It’s entirely possible to make music on a computer without having the faintest idea of how digital audio works, but a little knowledge can go a long way when it comes to pushing the medium to its limits.
For those unfamiliar with the basics of how sound works, let’s start at square one. Some of the following explanations might seem a little abstract out of the context of actual mixing, but introducing these ideas now is important, as they’ll be referenced when we get more hands-on later in the issue.
Sound is the oscillation (that is, waves) of pressure through a medium – air, for example. When these waves hit our tympanic membranes (eardrums), the air vibration is converted to a vibration in the fluid that fills the channels of the inner ear. These channels also host cells with microscopic ‘hairs’ (called stereocilia) that release chemical neurotransmitters when pushed hard enough by the vibrations in the fluid. It’s these neurotransmitters that tell our brain what we’re listening to.
The process of recording audio works by converting the pressure waves in the air into an electrical signal. For example, when we (used to) record using a microphone feeding into a tape recorder, the transducer in the mic converts the pressure oscillation in the air into an electrical signal, which is fed to the tape head, which polarises the magnetic particles on the tape running over it in direct proportion to the signal. The movement of sound through air – and, indeed, the signal recorded to tape – is what we’d call an analogue signal. That means that it’s continuous – it moves smoothly from one ‘value’ to the next without ‘stepping’, even under the most microscopic of scrutiny.
By the numbers
Computers are, for the most part, digital, which means they read and write information as discrete values – that is, a string of numbers. So, how do computers turn a smooth waveform of infinite resolution into a series of numbers that they can understand?
The answer is a method called pulse code modulation (PCM), which is the main system employed when working with digital audio information. It starts with the process of analogue-to-digital conversion (ADC), which involves measuring the value
