05.22.2006 12:00 AM
Dealing With the Pin-1 Problem
If the AES standard, AES48-2005, is followed correctly for any piece of equipment that has audio inputs and outputs (and that includes such devices as VTRs and video servers), then that equipment will not exhibit a pin-1 problem. This is a major step forward in reducing or eliminating noise when one piece of audio or audio/video equipment is connected to another as part of a total system.
But just what is the pin-1 problem?
The pin-1 problem is named after pin-1 of a 3-pin XLR connector that, in audio, is connected to the shield of an interconnecting cable. However, it is not limited to gear with XLR connectors. Any piece of equipment with audio inputs and outputs can have a "pin-1 problem" no matter what type of connector is used.
The problem occurs when the shield of an interconnection cable is wired so that it enters the piece of gear to be connected to the internal electronics. When a piece of equipment has a pin-1 problem, any noise flowing through the cable shield will flow through the audio circuitry, guaranteeing a noisy interconnection. Not really what you want in audio.
The remedy for the pin-1 problem is to tie all shields from interconnecting cables to the equipment chassis at the point of entry. The equipment chassis should also be connected to a common ground. (In addition, the equipment should employ good circuit design and board layout.) That way any noise on the cable shield gets immediately shunted to ground without hitting the audio circuitry at all. A cleaner audio interconnection is the result, something you really do want in audio.