looping pedal with decay?

["radio radio" <radiotelevision@gmail.com>]

I want to buy a pedal and get into looping but am having trouble
figuring out which one will best meet my needs (and budget). I've
learned a LOT from this web site, but still can't quite figure out
everything and would really benefit from a human (albeit
computer-mediated) interaction. Thanks in advance for taking the time
to read this and respond - I hope that I will be able to "give back"
some day when I know something worth while. Until then, I guess I
should donate to this site if I get any responses.

>From what I've read and thought about, it looks like what will be the
most important distinction for me is that the loops will be able to
decay. In other words, you can lay down a loop, lay down another one
on top, and then another, and so on, and eventually the first one dies
out, then the second one, and so on. I imagine this working like a
delay pedal in which you can set the decay (or is that called
feedback?). So you could "morph" over time into new things, without
being stuck with your original loops, and without having to open a new
loop and start from scratch with only one new track each time  you
wanted to change it up.

The three pedals I've looked into are:

BOSS RC20xl, Digitech Jamman, and BOSS DD-20 giga delay

I thought the BOSS was it, but now I'm thinking that it doesn't allow
this thing that I described. I can't tell if you can do this with the
Jamman or not - does anyone know? You could do this with the DD-20,
but I can't tell if you'd be able to set a loop/delay time up with
your foot or not (versus having to set it to a certain number of
seconds and then hope you can keep your riff to that length) or if
there would be other difficulties that I'm not aware of if you're
using this as a looping pedal when it's built to be a delay.

Should I be considering a different pedal? I don't really need a delay
pedal - I want a loop pedal that decays. I don't really need to be
able to save my loops - I just want to be able to set them up on the
fly. I don't need to be able to save them on my computer. I don't need
to be able to plug in a separate mic or instrument in addition to the
guitar, although that would be a definite bonus for me. I don't need a
long amount of time - I'm guessing 23 seconds is plenty. I don't know
if I need the ability to set up separate loops or not - I certainly
wouldn't mind, but I don't know enough about using a looper yet to
know about that. Also, how important is 'auto-quanitze'? Lastly, I
don't have a lot of money to spend, so the echoplex is right out. The
boomerang is also too expensive, and anyway I'm affraid of the noise
issues that people have written about with that one. I haven't really
learned about any other pedals out there.

Thanks again!
Eben