  We demonstrate a new tool for filtering technical and electronic noises from
pulses of light, especially relevant for signal processing methods in quantum
optics experiments as a means to achieve the shot-noise level and reduce strong
technical noise by means of a pattern function. We provide the theory of this
pattern-function filtering based on balance detection. Moreover, we implement
an experimental demonstration where 10 dB of technical noise is filtered after
balance detection. Such filter can readily be used for probing magnetic atomic
ensembles in environments with strong technical noise.
