Iain M Churches wrote:
(...)

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.

TBH, I would tend to present two musical intervals (I1 and I2),
consisting of the same musical passage played on the two bits of kit.
The listener would need to identify which interval contained (e.g.) cap
A. The listener would get accuracy feedback after each trial.

The one problem with this method is that it is less intuitive than
other methods (such as the one you describe). The advantage is that it
should be about the most sensitive method available for detecting
differences, and I suspect more sensitive than the method you've
suggested. Another advantage of the 2-interval method is that any noise
from the switching would occur in the interval between trials (and
could be muted?).

Your timecode response also has response time included in the ... er
.... response, so it's not going to be a spot on accurate measure of
when the listener detected the switch. You should also discard (mark as
incorrect) any responses that occurred early, even if this was just a
matter of ms early. Unless your listeners have ears sensitive to the
future...

I would also include 'switch' trials where no switch actually occurred.

Ideally you would do far more than 30 trials, and use something like d'
as a measure of ability to carry out the discrimination. It can take a
while to learn to use accuracy feedback and thus to zero in on what
exactly to listen for. With 30 trials, you risk not picking up small -
but detectable - differences.

Steve.