Bob, your earlier assumption of the vertical-lateral stereo record was
correct with regard to some of the early stereo proposals. But that system
would not have been compatible with playback of a stereo record on an older
mono lateral cartridge. This was one requirement of any stereo record
system that would get the blessing of the record companies. Thus, the 45-45
system was developed that does as you say - one channel is a combination of
vertical and lateral motion of one groove wall and the other channel is the
same on the opposite groove wall. To be compatible with mono lateral pickup
cartridges, this requires that the SUM or in-phase conponents of the two
stereo channels to be represented as the lateral components of both channels
which will then cause pure lateral motion of the pickup stylus and which
will present the stereo recording as fully "folded down" into mono and be
playable on a lateral pickup. The DIFFERENCE between the left and right
channels is represented purely as the total vertical component of stylus
motion. This signal is not pertinent when hearing the stereo program folded
down to mono, and this vertical signal is not detected by a lateral pickup.
You ask how it's possible to separate the two channels in one groove in
this manner. The answer is that each signal generator in the pickup
cartridge is responsive to only ONE axis of modulation. So if you cause
modulation on the axis which is purely perpendicular or orthogonal to the
sensitivity axis, there is no component of the signal along the sensitivity
axis and the signal generator does not respond to that modulation.
By placing two such signal generators in the stereo pickup cartridge, each
responsive to the 45 degree angle from the vertical as represented by one
groove wall, note that
one groove wall is 90 degrees differently inclined from the other - in other
words, the groove is cut with a 90 degree angle between the sidewalls.
Unlike the case with pure vertical or lateral cut mono records, this 90
degree angle of the groove is a REQUIREMENT of the 45-45 stereo groove.
This allows the wiggles from one groove wall to move the stylus in a
completely orthogonal motion relative to the modulation from the other
groove wall. Thus, each signal generator is responsive ONLY to the
modulation from the groove wall which causes stylus motion along its
sensitivity axis, and that generator does not respond to stylus motion
caused by the other groove wall whose axis of stylus motion is orthogonal to
its sensitivity axis. This allows the two channels to exist in one groove,
and the crosstalk between channels is theoretically zero.
In practice, real world stereo pickup cartridges do not achieve perfect
separation but they do a pretty good job, typically achieving from 20 to 40
dB of separation between channels over the entire audio frequency range.
Separation above about 20dB when auditioned via loudspeakers is essentially
indistinguishable from perfect separation by listeners.
Greg Bogantz
----- Original Message -----
From: "Bob" <[email protected]>
To: "Antique Phonograph List" <phono-l at oldcrank.org>
Sent: Sunday, November 02, 2008 2:47 PM
Subject: Re: [Phono-L] Vertical versus lateral records
> Hi Greg,
> This is all very informative. I always assumed that in a stereo
> recording, one channel responded to the vertical motion of the stylus and
> the other to the lateral motion. If I understand you correctly, this is
> not
> correct. One channel responds to both by both the lateral and vertical
> movement on one side of the groove and the other channel to the lateral
> and
> vertical movement of the other side of the groove. What I don't
> understand
> is how this is possible. It would seem that the motion in either
> direction
> on one side would affect the motion of the other side because the stylus
> can't be in two lateral or vertical positions at the same time. I hope you
> understand what I mean and can provide an explanation as to how this
> works.
> Thanks
> Robert Vuillemenot
> ----- Original Message -----
> From: "Greg Bogantz" <gbogantz1 at charter.net>
> To: "Antique Phonograph List" <phono-l at oldcrank.org>
> Sent: Saturday, November 01, 2008 9:00 PM
> Subject: Re: [Phono-L] Vertical versus lateral records
>
>
>> Well, Robert, with some trepidation do I want to open this can of
>> worms
>> again. I was involved in some knock-down-drag-out arguments on two other
>> phonograph forums over this topic in the past. It seems there are some
>> die-hards in both the Edison and Victor camps who want to retain their
>> predjudices regardless of knowing the facts. But in the interest of
>> showing
>> some scientific light on this question, I'll try to cite the most
>> important
>> aspects of the physics governing the analog recording and reproduction
>> process.
>>
>> First of all, you should dismiss nearly everything that Read and Welch
>> say in their book "From Tinfoil to Stereo". The authors have a very
>> Edison-centric point of view and most of their arguments regarding the
>> "superiority" of vertical recording is emotional and not backed up by any
>> science. It turns out that most of what we now actually KNOW about
>> vertical
>> versus lateral wasn't clearly understood until the dawn of stereo analog
>> disc recording in the late 1950s and early 60s. Stereo records are made
>> with a combination of lateral and vertical modulation, and early problems
>> with distortion in stereo LP reproduction led to an in-depth analysis of
>> the
>> physics of analog reproduction, complete with mathematical modeling and
>> computer analysis of the theories. It's very clear now what has REALLY
>> been
>> going on since Edison first shouted into his new invention.
