[ARSCLIST] Vertical Tracking Angle

[Doug Pomeroy <pomeroyaudio@xxxxxxxxxxx>]

REFERENCES:
1) "Disk Recording Volume 1: Groove Geometry and the Recording PRocess"  An
anthology of articles on disk recortding from the pages of the Journal of
the AES. Vol  1-Vol 28 (1953-1980).
2) "Tracking-Angle Error: A New Slant", by James V. White. High Fidelity,
June, 1979 issue ,p.62.
3) Audio Cyclopedia, by Howard Tremaine, Howard Sams & Co., Second Printing,
1973
4) Handbook for Sound Engineers/The New Audio Cyclopedia, Glen Ballou, Ed.,
Howard Sams & Co, 1987 Edition (a complete re-write of the 1973 version).

By 1963 the NAB and RIAA agreed to a standard VTA for stereo microgroove
recordings of 15 degrees.
This figure refers to playback, since the cutting angle differs due to
"lacquer spring-back".

The first reference, available from the AES, will give you reprints of
several seminal studies of the subject of VTA. One of these (by Teldec
engineers) describes the tracking angles for many pickups available in 1964:
the stock Shure M44, for instance, has a VTA of 16 degrees.
This suggests you need not worry about making adjustments when playing Lps.

None of the references above address the period before lacquer was used for
disk mastering, and I have no information on what cutter tilt, if any, was
typical of the early Western Electric cutters used for inscribing warm wax.
I have assumed best playback of shellac 78s with a perfectly vertical
stylus, but have found mono lacquers generally to sound best when played
with some negative tilt.

It never hurts to experiment.

Regards,

Doug Pomeroy
Pomeroy Audio
Audio Restoration & Remastering Services

-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:ARSCLIST@xxxxxxx] On Behalf Of Eric Jacobs
Sent: Friday, January 07, 2005 11:50 AM
To: ARSCLIST@xxxxxxxxxxxx
Subject: [ARSCLIST] historical stylus rake angles (SRA)

Does anyone know of a reference where I might find historical stylus
rake angles?  Even some rough guidance on this list would be useful.

Note that SRA (the angle the stylus makes with the record surface) is
not to be confused with the Vertical Tracking Angle (VTA) which is the angle
the cantilever makes with the record surface.

Modern cartridges and tonearms are designed for SRA values of zero
(ie. a vertical stylus, perpendicular to the record surface) or slightly
positive to about 3 degrees or so.

I realize that SRA values, like VTA, will vary by record label and need to
be adjusted for each record for optimal playback if you are a
perfectionist.  SRA and VTA are primarily affected by record
thickness and cartridge height.

Variations in SRA (fractions of degrees) are most audible on LPs with
their lower noise, wider frequency response and narrower grooves making VTA
an important adjustment for each LP.

How critical is SRA for accurate playback on acoustic or electric 78s
or transcription discs?  Am I making a mountain out of a mole hill?

The reason behind my question is that the 1-2 inches of VTA adjustment
on a tonearm will only compensate the SRA by a few degrees.  In fact,
tonearm VTA adjustment is best suited to compensate for variations in
cartridge
height and record thickness since it is assumed that the cartridge SRA is
correct when the tonearm is level.  If historical SRAs used rakes of 5
degees
or greater, some sort of custom cartridge mount would need to be devised
(a wedge shaped block or shim) to achieve the correct SRA.

Because of the limitations of tonearm VTA adjustment, it is not
possible for me to experiment with large variations in SRA and listen for
differences. Optical measurements of SRA are not possible with my 150x
microscope
with 0.01 mm measurement reticle.

Thanks in advance to anyone who can shed some light on this question.

Eric Jacobs
The Audio Archive
San Jose, California

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