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Author Topic: When to use a compressor  (Read 2312 times)

Steve Mick

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When to use a compressor
« on: May 04, 2018, 05:41:32 pm »

I have a bit of confusion about when it's appropriate to use a compressor and when it's not.

I'm coming from the perspective of a nightclub DJ and the sound systems that nightclubs use. I don't really think this topic is appropriate for the DJ forum however.

I understand that if you are in a live band, you're going to need a compressor. There's a lot of microphones and line inputs coming from various places (Guitar, Bass, Drums, Vocals, etc...). A compressor helps to balance out all those input volumes so that none are too loud or too soft.

But with a DJ sound system, I don't understand why the compressor is necessary. All of the music that we play as DJ's has already been compressed in the studio when the track was mastered.

I've been looking at the sound systems at a couple of the clubs in town and they're all using compressors. But why? Is there some reason for needing to compress all these songs that have already been compressed?
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Ivan Beaver

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Re: When to use a compressor
« Reply #1 on: May 04, 2018, 07:24:54 pm »

I have a bit of confusion about when it's appropriate to use a compressor and when it's not.

I'm coming from the perspective of a nightclub DJ and the sound systems that nightclubs use. I don't really think this topic is appropriate for the DJ forum however.

I understand that if you are in a live band, you're going to need a compressor. There's a lot of microphones and line inputs coming from various places (Guitar, Bass, Drums, Vocals, etc...). A compressor helps to balance out all those input volumes so that none are too loud or too soft.

But with a DJ sound system, I don't understand why the compressor is necessary. All of the music that we play as DJ's has already been compressed in the studio when the track was mastered.

I've been looking at the sound systems at a couple of the clubs in town and they're all using compressors. But why? Is there some reason for needing to compress all these songs that have already been compressed?
A compressor is not for balancing out the various instruments, it has no way of knowing how to do that.

In a DJ application, it is best used to keep the system from being damaged by DJs who only know that "UP is loud".

If set properly (and THAT is a big question-often it is done wrong), you should run the system up to the point at which the compressor reduction lights are just barely showing.  That is your limit.  If you run it any louder, the sound will lose punch and impact and start sounding squished.

But many DJs think that the more lights you can light, the "better" you are.

It doesn't take any talent to simply push faders up- but somehow they think makes this "important".

The compressors are there for the idiots.

Sorry to be so blunt, but most DJs simply have no knowledge of proper/safe operation and simply don't care-as long as the system belongs to somebody else and they don't have to pay for any damage.

I have run into a good number of DJs, who PRIDE themselves on how many speakers they have torn up.

THAT is why DJs have such a bad reputation among sound pros
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Ivan Beaver
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Steve Mick

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Re: When to use a compressor
« Reply #2 on: May 04, 2018, 08:18:16 pm »

A compressor is not for balancing out the various instruments, it has no way of knowing how to do that.

I thought the purpose of a compressor is to take the sounds that are too loud and quiet them down while also taking the sounds that are too quiet and lifting them up.

Is that not what a compressor does?
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Neale Watson

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Ivan Beaver

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Re: When to use a compressor
« Reply #4 on: May 04, 2018, 09:12:23 pm »

I thought the purpose of a compressor is to take the sounds that are too loud and quiet them down while also taking the sounds that are too quiet and lifting them up.

Is that not what a compressor does?
A compressor has no way of knowing if a signal is a vocal or guitar or keyboard.

Below the threshold setting, nothing happens.  But when the level exceeds the threshold, the compressor "compresses"  or limits the signal.

How much or how fast depends on the settings.

It can be set for gentle reduction or aggressive reduction.

So it will basically reduce the level, but does not increase the level.

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Rob Spence

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Re: When to use a compressor
« Reply #5 on: May 04, 2018, 11:05:04 pm »

A compressor has no way of knowing if a signal is a vocal or guitar or keyboard.

Below the threshold setting, nothing happens.  But when the level exceeds the threshold, the compressor "compresses"  or limits the signal.

How much or how fast depends on the settings.

It can be set for gentle reduction or aggressive reduction.

So it will basically reduce the level, but does not increase the level.

It reduces the rate of increase in level by the selected ratio.


