[Al Stevens]

Would the gearheads here please discuss in lay terms the effect called "compression" found as a plugin on many audio software consoles.

I'm not referring to the compression of audio files to make them smaller as in mp3s, for example. This is about the audio effect called compression.

I've played with it some, but my hearing is poor enough to keep me from hearing much change. How is compression applied? I know what it does to the waveform—it changes the dynamic range, the difference between loud and quiet signals, and there are various aspects of it you can control. Attack, for example.

But when do you do this? What do you hear in a recording that tells you that compression is needed? Can you use it to enhance the sounds of specific instruments, for example?

Remember, lay terms, if that is possible...

 

[crazydaisydoo]

Al,

Good question, compression basically squeezes the dynamic range. That is the difference between the loudest part of your track, and the softest. This means that soft passages are artifically boosted in volume, and the loudest (sometimes depending on the type of compression) is reduced or limited

It is used to create impact and add punch to a sound. For example, bass guitar is ofted compressed.

Compression is even added after the recording is made. Some radio stations compress their output to make it more suitable for listening in car radios.

Most jazz and classical artists hate the idea of using compression, but the reality is most good quality recording engineers use it (sometimes without telling the artist!)

I dont use compression, because the quality of the effect on my multitrack is poor. If I had $5000 to spend on a good one I would probably use it, because it can be very benefitial to your overall sound. I think rock and roll sax would benefit from it, to add punch.....

 

[docformat]

The stuff about the dynamic range is the 'mathematical' reason for using compression but most engineers use it at least as much for its sonic quality. These qualities are often dependent on how the signal path has been put together - is it valve, solid state, does it have an optical circuit or does it emulate these (in the case of software or digital consoles). You can also radically alter the sound by using 'attack' and 'release' settings to create a sort of 'pumping' sound. To be honest its hard to describe because different people use it in different ways, but Crazy's right - you need to have decent (but not necessarily expensive) kit to make it work right.

 

[DougR]

As the man said, "compression basically squeezes the dynamic range".

There are one basic mechanism, it is the control of the "Gain" of an amplifier in response to the sugnal level so that loud sounds get turned down and quiet ones turned up.

If you look at an unprocessed recording of a Guitar string being plucked, you get a sharp initial transient at a high level followed by a long period of the note decaying away to (eventual) silence.

IF you run this through a compressor then you can "knock the top off" the pick transient, and then boost the sound as it would have been decaying - the result is a long-sustain even sound without the "T" from the Twang - which is of course why guitar players are often called "Wangers".

Usually compression is pretty pointless on a sax - but its baby brother "Limiting" can be very handy in a live situation.

 

[Rowka]

Live, it can greatly help with a vocalist (or saxophonist ) who has poor mic control. It can even out the dynamics of someone who randomly is closer or farther from the mic.

 

[potiphar]

As well as the above, in mixing tracks compression tends to turn make an ensemble sound LIKE an ensemble rather than several different instruments recorded separately.

To hear the sound of quite heavy compression on a sax section listen to something like the Beatles' "Lady Madonna", or "Got to get you into my life".

 

[Bill Mecca]

Live, it can greatly help with a vocalist (or saxophonist ) who has poor mic control. It can even out the dynamics of someone who randomly is closer or farther from the mic.

I have a DBX here in the "studio" at work and only really use it when I have non-pros do a voice track, they just don't have the mic technique.
Basically it will even out the track and give it more volume and presence in the mix. At least that is how I think about it. I don't like to use many effects in my lame recordings, I prefer to have it sound as it would live, as much as possible.

 

[tjontheroad]

It's used for the effect of being able to increase the overall output level of the signal without creating distortion. Said another way, By narrowing the highest and lowest signal levels, you also allow the average level to be raised closer to the "red".

 

[DanPerezSax]

Sometimes you want to play a quiet subtone... sometimes you want to scream. You can do both within the space of a bar or two, but look what happens to your levels when you record it: chances are you're much softer than your accompaniment while playing the subtone, and too loud while screaming. Compression lets you play whatever you want and get it "just right," without having to ride the faders through the whole take. It's also the gizmo that makes your attacks sound completely unnatural when your engineer doesn't know what he's doing.

