Re: IM distortion: why related to level?

Randy Yates <yates@xxxxxxxx> writes:

dpierce@xxxxxxxxxxxxx writes:

On Oct 25, 9:13 pm, dpl...@xxxxxxxxxxxx (Dave Platt) wrote:
In article <1193360000.866744.301...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,

MRC01 <m...@xxxxxxxxxxxxx> wrote:
But on Oct 24, 11:38 am, Dave Platt wrote:
Every combination of samples is valid, and corresponds to a unique
(within the system's quantization limits) bandwidth-limited analog
waveform.

This is an interesting mathematical question. Do there exist some
combinations of samples that are invalid?

Nope.

Yes, there is. The most trivial example is an alternating
positiive and negative stream of constant values. It's a
waveform which is at precisely 1/2 the sample rate,
which violates the Nyquist criteria.

I had forgotten this type of case.

The Nyquist criteria is not an "if and only if."
That is, it says that IF an input signal satisfies the
criteria, then it can be converted to digital without losing
any information. It does NOT say that if a digital signal
represents an input signal without losing information, it
satisfies the Nyquist criteria.

Show us an input function to a properly implemented
sampler that would result in such a waveform.

f(t) = sin(2*pi*(F_s / 2) * t),

assuming the sampler samples at times n*T_s, where n is integer and
T_s = 1 / F_s.

Let me be quick to add that I know this signal violates the Nyquist
criteria because it is NOT < Fs/2. However, the point I am attempting
to make is that all possible digital sequences produce valid analog
signals.
--
% Randy Yates % "Bird, on the wing,
%% Fuquay-Varina, NC % goes floating by
%%% 919-577-9882 % but there's a teardrop in his eye..."
%%%% <yates@xxxxxxxx> % 'One Summer Dream', *Face The Music*, ELO
http://www.digitalsignallabs.com
.

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