My violin is not very loud (I like it that way, since I play just for myself), but on louder instruments I do prefer a hearing protection in the left ear, otherwise it hurts.
Besides what are you going to do in he 'con sordino' passeges? Leave it off and play quietly (that does not work)'
I had quit violin lessons before I was 12 and only practiced a few times before I resumed (forever) at age 13. But I did practice a few times in that era with a mute (even Dad's old heavy mute) and I liked that I could really hear my intonation. But a mute kills a lot of the higher overtones and so eliminates much of the audible contributions of vibrato. So, in my opinion it can be helpful for some aspects of left-hand playing but it is more like hearing the sound coming from behind a closed door.
The medical world knows that violinists progressively destroy their left ears. Violists too: violas are louder, even if they "project" less, and they may also be just in front of the brass..
She discourages heavily practicing with earplugs and she told me if the violin is 'too loud' to my ears (ie it starts to make me feel like my ears are hurting) then to practice with the tourte mute on.
She uses the mute 'mostly' but not 'always' she told me, and yes from a very young age. She said Milstein used it too.
I really do not think the tourte mute can hinder your intonation learning/skills as others have said.
So I practice with no mute, but have done on the odd occasion and on her advice I use the tourte mute when I do.
Consequently I wouldn't expect impaired pitch discrimination to be among the first symptoms of cochlear hair cell loss which predominantly affects the cells that are selectively responsive to higher frequencies.
I'm not sure exactly how loud sounds damage hair cells, but I have the strong impression that such damage affect pitch acuity.
I do remember she gave a very determined NO to the ear plugs, and again I don't know if she would say this to anyone or if she thought it was not a good idea for me as I am intermediate in my playing, would it be the same to an advanced player? I assume so as she never uses them herself and seemed to oppose to them even for her own playing.
I will speak to her tomorrow and make a point of asking her again so I'll come back here and let you know :)
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