>>
>> One of the several problems with analog recording is the FACT that a
>> rounded playback stylus cannot perfectly trace the exact motion in a
>> groove
>> created by a sharp-edged cutting stylus. This is a purely geometrical
>> problem related to the difference between the stylus shapes and is now
>> known
>> by the name "tracing distortion". It is a separate mechanism from the
>> several other types of distortion that happen in analog disc
>> reproduction.
>> This wasn't a problem with tinfoil recording because the recording
>> indenter
>> was (or could have been) exactly the same shape as the playback stylus.
>> Note: tinfoil recordings are not actually "cut" but rather the foil is
>> indented by the recording stylus. This is an important difference -
>> there
>> is theoretically NO tracing distortion with an indented type of recording
>> when played back with a stylus of the same shape. But this statement is
>> purely theoretical because it disregards the deformation of the recording
>> medium during playback which really can't be disregarded in practical
>> terms.
>>
>> Tracing distortion produces primarily harmonic distortion which is
>> rich
>> in the even order harmonics (2nd, 4th, etc. harmonics), and it increases
>> with increased loudness and with increasing frequency of the signal.
>> Tracing distortion also generates a type of intermodulation distortion of
>> the high frequencies by the low which is particulaly unmusical and
>> objectionable.
>>
>> How big a problem is this really? If you ask an old hifi listener who
>> had experience listening to quality hifi equipment back in the late 1950s
>> what his opinion was of the new stereo LPs, he will tell you that the
>> stereo
>> LPs had noticeably more distortion. This was uniformly complained about
>> by
>> all the hifi pioneers and was the reason that further research was
>> required.
>> One way to think of stereo recording is to understand that the left and
>> right signals in the 45-45 system of recording (which is now standard)
>> are
>> each vertical recordings which exist mutually exclusively on the two
>> walls
>> of the stereo record groove. Early stereo pickup cartridges used conical
>> styli which were still the standard shape for mono LPs of the day. What
>> the
>> early stereo LP listeners were hearing for the first time in decades was
>> the
>> same as VERTICAL reproduction coming from each of their two speakers.
>> And
>> they were hearing tracing distortion and they were complaining about it
>> because it was THAT noticeable. So why didn't they complain about it in
>> their earlier monophonic lateral LPs? Because it wasn't there for all
>> practical purposes in the signal that emerged from the monophonic lateral
>> pickup cartridge. It is still true that each sidewall of the monophonic
>> lateral groove produces tracing distortion, but the phase of the
>> distortion
>> products produced by the playback stylus is reversed from the left
>> sidewall
>> relative to that from the right sidewall with respect to the LATERAL
>> motion
>> of the stylus (whereas they add together in phase in the VERTICAL motion
>> of
>> the stylus). These out-of-phase distortion products literally physically
>> canceled each other out mechanically in the net lateral motion of the
>> playback stylus and that's why the listeners didn't complain about this
>> distortion - it wasn't actually present in the signal from the mono
>> lateral
>> cartridge. I'm describing this scenario to you in this way because it
>> demonstrates how MUCH tracing distortion there actually is in vertical
>> playback. When listeners accustomed to hearing their mono LPs first
>> encountered tracing distortion with their stereo records played back with
>> the same conical stylus shape, they readily noticed the distortion and
>> reacted unfavorably to it.
>>
>> There were several remedies tried during the years to reduce this
>> distortion (RCA's Dynagroove recording system of the early 1960s was one
>> rather complex effort at predistorting the groove to deal with the
>> problem),
>> but ultimately the best answer was to get the playback stylus to assume
>> the
>> shape of the recording stylus as closely as possible. Note that it is
>> impossible to use a sharp edged playback stylus of the same shape as the
>> cutting stylus because it would cut, gouge, and otherwise ruin the
>> record.
>> BUT, the "scanning radius", that is the radius which contacts the
>> longitudinal portion of the groove wall can be made much smaller than the
>> traditional radius of a conical stylus while retaining the customary
>> radius
>> in the vertical dimension. This resulted in the so called "elliptical"
>> or
>> "bi-radial" playback styli. Although the tracing distortion was not
>> fully
>> eliminated by the use of elliptical styli, the reduction in distortion
>> was
>> dramatic and listeners were duly impressed. Edison followers are
>> probably
>> aware that Edison himself actually invented the elliptical stylus around
>> 1900 when he made the so called "doorknob" shape for his 2 minute wax
>> cylinders. He did it for the same reason - better fidelity because of
>> lower
>> distortion. But that shape had been forgotten until the need for it
>> arose
>> again with stereo LPs 60 years later. Further research has resulted in
>> yet
>> smaller scanning radii which would ordinarly start becoming dangerously
>> close to damaging the records were it not for the further INCREASE in the
>> "bearing" radius of the stylus, that is the vertical dimension that is
>> orthogonal to the scanning radius. Again, this makes the stylus more
>> closely approximate the shape of the cutting stylus, but the small
>> scanning
>> radius is still sufficiently rounded to keep record damage from occuring
>> so
>> long as the tracking force is sufficiently low. These styli are now
>> generally known as "line contact" styli and have variously been marketed
>> as
>> Shibata, Pramanik, Tetrahedral, Quadrahedral, LC, CL, and Micro-Ridge
>> shapes. They remain the BEST reproducing stylus shape you can use for
>> stereo records, and they work just fine with mono laterals, too.
