So I don't normally do remixes very often. But one thing i've found when trying to remix a pop/rap type songs... I could sit there through the whole song and count 1, 2 ,3 ,4 and it stays in perfect 4/4 time on whatever tempo the song was supposed to be in.
 
Yet If I remove all the music and add a simple 4/4 drum loop, inevitably, it always ends up off from the vocals after some amount of time. It's like at some point they must change the timing or tempo even if it's just for the slightest split second, then resume the 4/4 time.
 
Does anyone know of a good way to analyze and figure this out to make this process easier? I'd love to do a remix once in a while, but it makes it so hard and annoying.
 
Thanks

The good news is most original tracks/stems were originally tracked to a click.  If I do a remix at least we know the tempo. They tell you that.  So what I do in Studio One for example is bring in the stems.  Set the DAW click to the desired tempo.  Line up the very start of the music to a click  (say bar 3 for example) and usually it will be very tight right at the beginning.  (and for quite a while too) 
 
Then I check down the end of the music.  What happens here is sometimes it might be a bit out.  So instead of the tempo actually being 100 BPM I might have to alter that in Studio One to say 99.98 or 100.07 etc in order to get the end of the music still in time with the DAW click.  As you make very fine changes to the tempo I can see the transients in the stems either lining up with the grid or going away from it.
 
Usually it is a matter of getting the start and the end in sync and the rest should take care of itself in the middle.  It is important to get the stems matching your DAW click all the way along then importing any loops etc at any point should be a breeze.
 
Hopefully you won't have to make any tempo changes along the way with the tempo but it has been known to happen.
 
Don't make the mistake of just remixing the stems and maybe adding in a few things here and there.  I found out from doing one with Indaba for example what they really want is something almost completely different from where it started.
 
 

you could do a quick audiosnap job maybe..
enable audiosnap on the original kick and snare tracks, and lock your own kick/snare to these with audiosnap.
I'm in X3 but 'drumreplacer' in Platinum could maybe help you as well.
 

thanks for the suggestions. i'm gonna look into both when i get back to working on this a little later

I've done series of songs that are basically just instrumental versions of pop songs (  a few Sting tunes, Steely dan, Toto....etc. I've found my best method is to monitor the original song and go through the effort to just over dub a click along with the original. There are of course subtle tempo changes in nearly every measure of a " real" performance track. Actually I don't consider them strict tempo changes as such. But, I think anytime you're working with loops and using a grid you'll run into timing problems. I never, ever use a grid. I treat the daw like a tape recorder - as real time as possible. Midi quantizing is never used and I keep midi clock at it's highest resolution.

I don't think that is what the OP is about.  I am assuming (and I could be wrong) that what the OP is about is remixing songs that have been done by someone else and the music was all done to a click and that David is interested in doing a remix of that song.  Which involves working with the stems and adding in new material, taking out old material etc.. Creating a new piece of music if you like.
 
It is actually more fun and interesting to do this rather than attempting to do a remix of your own material or even a cover that you have covered.
 
The real interest is working with material that you have not heard before.  And doing something interesting with it.  Most of this type of material has been tracked to a click and what I suggest is actually the right way to go about it too.  Once you line up the beginning and the end of the music to your DAW grid and this usually only requires a very slight change to the original tempo then you can work with loops and stuff because they will in fact play real nice against the stems that you have imported.
 
Music does not have to be non click based in order for it to be good.  Some of the best music I have ever heard is quantised etc..  It comes down to how it effects you at the end of the day.  And music that effects you can be either very grid based or totally free.  It does not matter.
 
So David remixes are fun and interesting and quite challenging too.  The only problem with it is that it can take up many hours of your time and you will more than likely not get paid for it.
 
 

Why not take the drums or bass part of the original and use it to create a tempo map with Melodyne?

Yea like Jeff said, we're specifically talking about click based pop genres of music here that keep a steady 4/4 constant tempo time and never deviate... Unless of course you break apart the stems and start trying to play a new instrument to it and then it's like "what in the world tempo was this played to?" haha.
 
I haven't had a chance to go back to it, but I think the answer is going to be like he said, just figuring out an exact tempo, even if it's not an even number, that works with the beginning and end of the song and the rest SHOULD then fall into place. I had clicked along with the metronome and found it at 110bpm, but maybe its really 109.7 or 110.3. Something like that.

sharke
Why not take the drums or bass part of the original and use it to create a tempo map with Melodyne?

I didn't even know Melodyne could do that. I really haven't dug into Melodyne as much as I should. I don't normally work with much Audio, so I just figured out how to do some simple pitch correction and that's about it.

The other thing you can do of course is once you do have the tempo lined up at the start and the end of the tune then in the middle you may have to cut some sections and move them usually only very slightly or quantize the audio in spots to move things back onto the grid if you feel they are drifting.  I have found from experience it is better to move the audio around to the new DAW grid rather than the other way around as well.  Studio One makes all this very easy which helps a lot.