---
tags: [sound, analogue, physics]
created: Thursday, January 02, 2025
---

# Recording and playback of sound

## Analogue

### Recording

The microphone converts sound waves into a continuous electrical signal.

The signal drives the recording equipment.

In the case of a vinyl recording: the signal drives a cutting head that carves a
groove into the master disk.

In the case of a tape recording: the signal drives electro-magnets that align
magnetic particles on the tape.

In both cases, **the recording medium physically mirrors the shape of the sound
wave**.

### Playback

In the case of vinyl, the needle follows the groove, moving up and down to
recreate the electrical signal.

In the case of tape, the magnetic patterns induce electrical current in the
playback head.

In each case, the signal is transferred directly to amplifiers and speakers.

## Digital

### Recording

Mostly covered in [Binary encoding of sound](Binary_encoding_of_sound.md).

An important point to note is that the binary encoding that results from the
sampling is lasered into the CD as microscopic impressions and depressions (pits
and lands)

### Playback

A laser in the reader reads the pits and lands and converts them back to binary
numbers. A DAC then converts the numbers back into a continuous electrical
signal which is then channelled to the amplifiers and speakers.

## From recording to production of storage medium

With analogue production recordings would be made onto tape. Multiple takes are
recorded, mixed and edited. This results in a master tape which is the final
version of the recorded sound.

This then goes to a mastering engineer for mastering which creates the master
mix. This consists in optimising the sound for the given format (vinyl or tape).
Also includes adjusting frequencies, levels and adding spacing between tracks.

Then the master disk enters production. A recording is made onto lacquer disc
which is very delicate. Often known as the "acetate". This is coated in metal to
create the "metal master", after various processes this goes to the pressing
plant who press vinyl copies from it.

Each stage can introduce subtle variations, especially with re-pressings.
Re-pressings require new stampers from the master which may have degraded in the
interim. Plus there is a limit to the amount of pressings possible with a given
stamper. The earlier pressings are therefore less degraded making them more
valuable.

## Degradation

With tape and vinyl each playback wears the medium, degrading the quality of the
captured signal. With CDs, there is no degradation and every copy is a perfect
copy of the original signal. However this capture, necessarily contains less
information than the analogue version because of sampling.
