Complex sentence: The first was the'Dolby SVA' (stereo variable area) system used with optical soundtracks on 35mm film, and the second'Dolby Stereo 70mm' which meant the use of Dolby noise reduction on the 6-channel magnetic soundtracks found on 70mm prints.
Split into simpler sentences: The first was the'Dolby SVA' (stereo variable area) system used with optical soundtracks on 35mm film. The second was "Dolby Stereo 70mm", which referred to Dolby noise reduction on the 6-channel magnetic soundtracks on 70mm prints.