What is the difference in pronunciation between ח and the guttural כ

Question

What is the difference in pronunciation between ח (khet) and the guttural כ (khaf)? And when do you know which one to use in a word?

Answer 1

From my experience, in modern Ashkenazi non-Israeli pronunciation they are the same. In Sefardi pronunciation, the chet is produced lower in the throat, whereas the chaf is produced in the back of the mouth.

An interesting proof that the Sefardi pronunciation may be more true to the historical practice is the following phenomena. When a shoresh has a gutteral in the final position, such as פתח, "opening", we find the introduction of a second vowel sound before the gutteral in forms such as the participle, eg פּוֹתֵחַ, pote-ach, "opens". This is as opposed to the normal vowelization of the participle, eg כּוֹתֵב kotev, which just has a single "e"/"ei" sound. This switch however does not occur for shorushim that end in chaf, eg הולך, holech, "walking" (ie, it isn't hole-ach.)

One explanation of this is that the ches sound was produced so low in the throat that it isn't possible to go from a "sere", which has the mouth in a horizontal semi-smile, directly to a chet, which has the mouth and throat open vertically, in one step. Verb forms like פָּתַח which have a patach before the chet don't display this phenomena, perhaps because the patach "ah" sound has the mouth already open vertically making it easy to transition to a deep-gutteral.

One potential reason for the cultural difference is that Ashkenazim lived in countries without deep gutterals, making the pronunciation of the original forms uncomfortable, whereas Sefardim lived in Arabic-speaking countries where deep and varied gutterals are very common.

Answer 2

I don't have the sefer I had on pronunciation any more (can anyone tell me the name for such a sefer?), but here's what I remember:

1. The kadmonim refer to both ches and ayin as "גרוני", gutterals in the back of the throat. See Sefer Yetzirah for its list of where different letters are pronounced. See the Ramban on Parshas Devarim on the verse about the "עוים", where he explains how the ayin and ches often interchange (something I wrote on this btw). There were Jews in old times who had trouble pronouncing them differently, as comments here from @Harel13 mention.
2. Unlike Arab countries, where Arabic has both these sounds (see Wikipedia for their pronunciation - ches is not voiced [hummed], ayin is), European countries generally could not pronounce these gutterals. Jews in those countries had trouble, and ayin drifted into not being pronounced at all.
3. Ches was more complicated, because it is unvoiced like an H, countries around Russia can't say an H sound. Ask any Russian speaker about H: the closest they have is their "X", pronounced like a chaf: Cheh, cheh, cheh. So Russian and Polish Jews drifted into pronounced a ches more like a chaf.
4. German Jews have a H sound, so ches wasn't such a problem. Up till recently that's how they pronounced it, so that the common spelling of חנוכה in English and German was always "Hanukkah" till recently. More recently they began to pronounce it more like Polish Jews, and pretty much all Ashkenazim now say an ches like a chaf.
5. Note that Yemenites still use the original/Arab pronounciation, in the back of the throat - unlike most Sefardim who say the ches in the soft palate, farther back than the chaf in the hard palate, not as far back as the throat. I have been told that official Israeli protocol was to use Yemenite pronunciation on news stations and the like, till fairly recently; they held it was more accurate.