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Create sounds using analogue electronics (Part 1)

Posted: 04 Oct 2011     Print Version  Bookmark and Share

Keywords:audio electronics  Oscillators  synthesisers  amplifier 

The use of electronics for audio started with the invention of the telephone in the last part of the nineteenth century. Before this, microphones were quite insensitive and produced lots of distortion, and loudspeakers were actually quiet! Since then electronics has developed enormously and now offers sensitive microphones with low distortion, as well as loudspeakers that are loud, plus many other inventions.

Microphones, loudspeakers
Microphones and loudspeakers turn sound into electrical signals and vice versa. It is now such an everyday experience that it is difficult to appreciate how significant it was to the world of just over 100 years ago that had only natural sounds and gramophone recordings. Since then microphones and loudspeakers have been refined, and Alan Blumlein's invention of stereo in the 1930s enabled the positioning of sounds across a sound stage.

By the 1960s, affordable hi-fi meant that anyone could experiment with audio. The 1970s saw commercial experimentation with what was then called quadrophonic sound, but would now be called 4.0 surround sound: four speakers instead of the two used in stereo. Quad's complexity, plus problems with standards for LP discs, meant that it was not a commercial success. In the twenty-first century, a number of researchers are using multiple microphones and surround sound loudspeakers to move complete sound-fields from one location to another.

Oscillators are pieces of electronics laboratory equipment that were used for musical purposes long before synthesisers became affordable. Simple oscillators provided sine waves, whilst more sophisticated ones could provide other waveshapes. Intended for use in radio or audio testing, they were usually not temperature stable and had continuously variable frequency dials that made their use for any pitched music difficult. Despite these problems, early experimental music groups such as The Silver Apples used multiple oscillators in performance in the late 1960s.

Although better known now for printers and computers, Hewlett HP, the US technology company had its roots in audio oscillators. The first product from Bill Hewlett and Dave Packard (Hewlett-Packard (HP)) was the Model 200A oscillator, the origins of which were in Bill's thesis at Stanford University in the late 1930s.

Mixers take several audio sources and combine them. Often, mixers are used to combine a few selected audio signals from a larger set and so are also used as selectors or switches. Mixers effectively move the level or volume controls from the outputs of all the connected audio devices and put them into one device. This greatly eases the selection and balancing of levels from the audio devices.

Amplifiers take an audio signal and amplify it. Microphone amplifiers are used for low-output microphones or for extra gain with quiet sound sources. Power amplifiers are used to drive loudspeakers in public address (PA) applications. Guitar amplifiers turn the quiet sounds produced by the strings and amplify the outputs from the electromagnetic pickups on the guitar to produce audible sound.

By connecting a microphone into an amplifier that is driving a loudspeaker, it is possible to create feedback by adjusting the gain of the amplifier and the positioning of the microphone and loudspeaker. This can be used to create some interesting sounds, especially if the gain is reduced slightly so that it is just about to break into oscillation. Electric guitars can be used instead of a microphone, and the same effects can be produced because the strings and body of the guitar can pick up enough of the amplified audio to create a feedback loop.

Filters allow some frequencies to pass through, but reject others. They range from subtle tone controls to making large changes to the sound – one common use is to simulate the restricted bandwidth of telephones. Filters are used as audio laboratory test equipment and in recording studios.

Radio technology spin-offs
Oscillators, mixers, amplifiers, filters, modulation and many other devices and terms that are used in audio electronics are derived in part from radio electronics. Radio uses a combination of audio frequency electronics with much higher-frequency radio electronics.

Sounds produced by radio receivers as radio stations are tuned in, or deliberately mistuned, are often used as sound effects or metaphors for communications. Radio modulation circuits, adapted for audio frequencies, are used to produce complex transformations on audio signals. In particular, ring modulation is frequently used to create alien and robot voices by processing speech.

Disks, wire, tape recorders
Pre-recorded sounds on disc can be used as sound sources, and a disc-cutting lathe can be used to create special effects such as looped tracks, or multiple sets of spiral grooves instead of just one. Loops can also be simulated manually by a human being manipulating the disc or turntable.

Tape recorders (or their older counterpart, wire recorders) can not only be used as sound sources but also be used as simple echo units by using one as a recorder and a second as a playback unit, with the tape passing from one to the other. By adjusting the distance between the two tape recorders, the echo time can be controlled. By feeding back the echo signal to the recorder, further echoes of the echoes can be produced, but this technique is prone to feeding back or amplification of the noise introduced by the tape recording and playback process.

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