[georgia]

Time Code
• Time code was originally developed for video tape editing in an effort to make that process more accurate. Over the years it has been adapted for film production
• The main difference between time code and 60hz. sync has to do with time code's ability to stamp each and every frame with it's own special time marking.
• Since every frame has it's own unique code it is possible to not only locate a specific point in the film or audio track but, it is also possible to sync up to any specific point between the two mediums (also known as chasing).
• Time code, while a very useful tool for the advanced film producer, is not a requirement for double-system sync sound film production. You can make a film with perfectly synced audio by using the same old 60hz. system people have been using for years. Just make sure you use a slate to mark your scenes!
60 Hz sync
• The term 60hz. sync is a method of producing lip-synchronized motion pictures.
• In the early days of double-system sound recording, both the motion picture camera and the magnetic film recorder driven by "synchronous" AC motors.
• In North America we use an electrical frequency of 60hz. and a voltage of around 120vac.
• A synchronous motor is designed in such a way that it's rotational speed is in direct relation to the frequency of the AC current powering it rather than the voltage level of this current.
• even though the voltage might vary up or down, a synchronous motor would always run at a constant speed regardless of these fluctuations. Since both the film camera and film recorder were equipped with synchronous motors, they would both always run at the same speed (i.e. 24fps @60hz.).
• Thus, early picture and sound synchronization was achieved by the ability of the synchronous motor to maintain an accurate speed. as long as you remained in the studio and had a source of AC current to plug everything into this worked.

When it became necessary to take the camera out of the studio and away from any source of AC current a new method had to be devised.

Early attempts at so called "portable" double-system sync had the camera and recorder tied together by a cable.

Cable sync was accomplished by deriving a signal from the camera to indicate the exact speed at which it was running from moment to moment. Therefore, when the camera was running at exactly 24fps, a small electrical generator fitted to the camera's drive motor would produce a signal of exactly 60hz. This sync signal was then sent by a cable to the battery operated tape recorder where it was recorded on a separate channel of the tape as a sync track. Cameras now had to only have a motor that ran relatively constant (i.e. constant speed motors) since any speed fluctuations between the camera and the recorder would be reproducible when the sync track on the tape was played back, later.

Pilotone

The term Pilotone was originally a trade name for this process and is now more or less synonymous with the phrase 60hz. Sync

With 60hz. sync every frame looks like every other. If it were not for the slate markings created at the head (or sometimes the tail) of every scene it would be almost impossible to match up picture takes with audio takes (known as synching up the dailies) during the editing process.

Resolvers

Resolving is the process used to obtain lip-synchronization between two different mediums. A resolver is an electronic device that matches the speed of the sound recorder it is connected to (usually called the slave) to some other reference (known as the master). The most common use for the resolver is transferring audio recorded in the field to an editable medium such as magnetic film or video tape.

Without the resolver it would be impossible to provide for an accurate, frame-for-frame relation between two dissimilar devices since their running speeds would be completely independent of each other. The resolver can overcome this problem by comparing the frequency of the 60hz. signal from the sync track recorded on the tape to the master frequency it has been set to.

If the resolver detects a difference between these two frequencies it will create an error signal equal to this difference. The error signal is returned to the slave recorder causing a speed correction to take place until the two sync frequencies match each other exactly.