Handbook for Sound Engineers

1068 Chapter 28

film to align the particles, a technique known as rheo-
logical orientation.

As a result of these improvements, squareness ratios
have increased dramatically. Over the past 30 years the
squareness has improved from 0.8 to better than 0.9 for
the best current audio tapes. This improvement trans-
lates to more available output and less harmonic distor-
tion from the tape without requiring any increase in bias
or record signal.

Table 28-5 summarizes the characteristics of several
of the particles used for magnetic tapes.

28.3.11 Magnetic Tape Specifications

The performance of a magnetic tape involves many

parameters such as maximum output level, distortion,

noise, print through, and frequency response. As a

result, the data sheet that characterizes this performance

must include many operating characteristics. The user

must be very careful, however, to determine the test

conditions under which the data is derived, including

record head gap length, tape speed, operating level, and

equalization.

One form for presenting this data is shown in Table

28-6. The data entries are measured for one specific

recommended bias setting. Some of the values, such as

sensitivity at long and short wavelengths, are compari-

sons to the performance of a standardized reference

tape. The notes contain important information defining

the test conditions used to derive the data.

Figure 28-32. Squareness ratio.

"S

"r

(c

Squareness = "r/"s

"r

"s

A. Low squareness.

"s

"r

(c

Squareness = "r/"s

"r

"s

B. High squareness.

Table 28-5. Characteristics of Tape Particles

Size Coercivity Reten-

tivity

Square-

ness

Fe 2 O 3 (Gamma

ferric oxide)

Low

Noise

0.3 μm 350 Oe 1500 G 0.75–0.9

Normal 0.7 μm 280 Oe 1100 G 0.75

Co-doped

Fe 2 O 3

0.3 μm 650–700 Oe 1300 G 0.75

CrO 2 0.6 μm 600 Oe 1500 G 0.9

Metal particle 0.2 μm 1100 Oe 3500 G 0.8

Table 28-6. Tabular Tape Specifications

Unit Typical

Values

Test

Notes

I. Electromagnetic Properties

Recommended Bias Setting dB 3.0 1

Sensitivity at 1 kHz (81 kHz) dB 0.8 2

Sensitivity at 10 kHz (Sl 0 kHz) dB 1.1 2

10 kHz Saturated Output (SAT,

0kHz)

dB 18.5 13

Third Harmonic Distortion at

Reference Level (THD)

%0.063

Output Level at 3% Third

Harmonic

Distortion (1 kHz) (MOLL kHz) dB 17.5 4

Weighted SNR

a. related to reference level dB 58.0 5

b. related to output level at 3%

third harmonic distortion

dB 75.5 5

Modulation Noise Ratio dB 73.0 6

Print through dB 58.0 7