What the tape had to do
An answering machine has two recording jobs. It has to play a greeting each time a call arrives, which means the same short recording must be available again and again. And it has to record a new message from each caller, and let the owner play it back later. The tape formats used in machines developed to handle those two jobs in a small, cheap package.
Magnetic recording in brief
Magnetic tape stores sound as a pattern of magnetization along a plastic strip coated with fine magnetic particles. A recording head turns the electrical signal into a magnetic field, which magnetizes the tape as it passes. A playback head does the reverse. An erase head clears old recordings. Inside an answering machine, these heads sat along the tape’s path, and a motor drew the tape past them.
Magnetic tape was a postwar technology in widespread use, replacing earlier wire recording, which tangled and was hard to splice. Tape was cheaper, better sounding and easier to handle. Those qualities made it the natural choice for early answering devices.
Open reels and endless loops
Early machines for professional users often used small reels or tape cartridges. A common trick was the endless loop: a length of tape joined into a continuous circle in a cartridge. The tape could run in one direction forever without rewinding, and a section of the loop could carry a greeting that replayed whenever needed. The same idea was used for other short repeating recordings, such as announcements.
Loops had drawbacks. Tape tends to wear out where it repeatedly passes over heads, and a loop with a short message was played so often that wear showed. Loops also had limited length, which limited the length of both the greeting and the messages.
The compact cassette arrives
The Philips compact cassette, introduced in 1963, changed the economics. A cassette is a pair of reels in a small plastic case, standardized, cheap and easy to insert. By the 1970s, it was mass-produced in huge volume for music and dictation, and manufacturers could use it in answering machines with confidence that tapes would be available and compatible.
Early home answering machines typically used two tapes. One carried the outgoing greeting, usually a short loop of tape in a cartridge, and the other recorded incoming messages, usually on a cassette. Having two tapes meant that the greeting never had to be rewound or overwritten when messages were recorded. The machine started the greeting tape when a call arrived, then switched to the message tape after the tone.
Microcassettes
Smaller cassettes were developed for dictation and portable recorders, including a microcassette introduced by Olympus in 1969. These tapes were about the size of a matchbook and ran at slower speeds. Answering machines that used microcassettes could be smaller, and manufacturers could put them into compact desk units. The sound quality was lower, which suited the narrow frequency range of telephone lines anyway.
Tape speed was a trade-off. Slower speeds allowed more minutes of messages on a tape, but reduced quality. Because telephone speech does not need wide bandwidth, machines commonly ran slowly.
Fitting everything into a box
Designers had to solve several practical problems.
- Starting and stopping. The machine needed to detect ringing current, answer the line, and operate the tape mechanism at the right moment. Early machines used relays and small motors, later replaced by circuits and microprocessors.
- Message length. Many machines limited each message to a fixed time. Some used a voice-operated switch, called VOX, to stop recording when the caller went silent, which saved tape.
- Playback and rewind. Owners needed to rewind and replay messages quickly. Counters, lights and indexing signals helped them find where messages began.
- Reliability. Tape stretched, jammed and wore out. Heads accumulated oxide and needed cleaning. The mechanical complexity of the cassette deck was a main source of failures.
- Line connection. A device had to couple its audio to the telephone line safely, using a transformer and circuits that met safety rules.
Many of these functions improved with the arrival of integrated circuits, which could handle the logic in a small area at low cost.
The move away from tape
As memory chips became cheaper, makers began to store greetings and messages digitally. A solid-state recorder had no tape to jam or wear, started instantly, and could jump to any message. By the 1990s, digital machines were common, though tape models continued to be sold for some time because they were cheap and familiar. The development of network voicemail then reduced the need for home hardware in general.
A small chapter in a larger story
The tape formats of answering machines were part of a wave of consumer devices built on magnetic recording: music players, dictation machines, camcorders and answering machines. Each borrowed from the others, and the cassette, perhaps the best known, found a use in the humble business of taking a message.