 

[Mark5047]

It's also the gizmo that makes your attacks sound completely unnatural when your engineer doesn't know what he's doing.

That's a very funny quote! I totally agree.

 

[Bill Mecca]

It's also the thing that makes watching shows on TNT on my cable system very trying. volume keeps pumping. Show audio is compressed, TNT signal is compressed, the Comcast compresses (at least I believe they do) so I watch The Closer and listen to the audio pumping. :evil:

 

[Al Stevens]

This reminds me of the old Dolby noise suppression algorithm that they used to change the signal-to-noise ratio of cassette tapes and make hiss less audible. It reduces the signal volume and adds a subsignal that encodes where in the waveform the higher volumes are. During playback, it uses the subsignal (which it then discards) to raise the volume for only those parts of the signal that were originally louder. The idea is that all of the noise is reduced in volume but the loud stuff, when raised in amplitude, masks the noise. Or something like that.

I read somewhere that they use compression to increase the average volume of TV commercials as an attention grabbing technique. The highest volume does not exceed broadcast standards but the lower volumes are louder. The track sounds louder but isn't. Sneaky, wot?

 

[chops2200]

Compression is used very heavily in pop music....makes it very radio friendly, no need to turn the volume up or down, or risk losing very much in transmission.

 

[bfoster64]

I claim no expertise in these matters, and I no very little about recording, but when I play live through my Digitech with the band I use a little compression; primarily because my clip-on mic picks up some registers better than others. The compressor seems to even things out a bit so the sound coming out of my mains and monitors seems closer to what I am hearing from my horn, regardless of what register I'm playing in.

 

[hakukani]

I always called compression 'finger on the fader in a box'. It electronically reacts to peaks in sound, and automatically pulls back on the 'fader', then restores the 'fader' to it's former level. If set up right, compression is handy, especially for instruments that have large transients (pluck of a pick, finger, or the very beginning of a percussive sound). TJ is right--if compression is set up wrong, it sounds like a monkey is turning the volume knob semi-randomly.

If the compression ratio is set high enough, it's called 'limiting'. That's what radio stations do, so they don't over-modulate and get into other station's frequencies (and get the FCC after them).

 

[tjontheroad]

Correct settings of threshold, attack and release is an art and the mark of a great sound engineer. Compression can be even used in heavy doses with little notice if these settings are given close attention to. Some examples of use are;

Light amounts of "comp" and peak limiting are often used at the mike pre-amp stage to allow for higher signal-to-noise ratios at the recording stage in vocals and acoustic instruments like guitar that have a wide natural dynamic range. Electric guitarist use heavy amounts of comp to create the effect of longer string sustain since the lowest amount of the vibrating string at the end of it's plucked life will still sound at it's max volume at the output stage of the compressor. At the mixing stage, comp will be used to limit the amount of fading transitions between instruments. Frequency controllable comp is used greatly at the mastering stage to narrow the range of the low end in the mix in pop records thus creating the big subwoofer booming effect.

 

[Turnaround]

I look at compression as basically volume control (in layman's terms). Imagine having your finder on the fader and controlling the volume of a sound. It's easy to adjust the volume for a whole section or phrase using your finger on the fader, which many compressors are designed to do that have long release times. But imagine trying to react to a bebop horn player that jumps around a lot. Your finger cannot move fast enough. So most compressors (at least the ones people are generally confused about) are designed to be able to react (attack time) from <1ms to >100ms (ms = milliseconds) and return to 0 compression (release time) using the same time measurements. Sounds with longer sustain will need longer release times (like a long slow bass line) and sounds with short sustain will need shorter release times (like a vocal or kick drum). Hope that helps.

 

[SactoPete]

Al, Compression on the sax makes you sound more like Ben Webster. Well, maybe not, but it does tend to bring out the hiss and spit if you are playing a quiet ballad, which makes me feel like at least that part is like Ben Webster (skill, technique, and musicality aside).

Pete

 

[Al Stevens]

Is there a Dexter Gordon setting?

 

[SactoPete]

Oh, how I wish....