The music has to be stored and played back somehow. This is the source. It could be a traditional analogue source such as a vinyl record or a tape, or could be digital.
Digital & Analogue
In electronics, a signal can be transmitted in either digital or analogue forms. A digital signal works a little like morse code, made up from ‘1s’ and ‘0s’, or ‘on’ and ‘off’ pulses. An analogue signal is a continuous signal which varies in either frequency, amplitude or both.
Music can be stored and transmitted in either analogue or digital forms. However, a speaker has to receive an analogue signal, which is amplified to the correct volume, to produce an audible sound.
Music can be stored in analogue form using records or tapes. As the needle rides in the groove of a record, or the tape passes along the head in it’s player, the analogue signal is read in real time. It’s then amplified, and taken to the speakers, which make the analogue electronic signal into the sound waves which we hear.
Music can also be stored as digital data using either CDs or any other digital medium such as a hard-drive or a server. Digital has some huge advantages, in that it is very easy and convenient to store, distribute and reproduce. Digital broadcast transmission is also less prone to interference. For these reasons, analogue storage and transmission has been almost completely superseded by digital.
However, many people still love the quality and experience of listening and playing records.
A digital signal has to be converted into an analogue signal before it can be amplified and payed through a speaker. This is where a Digital to Analogue Converter (DAC) comes in.
You can get stand-alone HiFi DACs which can be used with a variety of digital sources. However, any digital device which plays music, whether it be a CD player, a streamer, a TV, your phone, your laptop, a wireless/Bluetooth speaker and AV-Receiver or a DAB radio, has some kind of DAC built in.
A DAC is what converts a line of 1s and 0s and makes it back into sound. I go into more detail about the varying qualities of digital audio here.