Flange, reverb, compression, limiting and companding explained

Courtesy of David Fiedler

When first getting into music, it's easy to get overwhelmed by all the terms that get used. You might go to your local music store and get asked how much reverb you like when you play. Perhaps you've just started recording and wondering if you should use compression with a vocal take. It's easy to get lost in what people are going on about because writing and recording a song is not as easy as many often think.


But, luckily, the Web has allowed musicians to communicate with each other and share ideas in a global forum. One example of this is the 4-track FAQ (Frequently Asked Questions) which is a moderated series of questions and answers from home recording enthusiasts around the world who frequent the alt.music.4-track newsgroup. We've provided an excerpt of it below for those of you just entering the world of recording.

Q2.1 What is flange?

benl@mojo.europe.dg.com (Ben Last) writes:

Roughly speaking, what you'd get if you recorded the same guitar onto two tape recorders at once and during replay, slowed one of them down *just a little* by putting your finger on the reel. A bit like a chorus.

This is *not* a general effect with which you'd treat a whole mix.

[Is this explanation okay?? I thought it produced a somewhat time-varying signal that sounded a bit like a slow "wa-wa" sound. --DSF]

Q2.2 What is reverb?

benl@mojo.europe.dg.com (Ben Last) writes:

The technical explanation would be something like: "a composite of echoes from many sources, including early reflections from nearby surfaces and remote echoes of longer duration from distant surfaces."

Ben's Patent Simple Explanation is: think about standing on the stage of an empty theatre (theater for Americans :-). Shout. Imagine how your voice would sound; sort of echoed back from lots of different places. Consider how your voice would sound if you were inside a wardrobe (closet). No echoes at all. The one with the echoes has more reverb.

Q2.3 What is compression?

Adapted from stabnste@phoenix.phoenix.net (Erik Karlson):

A compressor reduces by a preset ratio the level of any incoming signal which exceeds its preset level. For example, if your compressor is set for 10 db and has a compression ratio of 2 to 1, any signal that comes in over 10 db would be reduced by a factor of 2. For every 2 db of input signal over 10 db, the output level would only be increased by 1 db. This is very useful when recording vocals because they tend to have varying levels. As with all things, too much of a good thing can be bad. Too much compression can leave your sound dull and choppy.

pseo@mail2.sas.upenn.edu (Peter S Seo) writes:

[S]ay you're playing the guitar for instance, and for some reason, the dynamics (loudness, volume, whatever) of each pluck is different maybe because you're just really bad at playing guitar. (btw, i'm not inferring that [only bad guitar players] use compression...) [Compression will] "smooth" out the signals, the plucking, so that each pluck will be of the same output level or volume.. it makes the signal much "tighter" i suppose.. this helps out alot for vocals too.. but it is something that you the musician have to decide to use.. maybe you don't want it smooth..

you can also use a compressor to sustain a guitar signal.. though someone else will have to explain how that works.. all i know is that it does.

benl@mojo.europe.dg.com (Ben Last) writes:

Same way as it sustains everything else: You pick the string. The note starts, and as it goes on, it gets quieter. Without a compressor, it'd die away. What the compressor does it to keep 'turning up the volume' so that the note appears to stay the same level. Eventually, the volume (amplitude) of the note coming from the guitar gets so quiet that the compressor gives up and turns the volume back down.

Similarly, a compressor can reduce the volume when it hears notes which are too loud; the end result is that the volume level coming from the compressor is much more constant than without it.

Q2.3.1 Do I need stereo compression?

