Logic's "Flex Time" feature is easily the most significant upgrade in Logic 9. It is mainly intended to offer the same 'elastic audio' abilities Ableton Live is known for, for matching tempos of audio snippets or quantizing audio just like it was MIDI. But my first thought when I heard about it was "How can I abuse this for some cool effects?" Turns out it's pretty damn good for that too.
What makes it great for sound design and abuse is that it features several different flex modes specializing in different types of audio. Each one sounds a bit different and produces different kinds of artifacts when pushed to extremes, so I thought today I'd talk a little about those and give some examples.
To demonstrate the way these different modes sound, I took a short vocal and time-compressed some bits, while stretching out others at random. So while these examples may not be terribly musical, it gives you an idea of how the different modes could be used for special effects. The piece of audio and the portions that are stretched or compressed are the same in every instance. Only the Flex Mode was changed.
The first mode available is the SLICING mode. You can think of this as being similar to Propellerheads' Recycle. Its specialty is drum and percussion loops. It looks for attack transients and divides the file into slices so that when you adjust the tempo of your project, the drum or percussion loop plays in time at the new tempo without playing at a higher/lower pitch. Used on non-rhythmic material, its effect is a bit like gating:
The next available mode is the RHYTHMIC mode. This is similar to the SLICING mode in both function and sound, but it is aimed more at non-drum or percussion-based rhythmic parts such as a clav or rhythm guitar riff. Here is the same piece of audio used above, this time in RHYTHMIC mode:
The MONOPHONIC mode is specifically designed to be used on melodic instruments only playing a single note at a time, such a singer's voice. Although it is a more hi-fi type of time stretching, at extremes, you still get some cool artifacts:
As you might guess, the POLYPHONIC mode works in a similar way, but adapted for use with material where chords or intervals are present in the material. It creates a subtly different kind of audio artifact that sounds like this:
The TEMPOPHONE mode might be better named the "old school" mode because it emulates the time stretching algorhythms used by early samplers and computer audio editors. You've no doubt heard this effect on countless 90's dance tracks. It has a bit of a metallic/robotic sound to it:
Whereas the other modes are designed to effect timing without effecting pitch, the SPEED mode essentially emulates the behavior of tape. Audio you stretch out will play at a lower pitch, while audio you compress will sound "munchkinized". Combining the two can create some crazy effects like you might hear on an old Severed Heads record: