Could someone please explain "compression"?

[kevin-h]

Could someone please explain "compression"?

As far as I understand it, it may be applied in two ways (by the way I am a complete numpty with absolutely no technical understanding of recorded music);
1. The entire album is recorded using equipment to record the dynamic range from 20 Hz to 20 KHz, say, then software is applied to "squash" that range down to, for instance, 10 Hz to 10 KHz.
2. Or else, microphones are used with a "reduced" dynamic range such that they do not record a full range, but can only record a limited "bandwidth'.

I feel the former is perhaps more applicable.

Please can someone explain this to me?

Thanks in advance for all input,

Kevin.

 

[Tony L]

Compression is a largely misunderstood thing by audio folk. In a studio environment there are many uses for it, as an example most bassists will either stick their bass guitar through a compressor pedal or use an amp to similar effect as otherwise the dynamic shift from playing with fingers, to pick or slapping the thing is just too extreme – a sensibly set compressor controls the volume without impacting these tonal changes. Likewise on vocal – the dynamic range of a voice is huge, certainly far more than a tape can take when close mic'd, so compression or limiting is normal procedure, plus, being honest, most vocalists are pretty crap and can’t control their levels so one has to do it for them. Compression is also good with drums, it can really fatten up a kick or snare. When used well it is a truly great tool. You won’t own a rock or pop album recorded without a compressor or limiter somewhere. They are good things if used with a degree of taste.

The problems come with overuse after the recording stage, i.e. applying an overall compression to a finished mix. It is this which is causing an outrage at the moment in CD mastering due to the so called ‘loudness wars’. When applying it to individual instruments on a multitrack (i.e. recording stage) one obviously has complete control, and as it is isolated, it does not impact other aspects of the song. This is simply not the case with overall compression, and once you learn what to listen for it’s effects are intensely irritating. Try listening for a long sustained note, say an organ or synth pad, does it ‘breathe’ with the drums, i.e. rise and fall in level? If so it’s been mastered by a complete moron. The sound of bad overall / post-production compression is akin to the auto-level function on cheap cassette / mini-disk recorders etc, i.e. it ramps the level up until something loud comes in then reduces it – exactly what you don’t want on a final mix.

If you want to learn more download a copy of Audacity, it’s a neat little freeware wave file editor and has quite a few effects including a simple compressor. Have a play – it doesn’t sound anything like as good as a decent studio compressor, but it will give a good enough indication. Also have a play with the 'normalise' effect. By using both you should be able to f*** up a good CD and make it sound like a modern one.

Tony.

 

[cubastreet]

Dynamic range is to do with range of volume rather than range of frequency, as far as I know.
When you compress music you reduce this range and end up with music which sounds just as loud all the way through.
This is most apparent in the ads on tv, which are often compressed and set to max volume to get your attention.

.... or so says the Casillero del Diablo Carmenere cheap red anyway

 

[narabdela]

All is explained here: http://uk.youtube.com/watch?v=3Gmex_4hreQ

 

[concrete]

good question Kevin. nice to learn something on a Sunday morning! for I too am a complete numpty with no technical understanding. The difference between the way that I and my friends with said knowledge listen to music is incredible -- I guess in a way I take it far more at face value, as a finished object, than people who can dissect it and be impressed by complicated technical ability, as opposed to distinct musical ability.

 

[Anex]

When you compress music you reduce this range and end up with music which sounds just as loud all the way through.

No, that is if you use to much compression at mastering level. As Tony says, it's used everywhere and if it wasn't your speakers would probably blow within the first few bars of a piece of music. Particularly as you'd have to turn the volume right up to compensate for the quiet sections being so quiet relative to the loud bits.

 

[cubastreet]

that is if you use to much compression at mastering level.

or just the right amount, depending on the effect you're after.

As Tony says, it's used everywhere

As Tony probably knows, that is not true. A good engineer knows when to use compression and when not to.

if it wasn't your speakers would probably blow within the first few bars of a piece of music.

hasn't happened to me yet. Have you never made a recording and played it back?

Particularly as you'd have to turn the volume right up to compensate for the quiet sections being so quiet relative to the loud bits.

surely that would depend on the dynamic range of the source

But yes, what I meant was that as you reduce dynamic range, you eventually end up with music that sounds just as loud all the way through. I figured an extreme example would be useful to explain the concept.

 

[Anex]

or just the right amount, depending on the effect you're after.

Well given that you cast it in a negative light, I assumed you didn't like it.

As Tony probably knows, that is not true. A good engineer knows when to use compression and when not to.

That's pretty obvious really.

hasn't happened to me yet. Have you never made a recording and played it back?

Yes, and I know where problems might happen by looking at the levels on the wave form display.

surely that would depend on the dynamic range of the source

I was generalising.

 

[390amx]

Could someone please explain "compression"?

As far as I understand it, it may be applied in two ways (by the way I am a complete numpty with absolutely no technical understanding of recorded music);
1. The entire album is recorded using equipment to record the dynamic range from 20 Hz to 20 KHz, say, then software is applied to "squash" that range down to, for instance, 10 Hz to 10 KHz.
2. Or else, microphones are used with a "reduced" dynamic range such that they do not record a full range, but can only record a limited "bandwidth'.

I feel the former is perhaps more applicable.

Please can someone explain this to me?

Thanks in advance for all input,

Kevin.

there is a nice article/special report on musical compression...titled:The death of high fidelity in Rolling Stone magazine (dec 27 2007 issue) pg 15-17

hope this helps...very informative

 

[Zombie]

just threw out 5 of my Beatles albums 'cause I can hear the other intruments and cymbals breathe with the drums...crap...good I got rid of them

 

[Cesare]

Just to flesh out the description, compressors work by having a voltage controlled amplifier (VCA) which is driven by a voltage derived from the source material. A typical process applied to the source would be an envelope follower - that is, a circuit which tries to average the amplitude of the source signal. You will get controls for attack and release speeds to give a range of responses.

Much fun can be had altering how the envelope follower reacts, and this is basically what gives different compressors their distinctive sound.

In mastering the process is slightly more complicated, with a typical compressor being multi-band. What this means is that the sound is split into different frequency ranges, each of these ranges having it's own compression applied before the ranges are recombined. A typical multiband compressor will be run with 3 to 5 ranges.

Compressors with seperate signal and sidechain inputs allow you to have fun compressing one signal with the dynamics of a separate signal. You can get some creative ducking effects for example.

Compression is quite a big subject, and you should check out expanders and limiters as well. They are all related but tend to get used creatively.

Oh, and if you want to have some real fun, the SPL transient designer is very intuitive and sounds great.

http://www.spl-usa.com/Transient_Designer2/in_short.html

Cesare