[Table of Contents]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: CDs, was DATs, Was Re: arsclist Duplicating casette tapes

George Brock-Nannestad wrote:
> From: Patent Tactics, George Brock-Nannestad
> Mike Richter wrote:
> >
> > Note that as Jerry has pointed out, BLER is not a sufficient measure
> > of quality. However, it may be adequate for purposes such as
> > identifying the faulty disc in an archived pair.
> ----- the usefulness of BLER in this context is that its increase over
> time (cleaned of inter-apparatus variability!) will indicate the
> progress of decay. If it does not increase, there is no need to
> recopy yet. Do not make a BLER determination based on just one
> run, but average e.g. three consecutive runs and repeat after a
> month. If there is no change, repeat after two months. Still no
> change, repeat after 6 months, and if you are lucky you may go
> annual. Once an increase is noted reduce the time interval again.
> For a large collection you will need a log file and staff.
> The expensive testers are able to test the media before recording,
> but the cheap (but time-consuming) BLER test needs a recording,
> the erroneous reading of which activates the error correction. The
> output signal is perfect up to the time where non-correctible errors
> occur.
> George

Although BLER is one of many useful quality indicators, it is a poor
end-of-life indicator. See http://www.mscience.com/longev.html for test
results instead of opinions. A disc may degrade to the point of read
failure without a perceptable increase in BLER.

Our FAQs at http://www.mscience.com/faq.html point out the problems of
using BLER as a sole indicator of quality. Drill one 2 mm diameter hole
in the information area of a CD, making it unreadable in most drives.
BLER will increase slightly but will remain well within spec.

Media Sciences

For subscription instructions, see the ARSC home page
Copyright of individual posting is owned by the author of the posting and
permission to re-transmit or publish a post must be secured
from the author of the post.

[Subject index] [Index for current month] [Table of Contents]