audio-->A/D level conversion

[David Stoutamire]

I am building a project to do some digital signal analysis of
`standard' audio input using Motorola's 68HC11 evaluation board.
I would like to use the on-chip A/D converters to sample input,
but the range of convertion is fixed to a range roughly
Vss---Vdd. I would appreciate any input on:

o I would like to do sampling with as little disturbance
to the input line as possible. What sort of high impedance
w/amplifier circuitry should be used?

o I will not know the voltage ranges before hand, and of course
the input may be subject to excessive voltages. How can I
get the voltage levels to the proper range? Will a pair
of back-to-back zener diodes give adaquate protection?

Losing a few bits of precision from the 8 bit converter is okay -
the software should be robust enough to deal with noise. Mostly
I am worried about getting out of range of the 68HC11 and frying
it in one way or another. Frequency response needs to be good in
the human audio range but doesn't matter above that.

Thanks in advance; I have experience designing digital hardware
and software but my analog is too shaky to trust this design on.

-= David Stoutamire =-

[Stephen Kosonocky]

There is a term used "Effective Bits" to describe the quality of an
A/D converter. Does anybody know the definition? Please E-Mail responses
if possible. Thanks.

~~~~~
- - )