I recently was given about 600 LPs, of varying material. After eliminating
Mrs Mills Piano Party, Suddenly it's Des O'Connor and The Hits from the
shows played on the Kazoo, I have got about 150 classical LPs in pretty good
condition, even though many go back to the early 60s and a few to the late
50s.

Some of the RCA discs have the Dynagroove system, which, if I remember
correctly, involved pre-distorting the recording to compensate for the
tracing distortion of a 0.7thou spherical stylus. The system wasn't taken
up by other labels, and anyway, 0.5thou sphericals soon were available as
were ellipticals, rendering the system unnecessary.

Playing the LPs with my cartridges, all of which have line-contact styli, I
would have expected that the treble would have sounded more distorted than a
non-Dynagroove LP, but in fact, these seem to be quite clean at the top,
certainly no worse than others.

Does anyone know the detail of how the Dynagroove system worked, and what
effect it would have on being played with a modern non-spherical stylus.

Thanks

S.

"Serge Auckland" wrote in message
...
I recently was given about 600 LPs, of varying material. After
eliminating Mrs Mills Piano Party, Suddenly it's Des O'Connor and The
Hits from the shows played on the Kazoo, I have got about 150 classical
LPs in pretty good condition, even though many go back to the early 60s
and a few to the late 50s.

Some of the RCA discs have the Dynagroove system, which, if I remember
correctly, involved pre-distorting the recording to compensate for the
tracing distortion of a 0.7thou spherical stylus. The system wasn't
taken up by other labels, and anyway, 0.5thou sphericals soon were
available as were ellipticals, rendering the system unnecessary.

Playing the LPs with my cartridges, all of which have line-contact
styli, I would have expected that the treble would have sounded more
distorted than a non-Dynagroove LP, but in fact, these seem to be
quite clean at the top, certainly no worse than others.

Does anyone know the detail of how the Dynagroove system worked, and
what effect it would have on being played with a modern non-spherical
stylus.


I'm sure I've got a disc or two that claim to be 'Dynagroove System' or
somesuch, but I can't say I've noticed anything out of the ordinary.
Wakipaedia has this on it:

http://en.wikipedia.org/wiki/Dynagroove

"Keith G" wrote


I'm sure I've got a disc or two that claim to be 'Dynagroove System'
or somesuch, but I can't say I've noticed anything out of the
ordinary. Wakipaedia has this on it:

http://en.wikipedia.org/wiki/Dynagroove



Seems to have been about as popular as a trip to the dentist anyway:

http://ernienotbert.blogspot.com/200...ynagroove.html

"I have got about 150 classical LPs.....Some of the RCA discs have the Dynagroove system..."

Er, well - typically only if they were the US releases.
Decca stopped importing Dynagroove stampers after just a few years
(c.'65/6) - even though 'Dynagoove' was still emblazoned on the
sleeves/labels thereafter (and until RCA set up their own UK factory
in Washington, Durham in about 1969. AFAIK RCA UK didn't utilize the
system - also they re-cut back-catalogue titles, but sleeves weren't
amended/old stocks used).
In other words, there are not too many genuine Dynagoove's pressed in
the UK.
They can be pretty 'dynamic' - but it wasn't really RCA's best
recording period.
For a good classical original RCA/Decca-pressed Dynagroove, Ravel:
Daphnis et Chloe / Roussel: Bacchus et Ariadne, 2nd Suites - (Chicago
SO/Jean Martinon) - takes some beating.

Seems to have been about as popular as a trip to the dentist anyway:

http://ernienotbert.blogspot.com/200...ynagroove.html

Trying to ensure that the signal coming out of your cartridge is as
close as possible to the original recording signal is a laudable
exercise. If they'd got it right you'd be able to get superb music using
a 6 inch nail as a stylus (an extreme example). Or perhaps we'd all
still be using those wind-up gramophones with the large horns and
(optional) small dog?

I wouldn't criticise adding one form of distortion to offset another
form of distortion - that's all that negative feedback loops do, and who
manages without those, these days?

Of course, tuning the groove to fit every "Mr Perfectionist"s view of
ideal was an exercise in futility.

--
Steve Swift
http://www.swiftys.org.uk/swifty.html
http://www.ringers.org.uk

In article , Serge Auckland
wrote:

Some of the RCA discs have the Dynagroove system, which, if I remember
correctly, involved pre-distorting the recording to compensate for the
tracing distortion of a 0.7thou spherical stylus. The system wasn't
taken up by other labels, and anyway, 0.5thou sphericals soon were
available as were ellipticals, rendering the system unnecessary.

IIUC The above is correct. Although I think they were a bit vague about how
the 'correction' was done in practice, so what they did may not have
actually corrected the spherical distortion with realistic cases. Possible
just make some sine test tones seem better in specific cases.

Playing the LPs with my cartridges, all of which have line-contact
styli, I would have expected that the treble would have sounded more
distorted than a non-Dynagroove LP, but in fact, these seem to be quite
clean at the top, certainly no worse than others.

Does anyone know the detail of how the Dynagroove system worked, and
what effect it would have on being played with a modern non-spherical
stylus.

It will change the resulting distortion. The problem is that there are a
number of 'competing' distortion mechanisms involved in the LP recording
and replay, so it is difficult to say how much effect this will have. You
could model the differential between the contact radii, but there may be
other - bigger - contributions that swamp this difference.

I suspect that for the above reasons 'dynagroove' was seen as a waste of
effort by most LP manufacturers.

