how to ditermine causes for the brake pedal to chatter?

Chatter as in vibrate up and down rapidly when braking? Does your steering wheel also shake at same time?

yes the steering wheel shakes slightly. when i depress the brake pedal lightly the chatter is noticable and with more pressure it goes away.

If your brake pedal pulsates and at the same time the steering wheel shakes then your front brake rotors are warped slightly. If they are not below minimum thickness then they should be able to be resurfaced at a machine shop. Would also be a good idea to consider new front brake pads at the same time. Make sure to check that the calipers are not sticking and causing the rotors to overheat.