Im about to receive my first ultrasonic machine for animals. It has 2 settings, low and high. High is to avoid dangerous dogs in the street and low is just a small weird noise for the dogs.

Using this to teach them not to bark and some other behaviors, is it found to be negative reinforcement or neutral? I dont want to make the same mistakes i always made with dogs, i want to make sure it will be correct to use this machine to stop barking, biting, eating food from strangers and a few other stuff that are hard to teach with food

No, it is not positive reinforcement.

Positive reinforcement means starting or adding something that the animal likes or enjoys. It gives the animal a good feeling. And in order to gain that good feeling again, the animal will repeat the exact behavior that seems to cause that consequence.

In your case you want certain behavior to stop (stop the barking, the biting, the accepting food from strangers) by adding something unpleasant.

In that case you speak of "positive punishment": something unpleasant to the animal is started or added. It gives the animal an unpleasant feeling. By not repeating that exact behavior again, the animal can stop the unpleasant feeling.

"Positive" stands for 'something pleasant is started or added', "negative" for "something unpleasant is finished or taken away".

"Reinforcement" stands for 'behavior increases', "Punishment" stands for 'behavior decreases or stops'.

I expressed my self wrong. If i use on my next dog positive reinforcement for everything, except those hard stuff. Will it alter its personality in a bad way like doing physical punishment for everything would do?

I want my next dogs to respect me more than fear my wrath. The Noise thing only last 1sec or less, i would not hold it down. it's just like if i ring a bell everything a child does something wrong, to get his attention