Besides the theoretical or rather philosophical differentiation of analog and digital features, the media we use today, from audio, video, over photography to print, offers more practical explanations.
Speaking of analog and digital in the field of audio, from recording to playback, the differentiation only concerns the features of the audio signal. The signal, either analog or digital, will at least need an analog device for output – e.g. analog speakers resembling the audio signal into acoustic sound waves.
However the audio signal can be either an analog or digital model of a real (recorded) sound wave but also a model for a real sound wave – playing a string of an electric guitar creates an analog audio signal that runs through a cable and after being amplified will result in sound waves created by the vibrating membranes of the speaker. Similiar like this the audio signal can also be created digitally, e.g. by using a midi-keyboard.
Technical charecteristics
On the one side, for analog audio, soundwaves are converted to an electromagnetic signal that’s stored as data on a magnetic tape. The sound quality or the amount of information that can be stored on the recording tape refers to the tape width and tape speed.
On the other hand digital audio uses so called pulse code modulation or PCM which is the primary method to store digital information. This method creates a model of sound waves by „storing a sequence of numerical values that represent the amplitude or intensity at various points along the wave“, referred to as samples. The two crucial factors for sound quality in digital audio is bit-depth, through wich the amount of possible values is defined and the sample rate defined in kHz.
Advantages and disadvantages
The major disadvantage of digital audio is that there will always be a finite amount of samples. Even if you raise the bit depth and sample rate you will never be able to resemble anything between two samples or values. As analog audio with the electromagnetic signal resembles the sound waves more naturally it can „catch infinitesimally small variations in amplitude“ and thus smoothly fill the gap that would be between two digital samples.
However analog audio signals will always be featuring a certain ground noise coming from the recording components. Even if this noise floor is very low on tape, it will increase by running through more analog components like cables, analog effects or (pre-)amplifiers and can become a major distracting noise. In digital audio the noise floor of a 24-bit sound file is -144 dB which is practically no noise, though it still can add up running through analog components (in playback).
Besides the quality of information stored on analog media or digital sound files there’s more practical features that add on the advantages of digital audio.
Firstly, magnetic tapes can not only be physically damaged or destroyed but stored information will be deleted immediately when approaching them with a magnet.
Digital files on the other hand are nowadays immune to magnetic fields and additionally from one digital sound recording infinete copies can be made without losing information in contrast to tapes that will lose sound quality from copy to copy. Thus digital audio files can be easily reproduced and distributed enormously fast around the globe without the needs of physical storage.
Acoustic Features
The acoustic features of analog and digital audio signals are subtile and often highly subjective but there are obvious differences. First of all, in this discussion you will very often hear that audio coming from an analog source (tape, vinyl) has something like a more warm and soft sound, whereas digital signals coming from digital media (CD, wav or mp3 files passing the sound card) feature a rather cold and harsh sound. Depending on how trained your ears are you will most certainly hear some differences like these when comparing the same audio played via different media.
However the acoustic features are rather connected to the nature of the playback device and nature of the media (vinyl = analog, CD = digital) than to how the acoustic signal was originally recorded. Because still it is possible to record and mix a song with analog equipment and put it on CD (after digitalisation) and of course digitally recorded sound can for example also be reproduced on vinyl after converting the signal into grooves cut into vinyl (a process that’s also necessary when converting audio signals from analog tape for vinyl).
Summing it up analog and digital sound recording, audio signals, reproduction and playback are simply different ways to model and resemble sound waves. Both have different physical and technical features resulting in more or less different acoustic perception of basically the same sound – call it the analog charme and warmth due to infinite small intersecting vibrations or the digital precision and sharpness due to the isolated samples.
The question is not which one is better in general, but which one suits your purpose best.
Sources:
ANALOG AUDIO vs DIGITAL AUDIO: The REAL Difference
Analog vs. Digital As Fast As Possible
Analogue vs Digital – Episode 9 | The Mastering Show Podcast