What Manfred said and this, offered up by one of my all-time favorite mastering engineers:
Ghost In the Machine: groove echo in vinyl disks.
"One of the great advantages of digital audio is that both vinyl records
and analog tape suffer from the transmission of sound from one recorded
layer of tape or record groove to the next. There is no cross-talk in
digital, it is only limited by the associated analog circuitry.
Groove echo, as it is called in the industry, is the result of a double
whammy. The first whammy occurs in the cutting process and the far worse
whammy occurs in the plating and even some in the pressing process.
When a groove is cut into a master acetate the grooves are purposely cut
as close to one another to maximize the recording time of the disk. The
RIAA recording curve is designed to greatly diminish the bass
frequencies so, while recording, the bass wiggles take up 400 times less
room than they would without the curve. On a good lathe, each rotation
of the lathe will result in the newly recorded part of the groove just
touching the previous rotations engraving. On the last state-of-the-art
lathes with computers (starting from about 1978) the newly recorded part
of the groove actually nestles into the previous rotation! The sound
of the deformed plastic of one revolution is probably always measurable
in the next and on some occasions is audible.
A newly recorded acetate is a joy to listen to. It is far, far quieter
than the final pressing (no matter whose vinyl formulation is used), it
is totally free of ticks and pops (until you touch it) and the groove
echo is very low.
The acetate is almost a living thing. How a lacquer electroplates is a
function of how well cured the lacquer is. The amount of oils in the
acetate are a function of how the manufacturer made it, how long it was
cured at the plant, and how long it was allowed to acclimatize to the
cutting room environment before cutting. After cutting, time starts to
act on the blank and the groove echo begins to build up within the
master lacquer. The first 24 hours are the most critical for avoiding
groove echo build-up. The idea is to get the lacquer into the plating
bath as quickly as possible.
Pop music is so limited in dynamic range that groove echo is rarely a
problem except in the lead-in and in-between bands. Classical music is
difficult to cut, plate and press. It is ideal to have the lathe in the
same building as the plating plant. The only East Coast pressing plant
that has this is Europadisk in NYC. In the hey-day of lacquer cutting
there were 2 independent electroplaters in NYC and they would have
messengers pick-up the lacquers from all the cutting houses in New York
every day.
Obviously sending lacquers by over-night delivery is less than ideal but
works well enough. Because of this groove-echo problem, lacquers were
rarely sent overseas to foreign licensees. This is why European cuts
were different from the American originals. The European cuts were
almost in every case cut from 15ips ¼ inch Dolby noise-reduced tape
copies of the mastering done in America. Many aficionados of course feel
that anything European must de facto be better than the US but they were
always working from tape copies, as we did from their releases. With
digital masters for CDs and cassettes, this is no longer a problem,
merely send a clone overseas and every licensee puts out the exact same
product (except for countries like Japan where the record companies
almost add a bonus track to cut down on imports).
The plating process is where most of the groove echo was added. If the
bath the lacquer was put into for cleaning was too hot it would greatly
add to the echo problem. In the electroplating process there were
theories that the best plating had to be done very slowly and with the
lowest current possible to prevent groove echo. Once the first few
microns of nickel were set in place the intensity of the plating could
be greatly increased. Obviously when they were in a great rush they
would speed this process along. Test pressing were often rejected for
groove echo problems. The mastering engineer would often have to re-do
a lacquer and use the "echo" or "add land" facility on the lathe to
artificially spread the spacing between the grooves. On some classical
cuts, especially contemporary recordings, one can usually see with the
naked eye grooves spread-out before a big percussive attack.
DMM, Direct Metal Mastering in which the master disk is cut into copper
foil instead of acetate has far less groove echo problems because of the
much harder surface and because of eliminating the silvering process.
There still can be some however.
I hope this isn’t more information that you ever wanted to know.
Enclosed are 3 jpg photos, one is the VMS-80 (Neumann) lathe at Gateway
Mastering. The next is the control panel on the lathe and finally a
close-up of the "add land" button that spreads the grooves out when one
pushes it to the degree set by the little wheel-knob under it!
Sincerely,
Bob Ludwig"
