There a lots of reasons to manipulate the timing of audio in Logic- here's the quick and dirty way to get started!
1) You need a track with audio on it
2) Click on Audio > View, and choose "Flex View" (or use COMMAND F)
3) Nothing seems to happen except for a new box in the track box...
4) Before you can do any stretching or compressing, you've got to choose an ALGORITHM!
Algorithm is a fancy word that refers to the way Logic will do the stretching. Different kinds of algorithms work in different ways; some work best with percussive elements (i.e. rhythmic) and some work best with monophonic lines (i.e. monophonic)
The truth is you can use any algorithm on any type of audio, but they will sound different!
4) Click on "off" to see the list of choices:
5) Once you select an algorithm, Logic will analyze the track (ALL audio regions on the track)
This will take a bit!
10-15 minutes later (just kidding... more like 30 seconds later) you should see something like this:
What you just did turns out to be the equilvalent of going into the SAMPLE EDITOR and clicking this icon:
6) What just happened?
Logic added TRANSIENT MARKERS for every large TRANSIENT in the audio
What's a transient? Basically it's a part of the waveform that's louder...
From this point, to stretch and compress, just move your cursor to a transient marker, and drag!
The waveform you see is the waveform you get!
i.e. I took this waveform, dragged the transient markers...
...And now all those hits will occur on quarter notes!
7) Pay attention to THE COLORS!
ORANGE = the sound has been stretched
GREEN = the sound has been compressed
RED = Logic will freak out at you
basically you're compressing the audio "way too much"
...For normal use, you want to avoid this situation..
...For CREATIVE use, this can sound really cool!
8) If you now select a different ALGORITHM, Logic will re-scan the audio, but will KEEP YOUR EXISTING STRETCHES AND COMPRESSIONS!