Hello,
I'm creating MIDI/audio music with Sonar, and I have a weird intonation issue with the bass track. The bass pitch I hear during playback seems to go flatter or sharper as I move around relative to the computer's subwoofer speaker. E.g. The bass sounds relatively sharper when I'm sitting in front of the computer screen than when I stand up, and then it seems to go flat by as much as a 1/8 step. I hear similar changes just from walking around the room! It always sounds out of tune at SOME location where I stand or sit relative to the subwoofers, so how do I know if the bass will sound in tune (relative to the other tracks) when other people hear my music on their systems?  Is there a standard way to deal with this?  I assume I'm not the only one to notice this.
My MIDI bass track is Sonar's SI-Bass Guitar (Default). My bass line mainly uses notes A5, D5, and E5 (below middle C4). To my ears, the E5 sounds sharp, so I bounce it to audio and pitch-shift it down a bit. And the E5 sounds ok or flat, so sometimes I pitch-shift it up. But as I described above, it can never sound "perfect", depending on where you stand. And when I listen to the exported WAV on my 2nd computer & speakers, the bass sounds flatter than on my 1st computer & speakers. So what would a professional audio engineer do? Is SI-Bass Guitar known to be correctly in tune, and maybe it just sounds out to me? Or are there known retuning parameters for SI-Bass, to make it sound the best?
 
Thanks,
Gordon

Oops, meant to say the E5 sounds sharp, and the A5 sounds ok or flat.

How do they sound through headphones?
My only idea for an explanation would be that, depending on your position, different frequencies are boosted or cut.
Then again, there's been many threads about some soft synths being out of tune in certain situations or keys.

Kalle, I'm guessing the subwoofer vibrate the desk, which adds its own pitch a little off from the actual bass pitch, and as you say the frequencies are boosted or cut at different hearing positions.  Good idea about trying it with headphones, since that will eliminate the desk vibration issue. I don't have any headphones at the moment, but I'll find a pair and give it a try.

The subjective pitch of bass changes with volume.

sounds like you are a serious candidate for room treatment.
 
STAT.
 

Sorry not to get back sooner (very busy with my day job).  I found that if I turn the bass way down on my computer speakers, then what I hear is flatter, and I guess that's the "true" pitch.  When I turn the bass way up, it sounds at least a quarter step sharp.  And with headphones, it's flatter (apparently the "true" pitch).  Also, I had my computer's subwoofer almost against the wall, and when I moved it away (room treatment, as batsbrew said) the tone got flatter, so I guess the bass was vibrating the wall at a slightly sharper pitch.
 
Now I understand better why the bass pitch varies.  But what's weird is that I only notice this happening with my Sonar piece, not with tunes I hear on YouTube.  Maybe it's my choice of Cakewalk's SI-Bass
 Guitar - the default sound, which has so little treble in it.  I'll experiment with other SI-Bass
 Guitar sounds and see if I have less trouble with them.

like i already said,
room treatment.