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Need help w/ PA Compressor

jtc_hunter

jtc_hunter

Feb 16, 2007
1,398
7
#1
I bought a 4 channel compressor to add to my PA. I want to use it for vocals and especially the kick drum mic. I have the manual, but I am having a bit of trouble really understanding the controls for each channel. If someone could please explain in lay mans terms what these controls do, I would appreciate it.
1. Threshold has a range of -40 to +20

2. Ratio has a range of 1:1 to 8:1

3. Output up to +20db
 
#3
Threshold sets the level at which the compressor will begin to apply gain reduction to the signal.

Ratio sets the amount of gain reduction applied. With a ratio of 4:1 an input signal 8dB above the threshold will result in an output signal 2dB above the threshold.

Output is simply make up gain.
 
#4
projectMalamute said:
Threshold sets the level at which the compressor will begin to apply gain reduction to the signal.

Ratio sets the amount of gain reduction applied. With a ratio of 4:1 an input signal 8dB above the threshold will result in an output signal 2dB above the threshold.

Output is simply make up gain.
Click to expand...
Yes to this. I think of it this way because it's simple for me:
Threshold is like a sensitivity control- adjusts when the compressor will 'kick in.'
Ratio adjusts how much the compressor will compress, once it kicks in.
And output is make up gain, or volume, of the now compressed signal.
 
#6
it's good for vocals, but i'd skip it on the kick drum.

now if it also has a gate, i would use that on the kick drum.

set the gate so it opens immediately on even gentle kicks but stays closed otherwise. this will reduce low end feedback and let you adjust how long the kick drum sustains.

oh, as for vocals, if you insert it on a vocal channel, it will compress that singer's monitor, which is very bad. it will feed back and also make the singer blow out their voice.

put the compressor on a subgroup and send all the vocal channels through it, or use a mic cable splitter and make two channels for the singer, one just for mains with the compressor inserted, and one just for monitors with no compression.
 
#8
walterw said:
it's good for vocals, but i'd skip it on the kick drum.

now if it also has a gate, i would use that on the kick drum.

set the gate so it opens immediately on even gentle kicks but stays closed otherwise. this will reduce low end feedback and let you adjust how long the kick drum sustains.

oh, as for vocals, if you insert it on a vocal channel, it will compress that singer's monitor, which is very bad. it will feed back and also make the singer blow out their voice.

put the compressor on a subgroup and send all the vocal channels through it, or use a mic cable splitter and make two channels for the singer, one just for mains with the compressor inserted, and one just for monitors with no compression.
Click to expand...

I would disagree with this. A compressor is perfect for a kick drum as it will tighten it up. Delay the attack just a bit to let the natural attack of the drum come through with a medium ratio (around 5:1) and a quick release will tighten the drum up and let it sit better in the mix. I agree that a gate is good to have on any drums for isolation, but if you are trying to correct feedback with it, something is too loud. It is simply to remove bleed over between the drum mics and not to stop feedback.

As far as vocals, if you are squashing a vocal so much that the person can hear it, it is far too much. You either have too high of a ratio, or the threshold is set far too low. Compression should be a subtle effect. If you hear it "pumping" you have too much. Also, if you insert the compressor on a sub group, the compressor threshold is reacting to the strongest signal (i.e. a single loud vocalist, etc.) and compressing everything in the entire sub group down including the softer background vocals unnecessarily. This can cause you to lose some of the softer signals in the sub group.
 
