American English Pronuncitaton Unvoiced S consonant and Voiced TH sound

[zoltankr]

Hi, I'm new here. Here's a question:

What's the matter?
wʌts ðə ˈmæt ɚ?

I wonder if Americans drop the "ts" in this situation because "ðə" sounds close to "ts" for my ears. I may be wrong.
wʌ_ðə ˈmæt ɚ? or
wʌts ðə ˈmæt ɚ?

Any suggestion appreciated. Thank you.

[Daniel]

It may depend on exactly which dialect you're referring to. But personally as a speaker of essential General American, I would not reduce it in that way. I would produce it in one of the following ways depending on how fast I'm speaking:

[wʌts ðə ˈmæt ɚ?]
[wʌtsə ˈmæt ɚ?]
( ?? [wʌsðə ˈmæt ɚ?] )
[wʌsə ˈmæt ɚ?]

I'm sure that I could produce the 1st, 2nd and 4th forms. I'm not sure if I'd ever produce the 3rd, but maybe. I know that I would not produce a form with the voiced dental fricative and no alveolar fricative.

I also would probably at times voice the to [z]. It's hard to be sure when, but probably at least sometimes in the last variant:
[wʌzə ˈmæt ɚ?]

It's unlikely I would voice the to [z] following [t] because that's voiceless. And I also think it's unlikely I'd voice the whole sequence to [dz].

[zoltankr]

Thank you. Your time is greatly appreciated.
May I ask you one more question?

Do Americans always replace the "u" in everyday informal conversation with the schwa? (in the middle of the sentence or question)

What did you say?
wʌ_dɪ_ʤu ˈseɪ? or
wʌ_dɪ_ʤə ˈseɪ?

What are you doing?
wʌd_ər_ju ˈdu ɪŋ? or
wʌd_ər_jə ˈdu ɪŋ?

Do they understand me when pronouncing in both ways? Which one is more popular and safer to use?

[Daniel]

Completely flexible. It depends on speed and formality. "You" is certainly pronounced [juw], but [jə] comes up often in fixed expressions and fast speech.