Voice source effects of diaphragmatic activity in singing

The transdiaphragmatic pressure was displayed on an oscilloscope screen as a visual feedback signal for singers and non-singers who performed various phonatory tasks with and without voluntary co-activation of the diaphragm. The diaphragmatic co-activation tended to increase the amplitude of the flow glottogram, i.e., the transglottal air volume velocity waveform as determined by inverse filtering and also tended to reduce the formant frequency variability under conditions of changing fundamental frequency.