an idea + zipper noise

[Ian A. Vine phone UK 0171 419 3450]

	Suggestions for hardware, there are some neat 8051 derivatives
	available these days with built in DAC/ADC and of course
	the standard serail i/o and a lot of digital i/o. So adding
	the MUX i/o, battery backed RAM, ROM, display and MIDI buffer
	to one of these '8051' and you're half way there (yea right).
	
	Seriously, the 8051 route seems good, cheap component cost, 
	cheap (or free) developement tools also using the chips i/p
	sorry should be i/o, ports you do away with a lot of the
	glue logic you normally need.

	Someone mentioned zipper noise when using ADC/DAC. I thought 
	that zipper noise was only caused like this. You have a signal
	(audio) going through a VCA the gain of which is controlled by
	a DAC. If the DAC output voltage is changed when the signal is
	not at the zero crossing point, you get a sudden jump in signal
	level giving rise to the unwanted distortion. Maybe the system
	needs some zero crossing feedback or the DAC/MUX outputs need toi
	be suitable filtered.

	Anyway I guess the idea is to keep it simple.

Ian