Circuits, methods, and apparatus are described that provide calibration of column-parallel analog-to-digital converters in image processing contexts only once per frame to reduce column-wise noise. A flow path is provided between the first and second chambers, for allowing flow to circulate between the first and second chambers, and obstruction means is provided in the second chamber for slowing flow through the second chamber. The invention also discloses a HGA and disk drive unit with such a micro-actuator. The circuit also includes a first termination resistor stack connected to a drain of a first resistor stack of the plurality of resistor stacks and a second termination resistor stack connected to a drain of a last resistor stack of the plurality of resistor stacks. A noise threshold for the mass spectrum is then applied using the calculated moments.