Labium and window:
The distance of the labium to the wind-channel, the open height of the window, must be in proper relation to the diameter of the instrument (Soprano: approx. 3,5mm; Alto: approx. 4,5mm). If the window opens not far enough, a quinty, close tone results. If it's too far, it produces a harsh noise and a bad speaking in the upper octave. Also the bending of the side panels influences the tone quality: steep walls give a more sweet, flat ones a softer tone. To the width of the labium applies: The more narrowly the more quinty. Modifications should be made only by a recorder-maker. The edge of the labium should not be razor-sharp. An easily broken or rounded edge gives a more pleasant tone without the worsening the speaking.