I have been trying to use Sonar X3 Producer to modify a background track using two audio sources. 
Right now it most certainly does not, but, I would like the transition to sound as though it comes from the same source.   I wonder if someone out there can do their magic and let me know how to achieve an apparently seamless transition.    

First, I'm not going to do this. You have all the tools you need to do it yourself. But I'm curious -- are you talking about the transition at :05, or :10? Cuz they both sound edgy to me (laptop speakers, sorry).

the clip sounds greatly quantized with lots of artifacts from doing so.  What I'm hearing is a lower fidelity clip, basically in mono...jumping to a higher quality, where the stereo becomes much more pronounced....around the 36 sec mark, near the end of your example.
If that's the *splice* you're talking about, make the 2nd clip mono as well, back off the volume a tad too.

I failed to say that although I have the tools I am still trying to develop the knowledge.  Hence I am reaching out to expert for guidance. Listening the the track again I find the whole thing is pretty bad; however, the critical transition I speak of is at :19/00:00:35:20 where two clips are actually spliced.  Other  transitions are things with which I can deal;but, there is a definite break in (I'll call it) orchestration at :19/00:00:35:20! I realize one can only do so much to soften that since different instruments, recording equipment etc. are used to create the original tracks. Are there tricks of the trade that experts might use?  For example,  I thought of incorporating a "ritardando" before the break to create the transition.   

mixmkr
 
If that's the *splice* you're talking about, make the 2nd clip mono as well, back off the volume a tad too.

Thanks Mixmkr
 
I'll start from scratch and re-do the entire track.  After I get rid of the garbage and convert everything to mono I'll try backing off the volume.  I've played around  Multiband 64  as well as Volume automation but frankly I am very very "green"  and need to better understand them.  As I suggested to Larry (above), are there tricks of the trade that might soften the transition?

cpkoch
 are there tricks of the trade that might soften the transition?

keep the tempo consistent.  Mistakes there will be the most noticeable... ..then not far behind will be volume, quality/fidelity, etc

what are you looking for exactly, btw?   A MacArthur Park backing track, tailored to a form you prefer??
 
 
and actually listening..your clip around 35 sec is pretty much in time....at the change, the fidelity is just greatly enhanced as is the stereo field.  Like the record needle finally jumped into the groove, so to speak

An alternative approach might be to make a feature of the transition in some way and work with the differences rather than trying to 'fix' them.

KPerry
An alternative approach might be to make a feature of the transition in some way and work with the differences rather than trying to 'fix' them.

That's a good way and I've given it a go by trying to ritard the last few beats before the abrupt change!  I am also finding that using the Multiband 64's Mid High Gain and Low Gain filter settings seems to get me close but "not quite there" to the audio timbre I am seeking.