VISUALIZATION OF CHANGE OF SOUND CHARACTERISTICS ON THE LEVEL OF THE VOCAL CORDS R. L U C H S I N G E R , M.D. Promenadengasse 18, CH-8001 Zurich, Switzerland SUMMARY The c o n s t r u c t i o n is reported of an apparatus for producing short s t r o b o s c o p i c films, e m p l o y i n g a n e w phase-shifting device. This apparatus provides the clini- cian w i t h a reliable record of the m o d e of vibration of the vocal cords (in b o t h the o p e n i n g and closing phases) alongside a tape-recording o f the voice. This makes it possible t o correlate recordings of t h e frequency and intensity and transitions of the v o i c e with a series of s t r o b o s c o p i c investigations. OPSOMMING Die konstruksie van 'n n u w e apparaat vir die produksie van kort strobosko- piese films w o r d bespreek. 'n N u w e fase-verskuiwingstegniek w o r d ingespan vir hierdie doel. Hierdie apparaat voorsien die terapeut van 'n betroubare weergawe van die w y s e van vibrasie van die stemlippe (in b e i d e o o p en geslote fases), asook 'n b a n d o p n a m e van die stem. Dit maak dit dus m o o n t l i k o m o p n a m e s van die frekwensie, intensiteit en oorgange van die stem te korrelleer met 'n reeks s t r o b o s k o p i e s e ondersoeke. In 1961, E. Nielsen and the author of this paper8 reported on the construct- ion of an apparatus for stroboscopic films. A 16 mm-reflex Paillard Camera was modified so that continuous speeds of up to 70 pictures per second could be obtained. The Philips stroboscope PR-1900 provided an adequate electronic flash of short duration and of great light-intensity. The optical system, with a solidly mounted laryngeal mirror which is contained in a small box, directs the light of the stroboscope to the vocal cords and transfers the picture of the vocal cords to the camera. By means of a system of mirrors and prisms, the .subject of the experiment can observe his own vocal cords and make the convenient adjustments for the picture. To be able to film the entire course of movements, it was necessary to provide the shifting of phase of the flash, from zero to 360°. At the time, this was done by mechanical means, with a subsequent 2 to 8-fold slowdown of the released light-impulses, depending on voice-pitch, up to 300 Hz. Since the flashes of the stroboscope often occurred irregularly and the mechanical change of phase was subject to a certain degree of inertia, a change to elec- tronic change of phase was eventually resorted to. Journal of the South African Speech and Hearing Association, Vol. 20 December 1973 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 2) Visualization of Change of Sound Characteristics of the Vocal Cords 43 Through a change of the optical apparatus made by the firm of Blattner and Picard, the volume of light reaching the vocal cord could be increased. The apparatus has been described in detail by Luchsinger and Pfister6 in connect- ion with slow-motion exposures with the use of an electro-glottograph by Cl. van Michel6, and further explanations therefore are not necessary. The apparatus for electronic shifting of phases was developed by the firm of Spring-Elektronik of Zurich. The frequency of the singing sound is registered by a laryngeal microphone. Special switches serve to determine the basic fre- quency. The stroboscope is activated by a switch which results in an increasing time-lag with respect to the basic frequency. By means of the phase-shifts produced in this manner, a vibration of the vocal cords per one second can be observed. Since the camera can take only 70 pictures per second, frequencies in excess of 70 Hz are slowed down 4 to 8' times. Even when no sound is produced, the apparatus transmits impulses to the stroboscope. Therefore, the vocal cords are continuously illuminated. As soon as the subject of the experiment emits a sound, the apparatus automatic- ally switches into operation, depending on the frequency of the sound. The spectrogram of the voices is determined through a "Terzbandpegelmeter". EXPERIMENTS: (a) Sustained sound of falsetto (e' Baritono), 280 Hz, 72 dB, Figure 1. TERZBANDPEGEL F A L S E T T S T I M M E Ι Λ Ι Λ Ο Ο Λ Ο Ο Ι Λ Ο Ο Ο Λ Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο NNM«ili)(OeOO CN (Ο Ο Hz Figure 1. Sustained v o w e l of falsetto. Tydskrif tan die Suid-Afrikaanse Vereniging vir Spraak- en Cehoorheelkunde, Vol. 20, Desember 1973 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 2) 44 R. Luchsinger (b) Sustained sound of an alto, pitch 217 Hz and c' (261 Hz); see illustra- tions of voice characteristics Fig. 2 and 3. ί i — 1 _ I - - 1 - - —· Γ ΐ Λ ί Λ Ο Ο Γ Ο ο ο ί Λ ο ο ο ί Λ ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο 7 Hz OjT-̂ LOtDCOOOJtDOUl̂ OOCnOOLOOOOLOOOOOOOOO — CO 1 rrrflflPlilDIDIDOfllDomrOOPlOOIDOO -I - - -