I, unfortunately, have sensitive ears.  I came across this full version of Tosca on youtube.  It was recorded in 1928-1929.  On youtube, someone had taken the trouble to removed all the noise and to make recording sound as if it had been issued yesterday.  When you remove noise from old recordings, you remove a lot more than just the noise. You absolutely kill the high frequencies.  In this case, a lot of the mid-range frequencies were killed as well.  So, I downloaded, and I fixed it.  That is, I remastered it.  Now, it sounds as if it had been recorded in 1928.  But the voices have come back.  If you’d like a comparison, here is the original

 

Tosca as posted

And here is the remastered version.

Part 1

Part 2

 

I went to all this trouble, because these musicians are extraordinary. We don’t have voices like this today. There are many reasons why, and I have touched upon them in earlier posts. Mainly, it is the way in which the sound is produced. Nothing causes the swallowing muscles or the muscles around the throat to squeeze. Today’s version of singing is the squeeze and swallow school of sound production, as a very knowledgeable friend of mine likes to say.

This is the entire opera. It is worth listening to.
The musicians are as follows:

Tosca: Carmen Melis
Mario Cavaradossi: Piero Pauli
Il barone Scarpia: Apollo Granforte
Angelotti, Sciarrone: Giovanni Azzimonti
Sacrestano: Antonio Gelli
Spoletta: Nello Palai
Direttore Carlo Sabajno
Orchestra e coro del Teatro alla Scala