> jthan@world.std.com (Jonathan M Richardson) says:

> My local music shop recommended a dual channel rack mount unit which > costs $180! Is there a cheaper solution?

adouglas@belvoir.com (Andrew Douglas) writes:

I have little experience with recording, but the conventional wisdom is that you really do need a stereo compressor. You compress vocals and bass, and in your case acoustic guitar, while laying the track down, then perhaps add just a touch during mixdown. (which is the reason for stereo)

A stereo unit will also allow you to put different amounts of compression on the two channels.

brianb@scorpion.iii.net (brian q. buda) writes:

Well, for one, who makes the compressor? $180 is really cheap. [Y]ou can save some money by going with a mono compressor. Stereo is all well and good but for small 4-tracks it has no use. That is if you don't mind compressing down to track and not on mix down. Stereo is really only for live gigs and when you have a multi-track system with several AUX sends so that you can patch each channel into a mix.

Q2.3.2 Should I use compression on drums? Vocals? Bass?

ertrinid@girtab.usc.edu (Elson R. Trinidad) writes:

If you mic up your kit and route it through a separate mixer before going to your 4-track, put the snare through a compressor (the kick, too, but through a separate compressor) and you'll have a more "professional" sound. But never try to compress the entire drum mix, especially if you use cymbals a lot - there will be a lot of unnatural-sounding "pumping and breathing".

brianb@scorpion.iii.net (Marc?) writes:

It's great for snares and kicks. (fattens up the kick alot) But I find that it kills rides and hihats. To really compress drums you need to have a system that can compress some, but not all.

Also, [noise] gates are needed to really make it sound right.

You need different amounts of compresson on different things. That is, vocals don't need as much as a bass does.

Q2.4 What is limiting? How is it different from compression?

ak748@detroit.freenet.org (Daniel W. Newport) writes:

It's compression in the extreme. That is, once the signal [level] reaches some preset threshold instead of compressing it at some ratio say 2:1 or 4:1, [the limiter] limits it at that level, (infinity:1) by not allowing the signal level to go beyond this.

lwillia@ix.netcom.com (Larry Williams) writes:

Some limiters will allow a slight increase in level above the threshold (a ratio of 20:1, for instance), others act as a "brick wall" limiter allowing absolutely no level above the threshold.

Limiters are useful especially on digital audio equipment where no signal above 0 VU should ever exist. They are also useful in live sound systems where feedback volume can be controlled, protecting both the speaker systems, and the performers' and listeners' ears.

[What is a Dietz dual limiter?? --DSF]

Q2.7 What is a noise gate?

A noise gate lets a signal through when it is louder than a certain level and cuts it off when it drops below that level.

Imagine you play a chord on your guitar, which is connected to a noise gate, which is then connected to your amp. The noise gate 'sees' a decent signal level and lets the sound through. You then damp the chord off with your hand.. The noise gate sees the signal level drop and cuts the sound off. If the gate weren't there, you'd still hear all the low level stuff like hum, the sound of your hand sliding on the strings, the sound of the guitar clanking against your belt buckle. As soon as you play a note, the gate 'opens' and you hear the guitar again.

Q2.5 What is (upward) expansion?

marcl508@hudson.iii.net (Marc LaFleur) writes:

Upward expansion is the inverse of compression. Where compression decreases excessive peaks over a threshold, upward expansion decreases excessive troughs below a threshold. As the signal falls below a preset lower threshold, the gain is scaled "upward" by the set ratio (e.g. an input signal falling below the threshold by 10dB would be boosted to 5dB below the threshold with a ratio of 2:1).

Q2.6 What is companding?

Adapted from lwillia@ix.netcom.com (Larry Williams):

Companding is a two-stage process of COMPression and exPANsion which reduces the lowest noise levels on the tape. Companding typically refers to a tape recording process (instead of live sound or effects processing). For example, a signal may be compressed at a 2:1 ratio when recorded, and expanded at a 1:2 ratio when being played back. This is also known as double-ended noise reduction, meaning that one has to have a decoder to listen to the encoded signal, contrasted with single-ended noise reduction where no decoder is required.

This excerpt from the Home Recording FAQ was supplied by its moderator David Fiedler. The FAQ cannot be used in part or whole without his expressed permission.

Related Article: Vocal Compression Settings: Practical Advice on Using A Compressor To Tame Wild Vocals

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