In article , Glenn Richards
wrote:
Ok, as promised, results of tests with various filters, power cables
etc...

[snip]

First things first, I plugged the DVD player and amplifier into an
unfiltered block. I then played the test track.

I then switched power cables on the DVD player to use the Isotek, and
played the track again. This made no difference whatsoever - which is to
be expected, as the DVD player is merely acting as a transport. I
switched cables back again and played the test track to be sure, and
indeed there was no difference.

You presumably were aware thoughout of what arrangement was in use. You
also seem to have only done this a few times, not many times to form
abody of data on which any meaningful statistical analysis could be
carried out.

I then switched the power cable on the amplifier to use the Isotek
cable. Immediately there was an improvement in dynamics, percussion in
particular had much more presence and depth.

....or at least that was the impression of those involved.


[snip]

What I discovered (and the two other people in the room also heard quite
clearly) was that a filtered distribution block makes a difference, but
there did not appear to be any audible difference between the Isotek
block at £150 or the Masterplug block. Both have RFI filtering and surge
protection, the Isotek has a metal case, the Masterplug is plastic. But
none of us could hear a difference between them.

The problem is that no-one else at this point can tell if your opinions
have any weight or not since your test method may not be reliable, and
you give no data which others could uses to assess the validity or
statistical reliability of what you report.

If you wish to obtain valid results which can be used as a reliable guide
then you would at least have to:

A) Do some tests where the results can be shown to depend *only* on the
sounds being produced. i.e. ensure that those involved don't know which of
the items being compared are in use at any point when having to make
decisions.

B) Do the tests enough times to allow the results to be assessed for level
of statistical significance.

It might also help if you'd tried actually measuring or examining the
output from the system to see if you could find any changes that might
account for the opinions you formed.

It would also help to take measures to check for, or control the risk
of interpreting an effect due to some other cause as being due to
what you may incorrectly assume. e.g. ensure that you have enough
test runs to deal with alterations in listening position (acoustics)
and reverse ordering to deal with psycho- or physio- adaptions due
to immdiately previous experiences.

In this particular case, it would have been useful to repeat the tests
in your friend's house, with someone else in another room either having
the PC (alleged to be the source of assumed 'interference') on or off,
and have you say which was the case simply by listening. If you could
do this repeatedly and get the answer correct then that would be a
useful result. But if you know the PC is on or off when listening, then
it is not really very useful.

Alas, in the absence of the above, the report you make tells us about the
opinions of those involved, but does not tell us if the cables, etc,
actually did anything to the output of the system. Nor if this had
anything to do with 'filtering'.

IIUC it has been explained on more than one occasion in the past that such
'tests' do need to be carried out in an appropriate manner if we wish the
results to have any reliability as evidence. It therefore seems a shame
that you seem not to have done this. The result is that your opinions
may or may not be well-founded, and no-one can tell which since either
possibility will seem equally probable to anyone other than yourself.

Slainte,

Jim

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