Understanding the PT2399 delay IC

[knutolai]

Hi everyone!
I recently stumbled by the Sewer Pipe Ring Verb thread here on the forum on got curious on fully understanding the PT2399. I thought it could be useful to make a thread devoted to questions and explaining of the chip as a lot of the pins are still half a mystery to me. 
So!
I've been over the datasheet (I've also been searching for other documentation without any luck) and the big mysteries to me are the pins 8 to 15. I have three main points I need help clarifying:

I:
Pin 16 "LPB1-IN" is the signal input pin Thats pretty obvious to me. I don't however understand why this is part of a low pass filter. 
To rephrase:
What is the point of filtering the signal before it has been delayed? Also is LPB2 just a spare low pass filter left on the IC for our convenience?

II:
why is the delayed signal split and sent through a modulator and a demodulator separately? How does these to signals stand out from each other?

III:
In regards to the modulator and the demodulator: What is the application of the accompanying current controls CC0 and CC1?

If anyone know of articles explaining any of there questions please post them here!

[CynicalMan]

http://valvewizard2.webs.com/PT2399_Data_Notes.pdf

[PRR]

> What is the point of filtering the signal before it has been delayed?

The "delay" actually chops the signal into many time-slices.

If an audio signal frequency is more than half of the chopping rate, it will be "aliased" to an utterly different and usually annoying frequency. We normally filter-off such inputs.

Keywords for search--  nyquist, aliasing, sampling

> why is the delayed signal split and sent through a modulator and a demodulator separately?

Are we sure the _delayed_ signal goes to "DEM"? Or is this just a case of twisting the drawing to fit the pin-out?

Looking at the schmitt-trigger near the input, I would assume a Delta-sigma technique for analog-digital conversion.

[knutolai]

CynicalMan:
That's certainly a more detailed schematic than the one I found in the datasheet! Thanks a lot!

LPF1:
Removes frequencies higher than the samplig frequency divided by two. That is the sampling frequency of the AD-coverter. Thanks PPR you are allways very helpful!!

MOD/DEM:
On both the datasheets I've looked at the digital delay is sent to both DEM and MOD. I found this (http://en.wikipedia.org/wiki/Delta_modulation) article which pretty much explaines the matter of there being a MOD, a DEM and their acompanying opamps. (I'll be doing my research more thoroughly next time) 
These components form a DA-converter.

Now about the CC0 and CC1 I found this in another thread:
"I've been told by the manufacturers (and there's no other way to find this out) that pins 7 and 8 are used to smooth the a biasing supply inside the modulator (MOD) and demodulator (DEM) blocks.  There's no reason to mess with these pins, or the caps on it.  (Initially I thought this was part of the ADM slope control but it's not)."
-Rob Strand
http://www.diystompboxes.com/smfforum/index.php?topic=29859.0

[PRR]

> article which pretty much explains the matter

Good. (Because although I know the words, I could not build or explain a delta-mod system.)