bass guitar high action vs low action

guys I've recently lowered action in my bass guitar and His voice has changed a little bit is this normal  ???

and Should I keep it high or low ??

Depends on what you mean by "voice". 

When you change action on your bass you need to re-tune it. Setting the strings higher or lower changes the tension.

Another possible side effect is setting the action so low that your strings are constantly rattling against the frets. A little rattle is ok, so long as it doesn't ruin the sound.

the tune is good and also There are no little rattle sound.... it just the  E string sound Different His voice became more sharp  ???

I can't really say what's happening without actually hearing it. 
The only problem I've ever had with low action was that at certain frets I was getting more buzz than tone...some could call it "sharper", but I can't guarantee that is what happened with your bass. 

As long as there is enough tone and it sounds good, it shouldn't be a problem.