#10
Bardley said:
A compressor is perfect for a kick drum as it will tighten it up. Delay the attack just a bit to let the natural attack of the drum come through with a medium ratio (around 5:1) and a quick release will tighten the drum up and let it sit better in the mix. I agree that a gate is good to have on any drums for isolation, but if you are trying to correct feedback with it, something is too loud. It is simply to remove bleed over between the drum mics and not to stop feedback.
Click to expand...
i'll not argue with any of this, except to say that for folks at the "what does a compressor do?" level, shaping the envelope of the kick drum is probably further on up the learning curve, and not so useful for little bar PAs. the kick drum is not nearly as important as the vocals, something even some experienced soundmen seem to forget.
Bardley said:
As far as vocals, if you are squashing a vocal so much that the person can hear it, it is far too much. You either have too high of a ratio, or the threshold is set far too low. Compression should be a subtle effect. If you hear it "pumping" you have too much.
Click to expand...
depends on the band. some vocalists sound right with quite a bit of comp, way too much for a usable monitor mix. you're correct about the "pumping", but a good comp set properly can squash pretty heavily without that effect, especially if it's not on the whole mix.
Bardley said:
Also, if you insert the compressor on a sub group, the compressor threshold is reacting to the strongest signal (i.e. a single loud vocalist, etc.) and compressing everything in the entire sub group down including the softer background vocals unnecessarily. This can cause you to lose some of the softer signals in the sub group.
Click to expand...
you're correct about the drawback of compressing a vocal subgroup, but in practice it's usually OK at the bar band level. the lead singer should be the loudest, so the comp tracks that while the backgrounds get pushed to, well, to the back.
 
#12
The best way to learn what your compressor will do is to set up your PA, and start twisting knobs. Try everything from no compression to as much as the unit will allow. Use your ears. The advice posted here already is good, but it's no substitute for becoming familiar with gear, and knowing how it affects your sound firsthand.
 
#14
So, no group inserts then. The XLR Y cord on the singer idea would be the best. One going to what the audience hears, with the compressor in the insert, and one for just the monitor send with no compressor. That is if you have the extra open channel. Other wise if you are going to use the compressor, it will compress the monitor feed as well.
 
#15
I am sorry, but I cannot think of anything to use that particular compressor on. Remember your audio quality is on as good as your weakest link in the signal path. Using a cheap compressor is - in my book - a major mistake.

But there are some people, and you could be one of them, that cannot hear any difference when using inexpensive gear. Even so, your are just adding to your sound problems instead of helping them, without realizing it.

Good compressors are not really all that expensive, by the way. Good luck with yours.

mark
 
#17
There's nothing wrong with Behringer compressors--I have used them for years.
(Until they break, that is).
I can hear the difference, and preferred my dbx for kick and lead vocals.
Just bought 8 channels of PreSonus, but the Behringers were WAY better than no compressors at all.
Just stay away from those old Alesis comps!

Go ahead and put it on the vocals and kick.
Start at 3:1 ratio at most, threshold 0bd, output +3db.
Raise the input gain on that channel until you see around 4 to 6 db of gain reduction during the loudest parts and you should be fine.
This is where I always start, and on most signals will help tame things a bit without causing trouble.

On your system the compressor probably WILL affect the monitors, so watch your levels.

Hope this helps.
Have fun!
 
#19
Bardley said:
I would disagree with this. A compressor is perfect for a kick drum as it will tighten it up. Delay the attack just a bit to let the natural attack of the drum come through with a medium ratio (around 5:1) and a quick release will tighten the drum up and let it sit better in the mix. I agree that a gate is good to have on any drums for isolation, but if you are trying to correct feedback with it, something is too loud. It is simply to remove bleed over between the drum mics and not to stop feedback.

As far as vocals, if you are squashing a vocal so much that the person can hear it, it is far too much. You either have too high of a ratio, or the threshold is set far too low. Compression should be a subtle effect. If you hear it "pumping" you have too much. Also, if you insert the compressor on a sub group, the compressor threshold is reacting to the strongest signal (i.e. a single loud vocalist, etc.) and compressing everything in the entire sub group down including the softer background vocals unnecessarily. This can cause you to lose some of the softer signals in the sub group.
Click to expand...


I agree with most of this - I run sound on a semi-regular basis, and use (4) dbx 266s in my effects rack for compression...

I've never run into any difficulty inserting compression on vocals, and ALWAYS use it for a "screamer"...

Also, I use a bit of compression on kick, and *most* of the time on the bass channel, depending on the bassist's technique... I'll PFL both for a couple of minutes, and if they're really up and down level-wise, I'll do what's necessary to protect my PA's speakers from their erratic levels...

Lastly, I mostly only use gating to help with toms that ring - which *seems* to happen more with rack toms than floor toms, IME...



- georgestrings
 

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