User`s manual

3-1
SECTION 3
AN OVERVIEW OF THE ALIGNMENT PROCEDURE
This section is an overview of the general principles involved in the
alignment of Dolby cinema equipment. It is useful to develop an
understanding of why the CP45 is aligned as described in this manual.
If the installer is already familiar with these principles, or is in a hurry
to complete the installation, this section may be read later. Continue the
installation procedure beginning with Section 4.
3.1 Aligning the A-Chain
The A-Chain optics is first cleaned and mechanically adjusted, then
calibrated by use of the Cat. No. 69T Dolby Tone test film. This film is
used to establish the correct Dolby operating level within the CP45.
Pink noise is used for equalization of the A-chain. (Pink noise is similar
to white noise but provides equal energy per octave of bandwidth.)
The optical slit is the key element in the A-chain because it imposes the
initial limitation on the high-frequency response of the system. Light
from the exciter lamp passes through the optical slit and is focused on
the optical soundtracks on the film. The light that passes through the
soundtracks falls on the stereo solar cell which generates an electrical
signal proportional to the audio signal recorded on the optical
soundtracks. The slit introduces high frequency loss which must be
compensated by circuitry in the Cat. No. 510 Input/Output card.
The slit image must be correctly focused on the film and must be
precisely at right angles to the direction of film movement in order to
maintain the correct phase relationships between the two optical tracks.
Any azimuth error will show as a loss of high frequency in the front
channels and potentially excessive crosstalk in the surround channels.
Each channel in the Cat. No. 510 Input/Output card is equipped with a
slit loss equalizer control. Adjustment of this control shifts a fixed
amount of boost upward or downward in frequency, but the shape of
the curve remains constant. A flat response up to a minimum of 12 kHz
can be achieved.
3.2 Aligning the B-Chain
In most theater playback systems, the acoustical qualities of the theater
are difficult to change. Therefore, the primary area where improvement
is possible is correcting system response errors caused by the theater
acoustic environment.