In article , Don Pearce
wrote:
[snip]

I just don't understand why these sorts of CDs need to be mastered into
clipping. I can understand a CD being normalised to 0dBFS, but that
would mean one hit at 0dBFS once per CD, or at worse once per track, if
tracks are mastered individually. There's just no excuse for it.

ahem Anyone in the UK who is interested in this may find the December
issue of 'Hi Fi News' worth a read. Should be out in a couple of weeks.
:-)

Note also that even just one sample of a sequence at or near the 0dBFS
level may mean a reconstructed waveform with an excusion *above* this.


However, try as I might, I can't hear the clipping in the Diana Krall
and Norah Jones, even sighted, knowing when it takes place. The Amy
Winehouse is , however, very obvious.

As an experiment, I made up a 'test CD' a while ago to try on some friends
and colleagues. This consists of a set of tracks of various types of music
where the original peaks well below 0dB, and versions I deliberately
clipped. Apart from the clipped sections the two versions of each example
are sample-by-sample the same.

It has been interesting to see how hard/easy people have found identifying
the clipped version to be. :-)

This seems to agree with something I discovered 20+ years ago. When I
designed the Armstrong 730/732 amps I fitted a clipping indicator. It
turned out to be quite difficult to hear the clipping in many cases -
although admitted this is at levels well over 200Wpc so I am not sure what
the speakers (or ears!) were doing in some cases at these levels in a
normal UK domestic situation. 8-]

Do remember that lighting the top bit light does not necessarily imply
clipping - it is just another value, and if the signal isn't trying to
go beyond that, it hasn't clipped.

Pop recordings use heavy compression, and when this is done in the
digital domain it is quite possible to have sufficient control to peak
to the same value every time. There is no reason not to normalize the
result up to max level.

Alas, my recent experience confirms that a number of CDs have successions
of samples well within 0.05dB or so of the peak values allowed on CD-A.
Level compression seems much more common, but flat-top clipping seems far
from rare. As you say, this seems utterly insane when many rock/pop CDs
squash the sound into a range of about 10dB - on a medium that should be
able to offer a range over a million times greater!

Slainte,

Jim

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