A filter assembly comprises a filter defining path for fluid passing to or from the filter. The compositions comprise dextromethorphan in combination with quinidine. The first signal adaptive filter estimates the noise mixed in the voice signal according to a reference noise. The pen also includes a higher frequency burst transmitter useful to generate a time reference, and to transmit the pressure information. Friction locking allows the axial position of the suction pipe in the hand piece to be freely varied, so that an effective length of the suction pipe and its rotation position in regard to the hand piece can be adapted optimally to the respective operation requirements, and can be readjusted as the operation progresses. The system altogether has 56 cells.