If you were like me iTunes Match made me very happy. Because, if you are like me, the majority of my digital music comes from CDs that have been ripped onto my computer and are now no where to be found. Great! I have no back up, until, of course, iTunes Match came around and fixed all of that. But not only that, they also fixed something else that plagues people like me: low quality songs.

With iTunes match, all songs that can be found in your library and in the iTunes store can be upgraded from whatever low-quality version you have into a brand spakin’ new high quality 256 kbps version for free.

But the question becomes, what does 256 kbps mean?

Before we explain that exactly, we need to understand a little bit about digital audio.

When an artist is recording, far more information is produced than you might expect. For example, 1 minute of absolute silence that is uncompressed will take up about as much space once encoded as one minute of music that is compressed (please note that this stat is from Wikipedia and has no reference so I can’t verify it). Clearly we need to slim it down a little bit.

The typical audio CD can hold around 800 megabytes of information. Typically, if you were to buy a CD directly from the label, the audio will be uncompressed. CD audio like this takes up around 10 megabytes of information per minute of playback time. This much information is prohibitive to store and to send over the internet, so compression was needed. MP3 is perhaps the most well known example of this. An MP3 file at 256 kbps (I’ll explain that later) would work out to a file size of up to 6.5 megabytes for the average 3 1/2 minute song (my own calculations, please correct me if I am wrong), where as that same file on the CD would take up around 35 megabytes. Considerable savings if you ask me.

So obviously, digital music compression is a must, but it presents us with all these strange numbers. Why?

To make this simple, we will go in order of the information in the picture above. I will skip the few that are completely self explanatory.

Kind (Format)

This is simply an indicator of white kind of file this is. Or, more accurately, what kind of encoding (explanation of the precise meaning of that word must wait for another time) it has. In this case, as we can see, the encoding is AAC (Advanced Audio Coding). AAC was built as a successor to MP3, over which it has many improvements. AAC is not actually a file type, it is kind of compression (or encoding). In this case, the file in question is a .m4a file.

Bit Rate

This one is what you might call the most important part of the compression. On a CD, the amount of information being read every second is about 1.4 million bits per second. When a bit rate it set, it is effectively limiting how many bits be included per second. 256 kbps (which stands for kilo bits per second) means that only 256,000 bits, less than a fifth the number of bits on the CD, can be included in the file. This means that the compressed file will be 80% smaller than the original file. Now you may ask, how can it have 80% less information and still sound good. I’m not sure. I’ll get back to you on that. 256 kbps is about as high as most mp3 songs are, but higher rates to exist..

Sample rate

A sound wave is completely continuous, which means there is no breaks in the sound. In order for the file to be read, it has to be broken up into little tiny packages that can then be encoded. Sample rate is simply an indicator of how many little packages each second of sound is broken up into. This music is, therefore, broken up into 44,100 (44.100 Kilo hertz) little packages per second. In theory, we could increase this. But this would produce a progressively larger file size until, once we started not sampling at all, the file size would reach infinity. Naturally, this would not work well, so we limit it.

Profile:

This is a piece of information specific to the AAC format, and I don’t really understand it. But as far as I can tell it is a particular way of encoding based on the type of audio being encoded.

Channels:

Back in the early days of music recording, all music was in mono. This means that, if you listen to this music using headphones, there would be no difference between the sound coming out of the left and the sound coming out of the right. Even when the ability to produce recordings where different things could come out of different speakers came into being, it was difficult and expensive to own a system that could produce it (a speaker system that played stereo cost, logically enough, about twice as much as a system that played mono). And even then, the difference was not great enough to be worth the money. With the advent of headphones, Stereo sound became very popular due to the fact that each ear had it’s own sound source and did not hear the sound source of the other ear.

And that, my friends, in a nutshell, is digital music specs. Naturally there is far more that we could get into, but I believe this is a good introduction to the topic. That being said, if you find something you have questions about, feel free to leave a comment below or shoot me an email.

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