In article , Richard Wall
wrote:
Cheap CD/DVD players usually are cheap, and are compromised. I wouild
assume the same to be true of cheap amps vs better built products.
That seems to me to be a reasonable assumption. However I'd also expect
this to depend on the conditions of use. e.g. a cheap amp might sound fine
(and similar/indistinguishable from) a more expensive/better one if the
required power/current levels were modest, but sound very different when
asked to play at high levels into a speaker tha was a 'nasty' load.
I think amplifiers and CD/DVD players etc. sound different because we
have not yet achieved perfect reproduction of the recorded medium.
Well, if the recording has an imperfection, then I'd expect that to show as
a 'common mode' effect when comparing amps or players.
So called "good" componants are very close to perfect and
differentiating by any method will be difficult.
That may be so. Indeed, it may well mean that the differences become so
small that they either become inaudible, or not worth bothering about given
much larger variations - e.g. due to slight head movements or changes in
the dampness of the air in the listening room.
Rather than the image of a straight line with amplification from source
to speakers I view a system as a filter with amplification between
source and speakers. The better the filter the less it removes/adds and
the closer to perfection it gets. It is still possible to measure
electronicly differences in amplifiers and also to make them react to
inputs in in different ways ( e.g. slew rate (?))
I'd agree. However with decent components my experience is that the main
'filter' effects (to use your analogy) tend to end up residing in:
1) Choice of the specific CD (or LP or whatever medium of choice)
2) Choice of loudspeaker, their placement, the listening position, and the
room acoustic.
What interests me about that is the way magazines devote thousands of pages
to discussing (relatively tiny) differences between amps, yet almost zero
space to questions of improving your room acoustics, etc.
There are even different topographies Class A, AB and I think C and D.
DBT should and I am sure can differentiate some of these classes of
products if it cannot then the testing method must surely be faulty ?
No. Your deduction does not follow from your comment. It may be that when a
test shows no difference, that the reason is simply that any difference is
too slight to be audible, or perhaps of any practical significance.
Thus if such a test 'fails' (a judgemental word, so should be used with
care) to show a difference, it may be due to there being no audible
difference.
In such circumstances you can propose two possible hypotheses.
1) That the difference is so small as to be inaudible in the circumstances
of the test
2) That the test 'hides' the difference in some way due to the
circumstances in which it was carried out.
However the normal scientific method then requires us to either propose a
test whose results would discriminate between the above two hypotheses, or
if we cannot, then simply use the one which follows 'Occam' and requires
the least number of assumed unknown or hidden effects/variables. This
implies that we are safe to choose (1) *unless* someone can propose and
carry out a test that will discriminate between (1) and (2) by providing
results that would 'falsify' (i.e. show results inconsistent with) one
hypothesis.
Alternatively, you can propose the hypothesis that the circumstances of the
test make it 'inappropriate' for the real listening conditions. But to
establish this, once again, you need a test that could be carried out to
falsify this or its converse.
FWIW I can't comment on class C or D, but I've built and tested/listened to
various A and AB amps over the years, and my experience is that although
some sound 'different' to the others, many sound indistinguishable to me in
normal use. Provided they meet a fairly basic set of requirements and are
used within conditions they are designed to operate under.
The one area where none of the above applies is the loudspeaker, which
is still frankly a disgrace. You don't need a DBT to reveal the
differences between speakers,
Indeed. Such differences are also often easily observable using a
microphone and some simple measurements.
My critism of DBT is that it is not simple to set up in a domestic
enviroment
I would agree. Carefully designed tests like these can be extremly
difficult to carry out in a reliable manner. But this does not make them
impossible.
and of the few test I have heard of that finds differences
(recent issue of Hi-Fi Plus on cables ?) the conditions of the test are
then questioned.
Can't comment on the HFP tests you mention as I don't know anything about
them. But, yes, if the tests are not carried out with appropriate care and
rigour, then their results may be questioned. Indeed, this is normal
practice in measurement science as all measurements will be of finite
accuracy, limited relaibility, etc. But - depending on the details - that
may be adequate for some stated purpose.
The advocates of DBT/ABX all seem convinced that
there are no differences between CD players, cables and amps,
I have no idea where your "all" comes from. However I have personally never
thought or written such a thing. That said, the only way I "advocate"
DBT/ABX is that it seems to me that it represents a test approach which may
be useful for some purposes. It may help reduce some confusing effects, and
make it easier to do a reliable statistical analysis where any response is
slight rather than obvious.
those more open qualify this with a definition of "good" componants.
Even here I would be wary as two 'bad' items may have flaws that produce
similar effects, so lead to the two souding similar or indistinguishable.
I am happy to agree that when talking about "good" components any
differences will be minor and most likely built in by a manufacturer
looking to differentiate their product from the rest. Hearing a
difference in a blind test will be unlikely. What I question is that a
lot of current equipment does not meet the "good" criteria and it does
not take a blind test to prove this.
That may well be so in some cases. Indeed some 'good' items sound different
(speakers). However in such cases I would expect a BDT/ABX to also show
differences, although such a tedious method may be felt not to be worth the
effort.
If DBT/ABX does fail to differentiate products that sound different
I note the "If" that starts your statement here...
then why does it fail,
.... I think that you will first need to catch your rabbit. Only then think
about making a rabbit pie. :-)
i.e. first you will need to address the test of mutually exclusive
hypotheses outlined above. This means first proposing a test that shows
that a given DBT/ABX test *has* 'failed' to show a difference which some
other non-DBT/ABX can be *established* to 'detect'. The problem, though,
then becomes how to establish that the non-DBT/ABX test result *is* a real
and reliable 'detection' rather than an error or a fluke.
my suggestion is that the detection method used (the listener) is too
subjective and without a massive sampling set any results are no better
at providing proof than simple A-B.
For all I know you might be correct in some cases. But I think you will
need to catch your rabbit, first... ;-
Having done that, you could then examine the conditions of the tests, and
ways to check which might be having an effect.
Until, then, though, the simplest course seems to me to work on the basis
that any 'difference' that was not detected was too small to be noticed,
and hence really may not matter one way or the other if all you want to do
is sit back and enjoy the music. :-)
Slainte,
Jim
--
Electronics
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Armstrong Audio
http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc.
http://www.st-and.demon.co.uk/JBSoc/JBSoc.html
DBT a flawed method for evaluating Hi-Fi ?
Linear Mode
