The release print

The film can live two lives : one in the festivals, where only a few prints will be manufactured (often times just one !), or one in the traditional commercial release, where hundreds (sometimes thousands) of theatres must get their copy on the same day, just before the release date.

Sep-mag and Sep-opt principle

The most economical release principle, consists in projecting the picture and sound on separate media, since no further process is needed than those we've explained in the previous pages. The festivals are all equiped with special projectors, so do film schools, which can seldom finance "com-opt" 35mm copies for their students !

Such a projector has a single motor driving the picture and sound media simultaneously. The projectionist will receive two reels : one picture reel and one sound reel. Usually, the picture projected is a copy of the conformed negative master manufactured by a lab. But sometimes, when the budget is really really low, it can be the edited work copy (!!!) with all the editing scotch tape, all the scratches, the stubborn white crayon marks that wouldn't erase completely, that is projected ! Now the sound reel can very well be the master tape we mentioned on the previous page, or preferably, a copy of that tape, you never know what can happen with sprocketed media (!!!).
		Projector
		seen from above
The projectionist just has to position the start crosses facing the projector's shutter, for the picture reel, and facing the magnetic playback head for the sound reel, in order to sync the two for the projection.

This type of sound and projection technique is officially called Separate Magnetic ("Sepmag"). There is also another possibility : Separate Optical ("Sepopt"), which was quite popular before the fifties, since magnetic tape recording will only be availible in the mid fifties. The perfect example is the projection of Walt Disney's FANTASIA in 1941 :

In those days, the film was projected with 3 audio channels (Left / Center / Right), with one projector for the picture and three optical sound playback systems, one for each channel, all four mechanism driven simultaneously.

Note that when a film is projected with DTS (Digital Theater Sound) sound, since the sound is recorded on magneto-optical disks, synchronized to the picture by a time code laid along the perfs (see below), it also belongs in the family of "sepmag" projection, or to be precise, "sepmag...neto-optic".

Com-opt and Com-mag principle

When you want to release a film in hundreds of theatres on the same day, you need as many copies ! A release using a separate sound reel wouldn't be cheap at all since you would need as many sound reels as there are picture reels. Optical sound prints are in this case a lot cheaper in the long run, since the costs involved in producing the original optical sound master is quickly balanced by the number of copies produced from it.

The audio tape master fresh from the mixing stage (see previous page) is sent back to the picture lab, where it will be combined with the picture on a single negative. Once again, there are two possibilities :

Common optical ("comopt") which is THE standard for 35mm prints, and even more so since the advent of digital optical sound. The anamorphosed (optically squeezed) picture is skewed to the right to make room for the double optical sound tracks, named LT-RT (Left Total & Right Total).It is from this double track that the 4 channels of Dolby Stereo or Dolby SR (very little difference between these two formats) will be extracted by a matrix system in the theatre.

Common magnetic ("commag") which was already a rare format in the 80s and 90s, under the form of 70mm magnetic 6-track prints. For this format, the release print comprises the picture as well as a magnetic coating on both sides for sound. These prints cost up to 10 times that of a comopt print !

Dolby D and SDDS (Sony Dynamic Digital Sound) digital audio release prints also fall in the "comopt" category. They are based on two innovations :

- new generation film stock, with a high resolution, high enough to correctly represent the little checker boxes of the binary message (opaque or translucid = bit 1 or bit 0). - data reduction algorithms which lead to a reasonable bit rate despite the many audio channels (6 or 8) and additional optional infos (control of hydraulic mechanisms / sub-titles / etc...) After multiplexing all the information (combining all the channels in a single data flux), the "continuous checker-board" representing that data is laid between the perfs for Dolby D and outside the perfs for SDDS. Note that the Time Code necessary for DTS being between the double analog Dolby SR tracks and the perfs, a single print can therefore be Dolby SR (4.1), Dolby D (5.1), SDDS (7.1) and DTS (5.1).

On the right is the audio playback system of an optical sound 35mm projector. I won't insult your intelligence by pointing the place where the picture is read. Sound cannot be read at the same physical position as the picture, because in front of the image gate (or shutter, if you prefer), the picture progresses in fits and starts, 24 times per second, which would end-up in a sound playback close to a DJ hysterically working his turntable !!! It has therefore been decided that sound would be read further down from picture playback. The lab takes care of that time shift when making the optical master print, the shift being, of course, standard worldwide in 35, in 16 and in 70mm. 21 frames offset in 35mm 22,4 frames offset in 70mm
For those of you who wonder what the big box with the pipe sticking out can be : that's where the projector bulb is housed, and the pipe is there to extract the hot air (or bring in cold air, whichever), otherwise, it gets pretty warm in there!!!
		35mm optical sound projector