Compression in the mains??

[exit143]

One of my sound techs compresses the mains. I've asked him why he did that, and he said that it's how he does it in his studio... He figures that he can reproduce his studio sound and it will sound good live. I think it loses the dynamic range (obviously)... and it sounds......... not great.

What are your opinions? Do you compress live audio (not individual instruments, but the mains themselves)... Why or why not?

[cmchamp]

No, do not compress the full mix, you are correct, it reduces dynamic range and increases susceptibility to feedback. It also doesn't sound that great.
You can and should put limiting on mains, preferably after crossover, before amplifier, to protect from clipping and over excursion. However, constantly hitting the limiters may be worse than allowing clipping and causes heat buildup in amplifiers as well.
C.

[2cool]

C. you are right about that. I have been dealing with this for a while as our mains blew out and the Pastor insisted that it was our Youth Band at fault, which is the group I do the sound for. Anyway when we got the new horns he insisted that we connect a compressor and limiter which has KILLED the dynamics and is a constant struggle with feedback. BTW I know it wasnt us. We share the system with 3 other groups.

[pdc]

I use multi-band compression on channels and groups. I use limiting as protection on the main sometimes.

Why someone would compress the whole mix is beyond me. The band's components have differing dynamics. Vocals have differing dynamics. The room's sound is going to come into play even more. Compress hard enough and you will have nasty room roar equaling the source and then a feedback fiesta. The operator will then start hacking away with the EQ. Nah. Forget it.

If your guy doesn't know the difference between live sound and recording, he should not be behind your desk. The two are not the same thing.

[2cool]

PDC that is exactly what I am dealing with right now. HELP. I am going to connect an outside fx unit in hopes it will solve the clip level on the fx's needed. I sorry to ask again but can you give me the exact wiring setup for this. I have the 32unit mixer, fx unit, 2 power amps and a limiter unit.

[pdc]

1. What are the components of your system (Make and model)?
2. If you have that many people using your system, I can almost guarantee that you have operator error as the biggest concern. No piece of gear is going to replace education by an experienced person on-site. Your gain structure could be completely wrong, you could have a lack of headroom or both.
3. If you do use a limiter, it should be the last thing in the chain before your crossovers and amplifiers. FX processors will not help you.
4. If you have internal FX units in your mixer and those are clipping, it is most certainly your gain structure on the mixer that is the problem.

[Brad Weber]

Going back to the point of reducing dynamic range, the related issue is that the compression can raise the average level. If you compress the signal and then raise the overall level the same amount as the compression you maintain the same peak levels but increase the average level. This is a common, and increasingly discouraged, studio and broadcasting trick to make things louder without increasing the peak levels.

In a sound system, this practice means the system works harder and makes thermal failures more likely. And unless you have very fast or look ahead peak limiting, it also means any unexpected peaks now hit the system that much harder.

[exit143]

Since I was receiving all these replies, I asked him to clarify his reasons for compressing the mains. He replied:

Let me explain why I use the compressor in the overall mix.
First of all it is used in moderation, more like a gentle limiter. meaning it does
not have a flat ceiling like a limiter. When I apply around 2:1 compression to
the signal the compressor is barely active, threshold is near 0db. The
compressor is not being used like on a channel instrument.
This keeps me from riding the mains fader. The compressor helps prevent
sudden volume peaks, crescendos. If the volume jumps to an uncomfortable
level, by the time one react to fix it it's already too late. Everyone felt the
discomfort of the volume and then heard you fix it.
I am not compressing to raise the overall signal like in studio recording or like
in a tv commercial.

Thoughts?

[pdc]

If you do not have compression for your channels and or groups and this is his only option for dynamics control, then I see nothing wrong with this. 2:1 compression on a system with proper gain structure is not going to do drastic damage to the sound. 2:1 compression is not going to protect your system from damage either.

The ratio is only part of it however. The attack and the release is what makes the sound pump.

If there are specific bands of frequencies that are needing compression more than others, take a graphic or parametric EQ and insert it into the side chain of the compressor.