Home Movies and Home Talkies (Jun 1933-May 1934)

HOME MOVIES & HOME TALKIES 331 {Continued from page 322) immense degree by the amplification circuit. Now any type of sound track is made up of dark portions and light portions, and quite early experience showed that it was the clear parts that caused the trouble. Obviously a small scratch or few particles of dust on the darker part was not likely to have any effect on quality, much after the style that ink spots do not show on dark cloth. If the average clearness or transparency of the sound track can be reduced so also will be the ground noise and this is the principle behind noiseless recording, although it is carried out differently according to the types of sound tracks with which it is used. In an earlier article of this series it was pointed out that sound is dvie to difference in opacities of sound track and not to any absolute value of darkness and light. It is important to bear this in mind for upon it rests the principle of noiseless recording. Fig. 66 shows two variable density sovmd tracks recorded by the light valve. That marked A and to the left is an ordinary recording, while the other, B, is exactly the same soiind but treated by the newer noiseless process. Above the arrows in both of the illustrations is a period of silence during which the ribbons of tlie light valve remain luimodulated or perfectly at rest. In ordinary recording the sound track is more or less transparent, but in the noiseless recording has been completely blackened out. Grit and scratches naturally occm on noiseless recording just as much as they do on the other, the only difference being that where the track is blackened out the sound is not affected. Fig. 67. A comparison of variable area track Such changes to the density of sound track take place automatically by a special piece of apparatus attached to the recording machine, and added to this a rather different technique is adopted for printing. It must be borne in mind that the jDrinciple just mentioned applies not only to absolute silences but to every jaart of the track. It is a type of ' ' averaging ' ' and the loudest \yB,vi,>^ of a noiseless track should possess the same opacity as the average track in ordinary recording. It is a little difficult to grasp at first, but if you bear in mind what was said above about differences in density causes sound, you should arrive at the idea. In the glowlamp system of variable density lecording a noiseless track is produced more easily by an electrical circuit which suitably modifies the intensity of the lamp. With variable width recording (that with the peaks ^and hollows) a noiseless track is produced by cutting to a minimum the ti-ansparent portion. This will be clear by an examination of Fig. 67 showing two similar recordings, one ordinary and the other noiseless. It will be seen that the black margin on the noiseless recording only just clears the tojD of the peak ; this is naturally catered for in the oscillograph recording machine which possesses a shutter operated tlirough an amplifier which sets the margin according to the amplitude of the signals. It may well be asked that if this margin is varying in width throughout the film does it not constitute another sound track ? If so are we not likely to hear it through the loud speaker ? As a matter of fact the wavy margin does form a sound track, but its peaks are so far apart that the sound produced is below audible limits and thus really not a sound at all. THE PERMAREC SYSTEM OF HOME RECORDING FOR HOME-TALKIES NOW OFFER THE ENTHUSIAST THE SUPER 16-inch DISC With which it is possible to record speech and music synchronised to a super reel of 450ft. of i6-mm. stock at 33^ r.p.m. on one side for a cost of less than 2/ per 100 ft. These are the Baked Records played with steel needles for several hundreds of times without loss of reproduction. The feature of the recent Cine Exhibition and acclaimed the only satisfactory medium for the home production of sub-standard Home-Talkies. ^ f aiii|| I f THE "PERMAREC" ELECTRIC THERMION (Fig. G) The "Permarec" Electric Thermion (Fig. G), consisting of : An aluminium container and lid with an electric heating element in the base PRICE £3 12 0 Demonsladon7o M U DIAUJM IjIQ. LONDON, W.C.2. Cer. 4476. 17/19 LISLE STREET,