"Jim Lesurf" wrote in message
...
In article , RdM
wrote:

Just one small typo;- eh? :=})

"it is hard to answer this question with any confidence as we lack the
necessary date"

I must have been thinking of Christmas... No mention of walnuts, though.
:-)

Cheers,

Jim

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It's interesting (at least to me!) that although this problem has existed
for as long as digital audio has, in the early days of digital, we always
left a few dBs headroom, even as much as 10 dB if the levels couldn't be
precisely controlled. (1)

Finished CDs still left several dBs headroom, and never used to be
normalised to 0dB as they are now. Consequently, we never experienced this
sort of problem, and it was then acceptable for digital players to clip at
just over 0dBFS, albeit for the wrong reason.

(1) BBC practice is still to leave 10dB headroom by using the EBU stanrdard
of 0dBFS=+18dBu for their converters. Peaking the signal at +8dBu on BBC
PPMs leaves the theoretical 10dB. However, it is now recognised that the BBC
PPM underreads on very short term peaks by something like 4dB depending on
programme content when compared to a true-peak meter, so the actual headroom
left will be closer to 6dB.

I have recently put our local Hospital Radio Station on the Internet, and
had to put a hard-limiter before the encoder as even though the PPMs peak
at 6 (+8dBu) on music which is hard-disk or CD derived, the real levels go
over and clip the encoder. The gain-reduction meters on the limiter indicate
2-3dBs gain reduction fairly frequently even though this doesn't show on the
desk PPMs. It also helps with some of our more enthusiastic presenters who
don't watch their levels....

As Jim says, this might account for why some CD players sound different to
others. There is a supreme irony here that all CD players *would* sound the
same if CDs were mastered properly. Ah well....

S.


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