I guess I shouldn't count my chickens before they've hatched, but this morning I feel as though I've cracked three old, seemingly chronic problems in one blow. They were:
1) Until CornyAndy mentioned something last year about the way some people in our region articulate most "k" sounds (at the back of the throat rather than on the hard palate), the art of multiple tonguing was totally lost to me.
2) I'm sure my single-tonguing didn't sound as bad to an audience as it did to me, but in my head I was mainly hearing "thu-thu-thurr". I probably overcompensated for this with hammer-tonguing.
3) The sound I've been getting recently feels a lot closer to soprano cornet than trumpet. Not a bad sound by any means, but not what you want for Prince of Denmark's March etc.
Anyway, a few weeks ago I was given permission by a higher authority () to start working on tongued notes again after 6 months or so on untongued legato. The doubletonguing in particular has felt really strained as I learnt to cope with this "foreign" k-articulation, worked on making ku match tu, getting the timing even, gaining control of a steady pitch and tone through the articulation, and exiting with a clear "taaaaa" from the "tukutukutukutaaaaa".
Gradually, I've been working the speed up and eventually started hitting a level where my tongue felt as if it was just bouncing on my palate rather than being driven. When this happened, there was a fair drop in resistance and (as I gained control of the note) a major improvement in tone of not just the short notes, but also the "taaaa" exit.
It didn't take me long to try to produce the feeling of that bounce on single tongued notes, and lo and behold! I was getting much crisper single notes than I ever remember having coupled with the tone I'd previously only got on untongued notes.
And it gets even better. I found that altering the degree of 'U' shape across my tongue produced a considerable variation in sound with a more pronounced 'U' giving that brighter more focused 'Prince of Denmark' trumpet brilliance.
I'm guessing the key factor is learning to get your tongue out of way of the airflow as quickly as possible.
And all from learning to say 'K' in a new way.