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Pre or Post?
Like most technical crafts, sound system operators have a language of their own. The key to understanding other operators and technical manuals is understanding the language. It is not enough to know the words. The key to expert sound system operation is knowing the meanings of the words too. Pre and post are terms that are often used in relation to operating a sound system mixer. Let's explore the meaning of those terms. Pre and post are usually heard when someone is talking or reading about the Auxiliary or Aux Sends of the mixer. These sends could also be called Monitor or Effects Sends. Whatever the names on your mixer, they are used to send a signal to another separate speaker or device besides the main sound system speakers. We will use the term Aux Send in this article. Pre or post tell the operator what path the sound signal is traveling. But pre- or post-what? The "what" is the Channel Fader or volume control. In other words, the Aux Send is pre (before) or post (after) the Channel Fader. | 
| When the Aux is pre-fader, the sound operator can adjust the sound level in the main system without changing the level of the monitor speaker. | 
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If the Aux Send is pre-fader, the Aux signal is independent of the Channel Fader. Any change in the Channel Fader will not affect the Aux Send. This is commonly used for sending a signal to a monitor speaker. Because the Aux is pre-fader, the sound operator can adjust the sound level in the main system without changing the level of the monitor speaker. In other words, the signal will route through the Aux Send before the Channel Fader adjustment. This is very important when accompaniment tapes (trax) are used. The operator may turn the level down in the main system, but the singers still need the trax at a level to properly hear the sound for pitch and tempo. Post-fader means the Aux Send gets its signal after the Channel Fader. Now, a change in the Channel Fader will affect the Aux Send. The Aux "follows" the Channel Fader. This would be used when the operator wants to add artificial reverb to the vocal. The signal to the reverb device would need to "follow" the volume of the singer. If the operator turned down the vocalist with the Channel Fader, the signal going to the reverb device should also decrease proportionally. Knowing whether the Aux Sends are pre or post lets the operator use the mixer wisely and properly. Many mixers have 3 or 4 Aux Sends. More recent mixers may have up to 6 Aux Sends. The manufacturer will designate some of the Aux Sends to be pre and some post. Often, there may be switch to allow some Aux Sends to be switched to either pre or post. That feature provides a lot of flexibility to the operator. Some situations may require the use of the pre-fader control on some channels and post-fader on others. Figure 1 
If you have a mixer with Aux Sends, take the time to learn which Aux Sends are pre-fader and post-fader. Your mixer manual will help you or you could find out by experimenting. It will pay off with better sound and happier musicians. If you have trouble understanding your mixer give us a call. We would be glad to help solve the mystery. by Ron Huisinga © 1996 Internet Sound Institute (www.soundinstitute.com). This article is for personal use only. Any commercial reproduction is not permitted without permission. To obtain permission, contact ISI at hopi@soundinstitute.com
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