Handbook for Sound Engineers

1016 Chapter 27

record center. In practice, angles of between 0q and 25°
may be encountered.

27.2.5 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 far-
ther away from the center of the record.

27.2.6 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.

27.2.7 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 50μm or
0.002 inch in vertical plane.

27.2.8 Speed of Rotation

Records shall be recorded for reproduction at one of the
following speeds:

27.2.9 Lead-In Groove Pitch

The lead-in groove pitch shall be 16 ±2 lines/inch (l/in).

27.2.10 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 min-
imum of 0.003 inch (0.076 mm) when the pitch exceeds
¼ inch (6.4 mm).

27.2.11 Finishing Groove

The diameter of the finishing groove shall be:

27.3 Signal Equalization in Disc Recording

To overcome the limitations found in the basic disc-cut-

ting and reproducing process, special equalization of the

signals before and after the recording was developed.

When all signals that appear in the program bus are ana-

lyzed, we can see that the amplitude is the highest at

low frequencies and the lowest at high frequencies. The

relationship between the frequency of the signal and its

amplitude where amplitude is inversely proportional to

frequency is called a constant velocity characteristic,

Fig. 27-1.

If the signals are recorded without equalization as

they arrive, the low-frequency excursions would take all

the space. The high frequencies would be of such a low

amplitude that during the playback, high-frequency

signals could be very close to the noise level of the

system. The SNR then would be extremely small. This

problem was recognized in the early days of disc

recording, but the remedy used was only partial. At first

only the low end of the audio spectrum was equalized.

The cutting head sensitivity was decreased at low

frequencies so that the amplitudes in midrange and at

high frequencies could be recorded at higher levels.

Then, the playback amplifiers were adjusted to boost

the low frequencies to compensate for the losses intro-

50 Hz Electric Supplies 60 Hz Electric Supplies

45.11 rpm ±0.5% 45.00 rpm ±0.5%

331 e 3 rpm ±0.5% 331 e 3 rpm ±0.5%

(Note: 16¾ rpm and 78 rpm speeds omitted.)

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)

Figure 27-1. Constant velocity characteristics.

Constant velocity

Reference frequency

Frequency—Hz

50 100 200 500 1000 2000 5000 10,000

×10 ×5 ×2.5 ×1 0.5 0.25 0.1 0.2