Hi friends
Hope you are all having a great Christmas.
One of Santa's "Presents" this year is a Boss CS-3 Compressor pedal. Very pretty - very blue!
For all my recording work and Live gigging I have relied on the presets on the amp and/or software but now I have 4 real knobs to play with.
Trouble is that one knob is marked "Attack" which does not appear on my amp or on my old DAW software.
It has a Min and a Max (and anything in between of course) but what does it actually DO and what should a guitar be - Min or Max - and WHY?
So many questions - so little brain
Ian

Enviualize a little sound engineer inside the Compressor who can move at near the speed of light.

He is looking at two VU meters and has his hands on two Volume Faders.

One VU meter shows him your signal level at the Input and the other meter shows him that level at the Output.

When you set the Attack control, you are telling the tiny sound engineer who moves at near the speed of light at what point on that Input meter you want him to adjust the fader. In other words, should he start turning the signal level up or down to suit what he's reading a bit sooner, or a bit later as regards the VU meter reading.

The little guy is also monitoring the Output VU meter, turning the other fader up or down to suit where you have set the Threshold control.

So, if your guitar note is dying out, the little guy can make it seem to last longer at the same volume level by simply moving the output fader higher as the signal dies out. Voila, you have increased your Sustain of each note.

Lighter settings can be used as a Limiter, to better control overall volume levels, say, when chord comping.

Ideally, in the Guitar signal chain, the Compressor pedal should be the FIRST effect/accessory in the chain, right after the pickup and patchcord.


--Mac

Excellent anology, Mac. Merry Christmas, by the way.
The other knob is "Sustain" - I thought that did the job of making the sound last longer.
Ian

They just labeled the knob to suit what Guitar players know, Merry Christmas back atcha.


--Mac

This may help as a starting point:

http://en.wikipedia.org/wiki/Dynamic_range_compression

Compressor attack is the speed at which the compressor begins to reduce the gain of a signal once it has passed the threshold set by the user.

As a signal rises from zero, assume a linear rise like a slope on a hillside.... a threshold is set at some point up that hillside. Once the signal reaches and passes that point, the compressor starts to shut it down to keep it from rising more. How fast that shutdown or clamping is beginning to occur is the attack.

Fast attack is used more as a limiter to prevent large spikes from getting through. Fast attacks are very noticeable in the sound under some conditions and are not desired to be heard. Therefore, a slower attack is used to "round off" the signal according to a ratio set by the user.

Side story: I was in a band with a substantially large and powerful PA system. I had bought a compressor/limiter for the PA gear rack. Our band had a major flashpot explosion. It was as if someone dropped a frag grenade on the stage. Without going into details, the blast was immense. It literally ripped every speaker from it's basket in all the open back cabinets. It was picked up by 2 vocal mics not 10 feet away and run into the PA system. It went through the board and out to the monitors and through the gear rack to the main PA. The new limiter/compressor had a fast attack and clamped the signal going to the main PA. We only lost 1 15" speaker in the main PA. In the monitors, we lost every single speaker since the signal in the monitors did not have the limiter. Explosions, dropped mics, plosives, bumped mics, all create the spikes that are destructive to gear and not wanted in recordings.

There is also a release which on some compressors is totally under the control of the user. Some guitar compressors don't have them. With an improperly set attack/release/threshold, it's possible to get the compressor "pumping" as it works to quell the spikes from things like kick drums and snares.... if the compressor is on the mix as a whole, this results in an audible and noticeable volume pumping.

A compressor is a valuable tool but not knowing what it does or how it should be working can result in that tool being abused. It's probably the most abused tool in the audio world and it is so essential to a good mix.

pictures:

Light compression...taming just the spikes



A higher level of compression, still allows some room for dynamics. This level of compression is used on most songs these days. Retains good levels of dynamics but also has nice volume levels through out.



Over ambitious levels of compression. Pumping is likely to be heard on such a mix. I did this mix simply to illustrate a point. Although, it is a common way to use compression on many hard rock songs these days. There is NO dynamics left in this mix..... listening to this sort of mix will fatigue the ears quickly since it stays at full volume through out the song.