Los Senderos Studio
Compression and Expansion
 Issue 62 November 2014 
Live Recording

Words from the Glossary

This month we take a look at compression and expansion.

Compression and Expansion

This month's terms: compression, compressor, threshold, compression ratio, gain reduction, makeup gain, dynamic range, attack time, release, knee, hard knee, soft knee, parallel compression, bus compression, limiter, expander, expansion, expansion ratio.
(Note: Click on the term to view its definition in the glossary.)


First of all, compression has three completely unrelated meanings as it relates to the recording studio. One meaning is the compaction of air molecules followed by rarefaction, which is what takes place in a sound wave. Another meaning is the computer process in which a data file is reduced in size by eliminating redundant, useless, or unnecessary information as determined by various algorithms, such as an MP3 file being created from a WAV file. The third meaning is the reduction in dynamic range of an audio signal using a compressor. It is the third definition we will be discussing here.

A compressor is used to even out sound levels of vocals or instruments. It does this by reducing sounds that exceed a certain level, called the threshold, by a given ratio, called the compression ratio or slope. Vocals typically are reduced with a ratio of 2:1 to 3:1, other instruments 3:1 to 5:1, and a bass by as much as 10:1. The effect is to reduce the overall level of the signal, which is called gain reduction. The signal can then be increased back close to its original level by an amount called makeup gain. This has the effect of raising the quieter passages which effectively decreases the overall dynamic range—the difference in loudness from the quietest to the loudest section in a piece of music.

There are several other adjustments for a compressor. How quickly the compressor starts to act is set by the attack time. How long before the effect begins to decrease is determined by the release time. Another adjustment is the knee, which is at the threshold point where compression begins. With a hard knee there is a sudden reduction in level, but with a soft knee the reduction takes effect more gently.

Parallel compression (sometimes called New York compression) is an technique created by highly compressing one copy of a track and blending it with an uncompressed copy of the same track. This technique preserves the transients of the original signal while increasing the level of softer portions of the signal, which tends to increase the overall level of the track without sounding overly compressed. Bus compression is compressing a bus or group of tracks. If it is applied to the entire mix, it is called mix bus compression.

A limiter prevents an audio signal from exceeding a certain preset value. It is essentially a compressor with an infinite or very high compression ratio.

An expander increases the dynamic range of a signal, which is essentially the opposite of what a compressor does. But it does not act exactly in the opposite manner. You might think that a signal compressed by a 3:1 ratio could be returned to its original condition by expanding it by 3:1 expansion ratio. Not true. Instead of expanding everything above the threshold by that amount, it actually reduces the signal by that ratio below the threshold, a subtle but totally different effect. Otherwise, all the other settings for the compressor are the same on the expander. So when would you want to use an expander? One application would be the case where you have background noise occurring in a live recording. Using an expander may be able to push that noise down to the point where it no longer obvious.

So there you have everything you wanted to know about compressors and expanders and more.

In This Issue

Music Trivia
How to Contact Us
Gift Certificate
$50 Off Coupon


Home Page
Previous Newsletters
Music Samples
Contact Us

Music Trivia

After Dave Prater shot his wife in a domestic dispute in 1968, Sam Moore of the R&B duo Sam and Dave vowed that he would never speak to Dave again, even though they went on to record and perform together for another 12 years.

Give a Gift Certificate for Christmas

Looking for something to give to a musician for Christmas this year? May I suggest recording time at Los Senderos Studio. You can give as little or as much as you want. And this year we're doing something new. For every hour you purchase on a gift certificate, we will give you one additional hour free, up to a maximum of 8 hours. That's as much as a $200 bonus. But hurry, this offer expires after we have sold 4 certicates. Call or email us now.

                          Join Our Mailing List

Save $50

Present this coupon when you come in for a recording session and receive $50.00 off the regular rates when you book a session of 8 hours or more. This coupon is good for new clients only, can be used only one time (only one coupon per person or band), and cannot be combined with any other offers. If you pay by phone using a credit card, please use coupon code NEWSLETTER. If you have any friends or relatives looking for a recording studio, please clip this coupon and pass it along to them.

Offer Expires: December 31, 2014

Los Senderos Studio, LLC

A sound investment in your musical career.

8409 N US Highway 281 ★ Blanco, TX 78606-5024
Phone: 512-565-0446 ★ Email: Larry@LosSenderosStudio.com

< Previous Issue | Newsletter Index | Next Issue >


Copyright © 2008-2016
Los Senderos Studio, LLC | Los Senderos Ranch | 8409 N US Highway 281 | Blanco | TX | 78606