All delay pedals can be basically put into one of two categories – analog and digital. The first ever delay units used tape to replay the guitar signal – we’ve come a long way from there (though these do still exist), with analog delay pedals superseding these.
Analog delays utilize something called a bucket brigade chip. The guitar signal passes through the capacitors within this, which slows it down, or delays it. The sound is often referred to as dark, or lo-fi – your delayed guitar signal’s tone isn’t exactly the same as your dry tone. As you turn up the repeats, you’ll hear the tone slowly degrading, sometimes becoming more ‘warbley’. This unique sound is preferred by many players as it’s full of character. You can also get analog delay pedals to self-oscillate which can be really cool.
Digital delay pedals can replicate your guitar tone pristinely, as many times as you like. Some describe this as sterile sounding, but it’s really subjective and it’s whatever you like the sound of and what works for the music that you play. Many digital delays can also replicate the sound of analog and even older tape units. It might not be the ‘real thing’, but with many of the top end digital delays, it’s pretty much impossible to tell.