I am wondering, isn't there any brief and common adverb (adjective plus -ly) in English that would enable me saying, e.g.
The transcript is imperfect because over lengthy periods people were speaking very xxxxx-ly
meaning: they did not speak loud enough to be intelligible on the record. They spoke with too low voices. Of course, I could say "... are speaking with too low voices", but I find this inconvenient: why use three words when one could do?
In German, I would simply say "... weil sie zu leise sprechen". I am a bit puzzled that in English I need to use complicated expressions for such a simple thing as the opposite of "speaking loudly".
I suppose, saying "they are speaking lowly" would be misleading. Right?
Note: there are related questions in English.Stackexchange, but none of them focussing my exact problem, as far as I see.
I am adding information here because the question got closed with a notification on alleged lack of preliminary research. Well, so, here are my preliminary attempts to come up with a solution based on a) my active dictionary of English b) various other dictionaries.
quietly - Problem: my understanding is, that "quietly" carries a positive connotation: It would be an indicator of being a person of good upbringing to speak quietly (instead of loudly); in my context of audio records of research interviews it is however a negative thing to speak too quietly. Please correct me if I am wrong.
muttering/mumbling: these describe certain ways of speaking, usually of course in a low voice, but also with e.g. a lack of physical movement of the speach organs. In my context "muttering" or "mumbling" would be over-specific. Moreover, I fear that using such words I would offend my client (to whom I want to communicate the reason for the imperfect transcript). I do not want to tell him "You were mumbling" because a) he was not actually mumbling, he simply spoke with very low voice and b) even if he did it would be too confrontational to use this very word, I believe.