Live Sound Reinforcement

Subject: Live Sound Reinforcement - Compression
From: GUEST,Pdbanjo
Date: 10 Dec 01 - 10:06 AM

How and Why are compressors used for vocals or in a sound reinforcement system at all? I'm trying to find this info for our Band on whether to incorporate them into our PA system. We're looking for the optimum clairity that can be acheived with eletronic gear. If such a thing is possible. I've heard some pretty awesome live sound in the 25 plus yrs. performing but until recently I've never payed too much attention to what the engineers were doing to get crisp voices and distinct acoustic sound during live performances. Help!! An inquiring dimwit needs to know!!

Subject: RE: Live Sound Reinforcement
From: JohnInKansas
Date: 10 Dec 01 - 12:57 PM

I have little experience with sound systems, but perhaps an incompetent opinion or two will get some discussion going.

My "cheapie" sound book, Sound Reinforcement Handbook, Gary Davis & Ralph Jones, Yamaha Corporation, 1989, ISBN 0-88188-900-8 (about $35 US) lumps compressors and limiters together, depending on how they are used. In either case, the device limits the amount of increase in "delivered" power as the input signal increases beyond some selected level.
Used as a limiter, the intent may be only to protect the speakers - as when someone drops a microphone.

The "extreme" use of compression is in voice/announcement types of PA systems, especially in noisy environments. By using a lot of compression, all of the signal can be delivered at essentially "full power" regardless of the dynamics (fluctuations in power level) of the input. The example given is the announcer at a "moteor race track."

It would appear that use of some moderate amount of compression could help solve the "mike distance" problem, - the variation in output as performers move around the microphone; and could be used to push more of the output dynamic range above any crowd noise threshold.

My favorite festival has gone through a long period (15 years) of degradation of their sound by hiring "experts" whose answer to everything was "more amps." This year they finally realized that "the louder the sound system, the louder the crowd, which means you have to get a louder sound system, which makes the crowd louder."

They finally cut back to a level this past year that sounds good if the crowd keeps (somewhat) quiet, and things were greatly improved.

Sophisticated limiters, compressers, and "companders" probably are most frequently used in recording/playback, where there are some well known "thresholds" like tape hiss (background noise) or needle jump/tape saturation limits.

Auditorium sound reinforcement possibly is more complex, due to the uncertainty about - and variability of - the background, and by how much additional power is needed/acceptable as the room fills. This means you may need more "adjustable" features - and also increases the possibility of messing things up if you don't have someone with experience and a good attitude running the system.

Now, lets wait for someone who actually knows something...

John

Subject: RE: Live Sound Reinforcement
From:
Date: 05 Mar 06 - 11:31 PM

where can i find a megaphone as used by "rudee vallee"

Subject: RE: Live Sound Reinforcement
From: treewind
Date: 06 Mar 06 - 03:59 AM

John's pretty well nailed it. The main need for a compressor on vocals in typical live sound is when your vocalist, whether because of singing style or bad mic technique, has a huge dynamic range i.e. is liable to change from inaudible to deafening without warning. For instance, some singers get suddenly very loud on high notes but don't know to back off from the mic when that happens.

I'd agree that a limiter might be used to prevent distortion if the levels threaten to hit amplifier clipping. Too much reliance on that will not protect the speakers if the amplifier has higher output power than the speakers can handle, as the avarage power levels still go up even if the peaks don't.

Over the whole sound mix, a compressor will help to keep the quieter parts above the background noise.

A compressor can also mess up the sound if you don't know how to use it. Using a compressor is a good way of encouraging feedback howls.

For clarity of sound (ref original poster), good speakers are often the ting tha make most difference.

Anahata