Well, the "th" can be pronounced the same in many ways. And yet, and pronounce it differently. I have nothing against this sound, I like it. But just as his pastor says - no. Maybe it's because she tries too hard to pronounce it as "th", but got used to the "S"?
Ok, i think i understand you now. Well Soraya and Lucia pronunce "z" in corazón as "th" too, because is the correct way to pronunce it in spanish. There is many ways to pronunce it too, but the correct sound in spanish for "Z and ce/ci" is "th". After reading your coments i think i understand what you meant at the begining. Probably it sounds forced (unnatural) for you since Pastora always has pronunced it as "s" since her childhood, so after diccion courses, she has a neutral accent now when she speaks in front of a camera or when she sings. Maybe it sounds weird or forced to you. Spanish people doesn´t notice it.
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Anyway, I respect your opinion about your preferences about latinamerican accent. I dont consider it is better, and i know sometimes it sounds softer and nicer, but i will tell you why i dont like it so much: in spanish there are many words that express an idea of strengh, harsh, (something no nice). Using the "th" you express that idea, because is a rough sound, but with the sound "s", you transform a rough word into a soft one with a rough meaning. Thats why i like when we make a difference between s an "th" (although it could sound less nice), but latinamerica don´t. Example: Zambombazo is a very strong sound, made because of an accident, something that falled, or something alike. In the way you like, you would say sambombaso. Another example is the word "excitar" (to excite)(ecsthitar), in latinamerica would say "esitar". I really love the words that combine both "s" and "th" sound.
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Besides of you would find a problem with phrases like this: Mi hijo se va a cazar with Pedro (My son is going to hunt with Pedro). In latinoamerican accent you would say : Mi hijo se va a casar con Pedro. This phrase with "s" means something totally different (My son is going to get married to Pedro). Sumo (= sumo's fighter, the Pope) and Zumo (= juice); sueco (= swedish) but zueco (= a kind of shoes).There are many words that means something different if you write them with s or z, so why to complicate to yourself, pronunceing them in the same way?. Thats why i prefer the way we pronunce it.
Anyway im agree with you about Pastora sometimes pronunces it too strong, as in the song Demasiado amor (i already had notice that the "z" in that song, sounds too strong for my taste.).