Handbook for Sound Engineers

Analog Disc Playback 1015

27.1 Introduction

In the past 100 years approximately 30 billion phono-

graph records have been produced and sold. Music of

the most famous composers and performers, orchestras,

and bands, and sounds of events have been immortal-

ized in intricate excursions of the analog record groove.

Millions and perhaps billions of discs are still in the

hand of the audiophiles, archives, musical libraries, DJs

and radio stations.

The contents of all of these records can never be

completely rerecorded onto the compact discs or

another medium, so it is important that we can preserve,

restore, and reproduce analog recordings.

The information contained in this section is directed

toward the new generation of engineers and technicians

so they may understand the reproduction techniques that

led to digital technology. As we witness the decline in

popularity of analog LP discs, remember that many

developing countries around the world are still very

much dependent on analog technology and in some

cases what we consider the old 78 rpm format is the

only source of prerecorded music and entertainment

available to them.

Early recorded sounds had a high-frequency cutoff

of 2–3 kHz. It took over 100 years to reach the sophisti-

cation of today’s recording technology only to take a

couple of steps backward in sound realism by approxi-

mating the waveforms at the high frequencies and

limiting them to 20 kHz with brick wall filters. Theoret-

ically digital recording is fine, but the human ear

deserves a higher sampling frequency. Perhaps only a

select few can really hear the difference, but then how

can we argue with them? In other fields, such as televi-

sion, the trend is toward high-definition TV, in VCRs

and camcorders there is a SVHS system, and yet

tube-type audio amplifiers are still sold at premium

prices because of many so-called golden ear audiophiles

don’t want to give up the tube sound. The same is with

LP records. For the average listener, CDs are great as

long as they don’t hear pops and clicks and cannot break

the stylus or the tonearm.

This chapter will discuss playback equipment. To

understand the production of records/discs, refer to the

Handbook for Sound Engineers–The New Audio Cyclo-

pedia First or Second Edition.

27.2 Disc/Record Dimensions

The analog record has been standardized to 7 inch,
10 inch, and 12 inch discs and 33^1 e 3 and 45 revolutions
per minute (rpm).

Excerpts from the latest EIA standard for producing

analog disc records are as follows.

27.2.1 Record Diameter

The diameter of records are:

The recorded surface shall start with at least one turn

of unmodulated groove.

27.2.2 Maximum Outer Diameter

The maximum outer diameter of a recorded surface

shall be:

27.2.3 Groove Dimensions

The groove dimensions shall be:

On stereophonic records, the instantaneous groove

width should be not less than 0.001 inch (0.025 mm).

The average groove width should preferably be not less

than 0.0014 inch (0.035 mm).

27.2.4 Stereophonic Groove

The stereophonic groove shall carry two channels of

information. The two channels shall be recorded in such

a manner that they can be reproduced by movement of a

reproducing stylus tip in two directions at 90° to each

other and at 45° to a radial line through the stylus tip

and the center of the record. The reproducing stylus tip

motion shall be tangential to, or lie in a plane through,

the stylus tip and the record center, preferably inclined

at an angle of 20 ± 5° clockwise to the normal to the

record surface through the stylus tip, as viewed from the

12 inch LP disc, 33^1 e 3 rpm 11.875 ± 0.031 inch

(301.6 ± 0.8 mm)

10 inch disc, 33^1 e 3 rpm 9.875 ± 0.031inch

(250.8 ± 0.8 mm)

7 inch disc, 45 rpm disc 6.875 ± 0.031 inch

(174.6 ± 0.8 mm)

12 inch LP disc, 33^1 e 3 rpm 11.500 inch (292.1 mm)

10 inch disc, 33^1 e 3 rpm 9.500 inch (241.3 mm)

7 inch disc, 45 rpm disc 6.625 inch (168.3 mm)

Minimum top width

(monophonic only)

0.0022 inch (0.56 mm)

Maximum bottom radius 0.00025 inch (0.006 mm)

Included angle 90° ± 5°