British Kinematography (1950)

Feb., 1950 gould and falkner : magnetic recording 57 After recording, the film and tape are rewound to their respective start marks and can then be run through together as a synchronised combination of picture and sound. The mechanical load of the tape mechanism is of the order of 5 oz.-inches, and although the majority of silent projectors are driven by motors of nonconstant speed, the mechanical filtering on the tape mechanism effectively eliminates flutter and wow. Recording a Film Commentary To record a commentary it is first necessary to get to know the film in detail, and to prepare a suitable script. A suitable means of synchronising film and tape is to place a small piece of adhesive tape on the film leader, and on the section of tape in the magnetic head. There are two inputs to the Cine-Soundmaster, marked respectively A and B. The former is for speech, and is intended for connection to a high-impedance microphone, while the second, also of high impedance, is intended for connection to a pick-up for musical accompaniments. The crystal microphone provided is very directional, and one has to speak fairly closely. Most recordings are done very near the projector, and such a microphone minimises the pick-up of projector noise. Each input is provided with a volume control, and that of input B serves as a mixer by which the music can be faded in and out. The recording may be monitored by listening to the mixed results of inputs A and B through the speaker whilst the play-record switch is switched to " record." Editing the Track For erasing, a permanent magnet may be put in contact with the tape ; this system facilitates editing the track. The supersonic bias on the recording head also has the effect of erasing all except the loudest passages, consequently, even if the erasing magnet is not in operation, a previous recording will be largely erased if one attempts to record over it. It is thus not possible to make separate recordings on the tape at different times. The life of the tape is almost unlimited. Provided the tape does not enter a magnetic field it should last longer than the film itself. A section of recording has been played through no less than 10,000 times without loss of quality or amplitude. The same tape may, of course, be erased and recorded as often as desired. DISCUSSION Mr. N. Leevers : In making recordings for I was conscious of harmonic distortion due subsequent transfer to photographic track, to overloading. Where was it in the great care should be taken to see that the system ? projector runs at a steady speed, and to avoid Mr. N. Leevers : Mr. Honri has raised serious over-modulation ; an overloaded an important technical point. Tape retrack raises difficulties in the transfer later. corded with standard modulation at all Mr. R. H. Cricks : Where is the amateur frequencies will, on reproduction, give a expected to get his music from ? If he copies response which rises by 6 db. per octave, up a disc he is infringing copyright. to a peak in the upper frequency range. Mr. J. Sheppard : There is, when using This means that in reproduction, the amplifier 16 mm. film for domestic purposes, a special should have a falling characteristic of 6 db. low rate of royalty. If you subsequently put per octave up to this peak in order to it on to a 16 mm. film you should declare equalise for the loss at low frequencies, it to the Sound Film Music Bureau. Obviously, if the same amplifier is used for Mr. P. Percher : Is it possible to use this recording and playback, this rising bass equipment for wild recording by an auxiliary characteristic has to be split equally between motor ? recording and playback processes, which Mr. Falkner : Yes, we are producing a means that the amplifier will have a charac motor specially for it. With a six-pole teristic rising at the rate of only 3 db. per induction motor you will have better results octave. Therefore, overloading will take than with a projector. place earlier at low frequencies, and this Mr. B. Honri : In the frequency film should be guarded against.