[sdiy] Re: SAD1024 different modes

[Mike I.]

Scott,
I believe the reason A/DA chose this peculiar output structure was to
increase the signal level at the BBD output... at the expense of clock
cancellation ....the reasoning being that the unit was intended for guitar,
and the input signal only changes very slowly compared to the sampling rate
(in other words, the components of the guitar signal are well below the
Nyquist frequency). So all four of the outputs will be putting out nearly
identical voltages at any given instant, reinforcing each other rather than
tending to cancel out. The "intended for guitar" rationale also helps
explain why there is almost no antialias filtering at the input (well, the
original actually had a decent filter but later versions omitted it
completely). There is also very little filtering on the output... so the
clock was always intended to be well above audible frequencies. One of the
recent fx books describes some of the ideas behind the design, as related by
the A/DA president.
Regards, Mike