The analog record has been standardized to 7 inch, 10 inch, and 12 inch discs and 33 1/3 and 45 revolutions per minute (rpm).
Excerpts from the latest EIA standard for producing analog disc records are as follows....
1 Record Diameter
The diameter of records are:
- 12 inch LP disc, 33 1/3 rpm 11.875 ± 0.031 inch (301.6 ± 0.8 mm)
- 10 inch disc, 33 1/3 rpm 9.875 ± 0.031_inch (250.8 ± 0.8 mm)
- 7 inch disc, 45 rpm disc 6.875 ± 0.031 inch (174.6 ± 0.8 mm)
The recorded surface shall start with at least one turn of unmodulated groove.
2 Maximum Outer Diameter
The maximum outer diameter of a recorded surface shall be:
- 12 inch LP disc, 33 1/3 rpm 11.500 inch (292.1 mm)
- 10 inch disc, 33 1/3 rpm 9.500 inch (241.3 mm)
- 7 inch disc, 45 rpm disc 6.625 inch (168.3 mm)
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).
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 record center. In practice, angles of between 0 dgrees and 25° may be encountered.
5 Channel Orientation
The groove shall be recorded for reproduction with the right-hand loudspeaker(s), as viewed from the audience, actuated by movement of the groove wall, which is farther away from the center of the record.
6 Channel Phasing
The phasing of the two recorded signals shall be suit able for reproduction on equipment so connected that movement of the reproducing stylus tip parallel to the record surface (as with a monophonic record) produces in-phase signals across the output terminals of the phono cartridge.
7 Channel Levels
The levels of the two recorded signals should be such that peak excursions of the groove should not exceed 100 µm or 0.004 inch in lateral plane and 50 µm or 0.002 inch in vertical plane.
8 Speed of Rotation
Records shall be recorded for reproduction at one of the following speeds:
50 Hz Electric Supplies --- 60 Hz Electric Supplies
45.11 rpm ±0.5% ---- 45.00 rpm ±0.5% 33 1/3 rpm ±0.5% --- 33 1/3 rpm ±0.5%
(Note: 16¾ rpm and 78 rpm speeds omitted.)
9 Lead-In Groove Pitch
The lead-in groove pitch shall be 16 ±2 lines/inch (l/in).
10 Lead-Out Groove
The pitch of the lead-out groove shall be 2-6 l / in. The top width of the lead-out groove shall increase to a minimum of 0.003 inch (0.076 mm) when the pitch exceeds ¼ inch (6.4 mm).
11 Finishing Groove
The diameter of the finishing groove shall be:
12 inch and 10 inch discs --- 4.187 ± 0.31 in (106.4 ± 0.8 mm)
7 inch discs --- 3.875 ± 0.078 in (98.4 ± 2 mm)
FIG. 1. Constant velocity characteristics.