On Tue, 1 Aug 2006 17:26:04 +0100, "Paul" wrote:


"Don Pearce" wrote in message
...
On Tue, 1 Aug 2006 16:32:38 +0100, "Paul" wrote:

snip

It is neither a bodge nor a fix. It is a way of using a resource that
would otherwise be wasted - high frequency headroom. An exactly
matched amplitude/phase curve is exactly equivalent to flat frequency
and phase, and there is no problem whatever in making that match.

Are you telling me that an RIAA filter is optional for vinyl?
My understanding is that it is a prerequisite and that it has to be employed
because it is impossible to cut a groove at high frequencies (perhaps even
low frequencies). The same being true for retrieval - a stylus simply could
not track it accurately even if it could be cut. Without it's use, the vinyl
experience would be appalling.
I believe that, because of the limitations, information is
compressed/omitted/converted or whatever and reconstituted in the amp. Am I
wrong here? I am more than happy to be told when I am wrong. If I am
correct, it is a bodge etc put in place to overcome limitations.


All pre-emphasis is optional - but things audio tend to work more
effectively with it, particularly vinyl, which needs all the help it
can get in terms of signal to noise ratio. FM radio uses pre-emphasis
simply because it is a good idea - it makes it a bit quieter. Many
years ago it was observed that the amplitude vs frequency distribution
of music and speech was heavily weighted to the bottom end. This meant
that there was a huge amount of modulation capacity going to waste at
the top end. It was an obvious thing to do to boost the top end
frequencies to fill that space, then cut them back again at the
receiver. It is trivially easy to match the two curves to a small
fraction of a dB.


And do remember that the CD specification includes the option to use
pre-emphasis.

But is it used? More to the point, as it is optional, it is clear that it
isn't necessary.

You will never know. Your CD player won't tell you. If you play mainly
modern pop you can be sure it isn't used, because that kind of music
tends to fill the frequency space without de-emphasis.

d

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