There is perhaps a parallel here with the way it is possible to 'tweak' the
IF system of an FM tuner to get lower distortion for some test signals.
This has on occasion allowed a tuner to get magazine measured THD values
below what is actually possible for an 'ideal' FM tuner. However it does so
by arranging for some cases to be 'better' at the expense of other being
'worse'. Not much help when music isn't just a 300 Hz L+R 30% modulation.
:-)

Slainte,

Jim

--
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Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

In article , Steve Swift
wrote:

I wouldn't criticise adding one form of distortion to offset another
form of distortion - that's all that negative feedback loops do, and who
manages without those, these days?

I would not agree with the above as it misrepresents what negative feedback
actually does.

Negative feedback does not 'offset' "one form" of distortion with
"another". (Nor is this "all" it does. :-) )

A better description is that it compares the input with the output and
adjusts the system to reduce discrepencies. Thus it changes the effect of
any nonlinearity within the loop. It doesn't do this by using "another"
form of distortion as a comparison for "offset".

Might be more appropriate (although perhaps a rather an obscure
description) to say it uses the the same "distortion" against *itself*. Or
it essentially *subtracts* the orginal distortion from itself. No "another"
involved.

Unless, of course, you regard the input signal as being "distortion". :-)

The problem with dynagroove was that it could not do this as it was trying
to 'guess' what distortion would arise on replay and pre-apply a
'correction' without being able to sense or respond to what would actually
happen when the result was played. Made worse as the replay would vary so
much from one system to another.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

A better description is that it compares the input with the output and
adjusts the system to reduce discrepencies. Thus it changes the effect of
any nonlinearity within the loop. It doesn't do this by using "another"
form of distortion as a comparison for "offset".

I was thinking of the Texan amplifier. It uses really cheap 747 op-amps
and a hefty feedback mechanism so that the output waveform is all but
identical to the input waveform (except in amplitude).

If you were to listen to the intermediate stages, you'd probably be
aware of all sorts of horrible distortions (the 747 never claimed good
linearity). So in the middle (between input and output stages) you have
distortion, and the negative feedback introduces and equal, but opposite
amount of distortion and feeds it into the -ve input of the input stages
747.

One fascinating aspect of the design was that the volume and tone
controls affected only the feedback loop. In effect, the wrong volume,
or a lack of treble was just another sort of error that had to be corrected.

I suspect we should be in alt.semantics :-)

--
Steve Swift
http://www.swiftys.org.uk/swifty.html
http://www.ringers.org.uk

In article , Steve Swift
wrote:
A better description is that it compares the input with the output and
adjusts the system to reduce discrepencies. Thus it changes the effect
of any nonlinearity within the loop. It doesn't do this by using
"another" form of distortion as a comparison for "offset".

I was thinking of the Texan amplifier. It uses really cheap 747 op-amps
and a hefty feedback mechanism so that the output waveform is all but
identical to the input waveform (except in amplitude).

[snip]

It is not unusual for a system to include more than one source of
nonlinearity. However the feeback can then act upon the entire system,
and reduce the nonlinearity of the system's response. So far as the
feedback is concerned, it can normally treat all the sources in terms
of their composite effect. It need not employ some 'extra' source
which would otherwise have been absent in order to 'offset' the effect.


One fascinating aspect of the design was that the volume and tone
controls affected only the feedback loop. In effect, the wrong volume,
or a lack of treble was just another sort of error that had to be
corrected.

Well, it would be unusual to do that as part of the power amp stages. But
it was common for feedback to be used for the tone control mechanism.

For example, the widely used 'Baxandall' tone controls used the feedback to
adjust the response in most cases I know of. Indeed, when I pointed out
that it wasn't correct that what you'd said was "all" feedback did I was
thinking of its use to control frequency and phase response (i.e. linear
properties, not nonlinear distortions).

I suspect we should be in alt.semantics :-)


That may well be so for various of the conversations on this group. :-)

However I don't think it is the case here. The problem is that the
comment you made about negative feedback presented it as working
on the basis of requiring "one form of distortion to offset another".
i.e. requiring *two* sources or forms of distortion. My point was
that this is simple incorrect. No 'other' form or source of distortion
is required.

So my point was that the engineering isn't as you described. I don't
regard it as 'semantics' to find that a description is incorrect. I
regard it simply as a mistake. Although I appreciate that the wording
did not say what you meant, and expect that you do understand feedback
perfectly well. But my concern is that someone who does not might be
mislead.

Your description would be more appropriate for a 'nulling' or cancellation
method where two sources are employed. But need not involve any feeback.
In the context of this thread, this distinction is relevant as the
'dynagroove' system was a method which tried to cancel or null one
distortion with another - but this involved *no* feedback mechanism
to compare the two in reality. The LP cutting system had no way to
sense what the LP replay system would actually do when playing the
LP.


Jim

--
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Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

On Sat, 19 May 2007 10:03:27 +0100, Jim Lesurf
wrote:

Your description would be more appropriate for a 'nulling' or cancellation
method where two sources are employed. But need not involve any feeback.
In the context of this thread, this distinction is relevant as the
'dynagroove' system was a method which tried to cancel or null one
distortion with another - but this involved *no* feedback mechanism
to compare the two in reality. The LP cutting system had no way to
sense what the LP replay system would actually do when playing the
LP.


This is pre-distortion. It is currently widely used in RF power
amplifiers to lift the third order intercept point sufficiently to get
acceptable output power from RF power transistors, which are notorious
for their "soft" transfer characteristic. GSM wouldn't be economically
possible without pre-distortion.

The transfer curve of the power amplifier is measured, and then one of
two things happens. If the solution is a hardware one, a matrix of
diodes and resistors is designed to straighten the overall curve.
Alternatively in software, the lookup table for the DAC that creates
the signal is changed to oppose the errors of the power amp.

d

--
Pearce Consulting
http://www.pearce.uk.com