We’re progressing nicely through what it takes to stream music and we’re still focusing on what it takes to play a track on your computer and get it to your DAC via USB. We started this section on streaming with an observation: when you stream audio through a fixed cable connection between your computer and your DAC it is significantly different than streaming audio to a network connected DAC. So while we’re still on DACS tethered via USB to your computer, let’s review a bit. We’ll soon move on to network DACS.
On a vinyl album we convert sound pressure changes into mechanical motion by pushing a needle around on a spinning disc and then reverse that process to get the air pressurized again and hear music.
In a digital system we convert sound pressure into an electronic representation of mechanical motion through the use of stored bits. In a future series I promise to explain how this works as well.
Yesterday we learned that when we get those stored bits copied over from a CD we have to place them in a container of software so the computer we copied them to knows what to do with them. Think of this container as you might a package of cereal. If you take Cheerios and bran flakes and mix them together in a large bowl, separating them out from each other would be a near impossible task – but if you place them in their own containers or packages, it’s easy to grab whichever you want and eat them. The same is true for musical bits – we place them in a container to keep them intact and accessible easily. The two containers we discussed were WAV and AIFF – both containers storing essentially raw audio data we can easily remove from the container and send to a DAC to playback the music.
But there are many other types of containers you’ve probably heard of: FLAC, MP3, ALAC, OGG, Vorbis etc. These too are containers storing music but, to the music they are storing, we are processing the ingredients – much like converting raw oatmeal into Quaker puffed oats – if we stick with our cereal analogy. These types of containers refer to music that has been compressed – or made smaller than the original file.
A CD has about 750mB of musical data on it – or, put in another term, about 3/4′s of a gigabyte (a gigabyte is 1000 megabytes). If we round up the CD’s contents to a gigabyte to keep the math simple, this means we can store approximately 1000 CD’s on a terabyte hard drive (terabyte is 1000 gigabytes). Most people who have a computer have far less hard drive storage than a terabyte and most of the hard drive space on a computer is used for programs and the operating system on the computer. So this limits the number of CDs we can store on our computers to probably around a couple of hundred. Additional hard drive space is cheap but inconvenient so it behooves us to stuff more in the same space.
To do this we can compress our music in one of two ways: lossy or lossless. In a lossy process we actually remove some of the precious audio data and throw it away – much like when we compress a photograph and it looks worse and worse as we throw away picture information to get the file size smaller.
As Audiophiles we’ve worked hard to get every ounce of performance we can out of our music so the idea of removing or losing some of our sound quality when we store it is abhorrent. I don’t know any Audiophile that saves their main music library in a lossy format such as MP3, OGG, Vorbis, APE, etc. Instead, we use what’s known as lossless compression which is typically one of two types: FLAC (Free Lossless Audio Codec) or ALAC (Apple Lossless Audio CODEC). Certainly there are others like WMA and Meridian, but most of us use one of the two I just mentioned.
A lossless format is like a zip file. If you write a document on your computer that is 1 megaByte big and then zip it up, the zipped file is quite small relative to the original. Yet, when you unzip that Word document, it returns to exactly the same size and content as the original. Amazing, eh? The same is true for a lossless audio file. With this type of file we can cut the size of our music in half and thus double the number of albums we can store on our computer.
Tomorrow, what is it the player in iTunes does with this lossless file.