I'm not sure if this is true or not (so don't go thinking I'm trying to offend or thinking I'm right or anything), but this is just what I've read somewhere. I've read that sometimes talking in a monotone means lack of confidence. And I've had personal experience of this too. When I'm with my family or friends, I don't speak in monotone at all. I have a ''colourful'' voice, and sound just like anyone else. But when I speak to some people, eg some colleagues at work who make me feel quite shy or agitated, or especially customers, I tend to speak in monotone, and if I ''break'' the monotoned voice, I stutter or mumble instead, or if I try not to stutter or mumble I tend to go all stiff in my arms and legs as though I'm clenching up inside. Although I don't generally suffer any speech delays or speech problems, sometimes I even pronounce things wrongly (which I don't normally do), or I use incorrect grammar (which is unusual for me too). I might miss out an ''S'' in a word, or use the wrong plural - and I hate this because it makes me sound really stupid, especially when I know this isn't my normal character to talk like this. If I keep it at a monotone, I don't tend to make these mistakes, but then speaking in monotone might make people (especially strangers) think I sound unconfident. Also if I try to use the same voice to customers as I do my family and friends (which is my normal voice), I tend to ''use the wrong tone for one word'', if you know what I mean. You know when you're playing a song (with one hand) on a piano, and you press the next key next to the correct key by mistake? That's what sometimes happens to the correct tones of the correct words of my voice.
For example:-
Look at the sentence ''I didn't take the money''. If you had borrowed the money and had asked someone to borrow it first, then somebody was accusing you of taking the money, you would say, ''I didn't take the money,'' but if I was saying this to a stranger or a person making me feel nervous (without using a monotoned voice), I would probably accidentally say it like this, ''I didn't take the money'', or something like that. That is the closest example I could think of. But I know how to do and say these things, because I speak fine to family and friends, or strangers who I feel rather comfortable with.
_________________
Female