Competency in general; disqualification

(a) General rule competency. Every person is competent to be a witness except as otherwise provided in these rules. (b) Disqualification of witnesses. A person is disqualified to be a witness if the court finds that (1) the witness is incapable of expression concerning the matter so as to be understood by the judge and jury either directly or through interpretation by one who can understand the witness or (2) the witness is incapable of understanding the duty of a witness to tell the truth.