The Cine Technician (1953-1956)

1 ! THE CINE-TECHNICIAN March-April, 1952 MA6 ^ HiAOHhiSi. in§ Peter Hm§lv A LTHOUGH there were much earlier patents the ^ first practical magnetic system was the Poulsen Telegraphone steel wire recorder of 1900, and recordings made with this system still exist. Since then there has been considerable development in the use of magnetic recording, especially in Germany. Up to the beginning of the last war there was little technical advance on the old Blattnerphone system, although the development of the use of plastic tape coated with ferrous oxide powder in the Magnetophone made a great advance on flexibility of use. During the war the Magnetophone was improved very much and the use of supersonic currents for erasing, biasing, and premagnetizing, developed by two engineers, Braunmiihl and Weber, in the German broadcasting organisation, made a great advance in this method of recording. The modern magnetic recording system, when a suitable coated material is used and with a good design of equipment, is capable of recording and reproducing sound of exceptionally high quality, with frequency range up to 20,000 cycles. At 35 mm. film speed the corrected frequency is essentially flat between 50 and 10,000 cycles. At 16 mm. film speed it is flat between 100 and 5,000 cycles, and at the low speed of 8 mm. film the response is flat up to 3,000 cycles. In addition to good frequency characteristics, magnetic recording has the advantage of a high signal to noise ratio, as compared with photographic methods. Scratches, dust and dirt have no appreciable effect. It is unusual to get more than 50 db. volume range with photographic recording, even with good noise reduction methods, but it is possible to get a volume range of 60 to 70 db. with good magnetic recording. Many of the advances made in the use of photographic methods will also, undoubtedly, be adapted to magnetic recording. Magnetic recording has been established for many years and is used a great deal by the B.B.C. and by radio transmitting networks throughout the world. In English studios experiments were made with the Blattnerphone system in 1932, but in spite of its potential advantage for the making of sound films, it is only recently that much serious consideration has been given to its use. In spite of the problems found in the use of magnetic recording, it is probable that it will eventually supersede most types of studio recording. Apart from the higher quality possible, the advantages are obvious. There is considerable saving, both in film stock and processing charges and it is no longer necessary to rely on laboratories for the preparation of the sound negative, it has as well the advantage of direct play-back. In addition there is a simplification in the design of equipment, as there is no optical system, no exposure lamp and its power supply, no noise reduction or compression. The sound camera and film magazines need not be light tight, and the necessity for a dark room or changing bag is avoided. As a result it is possible to use very light weight equipment for location and studio recording. Location sound is possible with good quality, without adding to the cost of production for film stock or processing. When it is necessary to record special effect noises there is often difficulty in avoiding the excessive waste of film. With mag netic recording it is possible to run all day in order to obtain some difficult effect, such as the song of a rare bird, without any additional cost for film stock. Apart from the more conventional advantages, there are others that the nature of magnetic recording has made possible. The single film type of newsreel camera has always suffered from the drawback that the requirements of processing and development are not the same for sound and picture. If the picture film stock is made with a magnetically coated edge, the sound is independent of the developing procedure of the picture. Magnetic apparatus may be used to produce reverberation erfects for recording. A small continuous loop of magnetic film is used. The sound is recorded on one head, is reproduced by two reproducing heads spaced a short distance apart, and is erased by a fourth head. The loop can be run at a high speed to allow for sufficient spacing. By varying the spacing cf the reproducing heads and mixing the outputs, varying effects of reverberation and echo may be obtained. One useful purpose for which magnetic recording may be used is to operate an anticipation form of noise reduction. This is referred to later in connection with the making of direct positive prints. The sound is recorded on to magnetic film and is immediately reproduced by two reproducing heads spaced a certain distance apart. The output from the second head operates the modulating galvanometer, and the output from the first head operates the noise-reduction equipment. By this means the clipping of the initial peaks on steep wave front signals is avoided, and no deterioration in sound quality need result from the transfer through magnetic. There are certain disadvantages with the use of magnetic recording, some of them being connected technically with the nature of the medium, such as the possibility of spurious printing from one layer of film to another, and the variations in the manufacture of the film stock itself. The principal disadvantage, however, has been in the difficulties of editing and the absence of a visible record of the sound on the film. In order to obtain a visible record of the sound, several methods have been adopted when necessary. The visible trace is usually made on the part of the film not used in the recording process. It may be by means of an inking stylus, or the record may be engraved in the emulsion layer. There is also a chemical process in which a stylus reacts with a coating on the film (zinc oxide mixed with a nitro cellulose lacquer and a bronze or brass stylus!. The disadvantage of a visible trace is that the re-use of the film for recording purposes must take into consideration the possibility of having a permanent visible record of the first recording. Established editing processes are not very suitable for the easy use of magnetic sound in place of photographic, but tin recent development of new editing and tracklaying methods indicate that the disadvantages will eventually be overcome, by the use of a new technique in the handling of magnetic material. The problem has been approached by accepting the limitations of magnetic film, and as a result, when a