no
one loop may have four tracks

half speed. Interval can be changed from an octave to a lower 2nd., 4th., 5th, or 7th.

half speed, 1/4 speed,

8

yes

only one layer back - then "REDO" back again

yes
battery or AC

"yes"
only during overdub

Boss DD

-20

Relateded links you may find useful:

• Loopeprs-Delight mailing list (you may also look for the Loopers-Delight Facebook Group)
• LiveLooping.org (web site resource with a certain educational inclination)
  
  

Rang III: (thank you Lee Hardesty for submitting this information)
The Rang III has a 'virtual' multiply capability. Create loop 3 first and let it be the base loop you want to multiply. Then create another loop of any length with loop 3 playing as the master. This secondary loop can be any number of multiples of the base loop you desire and there's no need to preset this length since the final length will be determined by the end-recording tap. In the parallel styles you can create up to three 'multiplied' loops that will play in sync with the master. These loops can be of any length, can be stacked on, reversed, erased and re-recorded, etc. It's a slightly different approach but the results are essentially the same I think. Some of the other products on the list may be able to do something similar but I'm only familiar with the Boomerang unit.

In the parallel styles (Sync and Free) you can have up to 4 loops ready for immediate playback. They can be started and stopped individually or the Play-Stop-All function can be used to start (or stop) playback of all existing loops simultaneously.

Pitch transposing now allows octave-up and octave-down capability.

The internal memory spec might be expanded to state actual recording time(s) since products differ as to bit-depth, sample rate, etc.

Augustus Loop Multiply: (Os)
If you turn off the 'tape inertia' feature, then you can change the loop length to anything you like, while you're looping, with no glitches. So you can record a phrase and later change the loop time to e.g. four times the original length - which is effectively a multiply. The joy of the complete flexibility this gives you is that you could e.g. record an 8 beat phrase and then change the delay time to 11 beats. So you have fractional multiplies going on, if you so desire. Same applies in reverse - you can change the loop time to lower than the original time. So e.g. go from 4/4 to 3/4 seamlessly if you like.

BOSS DD-20 multiple loops in parallel: (Rainer Thelonius Balthasar Straschill)
I describe the "parallel loop" function of the DD20 in some more detail below, but the quick answer is still "yes" (2) (Some of the details here do not apply if one of the modes in question is the stupid "SOS" mode): The DD20 has four memory slots to store your favourite settings and then switch between them and "manual mode" (i.e. what you set up with the dials and knobs). It also has a "seamless switching" function which will have the last delay playing - only disconnected from the input as well as from the controls - if you switch to a new memory slot. This last delay will then continue playing either until it has faded out or until you switch memory slot again. Note that you lose control over that "last loop" completely, so you can't adjust feedback or volume or even go back to it and overdub further. But it sure does qualify for your description of "making changes to one loop whil still hearing the other looping on". As a matter of fact, you can even create four loops in parallel, namely if you choose the double delay for both your memory slots ;)