AUTOMATIC PROCEDURE FOR LARYNGOGRAPHIC (Lx) ANALYSIS OF PHONATION CONTRASTS

This report describes an automated, microcomputer-based procedure for comparing laryngographic (Lx) waveforms. The program enables researchers to analyze the cycle-by-cycle changes in vocal fold vibratory characteristics that may signal linguistic contrasts or differences in long-term voice quality. The first differential of the original Lx signal, captured digitally, is marked to indicate beginning, ending, upper and lower limits. A set of ratios is then obtained relating increasing voltage to decreasing voltage for each period of the signal. Considerations such as the inherent variability of the Lx signal, techniques of Lx recording, and applications of the algorithm are discussed. 1. LARYNGOGRAPHIC ANALYSIS Electrical impedance laryngography has bgen used in phonetic research to quantify dlffcrcqces between contrasting types of Rhongupn [4]. Such contrasts appear lmgulstlcally in languages like Korean at the syllac level in conjunction with phonologlcally distinct manners of consonantal articulation [1] [6] [7] [8] [9]. Phonatory contrasts also appear as long-temp pos§urcs in voice quality with largely Indeigical significance [3, 10]. One problem 1n the analysis of the larynx wayeform (Lx) has been the highly vanqble data that it yields. The signal is obtamed by means of superficial throat Plectrodes which measure decreasing unpcdance as the vocal fold mass comes together, and increasing impedance as these structures separate [5]. Different models of laryngo . gra h and dxffenng recordmg procedures rgsult in Lx signals with varying phase characteristics. This makes it difficult to analyze characteristics of individual waveform pcriods to distinguish, for example, a breathy voice from a harsh voice. Another problem is the DC float that characterizes many Lx signals and which makes establishing a baseline for reliable measurement of individual period characten'stics particularly difficult. Aspects of obtaining an initial, workable Lx signal are dealt with in section 2. A solution to the . baseline problem is presented in secuon 3. The method of segmenting the waveform to obtain a ratio is presented in section 4. 2. RECORDING Lx Recordings of Lx signals made on a sgandard AM tape recorder tend to be 511§toned by phase shift. For this reason, It. 18 val_uablc to develop procedures for d1rect dlgitization of the Lx signal, using an adequate (16-bit) data acquisition systexp. However, if this is not possible, the s1gnal may be recorded using a system; that does not introduce phase dlstpmon, such as a Sony PCM digital audlo processor and recorder, as has been used for these experiments. Attempt? at controlling DC float in the Lx Slgna! Include assuring that proper cpuphng with the input preamplifier or Slmxlar analog conditioner is maintained. However, lowofrequency oscillations can be expected as a result of laryngeal movement around the axis of the electfodes. This is more apparent during contmuous speech than during examples taken from sustained vowels, owing to the natpral raising and lowering of the nx 1n the less controlled situations. The polarity of the Lx signal must also be System Speak Options Display Data Printer _ Fl 1» n:\32EIMHISP.SPL l B > H :\328HHISP . SPL '7 3 1.7111 < >