Archived from groups: rec.audio.tech (
More info?)
I used to be a CD mastering technician...years ago. Very interesting
science making those things...
It's been a while, but I seem to remember for the longer playing CD's we
would adjust the pitch on the CD master, get the 'groves' closer together,
within a spec, to get more information on the CD. Reckon there were specs
for how close to the edge we could place the information. The glass master,
with a photofilm layer on it, would be hand rinsed to remove material
exposed by the laser. We'd put that into a bell jar, pump out the air and
flash a silver coating on it. Afterwards we'd carefully place that silvered
glass master into a sealed container and it would go to a nickle plating
area. They would create a nickle Father from the master, a Mother from the
Father and stampers from the Mother. The stampers would go to the plastic
injection molding machines. Clear plastic CD's were produced. These were
individualy placed into a rig with aluminum wire wrapped on a tungston
filiment below each CD. The rig was rolled into a chamber and had the air
pumped out. The alumin wire was heated untill it flashed a coating on the
CD. The CD's were then sent through a laquering and silkscreen print
process. Our QC dept would inspect the first production run for CD's that
didn't have proper aluminum coatings (thin or holes), stains, physical
imperfections etc. We played them through Studer CD players connected to a
'computer' to look at the BLER, block error reates. The stampers had a
given life in the injection molding machines and you could see the BLER rate
going up over production runs. You could produce more stampers or mothers
to make more stampers but eventually they wore out. There were a lot of
things that could keep a run from seeing the light of day.
Anyway, it's easy to ruin a production run due to process or bad handling
anywhere in the chain. I remember in the early days we scrapped a lot of
stuff. In the modern days I believe the entire process is done in a single
enclosed machine and scrap would be very low.
To you original question about keeping the playing time down, it was easy
for us to make CD's of most any playing length becasue we would just change
the pitch. I bet the real problem would be how well CD players of the day
could play longer playing CD's with the 'groves' closer together. Just a
guess....
Brings back memories
Kevin
"Steven de Mena" <demenas@comcast.net> wrote in message
news:3vednYqcNtRItbTenZ2dnUVZ_smdnZ2d@comcast.com...
> Someone mentioned to me that when CD's first came out in the 1980's they
> initially had yield problems and thus intentionally tried to keep playing
> times down. This infers that here were more problems producing CD's of
> longer length. Is this true? By "longer" I mean 60-74 minutes, I am not
> talking about CD's longer than 74 minutes.
>
> I know when the factories started up they had production issues but I
> don't recall ever hearing it was connected to the length of the CD.
>
> Steve
>
>
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