Hello all, first post on this forum, even though i’ve being using audacity for years.
The projects i normally work with are mainly dj mixes, made by me, or others.
Some of them come to me after been abused by the "gapless"window cd maker.
This is when audacity shines with its unlimited waveform zoom and accuracy.
I always manage to put the pieces back together and the results are pro.
This time though, i had to save one of my own projects.
I made a mix with some songs from the 80’s and 90’s to listen while having my daily 4 km walk routine.
But since the tempo varies from 107 to 145 at the very end, first synch problems between tracks appeared.
I’m attaching two audio examples, with labels before and after to clarify the job i did with audacity.
The original mix being made with the help of mixxx. I’m on linux - arch, manjaro edition, unstable repos, and the latest audacity 2.1.
Thank you audacity for saving my day… 
https://clyp.it/rmdw3zb3
https://clyp.it/cr0wkpt0
https://clyp.it/j0kshdaa
https://clyp.it/shyco33q
We can’t fix your project for you - you have to do that.
If the audio at the wrong speed is at the correct pitch, try Effect > Sliding Time Scale / Pitch Shift… .
If the audio at the wrong speed sounds at the wrong pitch, try Effect > Change Speed… ( http://manual.audacityteam.org/o/man/change_speed.html ) or Time Tracks ( http://manual.audacityteam.org/o/man/time_tracks.html ).
Gale
Hi Gale, well you got it all wrong! I’m not asking for help regarding my project,
i just wanted to showcase how i used audacity to fix it. That’s why i attached the audio examples labeled before and after.
And also to thank the audacity team for this software.
Well, we get so few posts where people tell us that they solved their own problem that I probably missed the subtlety 
So how did you fix it, exactly? What tools? An MP3 only shows the results.
Gale
People often join a forum looking for help with a problem so you’re right.
Well, for songs like the first example when audio was out of phase, i did
what i like it to call a “surgery” when i simply start the transition before the bad part.
To do that, i made a loop with just the last bar of the first song on the refrain and another one of the second song
way after the transition when the beat was clean, and repeated accordingly to the voice on the first track.
I used phaser on both tracks with default settings since it works pretty good as is, for a few bars.
Lastly, just to emphasise the end of the transition and make it last a bit longer,
i used paulstretch with a stretch factor of 2. You can hear how good this one sounds.
As for the second transition, i took a kick from the second track and looped during the whole transition,
Then added phaser on the second track, and at the end i amplified the snare by 6 db to make it really kick in.
You can hear that on 0:29.
Thanks for the contribution philnice.
As this is mostly about “production values” I’ve moved it to the “making music with Audacity” section of the forum.
And thank you steve. Question: I like the idea of making future mixs with tracks on their original tempo and pitch, and then alter the tempo using a time track.
Is there a way to have a sort of pitch lock effect while doing it on a the whole mixed track?
The Time Track changes the playback speed, so it affects both tempo and pitch.
If you wish to “slide” the tempo without changing the pitch, use the “Sliding Time Scale / Pitch Shift” effect: http://manual.audacityteam.org/o/man/sliding_time_scale_pitch_shift.html
Niiiice. Gonna master that effect as well. Thanks steve.