It is very important to evaluate nasality objectively in terms of both intersubject (severity of nasality) and intrasubject (validity of treatments, i.e., operation, speech therapy etc.). But there is no definite methodology for an objective evaluation of nasality. Our objectives were to evaluate the degree of nasality with a laser Doppler vibrometer (LDV) and a subminiature electret microphone (SEM) (using an accelerometer as a known standard), and to discuss the possibility of clinical use of these methodologies. LDV, used recently in the industrial field as well as in the medical/biological field, is a generator and detector of lasers to detect the velocity of the object’s vibration by the Doppler effect. The subjects were five healthy Japanese males (Tokyo dialect speakers). Used were sustained phonations (about 2 s) of /m/ and five Japanese vowels (/i/, /e/, /a/, /o/, /u/), and the Japanese words, shinkansen and shimbunshi (six repetitions for each phoneme). By both LDV and SEM systems, a significant difference was found beween /m/ and each vowel, which means that both systems can detect nasal/non-nasal differences and seem valid to evaluate the severity of pathological nasality (e.g., a cleft palate). Further study is planned for not only sustained phonation and word but also for sentence level, using patients (pathology) as well as healthy subjects (physiology). Furthermore, LDV seems to be a powerful tool for speech physiology where vibration of the body wall can be measured during speech and singing, without any contact receiver.
A three dimensional intensity probe using four microphones is proposed. Four microphones are placed at apexes of a regular tetrahedron. One is placed in the front and three others consisting a vertical regular triangle are in the back. The microphones are attached at the tips of parallel thin tubes. The microphone arrangement is not the conventional face to face type. The aim of this type of microphone arrangement is to design a sound intensity probe with a simple structure, which is essential for reducing the diffraction problem. Algorithms for three dimensional intensity components from cross spectra are given as well as for leakage components. Measurements of sensitivity characteristics in an anechoic room using two types of probes with 60mm and 20mm microphone separations show that sensitivity fluctuations are small enough (less than 1dB) for the practical application of the sound intensity method. The leakage errors of approximately 5%(-13dB) seem also acceptable. The measurement results indicate that sensitivity and leakage errors will become smaller if a more ideal plane wave field in an anechoic room is achieved.
The polysomnograph analysis is used to measure an apnea hypopnea index (AHI) of sleep apnea syndorome. However, this method needs high grade devices and technique. To compensate the conventional method, the calculation of AHI using only the snore noise of the patient is invented.
In order to investigate the effect of hall response on players, field measurements on the stage of a concert hall and laboratory experiment using digital simulation technique were performed. In the field experiment, the subject, a professional violinist, was asked to play and to make comments on her acoustical impression of five points on the stage. As a physical measurement, impulse responses were obtained at the same points by using omni-directional loudspeakers as a sound source and an omni-directional microphone and directional microphones as receivers. As a result, it has been found that not only the strength of the early reflections but also their direction influences the subject’s impression. In the laboratory experiment (anechoic chamber), the sound field was modeled and synthesized by using a 13 channel reproduction system; ambient reverberation judged as being natural was provided by simple digital reverberators and different strength and direction of early reflections were obtained by real-time convolvers. For a constant value of reverberation, several conditions with a different level and direction of the early reflections were created. For each condition, the violin player was asked to make similar judgments as in the field experiment. The results of two experiments were examined.
The upper frequency limit of a p-p type sound intensity probe is mostly determined by the sensitivity reduction of the probe.The sensitivity reduction is caused by obtaining the pressure from the average of the two pressure signals including the phase, and by obtaining the particle velocity from the finite difference of the two pressure signals.This is a systematic error suggesting a possibility of correction.In order to compensate or correct the sensitivity reduction, the direction of energy flow must be known.If a one-dimensional intensity probe is used, the probe direction must be varied to find the direction of the energy flow.If a three-dimensional intensity probe is used, the direction of the energy flow can be at least roughly estimated from a single measurement and then the sensitivity reduction can be corrected.This paper proposes a method of sensitivity reduction correction in the high frequency region for a three-dimensional(3-D)intensity probe.A theory of the method is described first and then numerical results that validate the theory will be given.This method works even for a probe with some amount of phase mismatch among microphones and for a sound field with reflections.
The estimation of the impulse response of a transfer system by the cross-spectral technique is very popular and most FFT analyzers are equipped with that function. However, the deformation of the impulse response in the process of estimation is not yet known. The deformation of the impulse response is caused by the use of the time window in the FFT as the DFT of a windowed waveform is the convolution of the spectrum of the waveform and the spectrum of the time window. This paper first describes the theoretical analysis on the deformation. Next, the result is verified by the computer simulation. The estimation errors are also investigated for various types of time windows. According to the investigation, the deformation is significant if the duration of the impulse response (the reverberation time) is longer than 1/4 of the window length. Finally, the use of the rectangular window in order to not deform the impulse response by shortening the length of window for the source signal is described.
A commonly used sound intensity probe is one-dimensional, that is, only the sound intensity in the direction of the probe axis is measured. This makes the sound intensity measurement very time consuming if two- or three-dimensional intensities are needed. Very rarely a two- or three-dimensional intensity probe is used for practical applications. A conventional three-dimensional intensity probe consists of six (three pair) microphones, making the probe itself very clumsy. Due to its non-negligible size, the sound field is disturbed and an accurate measurement becomes difficult. A three-dimensional intensity probe was developed that solves this problem. Four 1/4-in. microphones are located at each apex of a regular tetrahedron. Each of them are attached at the tops of four parallel tubes with a 4 mm diameter. When viewed from the front, the four microphones are located at the three apexes and the center of a triangle. The pressure at the center of the tetrahedron is given by the average of the four pressure outputs. The intensities from the center to the four apexes are obtained by use of the average pressure and individual pressure output. These four components are distributed to three (x,y,z) components. Results of numerical calculations that show the accuracy of the algorithm will be given.
Objective measurement of nasality is very important in terms of clinical evaluation. But there is no definite methodology of objective evaluation of nasality. We already reported that new methodologies of the Laser Doppler Vibrometer (LDV) and Sub-miniature Electret Microphone (SEM), both of which could detect the nasal/non-nasal difference of sustained phonemes, seemed valid to evaluate nasality [Kumada et al., 140th ASA Meeting (2000); Kumada et al., 141st ASA Meeting (2001)]. LDV, used recently in an industrial field as well as medical/biological field, is the generator and the detector of the laser to detect the velocity of the object’s vibration by Doppler’s effect. LDV seemed a powerful tool for speech physiology by which vibration of a body wall can be measured during speech and singing, without any contact receiver. The objectives were to evaluate the degree of nasality of phonemes in words by LDV and SEM, and to discuss the possibility of the clinical use of these methodologies. The subjects were 5 healthy Japanese males (Tokyo dialect speakers). The materials were Japanese words /shinkansen/ and /shimbunshi/. Both LDV and SEM systems could detect a nasal/non-nasal difference in spoken words, and seemed valid to evaluate nasality in speech. Further study is planned using patients (e.g., cleft-palate) as well as healthy subjects.
