On Wed, 5 Jan 2005 08:38:13 +0200, "Iain M Churches"
wrote:

Greetings to All.

First of all, thanks to all who have given suggestion/
ideas/feedback regarding the capacitor evaluation
project.It had been suggested to me that
the ABX method should be used.

Does anyone have experience of or comments upon
this method, and suggestions as to how it should
be carried out?

I have a panel of ten people, and plan to test them
separately, with three pieces of music

1. Piano and female voice
2. String Quartet.

These in my experience are most revealing.

3. A title known to the listener, on CD,
which he/she may bring along.

It now seems, to keep variables to a minimum, that
the two caps to be compared will be fitted as output
capacitors to the same pre-amplifier, and comparison
made between the two outputs

The tests will be done in a studio control room
environment, with signals under evaluation fed
to a studio console, the automation of which can be
used to select the source at a pre-determined
instant following time code. This will
allow repetition of the test with great accuracy.

Each member of the panel will be tested separately,
and will listen to each piece of music twice. On the first
run there will be no changes, on the second, the outputs will
be switched at a TC known only to the tester. The listener
will press a cue marker, which will capture the time code at
which he/she perceived a change. This can then be compared
with the TC of the real changes.

This will be repeated once for each member of the panel,
so ten times per piece of music, so thirty times in all.
We are looking for a 60% result. By comparing TC markers,
we can rule out spurious or faulty reactions.

Any comments/suggestions welcome.


Iain


OK - comments.

First the capacitors. Go through many samples with a meter to make
sure they are as far as possible equal in value. Install them in a
switcher box so they can be changed without delay.

Check the whole system to make sure that when a change is made the
output level remains the same. Also make sure there are no switching
transients that could identify which is being used.

Put the whole thing in a separate room to the subjects. Identify the
point at which a change is made with some kind of signal light that
invites the subject to make his choice. Allow the subject to listen
for as long as he needs to make his choice.

At any point in the test, allow the subject to ask to hear either of
the capacitors identified, to verify impressions of difference.

The tester should determine the order of switching just before the
test with thirty coin tosses. He should write these down and follow
his list. The order should be a new random set for each subject.

Go for more than 60% - 75% would be more reasonable.

Do not let any subject meet the proctor at any point.

d

Pearce Consulting
http://www.pearce.uk.com