How can communicate clearly without having to raise my voice?

Hi,

It sounds like from your description a lot of your struggle revolves around 'knowing' you are raising your voice. So the first step to behavior change is helping you to be aware of when it happens. Maybe stating it as a goal and asking people, such as your partner, to help you be aware. You can try to go as far as keeping track of the times you raise your voice. This can help you keep track if the behavior is getting better or worse. Keeping track of a behavior can be done on a notes app or a calendar. I think keeping track and asking people for accountability will give you data. 

Beyond basically bringing awareness, you can use mindfulness. If you do not know what mindfulness is, then it can be summerized as bringing awareness and curiosity to your internal self. Bringing present awareness to your thoughts and feelings. Being more emotionally aware will help you to know when there are changes that are occuring that might lead you to raising your voice. This can be augmented by having people who call you out.

When you find yourself raising your voice, just allow yourself to be caught in a mistake. It is okay and healthy to ask for redos. Redos are as simple as saying 'hey I noticed that I just raised my voice can I please have a redo so that I can try again.' New habits take time and practice. We are going to backtrack a bit as we try to improve. Expecting yourself to perfectly get this habit changed all at once is probably not realistic. If you ask people for redos, you will be given a chance to correct in the moment. 

On the notion of correcting self in the moment, you need to keep in mind that you are probably going against years of hardwiring that has been behaviorally turned into a habit. Habits take time. You said that this relates back to your childhood. Exploring the unhealthy habits that you carried over from childhood and putting in conscious efforts to change them is going to be like building a new habit. 

So in review, really work on being aware of when and where this voice raising behavior happens. Invite people to call you out on it and admit to people that you want to work on it. Teach and train yourself to be mindful of when your emotional state is altering and keep track of times that you raise your voice. Finally allow yourself the grace to ask for redos and give yourself time to learn the new habit of not raising your voice. Have patience with yourself and you can get there.