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OT: reprocessing mono

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Old Today, 03:12 PM posted to uk.tech.digital-tv
Roderick Stewart[_3_]
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Posts: 2,506
Default OT: reprocessing mono

On Sat, 15 Jun 2019 11:57:15 +0100, Scott

I was told you had to change the stylus with every playing of a 78 rpm
record. Is this correct or urban myth?

When using a mechanical acoustic gramophone with a quarter-pounder
pickup, the needles didn't last very long, perhaps two or three plays.
Needles were sold in little tins of a hundred or more, and you could
get them in different thicknesses for different loudnesses. (Before
electronics with volume controls this was the best that could be done
if you couldn't afford one of the more expensive gramophones with
adjustable louvred flaps). Most needles were steel, but you could also
get "fibre" ones (not sure what they were made of) which were supposed
to last longer but didn't sound so loud.

I'd expect a sapphire or diamond stylus in a modern lightweight pickup
not to need changing so often, but the modulation amplitude of a 78
was much greater than a microgroove LP and the plastic they were made
from was harder, so perhaps even those styluses didn't last as long.


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Old Today, 06:01 PM posted to uk.tech.digital-tv
Max Demian
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Posts: 3,442
Default OT: reprocessing mono

On 15/06/2019 11:23, Roderick Stewart wrote:
On Fri, 14 Jun 2019 19:58:04 +0100, Scott

I'm just going through some old records and I see some are marked as
'mono recordings electronically reprocessed to give a stereo effect on
stereo equipment'. Before the days of computer software, how did they
do this?

The only ones I ever encountered were of classical orchestral works,
and it appeared that they'd just sent the signals through two
differently adjusted tone controls, so the high frequencies went to
the left and the low frequencies to the right. I found I could produce
an equally ghastly effect myself by using two separate amplifiers, so
concluded that that's what they must have done. Presumably somebdy
with cloth ears and who'd never heard of Adrian Boult had assumed that
high pitched instruments would always be on the left and cellos and
double basses on the right, so it would sound realistic. It didn't.

I bought a George Formby LP from a charity shop which is processed from
78s to stereo.

As well as mono playable in stereo, we also had stereo playable in
mono. This was the "mono compatible" gramophone record intended to be
safe to play with a mono pickup. This was done because the difference
component of a stereo recording resulted in vertical modulation of the
groove and it couldn't be guaranteed that all mono pickup styluses
could physically move vertically by the required amount without
damaging the record. I think they just reduced the amplitude of the
difference signal at low frequencies, which would have reduced the
largest amplitude vertical signals. The result could be a bit
lacklustre, but not nearly as bad as "fake stereo".

I've never seen one of those. In the days that many people still had
mono record players, most LPs were sold in both mono and stereo
versions. [1] The inner sleeve had a blue border for stereo and red for
mono, showing through a hole in the outer sleeve (Decca). The stereo
records had dire warnings that specifying the top radius required
(0.0005-0.0007") *and*, if being played on a mono deck, that the pickup
be stereo wired for mono or compatible, so that the needle can move
vertically as well as horizontally.

(Most people had crummy decks with crystal pickups and a crude spring to
balance the arm so I don't suppose it made much difference in practice.)

[1] Singles were always mono only until the late 60s as it was assumed
these would be bought by teenagers with mono players.

Max Demian

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