Compression - part 1

Compression is a great tool! When used during mixing and mastering especially, it has many uses. But during airplay it’s very rarely beneficial, especially when you have no idea what you’re doing…

A land of confusion

But when talking about compression, the first thing we need to define is what type of compression we’re going to look at. Because when it comes to audio, there are 2 types of compression that people might talk about. Welcome to the land of confusion! Hopefully, I’ll be able to help clear things up a little bit…

The first type of compression is the one we’re going to look at in details. It is the one used during mixing, mastering and also during airplay. It affects the audio directly, and you might see it referred to as dynamic range compression. Another term that we’re going to see used for compression is limiting (or even brick-wall limiting), which is nothing else but audio compression with extreme settings.

File compression

The second type of compression that you might hear about is file compression. This is the difference between a .wav (or .aif) file and a mp3 for example.

There are various types of file compression, some are lossless (because they will not affect the sound in the end, no information will be lost because these formats will be de-compressed when played) others are lossy (some information is lost during the compression process).

Think of lossless as a zip file. It is a compressed file, but you can always decompress it and get the contained files intact after the process. Lossy compression though will remove some information based on clever algorithms that analyze the sound to get rid of whatever is deemed non-essential to reproduce it. It’s based on the physics of how we perceive sound and what frequencies are more important than others, and on various other factors. How much the sound is compressed with lossy compression depends on the bitrate per second, measured in kbps (Kilo Bits Per Second), the maximum for mp3 being 320kbps, which is almost (but not quite) lossless.

So, in audio land you can have:

  1. raw files (not compressed at all), like .wav or .aif 
  2. lossless files like .flac or .ogg 
  3. lossy files like .mp3 or .aac

Although lossy compression affects the sound (and the lower the bitrate the more it will), this is not what we’re going to look at. The reason being that most radios will play at a rate of 128 kbps or 192 kbps (some use 64 kbps which is hardly listenable), and although of course this means a loss in quality compared to raw files (for 128 kbps it can mean as much as 90% of the initial information lost), it is bound to the bandwidth they have, that bandwidth itself being based on how much they pay and how many listeners the stream provider can support at that rate. So, in short, there’s not much they can do about it…

What online radios can work on to improve the quality of their sound is the first type of compression, which is audio compression (and limiting). So, this is mainly what we’re going to examine in detail, in the hope that it will give everyone a clue as to what they hear and whether too much compression is damaging it… 

Tune in next week to start diving into the wonderful world of audio compression!