4.4. Cassette tapes Cassettes operate on the same principle as open-reel magnetic tape. The 'compact cassette' (developed and marketed by Philips from the early 1960s) encloses the tape in a solid housing. There is only one format, designed for domestic rather than professional audio use: the tape is divided into four tracks, only two of which are played back at a time (comprising left and right; the other two play back when the cassette is turned over). There is one major drawback with cassette: the narrowness of the tape generally results in lower quality sound reproduction than with wider tape formats. For this reason it has never been regarded as a suitable medium for professional audio work. Note also that the standard format has sometimes been overridden by manufacturers of home-studio machines, which use cassette as a budget multitrack format. Though cassette is now less popular than it used to be, cassette machines are still mainstream domestic hi-fi equipment. Professional machines are also available. For digitisation purposes, it is best to use a machine that will get the maximum quality of reproduction from this limited medium. There are some good cassette machines on the domestic hi-fi market at relatively low cost, and it may be worth investigating these before spending money on professional level equipment. 4.4.1. Noise reduction Noise reduction is used on cassette tape for the same reason as open-reel tape. The commonest types are Dolby B, Dolby C, and Dolby S. Most cassette machines have one or more of these built in, with a switch on the front panel. As with open-reel tape, it is important to use the same kind of NR to decode a tape as was used to encode it. 4.5. Audio from film Various methods and formats have been used since the inception of film sound. These are outlined briefly below. Digitisation of film soundtracks will require specialist equipment such as sound-film projectors and will also require knowledge of film and soundtrack formats. 4.5.1. Film soundtrack formats The earliest methods for putting sound to film were the Vitaphone system (the first to be used for a full-length film: Don Juan, Warner Bros, 1926), and Tri-Ergon sound-film. The Vitaphone system used 16-inch acetate-coated shellac disks running at 33 1/3 rpm to carry audio. The disks were synchronised to the film reel through the use of electric motors and a gearing system (the 16-inch disk would become the standard audio format for the broadcast industry until the adoption of magnetic tape in the late 1940s). Tri-Ergon used the intensity of a light beam to record a sound signal onto the film itself; the sound was thus recorded optically as varying areas of light and dark. Following these early systems a variety of soundtrack formats developed, some using magnetic tracks and others using optical tracks. As stated above, digitising from such formats will require appropriate equipment and knowledge. See also section 5.7. 4.6. Audio from video As with film, a variety of formats has evolved since the technology's inception in the 1950s and the establishment of Sony's U-matic standard. Playing back modern video formats should be straightforward, as should digitisation from soundtracks. See also section 5.7. Top of Page
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