Hello knowledgeable hifi specialists

What exactly is a remastered track ?

I'm thinking of buying a few CDs of my favourite music from the 60s and 70s
(e.g. Cream, Led Zeppelin, etc.)
and there seems to be a choice between originals and remastered.
What's better ? What's the difference ?

Best regards and TIA from Ray

Raymond RUSSELL
Tel/Fax 0033-(0)388-808054