In article , Arny
Krueger
wrote:
"Jim Lesurf" wrote in message


Varies. IIRC The largest number I found was one track on a
'remastered' sic Hendrix CD where there were there were thousands of
samples in flat-top-runs of clipping.

But how do you know that they weren't simply too-loud, as opposed to
being a consequence of only samples at or below FS?

Two reasons.

1) In many of the cases I examined I have more than one version (different
CD issues and/or LP) and the stats of their dynamics clearly differ with
the clipped version showing clear signs of clipping. e.g. a secondary peak
at 0dBFS. In itself this is not conclusive. But when combined with...

2) The data shows runs of identical (or in some cases near identical)
values at each of the clipping points. The chances of this occurring
without clipping are statistically remote. Given the other issues of the
same source material without the effect it seems clear it wasn't part of
the source waveform.

Visual inspection (cf below) of the waveforms also tends to confirm the
presence of flat-top clipping.

FWIW I also found examples of 'soft clipping; where the waveform on the CD
can be seen to squash up against a max level, but where the sample runs
were similar, not identical. So in some cases you can identify runs which
seem to have been flat-topped, and others where the waveform has been 'soft
clipped'.

Have a look at the Henrix and 1812 examples I show as plots. They look
like clear cases of flat-top clipping to me. Afraid I didn't have the space
or time to do all the examples I found. If you examine the waveforms
the diagnosis seems fairly clear to me. However if you have other evidence
I'd be interested to see the details.

I'm speaking about just the latter kind of waveform that goes over FS
even though all the samples that make it up that ever existed are at or
below FS.

If you look at my HFN articles on the audiomisc website you can see that I
have dealt with three distinct problems in different articles. One is
flat-top clipping, another is excessive level compression, and the third is
where sets of samples indicate out of range intersample values.

However if you doubt what I report, then please do a similar analysis of a
range of pop/rock CDs of recent manufacture and report your results. I'd
genuinely be interested in seeing what you (and anyone else) gets as I was
only able to do a small number of examples for lack of time, etc. And the
more people pay attention to this, the more chance we have of getting the
producers to cease clipping the CDs. As I indicated previously, I can't
say how many CDs have the effect to a given extent as I was unable to
examine a large enough selection to get results that would have
statistical reliability. So can only say that I found it easy to
find examples from trying just a small number. I'd welcome more
data from a bigger range of CDs.

Slainte,

Jim

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