Sound-on-film
caption: Edge of a 35mm film print showing the soundtracks. The outermost strip (left of picture) contains the SDDS track as an image of a digital signal; the next contains the perforations used to drive the film through the projector, with the Dolby Digital track, the grey areas with the Dolby Double-D logo, between them. The two tracks of the analog soundtrack on the next strip are bilateral variable-area, where amplitude is represented as a waveform. These are generally encoded using Dolby Stereo matrixing to simulate four tracks. Finally, to the far right, the timecode used to synchronize with a DTS soundtrack CD-ROM is visible.