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[burakkucat]

For years I have just regarded analogue to digital and digital to analogue converters (ADCs & DACs) as "black boxes" which worked.

In catching up on my understanding of Beattie's System X (and System Y) exchanges I discovered simple descriptions of how the ADC process operates for pulse code modulation (PCM). However no matter where I looked I could not find any description of the DAC process. 

Does anyone have an appropriate link to a simple description of the DAC process, please? Or, failing that, could somebody please describe how the process operates?

[sevenlayermuddle]

The simplest, is simply to rely on different resistors, one per bit, to add to the current flow.

http://en.m.wikipedia.org/wiki/Resistor_ladder

The problem is that whilst those of us old enough remember 20% tolerance for resistors as OK and 5% as pretty good, once you get beyond a few bits you need incredibly close tolerance for it to work accurately.

Or such is my recollection, from an era in which exam results suggested I understood such things.   

[burakkucat]

Thank you for that link, 7LM.

After significant consideration, I can now "see" that a R-2R ladder, a voltage source, a clock source and logic gates make up a basic "proof of concept" DAC. 

I must admit that I found it somewhat harder to "see" than a PCM ADC.

[sevenlayermuddle]

That is curious as I am really struggling to remember how ADC works.  Intuitively, it seems much harder to me, that way around.   

But don't spoil the suspense.   I'll give it a week or so and, if I still haven't remembered, and haven't forgotten the question, I'll resort to Internet.