What is the difference between analog and digital recording?

All microphones are analog. They convert pressure waves in the air into electricity. Pressure waves in the air vibrate a little piece of metal, and that generates a fluctuating electrical current. Different kinds of mics have different specific ways of doing this. In dynamic mics, the air vibrates a magnet. This magnet is wrapped in wire, and its motion produces a current in the wire. In condenser mics, the air vibrates a metal plate that’s part of a capacitor with an electrical current already flowing through it. As the plate moves, it blocks or admits more of the current, making the current fluctuate. There are other kinds of mics with other physical setups, but they all do the same thing: they send out an electrical current whose fluctuations match (are an analog for) the fluctuations of air pressure.

The analog/digital split comes into play when you’re figuring out how to record the current coming off of the mic.

• In analog recording, you use plastic tape with little magnetic particles embedded in it. The recorder passes the current from the mic through the tape, and it changes the orientation of the little particles.
• In digital recording, the computer takes lots of very fast readings of the voltage on the wire (typically every 44,100th of a second). The computer stores its readings as an extremely long list of ones and zeroes on a hard drive.

Analog and digital systems also have different methods of playback.

• To play back your analog tape, you run it over a magnet again and pass a current through it. The little magnetic particles in the tape make the current fluctuate. This current then gets sent off to the speakers. Ideally, the reproduced current fluctuates in the same way as the one that you recorded off the mic in the first place, but you also pick up some noise and harmonic distortion along the way. In the speakers, the current agitates yet another magnet, and that magnet’s vibrations drive the vibration of the speaker cone. The speaker cone, in turn, vibrates the air.
• To play back your digital audio file, the computer sends its long string of numbers to a voltage generator, which sends corresponding electrical pulses down the wire to the speakers. These pulses reconstruct a fluctuating current that isn’t quite identical to the one you put in, but it’s very close, often closer than what analog systems can reproduce.

Typically, you aren’t just recording from one microphone, of course. You can combine the currents from lots of mic inputs into a mixing board, which lets you cut or boost them to change their volume levels. You can also apply effects by modulating the currents in various ways.

• An analog mixer is a big complex collection of transistors and capacitors and resistors and so on.
• A digital mixer is a computer program that mathematically models a big complex collection of transistors and capacitors and resistors and so on.

It’s possible to send the mic signals through an analog mixer to a digital recording device, and it’s possible to send the signals through a digital mixer into an analog recording device too. Usually, both the mixer and the recording device are digital, because digital is cheaper, easier, more reliable, and sounds better unless you are using very high-end gear. However, sometimes people do like to use analog mixing and/or recording, because they want to add a little noise and harmonic distortion to the signal. That said, there is nothing stopping you from adding noise and harmonic distortion using your computer, and plenty of people do exactly that.