Lexicon MPX 1 Looping
Delay with feedbackThe "M" is a mixer.
Luckily, the "Feedback" parameter on the MPX1 does just that when set for 100%. The real beauty, however, is that the feedback is all being done in the digital domain so the signal quality is not continuously degraded by the D-A and A-D converters so loops can be held indefinitely.

This gets you a very basic looper but doesn't allow you much control over it. Even a semi-serious looper allows you to add audio then play over it without adding to it. To do this on an MPX 1 you need to put a volume control effect block in front of the delay which will provide you with control over the signal level feeding the delay. You turn it on when you want to add to the loop and off to play over it. The basic picture looks like this:
a simple looper
In the MPX 1, the Pitch and Mod blocks contain Volume control effects. With a volume control loaded in one effect block, the other block is available for a Chorus or Pitch effect.  I usually place the free effect in front of the Volume block so that I can record the effected audio into the loop.

Note that V1.10 of the MPX 1 software allows slightly more effects to be loaded in the DSP than V1.00. While you lose the ability to merge up to 3 times, getting the extra DSP resources is usually a lot more useful. If you are using V1.00, for instance, the "Shifter" effects won't load with a Volume control and a Delay. With V1.10 it will.

One of my favorite looper programs uses the Mod block for Volume control and a "Shift (M)" in the Pitch block. If you set the pitch shift to an octave down, you can add a bass part to the loop). Use the "Delay (M)" effect for the actual loop and set up the Routing Map to look something like this:

Optionally, load a Pitch, Chorus, EQ or Reverb effect (I also like "Sweep Filter" effects). Remember that the Reverb effect doesn't use any DSP resources so you may as well include one to put some "space" around your sound. In this case I'm using the Mod block to control the input signal to the delay.

Controlling the Loop
Now that you have the basic effects loaded, it's time to set up the controls for the loop. There are actually a number of different ways of controlling the loop but they all involve making Patches. Refer to my Patching Quick Guide for information on Patching.

Setting the Loop Size
There are a couple of ways to set the size of the loop on an MPX 1. The most straight forward is just to dial up a delay time and play to the rhythm it produces. A more musical approach, however, is to set the delay "Time" parameter for "echos:beat". Now the Tap button can be used to set the size of the loop in real time. 

Background image by Pauline Moss. at http://paulinemoss.deviantart.com/art/Stars-307119758