Journal of the Society of Motion Picture and Television Engineers (1950-1954)

/hich I don't believe has been made too learly here, is that we have a perfectly antastic hum problem. I have made some ery crude calculations here and I believe hat for a 50-db signal-to-noise ratio, the lum signal must be less than —144 dbm t the input of the preamplifier. This is a airly severe hum problem and I therefore lope that we do not give up more than a Ib or so of the present low-frequency premphasis. Mr. Wirth: I would like to comment on ome of the points that have been made. ror one thing, I think that the concept »f using high-frequency preemphasis to :ompensate for inefficiencies in head design ir difficulties thereof is one of the evils >f the magnetic recording industry. The amount of pre-emphasis that ^mpex used for the Magna Theatre Corp. vas not tied down to any particular set >f specifications, since it was a development ystem which we hoped would be superior o anything that existed before. It thereore gave us the opportunity for experinentation to our heart's content with the variety of possible paths available. We nade a great number of narrow-track istening tests with different pre-emphasis characteristics in order that our conclusions /vould be based on CinemaScope condiions. I think that's the whole key to this discussion; we are now dealing with very larrow track magnetic stripes. With the •eplaying of CinemaScope films, no doubt, ,ve will be able to get some quantitative nformation as to deterioration of signaltoloise ratio due to the rubbing-off of the Dxide, and other effects. We're not saying that this proposed pre-emphasis characteristic is, by any means, the last word, but we're certainly interested in finding out what other people think about it. Mr. Athey: Was this equalization for a half-mil playback gap? Since our present system is designed for the half-mil gap we wouldn't like to go to a larger gap. Mr. Wirth: A j-mil gap is used. Ralph H. Heacock (RCA Victor Div., Camden, N.J.): There are several minor things that have come up in the field about which there may be some confusion. Someone asked about the adaptability of the various manufacturers of button-on units to various projectors. I think broadly and from an engineering view point, certainly all manufacturers plan to have their units adaptable to any type of projector that may be available in the field, but from a practical viewpoint at the present time we are so very busy producing equipment, that it may be that we haven't gotten around to making the necessary adaptor plates for some particular projector and, because of that, a report gets around that a certain unit will not work with a certain type of projector. Well, that may be only because that particular adaptor plate is not available to meet the necessary close opening date of a particular theater, so that probably, in the course of the next few weeks, it will be correct to say that any one of the units, at least to the best of my knowledge, will work with practically any one of the projectors in the field. There was one other question that was asked by someone about the standardization of sound take-off with relation to picture take-off. It's my understanding that the sound lags or follows the picture by 28 frames, so that there is actually a lag of 28 frames with all of the button-on types of sound heads. One other question that came up: someone asked about the effect of the narrower sprocket teeth when used with the conventional sprocket hole in the film. In general, the studio guides of the projector are the determining factor for lateral weave, so that even though the tooth is narrower than has been the practice in past years, the studio guides will still be the determining factor in lateral weave. It would, therefore, be my guess that it should not be any worse with a narrower tooth than it has been in the past with the standard tooth. There has been a lot of discussion about the new CinemaScope sprockets. That, I think, is probably a matter that comes under the Film Projection Practice Committee. Our meeting is at 2:00 o'clock on Thursday afternoon and we would very heartily welcome anyone who wants to come in and express any comments on the new types of sprockets, the root diameters and any other things that have been revealed in work of, say, the last six months, so that we can have the value of your experience in our Committee meeting. Mr. Hilliard: What do you mean by studio guide? Stereophonic Equipment Discussion 237