Abstract: A manually operated or automatic equalizer (1) with adjustable band filters for varying the frequency characteristic of an electric signal presented to an input (2) and for applying a frequency characteristic-adapted electric signal to an output (3). The equalizer has a plurality of band filters (F.sub.1 to Fn) with their bands located adjacent to one another in a given frequency range. The distance (frequency separation) between the central frequencies of filters having neighboring bands is greater than the distance between the central frequencies of one third octave filters having neighboring bands located at at least approximately the same frequencies as those of the band filters (F.sub.i). At least those band filters (F.sub.1 to F.sub.m) whose bands are located in the low-frequency part (f<450 Hz) of the frequency range have a central frequency (fc.sub.i) which is variable. A digital filter which can be used as a band filter in the equalizer is also described.

Abstract: The noise-dependent volume control in accordance with the invention is capable of distinguishing between the real background noise and speech in a space (8). The gain (A) of the amplifier (1) is corrected only depending on the level of the background noise, so that once a difference in level between the background noise and a desired signal has been set this is maintained. The volume control is based on repeated measurements of the acoustic signal in the space (8). If it appears that in at least one frequency range the measured energy content (E.sub.i) has fallen at least N times within a range of values .DELTA.M around a value (M.sub.i) stored in a memory (26) the gain factor is adapted.