>>
>> So if no other distortion mechanisms are considered, the tracing
>> distortion problem alone is sufficient to understand that playback of
>> lateral monophonic records is technically superior to that obtained from
>> vertical playback.
>>
>> With regard to acoustic reproduction in phonos, several other
>> distortion
>> mechanisms are in play, and there is probably a "wash" in how those
>> distortions compare between vertical and lateral reproduction. Because
>> of
>> the need to mechanically bias the diaphragm of a vertical reproducer by
>> the
>> tracking force during playback, the diaphragm exhibits more stiffness in
>> the
>> upstroke of the stylus as compared to the diaphragm's relaxation from the
>> bias position during the stylus downstroke. This produces a form of
>> harmonic distortion which is primarily composed of even harmonics (2nd,
>> 4th,
>> etc. harmonics) due to the asymetrical nature of the diaphragm stresses
>> from
>> peak to trough of the signal waveform. The diaphragm of the lateral
>> reproducer is not stressed in its unmodulated condition (or the center of
>> motion during modulation), but it is approximately equally stressed one
>> way
>> and then the other on both left and right excursions of the groove. This
>> produces flexing of the needle, needle bar, gaskets, and diaphragm which
>> leads to harmonic distortion which is predominantly comprised of odd
>> orders
>> (3rd, 5th, etc. harmonics). Even ordered harmonic distortion sounds
>> different from odd order, but both are noticeable if they occur in a
>> sufficient amount. Again, it's probably a wash as to which distortion
>> mechanism sounds "worse", but they DO sound different and contribute to
>> the
>> total listening experience when comparing vertical and lateral
>> reproduction
>> via acoustic reproducers.
>>
>> There are other factors involved, but I'll leave at these which are
>> among the most noticeable and which contribute largely to the difference
>> in
>> the vertical versus lateral listening experience.
>>
>> With regard to Edison's early cylinder recordings sounding better than
>> Victor's, I agree with that sentiment. But not because of any intrinsic
>> superiority of the vertical over the lateral technology. It's really the
>> opposite, as I've stated above. Edison's better sounding recordings are
>> a
>> result of his engineers taking more effort to have properly functioning
>> equipment and his engineers general preference for getting the talent
>> closer
>> to the recording horn and with recording in relatively acoustically
>> "dead"
>> environments. These preferences lead to capturing more high frequency
>> content in the recording. Edison's engineers also are known to have been
>> very careful to choose the recorder that best matched the nature of the
>> music and the talent, that is different recorders were used for
>> selections
>> featuring a solo vocalist than were used for band recordings or were used
>> for massed voices, etc. Victor and Columbia probably weren't as careful
>> in
>> the early days about these details of their acoustic recording setups.
>>
>> Greg Bogantz
>>
>>
>>
>> ----- Original Message -----
>> From: "Robert Wright" <esroberto at hotmail.com>
>> To: "Antique Phonograph List" <phono-l at oldcrank.org>
>> Sent: Saturday, November 01, 2008 6:46 PM
>> Subject: Re: [Phono-L] Research: Amberolas 1A and 1B (Greg Bogantz)
>>
>>
>>> With all due respect, how is vertical cut recording inferior to lateral
>>> cut?
>>> Certainly in the phonograph's first 25 years, Edison's machines sounded
>>> substantially better than respectively contemporary lateral phonographs.
>>> I
>>> hear more treble extension on direct-recorded 4M amberols than any
>>> acoustic
>>> lateral recordings, as well as more general naturalness. I must
>>> respectfully disagree that vertical recording can be regarded as
>>> inherently
>>> inferior to lateral recording, generally speaking.
>>>
>>> I should perhaps mention that I have no allegiance to one method over
>>> the
>>> other whatsoever. Greg B., may I ask your thoughts on this? Any
>>> information about specific frequency responses, and especially, the
>>> physics
>>> involved with both the recording and playback (and duplication if you
>>> care
>>> to get that deep) processes, would be fascinating and greatly
>>> appreciated!
>>>
>>>
>>> Best to all,
>>> Robert
>>>
>>>
>>> ----- Original Message -----
>>> From: <jimcip at earthlink.net>
>>> <snip>
>>>> Obviously the great weakness of Edison phonographs (aside from vertical
>>>> cut
>>>> recording)...
>>>
>>> _______________________________________________
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>>
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