I've just started studying Sanskrit with Charles Wikners 'A Practical Sanskrit Introductory' and have questions on the pronunciation of ऐ and औ.
For the ऐ he writes:
The ai sound arises when e is further combined with a as it were. The only difference between e and a is the raised back of the tongue, so to move from e towards the a sound, we need to drop the back of the tongue to a position half way between that used for i and e and the relaxed position used for a.
That sounds like an excellent explanation and there is no need to glide the sound from an a to an i. He says that explicitly:
...there should be no glide or slide in the sound from a to i.
A similar advice is given for the औ.
On the other hand many sites on the internet are telling, that the ऐ should sound like 'my' or the like, e.g. The Cambridge Introduction to Sanskrit on page 11. Some even say explicitly this vovel as a diphthong has a gliding sound from a to i.
Surly the 'my' for ऐ and the 'loud' for औ are good helpers to memorize the set of svara sounds for westerners. But what is the correct pronunciation when it comes to actually spelling words like ऐकपद्य or औपधर्म्य. Should they start with such a gliding sound or should it sound like one vovel as produced with Wikners tutorial?
EDIT: The Cambridge Intorduction to Sanskrit by A. M. Ruppel explains why the vovels ए and ओ are called diphthongs in the first place:
[...] They are followed by the complex vovels, e ai o au. At an earlier stage of the language, e and o actually were *ai and *au, and current ai and au once were *āi and *āu. Knowing that e ai o au were once *ai *āi *au *āu allows us to understand not only why all four of these are known as 'complex' vowels (all of them were once vowel combinations or 'diphthongs'), but also to see that the pattern of 'short vowel, then long vowel' that we saw in a ā i ī etc. is maintained here too. All four complex vowels count as long.
Listening to some good reciters and chanters I've come to the conclusion that the sounds in 'my' and 'eye' and 'loud' and 'hound' are the best choice to start with. I've also learned, that in india many shools of vedic knowledge exist all with their own treatise on voice and pronunciation called Shiksha.
However, I suppose Charles Wikner is not totally wrong with the way he explains pronunciation of ऐ and औ. Maybe his way is derived from a rather minor shiksha. I'd really like to know more about this topic so I leave the questions unanswered as it is by now.