"chris" wrote in message
...

"Oliver Keating" wrote in
message ...
I was flicking through "What HiFi" magazine and I came across
something very
odd - a series of reviews on *digital* audio cables, for connecting
a CD
player to an amp.

There are comments such as "this cable brings across a crisp sound a
cut
above the rest"

Now, at this point I have to shake my head in disbelief. Surely a
digital
cable about 1 metre long can easily carry a 1mbit data stream with
no
errors. Bear in mind ethernet has to carry 100mbits.


Yes a "DIGITAL cable most certainly can, but a lot of so called
"digital" interconnects arn't made with DIGTAL grade cables, and the
plugs also are not true 75 ohm, so you will start to get line
reflections, ringing on the recieved pulses (and if they are of
sufecent signal level cause pulse signal coruption and drop-outs) this
could start adding to the error rate, resulting in a less "good a
sound".

The thing is though, most of these phenominan only occur when you have
discreet pulses which travel down the line (and indeed get reflected), i.e.
you have a transmission line.

However, if you consider a data rate of 1mbit, or one pulse every
1microsecond, then say the pulse duration is 0.5micros, and say the
transmission line has a transmission speed of one tenth the speed of light
(in reality probably much faster, especially for good cables.) This means
the physical length of the pulse is 0.5e-6*3e7 = 15 metres.

So even with a lousy cable, the wavelength of the pulse is still 15 metres,
which is much longer than the typical length of an audio interconnect, so
you don't really have to treat the line as a transmission line - any
reflections would have the opportunity to bounce 15 times before the pulse
even ended, by which time it has decayed to zero and there can be sufficient
interval between that and the next pulse for any other artifacts to die
away.

Now, with a 100Mbit Ethernet cable, over a length of 100 metres, errors can
be a problem. But 1mbit over 1 metre? I would put money on it that the error
rate is zero, or negligably small.

about optical cables. There is absolutely
*no* way an optical pulse can be distorted sufficiently over 1 metre
that it
could result in an error.

This should be true ! BUT. Unfortunatly due to the design spec this
is not true.
There was some deep discussion on this whole issue a while back on
RAHE,
I too had thought like you. Then The Man from Belden explaind it
rather well: you could do a google on it his expanation should be a
lot better than mine.
But basically the Fibre call for in the spec is many times larger in
diameter that the wavelenght of the light used so instead on the light
bouncing down the fibre in a controlled fashon it bounces about in a
lot more random fashon and after a metre or three the uncontrolled
light bounces interfere with the main light signal generating extra
noise. This can cause misreading of the recieved signals, hence
errors, noise, distortion.
So by using a better fibre (which is not as cheap) that has a smaller
diameter, will improve the quality (by reducing the noise) at the
recieving end, resulting in less errors etc.

But the same arguement as above comes into play, especially with light,
where the typical pulse length is 150 metres. There is no way more than one
pulse can exist in the cable at once, so how is there any error possible?

I can only think that the testers suffered some sort of placebo
effect, or
they are in cahoots with the industry in order to provide a supply
of
customers who will shell out £350 for the "best" optical cable.

No, what they heard in the test is valid.
Sorry, its just good engineering to fix, bad engineering in the first
place.
As to the question is a cable worth £350 ? Well only your ears, brain
and wallet can make that value judgment.
I personaly would look for a much less expensive option (good dacs are
less than that).

In the end though, should you connect your CD player to your Amp using an
analogue or digital connection (I always assumed digital).

And if it is the latter, is there any point buying an expensive CD player?

snip

Who ever said life was easy :¬)

Indeedily

Happy New Year
Chris