1. Send a track to a new bus
2. Add a simple delay to the bus, choose your delay times to taste and make sure that no filters are doing anything to the audio. For this to work you want to keep the feedback between 0% and 10% - we'll be adding our own feedback loop later on.
3. Now add a distortion effect after the delay and a filter after that (I like either high passing or low passing but you could even go for band passing if you want).
4. Now to create the feedback loop, send your dub delay bus to itself (so if I'm using bus 1 for the dub delay, I send bus 1 to bus 1). I'd recommend putting a limiter on either the master or at the end of the dub delay channel to avoid damaging your speakers and your ears (my mate blew his by turning up the feedback on Logic's tape delay a little bit too much.
That's the basics of it, but you can get creative with this technique and add other kinds of effects to the delay chain.
Here's a couple of Audio Examples of me messing about with this technique.
