Optical sound troubleshooting

These are some examples of common optical sound issues, and their potential causes and remedies.

Buzz/Hum

Buzz and Hum can be caused by:

Ground Loop: If there is a hum in the system with no film running, there is likely a ground loop.

Light leak: Check for light from an overhead light or a reflection from the port window spilling into the optical sound system.

Lateral Guide Roller Alignment: Film is not properly aligned in the soundhead, and the solar cell is picking up parts of the image, DTS timecode, or perforations in addition to the soundtrack. Align with Buzz Track test film as described in your projector's manual.

Damage to Optical Soundtrack: scratches, gouges, or sprocket run can cause audible buzzing. If damage is limited to only one side of a mono track, the undamaged side can be isolated by blocking off half of the slit lens or solar cell with a business card, or bringing the gain all the way down on the left or right channel.

Shrunken Optical Soundtrack: Print is shrunken and not aligned laterally in the soundhead. As with soundtrack damage, part of the track can be blocked off with a business card. The lateral guide roller can also be adjusted to the shrunken film, but must be set back afterwards. Consult your projector's manual for this adjustment.