Imitating his pronunciation, I pronounced spät as ʃpeːt, using the same vowel sound as in Wie geht’s viː ˈɡeːts ‘how’s it going?’.
As I got to grips with the written as well as the spoken language, I learnt to treat the umlauted letter ä as being pronounced exactly the same as the letter e.
Years later, when I studied phonetics with John Trim at Cambridge, he told me that the German pronunciation I had acquired through total immersion, while commendably native-like in its way, was in some respects regional. If I wanted to speak proper Hochdeutsch, I ought to remember to say Guten Tag! with taːk, not ta(ː)x; the train, der Zug, should be tsuːk, not tsʊx; and for long ä, as in spät, I ought to add a new item to my German vowel system, namely the long ɛː, thus ʃpɛːt.
The standard set out in German dictionaries and textbooks treats orthographic e and ä as having the same value when short, ɛ, but different values when long, namely eː and ɛː respectively.
So fällen ‘to fell’ ˈfɛlən is a perfect rhyme for bellen ‘to bark’ ˈbɛlən (both have the short vowel). But wählen ‘to choose’ should not, in Hochdeutsch, be a perfect rhyme for fehlen ‘to be lacking’ (with the the long vowel): ˈvɛːlən, ˈfeːlən.
This distinction still feels artificial to me, and I don’t make it unless perhaps carefully reading some text aloud or making a phonetic point.
The pronunciation dictionaries tend to hedge their bets on this distinction. Here’s the sixth edition of the Duden Aussprachewörterbuch.
Der Vokal [ɛː] kann auch [eː] gesprochen werden… (p. 21: ‘The vowel [ɛː] can also be pronounced [eː]…’)And here’s the Deutsches Aussprachewörterbuch.
Der Unterschied zwischen [eː] und [ɛː] wird in der Aussprache meist nich stark verdeutlicht, so dass häufig ein Vokalklang zwischen [eː] und [ɛː] mit einer Tendenz zu [eː] entsteht. (p. 58: ‘The difference between [eː] and [ɛː] is for the most part not made very clearly in pronunciation, so that frequently a vowel quality between [eː] and [ɛː] arises, with a tendency towards [eː].’)Wikipedia says, I think quite correctly,
The long open-mid front unrounded vowel [ɛː] is merged with the close-mid front unrounded vowel [eː] in many varieties of Standard German…
I shall continue to speak German with an undifferentiated eː.