DCO's, Anti-Aliasing, and Filters

[John Speth]

> So, from what I have seen, all anti-aliasing filters do is limit
> bandwidth. The anti-aliasing filter is a bandpass filter with a steep
> rolloff after the upper and lower limits of our hearing (10hz to 25khz)
> that makes the aliasing inaudible, or at least lessened..

I'd like to add one more point: In addition to bandwidth limiting the signal
to be sampled (using a steep filter) you are, therefore, certainly required
to sample the signal at at least twice the filter cutoff frequency.  Failing
to do this will result in the *alias* frequencies being heard when the
sample is played back.

> But, if you did not record with sufficient sampling rate essentially you
> are just going to make muddy semi-sinusoidal noise. Try it sometime..
> I hope this helps anyone who was lost in the shuffle of the discussion.

You can learn alot about this by breadboarding an analog delay line with a
variable clock that drives the BBD at audio rates.  Then fiddle around and
listen to what happens as you vary the clock rate.

John Speth
Object Engineering, Inc
mailto:johns at oei.com