Synchronous sound made cinema an art of time. The stabilisation of projection speed, made necessary by the coming of sound, did have consequences that far surpassed what anywone could have foreseen. Filmic time was no longer a flexible value, more or less transposable depending on the rythm of projection. Time henceforh had a fixed value - sound cinema guarenteed that whatever lasted x seconds in the editing would still have this same exact duration in the screening. In silent cienema a shot had no exact internal duration - leaves quivering in the wind and ripples on the surface of water had no absolute or fixed temporality. Each exhibitor had a certain margin of freedom in setting the rhythm of projection speed. Nor is it any accident that the motoized editing table, with its standardized film speed, did not appear until the sound area.

I am speaking of the rhythm of the finished film. Within the film there are certainly may be material shot at nonstandard speeds - accelerated or slow-motion. The speed of these shots does not necessarily reproduce the real speed at which the actors moved during the filming - but the speed is fixed a a precisely determined and controlled rate.

Sound temporalized the image - not only by the effect of added value but also by normalizing and stabilizing the film projector speed. The sound cinema can be called "cronographic" - written in time as well as in movement.

Audiovison is highly recommended. 

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