[DECtalk] Too high-pitched notes, and DecTalk sounds distorted

[Talksina]

Hi,
I'd like to ask a question to DecTalk experienced users.
how to manage high-pitched notes?
Well, I tried to build the song "moonlight shadow", by Mike Oldfield, 
one of my favourite songs but the voice pitch was very very high and 
not nice to hear; notes are, if I can remember well, over the 26 
number! Or at least 24! The herz code to associate to the phoneme, 
for producing the note, I mean.
I heard many songs on the archive that I suppose are much more 
difficult than Moonlight shadow. That song "i swear" by Snoopi Boten 
especially. He managed to make it sing quite OK with All4one's voice 
in background! I'd never do something like that, using the original 
song, as it would confuse me a lot.
and Snoopi, if you read me, I am going to buy one of your cd's soon, 
after holidays. I'd like to promote your skills in my country too. 
You deserve it all.
Thanks in advance for advices on the high pitched notes
PS my next synth challenge will be the song "happy days"