In JWW First Greek Book it says in 1., that [size=150]ξ
Um… c is like the English X (ks). I believe you mean x, which is like the ‘ch’ in loch or German ich, or the Arabic letter ‘khaa’. It’s a grating sound from the back of the throat, but should sound more like ‘k’ than the French ‘r’…
I hope that helps.
[quote author=Raya link=board=2;threadid=157;start=0#745 date=1055097119]
Um… c is like the English X (ks). I believe you mean x, which is like the ‘ch’ in loch or German ich, or the Arabic letter ‘khaa’. It’s a grating sound from the back of the throat, but should sound more like ‘k’ than the French ‘r’…
[/quote]
That’s how it is pronounced in Modern Greek, which is where the conventional pronunciation of classical Greek comes from.
In classical Greek (including Homer, and into Hellenistic times), the letters with the ‘h’ after them were in fact strongly aspirated. Most native English speakers aspirate initial consonants when not in a cluster. So, the word ‘pin’ the ‘p’ has a puff after it, but in ‘spin’ the ‘p’ has rather less puff behind it. In the Greek alphabet: fin, spin.
So, classical Greek made a consonant distinction most English speakers have a hard time hearing, since for us the distinction has no impact on meaning, which is why when we hear a Spanish speaker, say, not aspirating the initial p,t and k, we don’t notice anything but an accent.
In languages where p/ph are distinguished, like modern Indic languages in India, the difference between non-aspiration and aspiration can be fairly strong. Greek probably sounded pretty windy. 
So, to be most strict q is not like English thin but a ‘t’ with strong aspiration; f is not ‘free’ but an aspirated ‘p’ and x is not the German ach-laut, but an aspirated ‘k’ sound.
This is why you get a)faire/w, not a)paire/w. The ‘p’ hasn’t become an ‘f’, but rather it is followed by the initial ‘h’ of ai(re/w.