Not sure if this has been done already but here it is anyway. This method requires a little bit of set up, but should hopefully work for everyone.
Settings vary depending on whether you use a 1,2 or 4 bar loop, and on the tempo stability of the original loop. I would recommend getting your original loop as clean as possible (in regards to your chopping/zero crossing etc). This might get revised as I play around with it somewhat.
In this example I’ll use a four bar loop of the Amen Break I downloaded from the internet.
Set the pattern length to 64/64.
I have the TUNE set to -2, and the FINE TUNE set to -22, at 120 bpm. This means that if I set a trig on the first step, I will roughly get a perfect loop when the pattern finishes on bar four. Aim to set the tune so that you get a loop playing as perfect as possible.
Place trigs on every step in the four bars. The fewer trigs you put, the less ‘accurate’ the time stretch will be.
In the TRIG menu, you should have the synth and LFO turned off, along the bottom row. Place a P-lock on the first step of the pattern, that sets the LFO trig to on for that step.
On the LFO Page, set the LFO to:
SPEED : +4
MULTIPLIER : X4
DESTINATION : SAMPLE START
WAVEFORM : RAMP
TRIG MODE : HOLD
DEPTH : +120
For 1 and 2 bar loops, increase the MULTIPLIER (to x16, and x8 respectively). If having problems with double timing or half timing, experiment with dividing or multiply the MULTIPLIER and DEPTH settings.
Press play, and start changing the tempo…