From: smee@bristol.ac.uk (Paul Smee)
Newsgroups: uk.misc
Subject: Re: Record shops (LPs)
Date: 21 Dec 92 11:01:07 GMT
Reply-To: P.Smee@bristol.ac.uk (Paul Smee)
Distribution: uk
Organization: University of Bristol

I'm suspicious of the shape of the attributions in here, so if something's
misattributed, sorry, but wouldn't surprise me.

In article <PD.92Dec18133642@mull.x.co.uk> pd@x.co.uk (Paul Davey) writes:
>
>>>>>> On 16 Dec 92 16:05:53 GMT, steve@acorn.co.uk (Steve "daffy" Hunt) said:
>-> Yes and in fact CD players gently roll off the high frequency
>-> information before the limit imposed by the sampling freqency to avoid
>-> coming to an abrupt ceiling.

Depends on the technology.  Oversampling and bit-stream players tend
not to.  That's the big theoretical advantage of oversampling players,
that they can move the hi-freq cutoff up in their filters.

>-> Although you cannot actually *hear* sound above 20-odd KHz, its
>-> absense supposedly alters our subjective perception of the audible
>-> lower frequencies.  
>
>I saw Prof. Jack Dinsdale of the University of Dundee lecture on CD's
>vs LP's last month in London.
>
>One quote was that CD's finish at 20kHz, whereas good quality LP's
>have a frequency range of up 30kHz, and that while you might not be
>able to hear a 26kHz tone very clearly, you can hear the difference
>between a 26kHz and 27kHz tone. I presume they beat together.

'Beat' is probably the wrong idea.  You can find authorities to argue
both sides of the question, but I think the general consensus is that
beats are an artefact produced in the measuring process, and so if you
can't detect the two original signals involved you don't get the beat
-- that is, it doesn't have an independent existence.

However, there are other complications.  Easiest one is that the 20kHz
limit on hearing is (as with other measurements of the limits of human
senses) a statistical thing.  Some people almost certainly go beyond
it.  (In particular, I've heard of research which seems to indicate
that chronic asthmatics may tend, as a side effect, to have a higher
upper frequency limit -- in some cases, up to an octave higher, i.e.
~40kHz.  Warning, don't quote this in learned circles unless you first
go look up the studies.  I can't provide references.)

>He also said that CD's distort most in the quiet sections (due to
>quantisation noise) whereas LP's distort most in the loudest sections.

Certainly true.  Modern CD (player) 'dithering' techniques can clean
this up so that most people shouldn't notice it, and an any case it
only really gets bad (in measureable terms) in REALLY quiet parts of
the music, which you're likely to have turned down enough to make it
unnoticeable.  Of course, not all players use the best state of the
art dithering techniques.  

The Chesky Jazz Sampler volume *2* has some examples of this; you've
got to really crank the gain up to hear it, and they warn you to turn
it back down before listening to real music, to save your speakers and
ears.  It does mean that distortion figures need taken with a grain of
salt, though, as they are traditionally measured at high levels, which
make them look unrealistically good for CD players.  On the other hand,
measuring them at low levels for CDPs would also be unrealistic, as the
distortion isn't normally audible (by most people, and assuming a good
player) at normal listening volumes.

>Summing up he said:
>
>A lot depends on the listener, but you can get sound that is as good
>as a CD or some would say better, from an LP.

This really verges on religion.  I use both, and find that there are
particular pieces of music which sound better on one or the other, but
I couldn't identify an overall trend of which is 'best'.  (However,
that's only my religion, anyway.)

-- 
Paul Smee, Computing Service, University of Bristol, Bristol BS8 1UD, UK
 P.Smee@bristol.ac.uk - ..!uunet!uknet!bsmail!p.smee - Tel +44 272 303132