I read the criticisms from viewers who couldn't hear/understand what Sarah Lancashire was saying.
As a hearing aid wearer, I put the subtitles on in anticipation of struggling, but to my surprise, I could hear every word she spoke, without even looking at the screen!
Could it be the timbre of a voice? As my hearing is diminished, perhaps it picks up 'lower/higher' (I've no idea which tbh) levels of a voice.
Interestingly, when I was working I couldn't be near 2 colleagues as the pitch/tone of their voices made me feel ill ! Neither of them had a loud voice but both really grated on my ears. Poor ladies obviously thought I didn't like them as I avoided them.