The figure presents the relation of the sound stimuli at the start of the different listening tests. Left: method A – The initial level of the fixed stationary complex four-partial tonal sound with 350 Hz fundamental frequency mixed with background noise (solid), and the adjustable pink noise (dashed). Right: method B – The initial level of the adjustable complex four-partial tonal sound with 350 Hz fundamental frequency mixed with the constant background noise (solid), and the stationary pink noise (dashed).