What is the difference between digital and analog audio?
In: Technology
I guess you mean analog and digital recording of audio.
Sound is vibration of air (or any medium it travels through). Its properties are frequency (how many oscilations it makes in a second, i.e. how high the tone is) and amplitude (how ‘big’ are those oscilations, i.e. how loud it is).
So, how to record that? In essence, there are three ways: vinyl records, magnetic tapes and digital.
Vinyl is the simplest one. Imagine a big membrane that is in the way of those vibration. From the air, the vibrating transfers to the membrane. Now connect a sharp needle to it so it vibrates too. And while vibrating, that needle leaves the marks on a rotating dics. Then you can go reverse and the needle follows the grooves on the record, vibrate, transfer vibrations to the membrane and then to the air so we hear the recorded sound. Sure, this is oversimplified but it shows the important part.
Tapes work similarly, but the membrane is not connected to a needle but to an electromagnet. Magnets and elecrticity have a love relationship. When a magnet moves near the wire coil it creates electricity in in. And vice versa, if there is electricity in a coil, the magnet will move. So, as the magnet vibrates it creates a small amount of electric current that magnetizes the small particles of iron oxide on a moving tape. What was a wiggly scratch on a vinyl is now a series of variating little magnets of different strengths. You play the tape by reverting the process: tiny magnets on tape create the electricity in the electromagnet in the tape-player head, which moves the magnet connected to the membrane which creates the sound.
Both these systems transfer physical properties of sound into some other physical properties – depth and width of scratch mark on the vinyl or strength of magnets on tape.
Now the digital recording… which also goes from the membrane and into electromagnet to transform the vibration into electric current but then that current get measured and stored as a number.
As the sound is vibration that changes many times a second (it goes from 16 to 20000 oscilations per second) it has to do quite a lot of these measurements and store a number for each one. For CD it is 44.1 thousand per second, film standard is 48000 and, more often than not, initial recording in profesional environment is 96000 times per second.
Difference between this and the previous two ways is that now we don’t have one physical property transfered into other but into a series of descrete numbers somewhere in memory of the computer.
To store them permanently, you can enrave them into silver foil (CDs and DVDs) or use magnetic disks (hard drives).
Magnetic disks use the same mechanism as the audio tapes but they don’t record the vibrations directly but the numbers created according to those vibrations. So what’s the benefit?
(edited this paragraph as it was badly formulated) Magnetic tapes and disks are losing a tiny portion of quality with every reading/listening. Here is the important difference. If you copy analog data from the tape, there will be more and more shhhhhh noise introduced in every new generation of a copy as the electricity makes noise. But the copying of a digital recording is immune to that as each new reading and copying gives the same series of numbers as the original even if the recording is faded or partly damaged. That is because even as the magnetic material wears off, reading of the numbers is the same and when you deal with numbers you have safety mechanisms to check if your reading is ok or even to recalculate a part that is missing (see checksums for more info on this). But eventually the hard disk will fail.
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