try this; when you sample, sample the piece you want and place each piece on different pads. when you are in the trim mode, hit one of the pads to hear the sound. now use the data digit wheel to trim the sample. look at the numbers at the end of the sample on the screen on the right hand side. use your judgement with this, take the digit wheel and roll the dial to adjust the sample or in lament terms trim. now when you get to the part you want cut, press cut, the screen will say discard , press do it.
that will help. use this method for all the samples on each pad that you want to chop. you may have to trim the numbers in the beginning of the sample to get where you want. trial and error. just practice.