Contact Quotient Versus Closed Quotient: A Comparative Study on Professional Male Singers *,†Filipa M. B. L~ a and ‡,§Johan Sundberg, *yAveiro, Portugal, and zx Stockholm, Sweden Summary: Objectives. The term ‘‘closed quotient’’ is frequently used for data derived both from inverse filtering and from electroglottography. In the former case, it is defined as the ratio between the closed phase and the period, as measured in flow glottograms (FLOGG), whereas in the latter case, it is defined as the time interval between the fall- ing and rising parts of the electroglottogram (EGG), measured at some percentage of the peak-to-peak amplitude. The study aims at analyzing differences between EGG- and FLOGG-based closed quotients and their relationships with voice source parameters. Study Design. Comparative study. Methods. FLOGG- and EGG-based measures collected from five professional male singers were compared, under different pitch and loudness conditions. Results. Compared with the FLOGG-based quotient, the EGG-based quotient (i) varied more between subjects, (ii) presented greater values, (iii) varied less with subglottal pressure, (iv) varied less with the normalized amplitude quo- tient (ie, the ratio between the flow pulse amplitude and the product of period and maximum flow declination rate), and (v) varied less with the relative amplitude of the voice source fundamental. Conclusions. Although positively related, FLOGG- and EGG-based closed quotients differ and must not be confused. Key Words: Closed quotient–Contact quotient–Flow glottogram–Electrolaryngography–Voice source analysis– Inverse filtering–Trained male voices. INTRODUCTION Closed or open quotients (Q Closed ,Q Open , respectively) have been used extensively in voice research as a standard measure of assessing vibratory, clinically relevant voicing patterns. 1,2 Mostly it is determined by either of two methods: applying inverse filtering or using electroglottography. The first method implies filtering of the audio or the flow signal by the inverse of the vocal tract transfer function. 3 This procedure of- fers a flow glottogram (FLOGG) showing transglottal airflow versus time. The electroglottography technique, first developed by Fabre (1957), offers measures of vocal fold vibration charac- teristics. 4 The signal, obtained from two electrodes placed on the sides of the thyroid cartilage, is modulated by the transglot- tal conductivity. 5 The term Q Closed is commonly used for values obtained both from FLOGG and EGG data. However, values derived from these two methods, henceforth Q Closed FLOGG and Q Closed EGG , tend to differ. The former refers to the ratio between the closed phase duration of the glottal vibration cycle to the vibratory period, whereas the latter is defined as the ratio of the time in- terval between the rising and falling parts of the EGG waveform at a given percentage of the peak-to-peak signal amplitude to the vibratory period. However, different percentages are used, 6–8 which limits the possibilities to compare Q Closed EGG data reported in different studies. The relationship between Q Closed FLOGG and Q Closed EGG has been studied in previous research. For example, in one study Q Open FLOGG and Q Open EGG values (1 À Q Closed FLOGG and 1 À Q Closed EGG , respectively) were compared; the FLOGG data were obtained from automatized linear predictive coding of the flow signal. 9 The subjects were 10 adult females, none of whom had any voice training. They were asked to produce the syllable /pa/ at four sound pressure levels (SPL) covering a range of 15 dB. The Q Open EGG was measured using a Kay El- emetrics Glottograph. A 50% and a 20% criterion were applied to both signals. As illustrated in Figure 1, the results showed that the Q Closed FLOGG was greater than Q Closed EGG . In addition, the former increased more with SPL than the latter. Henrich et al 10 compared the relative duration of the open phase as measured from FLOGGs with those obtained by applying different criteria to the EGG waveform. Data from five male speakers’ productions of the vowels /a, i, u/ were taken from Childers (2000). Q Open EGG was ex- tracted, applying three different amplitude criteria—50%, 35%, 3/7—and the so-called DECOM method, based on the derivative of the EGG signal. Q Open FLOGG was derived from inverse filtering the acoustic signal by means of a pitch synchronous covariant linear prediction method. Depending on the amplitude criterion applied, the correlation between Q Open FLOGG and Q Open EGG varied (0.429 < R 2 < 0.933). Of the amplitude criteria, the 35% criterion showed the best correlation with Q Open FLOGG but the DECOM method yielded an even better agreement. Herbst and Ternstr€ om 11 compared Q Closed EGG with the closed quotient derived from simultaneous videokymographic imaging in two subjects who varied register and glottal adduc- tion. The best agreement between the two methods occurred by applying and Q Closed EGG criterion of 0.2 or 0.25. They also found reasons to assume that the contacting and decontacting Accepted for publication July 14, 2014. From the *University of Aveiro, Aveiro, Portugal; yINET-MD, Aveiro, Portugal; zKTH, Stockholm, Sweden; and the xUniversity College of Music Education, Stockholm, Sweden. Address correspondence and reprint requests to Filipa M.B. L~ a, University of Aveiro, Aveiro 3810-193, Portugal. E-mail: filipasoprano@gmail.com Journal of Voice, Vol. 29, No. 2, pp. 148-154 0892-1997/$36.00 Ó 2015 The Voice Foundation http://dx.doi.org/10.1016/j.jvoice.2014.07.005