The invention relates to a filter manufacturing method and a filter manufacturing apparatus (1) having a device (31a-31e) for applying plasticizer (26a-26e) on filter material (3, 3a-3e) and a filter material conveying device (2, 9, 11, 28). DOLLAR A The filter production process according to the invention comprises the following process steps: DOLLAR A - Providing a web (3, 3a-3e) of filter material (3, 3a-3e), DOLLAR A - Applying a plasticizer (26a-26e) to the filter material (3, 3a-3e), DOLLAR A - forming a strand (32) from the filter material (3, 3a-3e), DOLLAR A - separating filters (34) of the strand (32), wherein at least in the conveying direction (40) of the Filter material (3, 3a-3e) is generated spatially resolved depending on the concentration of the plasticizer (26a-26e) signal and wherein filter (34) with filter material (3, 3a-3e), for which a signal below a first predetermined threshold or above of a second predetermined threshold, are discarded. DOLLAR A The filter manufacturing device according to the invention is characterized in that a measuring device (36a, 36b, 37, 38a, 38b) for generating a signal, the at least in the conveying direction (40) of the filter material (3, 3a-3e) spatially resolved concentration of the plasticizer (25a-26e) in the filter material (3, 3a-3e).