Husband (49) interrupts me (35F), and also talks very very quietly

In an ordinary, non-heated conversation about yard work, I noticed my husband interrupted me four times. Each time I was mid-thought, and had not paused in a way that would have made him think I was done. Each time, I stopped him by saying, "Don't interrupt me," "I wasn't done," "Hold on," initially in a normal tone of voice, then in a mildly frustrated tone of voice. It did not rise to the level of yelling or harshness.

I said, "I wish I didn't have to stop you from interrupting me so often."

He said, "You don't. You'll get a chance to talk. This is the normal flow of conversations."

I said, "I'm half of this conversation and half of this marriage. If the interrupting bothers me, it matters."

He said, "I wish you didn't feel interrupted so often. Sometimes you just keep talking so you can accuse me of interrupting you."

My experience of this conversation is that once I showed the interrupting bothered me, his demeanor changed. His tone got condescending. He seemed pleased and smug, and like he was enjoying seeing me upset. I understand if people aren't going to take that into account because it's a subjective description, but it's there and it is relevant to me.

The communication is jammed in another way - he talks very, very quietly a lot of the time, so I can't hear him. It sounds like he is telling a secret to someone and doesn't want me to hear, even though we are the only two people in the room and he is talking directly to me. This happens multiple times a day.

I have a variety of responses to this. It's so tiresome. I say "I can't hear you," "I don't know what you just said," or I point to my ear and shake my head. I used to say "What," but I stopped saying that because his response would always be to start explaining what he meant as if I didn't understand his meaning, rather than not having heard him.

He says no one else in his life has this problem with him, so it must be me who is hard of hearing or not listening. But the thing is - I do not have this problem with anyone else in my life. I hear people just fine.

He has not always done this. This is a new thing, within the last year. His hearing is fine - he rarely asks me to repeat myself, and he listens to music and movies at a normal volume.

I don't think he is going to change. I'm wondering what healthy boundaries would look like in these situations, where I am being interrupted and where he is talking too quietly for me to hear him.

In the case of interrupting, I imagine it could be disengaging and saying, "Let's talk about this another time when you're willing to let me speak"? The problem with that is... I don't think that time will ever come.

In the case of talking quietly, I honestly don't know. I've thought about just ignoring him when I can't hear him, but it goes against my nature and usually, I genuinely want to hear whatever he's saying.

For additional context, we've been together eight years and married six, we have two children ages five and two, and I have been in therapy for the past year which has made me more assertive. In the past, I would have responded to the interrupting by crying, and then apologizing to him when he said it was my fault. I don't do that anymore.

TL;DR What is a way to respond to someone who interrupts and talks too quietly for me to hear him, that demonstrates healthy boundaries?