M Test Definition: I inhale without forcing myself and produce a continuos and constant tone mmmm sound, till the tone breaks. I check the tone by the app Spectroid and aim an M sound at -30 dB and a constant frequency. I measure the duration of this constant M sound. Severe stutterers can't achieve more than 10 seconds. Normal speaking and healty people have it at least 30 seconds. That's why they keep so calm. I also do the same test by saying sssss.