Audio Tape Specifications - Tape Speeds

Tape Speeds

In sound recording, magnetic tape speed is often quoted in inches per second (abbreviated ips) for historical reasons. Magnetic tape speeds are commonly an even fraction of 30 ips:

ips cm/s Typical use
120 304.8 Used by some analog instrumentation recorders and loop bin duplicators.
60 152.4 Used by some analog instrumentation recorders, as well as loop bin duplicators.
45 114.3 Used by 3M's first digital audio recorder in 1978.
39.4 100 Used by the first AEG Magnetophon models in 1935.
30 76.2 The highest professional speed.
22.5 57.15 Audio tape coated on 70 mm motion picture film, necessitated by the 112.5 ft/min film speed for 24 frame/sec projection.
15 38.10 The most common professional and studio speed for reel to reel including multitrack.
71⁄2 19.05
  • The lowest professional speed, used on some single-speed studio recorders including multitrack.
  • The highest domestic speed.
  • Used on older single speed domestic machines.
  • The most common speed for pre-recorded reel to reel tapes.
33⁄4 9.53
  • Used on later single speed domestic machines.
  • The second most common speed for pre-recorded reel to reel tapes.
  • The speed specified for the 8-track cartridge and Elcaset.
  • Used by some consumer multitrack machines using compact cassettes.
  • Used later as "high-speed" in some dual-speed professional compact cassette tape decks (see Tascam 122)
17⁄8 4.76
  • The standard speed for compact cassettes.
  • The lowest common reel to reel speed.
  • Used for reel to reel message tapes.
  • Used for message logging and similar specialised applications.
15⁄16 2.38
  • The standard speed for microcassettes (although specified as 2.4 cm/s, see below).
  • Also used for some "talking books" on compact cassette for the blind & visually impaired, issued by the Library of Congress.
15⁄32 1.19 The standard alternative recording speed for microcassettes.

Tape recording first became common enough for the issue of compatibility between tape deck manufacturers to become an issue in the 1950s. At this time the most common speeds for professional recording were 30 ips and 15 ips, and some machines already supported both speeds. As the tape speed was determined by the speed of a synchronous motor driving a capstan, one way of achieving this was to switch the poles of the motor to a different configuration, halving or doubling the speed.

This system was extended to domestic tape decks, and so slower speeds as they were adopted tended to be exactly half the previous slowest speed. Pre-recorded tapes were mostly 71⁄2 ips, with a few at 33⁄4 ips. Message tapes transmitted by post and call logging tapes were commonly recorded at 17⁄8 ips or even 15⁄16 ips. The most common reel to reel speed of 71⁄2 ips is approximately 19 cm/s.

Another cause of incompatibility between tape decks was the lack of standardisation of track widths and the use of alternate (rather than adjacent) stereo tracks by many manufacturers (which limited compatibility with mono equipment).

When Philips introduced the compact audio cassette, they chose to specify the reel-to-reel standard of 17⁄8 ips (approximately 4.76 cm/s). Although with narrower and thinner tape. Higher speed machines using compact cassettes commonly use 33⁄4 ips.

Although the microcassette is specified to have a standard record speed of 2.4 cm/s and low speed of 1.2 cm/s, in the dictaphone application for which it was designed these speeds are in practice identical to 15⁄16 ips and 15⁄32 ips. Playback speed is not specified, and on many machines is continuously variable.

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Famous quotes containing the words tape and/or speeds:

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    —Henry David Thoreau (1817–1862)

    “An honest tale speeds best being plainly told.”
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