In the beginning, god created the music and the producers. And the music was without punch, and quiet; and lameness was upon the face of music. And the spirit of god moved upon the producers. And god said, Let there be Dynamic Compression: and there was dynamic compression. And god saw the dynamic compression, that it was good: and god divided the loud from the soft.  And god called the dynamic compression louder, and the lack thereof he called quieter.

Of all the technologies ever developed that affect the way music sounds, dynamic compression is arguably the most important.  It is responsible for making new records sound “new” and “punchier.”  It is the man behind curtain in the “Loudness Wars.” It is a powerful tool, used for either good or evil, and if you want your record to sound professional, you’d better make good friends with it.

In simple terms, dynamic compression limits or compresses the dynamic range of a given signal, making everything closer in volume. The louds become less loud compared to the softs, and the signal is boosted, giving the impression of a “louder” signal. It is used on a track by track basis, and during the mastering process on the entire mix. The next article will go more in depth in the track by track basis, this is just the basics of how compression works.

On any given compressor, you have 4 main settings: threshold, ratio, attack, release.  Usually, you also have an input and output gain settings as well, but the meat of the compressor is done with those 4 settings.

  • Threshold: the level in dB that the signal must be above for the compressor to start acting
  • Ratio: the ratio that the compressor reduces the volume of the signal, above the threshold
  • attack: the time it takes for the compressor after crossing the threshold to reach the ratio of compression
  • release: the time it takes for the compressor to return to a normal ratio after the signal goes below the threshold

Threshold and Ratio

Threshold and compression ratio are the two main settings on a compressor, and they work together. Anything louder than the threshold is compressed by the ratio. So, if our threshold was -12dB, and the ratio was 3:1, anything louder than -12dB would be compressed 3:1, or an increase of 3dB would be reduced to an increase of 1dB. The picture below shows this example, though it’s a little hard to see. The x-axis is input level, and the y-axis is output level. The “elbow” is the threshold, and nothing below it is affected by the compressor.

Since the loudest parts of the signal have been smashed so they are not as loud, the entire signal is able to be boosted, in this case up to 18dB, resulting in a sound that is almost 4 times as loud as the original, during the quiet parts at least. The loud parts don’t get any louder, but the quiet parts do. Here is a sample of a song compressed this much. I’m using a song which has a high dynamic range, you it’s easier to hear the difference.

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That track had already been mastered though, so let’s look at a mastered vs. unmastered version of a cd that has been released. I have to thank the music gods that this was even possible with this particular album, since it was the straw that broke the camel’s back in the Loudness Wars. I’m talking of course about Death Magnetic, the Metallica album that was so compressed, so loud, it was boosted beyond the limits of digital processing, and distortion is audible in the mix. This is easily the loudest mastering that has ever taken place under the sun, and there’s not a word to describe the ear rape that happens. However, to teach us a lesson, the music gods made it possible for us to be able to hear Death Magnetic PRE-master, via the Guitar Hero III extras. Guitar Hero utilizes the unmastered multi-track versions of songs so that if you mess up on guitar, that guitar doesn’t play, and now we can all hear Death Magnetic like it should have been, and it’s not bad, honestly. See for yourself, and begin to appreciate dynamic range in all it’s glory. It even has it’s own day, which means it’s important, like trees, and turkeys.

In summary, loudness is like salt: There should be enough of it to make things interesting, and to bring beauty, but only just. If it’s quiet, let the listener turn it up.

My Apocalypse: Original Master:

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My Apocalypse: Guitar Hero III No Master:

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