Unfortunately the answer is we just don't know. We don't have the depth of material about ancient music to give a satisfactory answer. There are only a handful of pieces of music that have come down to us, most are fragments and incomplete. Even with those pieces of music, they weren't written in modern musical notation, so you have to translate from the ancient notation to reproduce it. Thanks to Greek philosophical and mathematical thought we do know quite a bit about Greek music theory and have a pretty full grasp of their notation, but with so few and fragmentary surviving examples of music we will always have some doubt about exactly how it sounded. I'm sorry that I can't give you a better answer, but I do recommend you look up the "Seikilos epitaph" of "song of Seikilos" on YouTube. It's a complete, if short, song inscribed on an epitaph that is commonly dated to around the 1st century CE, and found in modern Turkey.