[PD] my inability to grok digital signals

[jfm3]

I fully admit that I am a lamer when it comes to digital signals. I made
this patch from one of the examples. It should just play back a loop of
sample data from a table. I basically understand how phasor~ drives a
quadratic interpolation lookup on tabread4~. It seems to me that 
samphold~ is just there to stop phasor~ from ever actually being zero by
the time it gets to the tabread4~, but I don't understand why, and when
I take it away the patch stops working. Also, this particular patch
takes quite a while to load the sample (30 seconds?), but once the
sample is loaded the first time, I can switch between samples without
any delays. It is definitely not the disk being completely stupid. I
checked that. I have a feeling I'm ordering the math incorrectly, but I
messed around with different orderings and didn't get any results. If
anyone could take a peek at this and help me understand it, I, uh, I'll
give you root on pure-data.org. Or at least, the pure-data.org web
application. OK that's a dumb reward. But please help anyway. Thanks.

(jfm3)