OK... Here's another question...  I've got an application where we need to
update a VU audio level indication maybe 10 times a second. One way to do
this is in hardware do rectification (ideal diode) and filtering to give
the appropriate ballistics (attack and release time). This'd then go into
an analog input on the PIC.

However, since the ideal design has zero parts, I'm wondering about
another approach. How about if the incoming audio goes through a current
limit resistor to the PIC analog input. Add a clamp diode so the PIC input
is not driven negative much. This would result in half wave rectification
of the audio, since the PIC A/D would read zero for negative inputs and
read a positive number for positive inputs.

The next trick is, since we're only updating the display 10 times a second
or so, how about sampling the audio with the PIC A/D 100 times a second or
so, then averaging those samples. I'd probably average a number of samples
that is a power of two so the division by the number of samples is just
throwing away a few least significant bits.

The question is... would the result of this average be similar to the
hardware approach? Sometimes the instantaneous voltage sample would land
on zero, other times it would land on the peak of the incoming audio. Most
of the time it would land somewhere in between. Since the sampling is not
synchronized with the audio in any way, would we get an average similar to
the hardware approach described earlier?

Harold
(The ideal design has zero parts)


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