This study is an investigation of the effect of the presence of the flow mask on voicing behaviour. Microphone and flow recordings were inverse filtered and compared to examine the possible effects of the flow mask. Closing quotient (ClQ), open quotient (OQ) and the amplitude difference between the first and second harmonics (H1-H2) were the parameters used to characterise the inverse filtered signals. The presence of the flow mask used for the recording of oral flow had an effect on these parameters, which is interpreted as being indicative of a more tense or more efficient voicing behaviour in the presence of the mask.