Tom Fine:

> Mark's method harkens back to the days of 1630 mastering,
> where you needed to find and set your peak levels before
> you made your A-D transfer. This was definitely how my
> mother operated with the Mercury CD's;
> There are technically some very brief digital over-zeros on
> some Mercury CDs here and there, but no one has ever returned
> one because it won't play or it sounds lousy. The manufacturing
> plants tolerated them because their own QC people couldn't hear
> anything that would lead to merchandise returns.

Technically there cannot be overs in a digital audio soundfile.

This is because you cannot exceed full level, 0 dB F/S, in a digital system.

You can not have 0.0001 dB above 0 dB F/S because it is not possible to
register anything in the code that describes such a condition.

Thus a standard evolved using the meter used in the Sony 1630 that indeed
was the de facto standard when sending U-Matic master tapes to the
replicating plant for at least 10 to 15 years of CD production.

The Sony 1630 meter was available as a free standing unit, Sony DMU-30,
costing USD $2500 in 1989.

So a legal over that should register as a clipping of the actual digital
signal has been and is still 4 samples in a row at full scale and this
should be registered as overload with a RED led lighting up or equivalent.

The Sony metering system has internal DIP switches which can be set to any
sensitivity of full scale samples in a row to indicate actual clipping,
overload, but the long time agreed standard is 1-3 samples in a row are
considered legal levels while anything above 4 samples in a row, or more, is
considered as illegal.

So four samples in a row at full levels triggers the "OVER" red led
indicating clipping and is considered "Illegal" and as any and all such
U-Matic CD master must have a PQ list and error report printed and delivered
with the U-Matic master to the replicator then any actual over was ALSO
printed and if a digital master did have any overs when verified at the
plant it was rejected and sent back to the originator to be redone since
overs was not allowed at all.

So in my experience most meters today DO NOT adhere to this standard and it
is anybodys guess what they do show.

It can be anything from -0.3 dB, Pro-Tools, to anything inbetween that and
the actual old Sony standard of 4 samples in arow at full scale.

The Sonic Solutions DAW I am using SSP/USP and HD lights up as "RED" or over
at just one sample over which have these meters light almost coninously when
adhereing to the Sony 1630 standard of 4 samples at full sclae for an over

So may I suggest that any observed overs on almost any CD out there, Mercury
or other, are all legal when observed on the world standard Sony 1630/DMU30

For any other claim that something is showing red or is over I would
personally have that digital meter be tested to understand what it is really
showing when going red as most meters are simply wrong in my experience.

The Mytek DDD-603 that I am also using is a Sony DMU-30 meter copycat in
that it follows the world standard precisely in every respect and can also
be set to any amount of overs to indicate a valid over but is normally
shipped to indicate a valid over at 4 samples in a row full scale as the old
1630/DMU.30 does it.

Best regards,

Goran Finnberg
The Mastering Room AB

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Learn from the mistakes of others, you can never live long enough to
make them all yourself.    -   John Luther

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