Articles, moving along a delivery path, are counted by directing a stream of pressurized air toward one major surface of the passing articles, the direction of the air stream being transverse to the direction of travel. Sensors arranged about the air stream detect the acoustic signal which varies with changes in the profile of the passing articles, exemplified by signa­tures. The detected acoustic signal is divided into a plurali­ty of frequency ranges which, in one preferred embodiment are averaged to reduce the effect of noise which may be present in only limited ones of the frequency bands. The averaged signals are then compared against the aforesaid thresholds to determine the instantaneous state of the articles, exemplified by a signa­ture stream to generate count signals.