Is raising your voice at your parents grave matter? I’m not talking about screaming to the top of your lungs, but it isn’t very respectful, it’s happened to me, I get frustrated and I raise my voice.
It’s definitely a sin, but you haven’t really given us much information to go on. The examination of conscience I normally use says that “serious disrespect for or disobedience to parents” is grave matter, while “disobedience to parents or failure to give respect to parents” is venial matter. It’s kind of a matter of degree then. Another examination of conscience that I sometimes refer to lists the following question under grave matter: “Have I habitually treated my parents harshly, speaking contemptuously to them or of them, ridiculing them, cursing them, causing them severe pain and sorrow?” Under venial sins it asks: “Have I failed in the respect due my parents, by laughing at them, being openly ashamed of them, talking harshly or angrily to them, saying unkind things about them?” Also, sometimes things pop out of our mouths before we realize it, which is venial sin. However, if we realize we shouldn’t say something, but we say it anyway, it’s either deliberate venial sin or mortal sin, depending upon the degree.