Re: Digital volume control question....

In article <slrne7avq0.1d7.news0309@xxxxxxxxxxxxxxxxxx>, John Phillips
<news0309@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On 2006-05-24, Nick Gorham <nick@xxxxxxxxxxx> wrote:


I noted, BTW, that the integrator used in the test setup employs another
capacitor which must be assumed to be linear for the test to work. I
hope the experimentor used a "good" linear capacitor there! Also I see
the X-axis (voltage) is capacitor-coupled to the 'scope.

Yes. These are examples of the reasons why the details of any such reported
'measurement' have to be treated with caution unless we know more about the
performance and calibration of the test system. (Also, as Arny pointed out
IIRC, the source using an audio transformer.)

However my reaction was to feel the above didn't matter once we'd
established that the actual conditions of the test were of dubious
relevance. No point in worrying about details if the test situation was
orders of magnitude different to those which are of actual interest to us.

Also I would point out that I believe the hysteresis observed is not,
per se, a linearity issue. I think hysteresis will arise from parasitic
series inductance or resistance, and also from dielectric absorption.
These may well be defects from ideality but in spite of the article's
title are not capacitor linearity issues.

Indeed. And may also in practice be orders of magnitude less significant
than implied by the curves when we move to a more relevant set of
conditions of use.

Alas, I have the impression that results like those on the pages Nick
directed us to are essentially produced on the basis, "We think the caps
sound different, so lets find a test which shows differences." This can
lead to a behaviour I have elsewhere called 'MOOM'. Mountains Out Of
Molehills. Another example being the way it became trendy some years ago to
claim that 'skin effect' or 'proximity effect' was a 'reason' for cables to
son=und different. Thus a real, but generally tiny, effect can be inflated
to be a 'reason' for a claim or belief...

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html
.

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