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Steve Mick

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Re: When to use a compressor
« Reply #6 on: May 04, 2018, 11:28:58 pm »

A compressor has no way of knowing if a signal is a vocal or guitar or keyboard.

Below the threshold setting, nothing happens.  But when the level exceeds the threshold, the compressor "compresses"  or limits the signal.

How much or how fast depends on the settings.

It can be set for gentle reduction or aggressive reduction.

So it will basically reduce the level, but does not increase the level.

I didn't really say that the compressor has to know if it's a guitar or what not. But I get what you're saying about reduction which is something that I didn't understand about compressors. I now get it. They only attenuate the incoming signal, and it will only do that when it goes over the threshold by an amount determined by the setting. If it doesn't go over the threshold, nothing happens.

If nightclubs are using compressors as limiters, that actually makes a lot of sense. It also answers my question. In a nightclub you would need some type of limiter because all these DJ mixers have a Gain/Trim on every channel and they're being misused. They just see it as another way of increasing the output volume when in fact it's increasing the input volume.

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Craig Hauber

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Re: When to use a compressor
« Reply #7 on: May 05, 2018, 01:14:11 am »

I didn't really say that the compressor has to know if it's a guitar or what not. But I get what you're saying about reduction which is something that I didn't understand about compressors. I now get it. They only attenuate the incoming signal, and it will only do that when it goes over the threshold by an amount determined by the setting. If it doesn't go over the threshold, nothing happens.

If nightclubs are using compressors as limiters, that actually makes a lot of sense. It also answers my question. In a nightclub you would need some type of limiter because all these DJ mixers have a Gain/Trim on every channel and they're being misused. They just see it as another way of increasing the output volume when in fact it's increasing the input volume.

A limiter is just a high-ratio compressor with a faster attack setting.

For artistic purposes you tend to use lower ratios and run above the threshold which tends to increase sustain or make quieter elements more apparent -leading many to mistaking believe they are actually boosting the quieter parts.
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Craig Hauber
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Tim McCulloch

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Re: When to use a compressor
« Reply #8 on: May 05, 2018, 02:46:03 am »

I didn't really say that the compressor has to know if it's a guitar or what not. But I get what you're saying about reduction which is something that I didn't understand about compressors. I now get it. They only attenuate the incoming signal, and it will only do that when it goes over the threshold by an amount determined by the setting. If it doesn't go over the threshold, nothing happens.

If nightclubs are using compressors as limiters, that actually makes a lot of sense. It also answers my question. In a nightclub you would need some type of limiter because all these DJ mixers have a Gain/Trim on every channel and they're being misused. They just see it as another way of increasing the output volume when in fact it's increasing the input volume.

Bingo!  We have a winner!

That's the reality of how too many DJs work and why installed systems often have rigorous limiting and protection.

DJs weren't the first to turn all the knobs to the far right stop and boost all the faders to the top and DJs wont be the last... it's just more fun to pick on them.

I asked a DJ why he did that and his answer was "because I can!  If I shouldn't do that the mixer shouldn't have those knobs."  I responded that seemed the equivalent of driving his car at maximum speed because the gas pedal still had some travel and he gave me a look that said 'discussion over'.  YMMV.

Back to protection - there are a couple of products that do a bit more than limit, they will audibly reduce the level.  The dbx 160 with a ratio of 1:-1 will result in 1dB of level reduction for every 1dB over threshold.  The more you push it the lower it gets...  There is another system from the UK (IIRC) that uses a measurement mic (or several) and has a booth display like a traffic signal with red resulting in lowering of system level no matter how hot the signal.  The concept of both these is probably aimed more at compliance with local authorities than system protection but they are useful either way.
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Steve Mick

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Re: When to use a compressor
« Reply #9 on: May 05, 2018, 05:12:26 am »

Thanks for all the input guys. I wasn't really getting the answers I was looking for just by Googling. I had to go somewhere and ask. Actually, I have one last question. Normally I would start another thread for this, but I think it can be answered quickly.

What is the order (Chain?) for all this equipment?

Does it go: DJ mixer - EQ - Compressor - Amplifier - Drive Rack - Speakers
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ProSoundWeb Community

Re: When to use a compressor
« Reply #9 on: May 05, 2018, 05:12:26 am »


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