up Piano Roll View, select the tracks tap, pick tracks and see both the notes of the bass and piano part. Under most musical situation we don't want to have 2 different bass notes.
 
If I were you I would try Studio Instrument bass which IMHO has a a few better bass patches than dim pro. 
 
You might also consider layer up a synth bass patch from example Zeta  with a lower volume and perhaps transpose it an octave lower to fatten up the bass.

Thanks for the ideas!  The parts are not quite the same, rhythmically or note-wise, so I may have to experiment with adjusting one or both of the parts.  I play piano in a Billy Joel/Elton John/Ben Folds style (though not as good!), so the piano tends to be more chord-based and rhythmic rather than melodic.  The artists I mentioned all had bass players in their bands and recordings, so there is a way to get the parts to fit.  I'll try to listen real closely to some of their recordings and see if I can identify how they're making it work.  And I'll have a listen to some of the SI Bass patches as well.  Thanks again!

Sounds more like an arranging issue than a mixing issue... Writing arrangements where the left hand of a piano playing in the same range requires many kinds of scrutiny... If they're not playing the same part, how do they relate? Are conflicting notes happening simultaneously? Is the rhythm getting crushed due to the competition?

If you're the writer of the parts, you might want to consider altering them so that they can act as one, whether doubled or complimentary... Clusterd notes are more difficult in lower octaves, so I would recommend writing the parts using more primary rhythms/harmonies. If I have a keyboard player who's parts are amazing, I rewrite the bass to compliment it... For me I'm very bass-centric so I write my bass part first then adjust my keyboard part(s) to fit... Gotta lose player's ego to make the arrangement work...

Keni

One thing I've learned is that live piano playing is very different from recorded piano playing.  You can get away with a lot more in a live setting.
 
You can certainly roll off the bass on a piano if that part of the spectrum is not completely essential.  I do it quite a bit.  Piano and organ (and most keyboard instruments) are frequency hogs anyway--they can take up the entire spectrum if you let them.
 
The first thing I'd do though, is decide if what I'm doing on the piano with my left hand is absolutely necessary.  I will sometimes reduce what I usually play to sometimes just partials (ie. not even playing full chords).  You've said that the song sounds empty if the piano's left hand or the bass guitar is removed.  How about re-writing the piano part so that it's not playing at all in the bass spectrum, but the notes are still there?  Can you work with different inversions?
 
It sounds like the piano is going to have to make concessions rather than the bass.  That's what usually happens to me anyway.

+1 to the above.
Yes, check the arrangement first. If you listen to/watch jazz piano players, you'll hear/see that they keep their left hand well out of the way of the bass player ... rarely going below the E below middle C and mostly don't play the root note of the chord.
 
(Not your boogiewoogie and the likes type of piano though, cos that's a particular style)
 
If the piano part exactly double the bass part, that can work too depending on the song, but you want to avoid the piano playing low chord notes in the bass region.
 
With the 'live' playing and the 'recording' thingy: you'll see Elton John hammering away on 'live' with his left hand, but most of it will be equed out of the way and the bright end of the piano focused on.
 
You want to avoid the piano area (kind of the octave below the G below middle C) being too chordal down there as it doesn't sit very well with bass. If you eq out a lot of the piano though and make the piano quite bright, that could work too.
 
It does depend a lot on the song though.
 
The thing is I suppose that pianists playing solo are used to covering all the parts (bass, chords and melody), but when playing piano in a band, you've got to adjust the playing style a lot or you run the risk of annoying the bass player because the piano is treading on his/her bass note choice and sometimes clashing badly. So they've got to be exactly together on the same bass note or the bottom notes of the piano removed.
 
I've seen myself sometimes recording a midi piano part and then going into the piano roll and taking a lot of the low piano notes back out!

Sad to say for me, but I get around it by mostly writing "right hand" piano parts... The piano is the on,y instrument other than synth that actually covers the entire range of the orchestra, so parts written for piano have to allow for the piano parts... Then the bass is forced to find a groove that fits in... Typically in a 4 piece rhythm section, the keyboard is mostl used in a mid range capacity ( pitch) so you allow the bass an kick to rule the bottom and the keyboard parts have to work into the scheme, not dominate it...

Not a right or wrong, just stylistic approach... There are plenty of players and groups that have no need of this handling... Fine jazz artists learn to work their ranges just as good rock bands do... But every set of guides has room to clash, so when the situation arises, these are some tools to work with...

Keni

Great suggestions, everyone!  I usually play solo piano, or in a small group with a drummer and guitarist, so my LH parts usually provide the bass.  It sounds like simplifying the LH along with some EQ would probably get the piano to fit with the bass a little bit better.  Also, some careful listening to the recordings of the artists I mentioned above is in order.  There's a band called The Fray who manage to get piano, bass, and electric guitar all fitting together without conflict, even though the frequency ranges can significantly overlap.  That's the sound I'm after.  Thanks for the advice!

1. If you're recording the piano part via MIDI, thin out the left hand notes and pedal events while listening to it along with the bass track. Listen for things like the left hand playing the third, or chords, or sloppy pickup lines - these will stand out easily when soloing the bass and left hand piano together. I often have issues with the sustain pedal being held down too long, which doesn't hurt anything when the piano's played alone but can wreak havoc on the bass when incompatible notes briefly overlap.
 
2. Separate the left and right-hand into two mono tracks. 
 
3. HPF the left hand part, perhaps as high as 200 Hz or more. It helps to use a spectrum analyzer to figure out where the highs of the bass and lows of the piano overlap the most.
 
4. If the piano's not the featured instrument, pan the left hand fully left, allowing the bass to occupy the center. The right hand can be center or right, as far as the bass is concerned. I usually have it 50% to 100% right to clear the center for the vocal. If it's a piano-centric piece, do the same thing, just with less-extreme panning.