here it is obvious that the aliasing components present in fig3 are vanished if there is no strong sinusoidal component the zeros will nevertheless be situated in either half of the z plane indicated by the sign of the channel and the channels will be grouped accordingly this means that there is no need for detection based decision making whether there is a strong tonal component present or not in a real valued filterbank the energy estimation is not straightforward as in a complex representation if the energy is calculated by summing the squared subband samples of a single channel there is a risk of tracking the time envelope of the signal rather than the actual energy this is due to the fact that a sinusoidal component can have an arbitrary frequency from 0 to the filterbank channel width if a sinusoidal component is present in a filterbank channel it can have a very low relative frequency albeit being a high frequency sinusoidal in the original signal assessing the energy of this signal becomes difficult in a real valued system since if the averaging time is badly chosen with respect to the frequency of the sinusoidal a tremolo amplitude variation can be introduced when in fact the signal energy actually is constant the present invention teaches however that the filterbank channels should be grouped two by two given the location of the sinusoidal components this significantly reduces the tremolo problem as will be outlined below in a cosine.