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In stereo or multi-channel system identification, the most critical problems regarding online identification, e.g., for acoustic echo control, are the correlation properties of the excitation signals of the different audio channels. In this paper the impact of both the auto- and cross-correlation properties is considered and investigated. A new system combining appropriate decorrelation techniques with a Kalman filter driven adaptation algorithm in the frequency domain is presented. For the auto-decorrelation a new structure is proposed where the signals in the adaptation paths are decorrelated via linear prediction without affecting the acoustic signals. A small non-linearity is added into each channel for the reduction of the cross-correlation between channels. The performance evaluation clearly shows the influence of the different countermeasures and the effectiveness of the combined approach.

Sonotubometry with perfect sequences (PSEQ) was able to detect eustachian tube (ET) openings in both normal and pathological ears. Impaired ears showed ET openings in almost all cases; however, these proved to be not only less frequent, but also with lower amplitude and shorter duration.To investigate the function of impaired ET under physiological conditions, using a novel kind of sound stimulus for sonotubometry – the PSEQ.Twenty otologically healthy subjects (40 normal ears) and 32 patients with ear diseases (40 pathological ears) were examined sonotubometrically using noise signals with an ideally flat spectrum (PSEQ). Dry swallowing, water swallowing, and Toynbee maneuver were used to induce ET openings. Analysis was performed regarding the frequency of occurrence, duration, amplitude, and form of the ET openings.PSEQ allowed the detection of an ET opening in all 40 normal ears (91% of the performed maneuvers) and in 87.5% of the ears with impaired ET function (but only 47% of the maneuvers). The average amplitude of the openings in healthy ears was 16.86 dB, the average duration was 363 ms. In diseased ears these values were significantly lower: 9.73 dB, p0.001 and 280 ms, p0.05.

INTRODUCTION: Sonotubometry allows an assessment of the Eustachian tube (ET) function under physiological conditions. The application of conventional sinus signals is not reliable enough for routine clinical use. The aim of this study was to investigate ET activity with so-called perfect sequences (PSEQ). PATIENTS AND METHODS: PSEQs generated by a custom-made device were applied in 25 healthy subjects. ET opening was induced by Toynbee manoeuvre, yawning, dry and water swallowing. All sonotubograms were qualitatively analysed according to their shape, and quantitatively according to increase of sound intensity, frequency of opening and opening duration. The sonotubometry results were combined with the patients' perception of tone variation. RESULTS: A number of 400 measurements were performed. In 92.75 % measurements the patients reported ET openings. These were confirmed by 81.5 % valid sonotubograms. The swallowing manoeuvres dry/water swallowing and Toynbee yielded with 94 %/90 % and 93 % valid measurements favourable results. Yawning was associated with 49 % valid measurements. Sound level increase was also significantly different in these manoeuvres when compared to yawning (p > 0.0001). Nasal decongestion had no influence on the results (p < 0.05). CONCLUSIONS: PSEQs allow an evaluation of ET function. The chosen manoeuvres trigger in healthy subjects objective ET openings with a high reliability. The application of PSEQs can detect ET activity with a high sensitivity and good specificity. By further technical refinements specificity may also be enhanced in future studies.

Sonotubometry allows an assessment of the Eustachian tube (ET) function under physiological conditions. The reliability of the application of an 8 kHz pure-tone signal was investigated. In 40 normal subjects (80 ears) sonotubometric studies were performed with a custom-made device. ET opening was provoked by swallowing, yawning and Valsalva manoeuvre. An opening was detected in all patients but not in all manoeuvres. Four characteristic sonotubogram types were found. Most common was the spike-type (60%). The double-peak and the plateau-shaped curves occured in 17% each. The finding of an descendant curve was rare (5%). Of 623 measurements, only in 55% manouvres a positive sonotubometric result was found despite the fact that the patients reported an opening in all cases. The median opening time in dry swallowing, liquid swallowing, yawning and Valsalva was found to be 486, 355, 1,263 and 1,250 ms. A median sound increase of 16.0, 13.8, 15.0 and 15.0 dB was recorded for these manoeuvres. There was a statistic significant difference (P < 0.02) between the increase in sound intensity of liquid and dry swallowing. There was also a statistic significant difference found for the duration of the forced manoeuvres Valsalva and yawning as compared to dry and liquid swallowing (P < 0.0001). The use of an 8 kHz pure-tone signal showed a limited sensitivity for the detection of ET openings. This is mainly due to noise pollution, but also because of an altered positioning and/or dislocation of the probes and compression of the nostrils. The application of an 8 kHz signal is therefore not reliable enough for the use in practice. Further technical refinements and the use of alternative signals are necessary for a broader clinical application.

The aim of this study was the introduction of a specific class of signals, the so-called perfect sequences (PSEQ), in a novel approach for sonotubometry of the Eustachian tube (ET). Sonotubometry using PSEQ stimuli was performed on 20 healthy subjects in order to gauge its potential for clinical applications. In a series of 320 measurements ET opening was probed, which was induced by dry and water swallowing, Toynbee maneuver, and yawning. All sonotubograms were analyzed with respect to their shape, increase of sound intensity, and opening duration. In 298/320 measurements (93%) the subjects reported subjective ET openings. The evaluation of the recorded sonotubograms showed good detection of ET opening for the inducing maneuvers of swallowing (dry and water swallowing) and the Toynbee maneuver, with 90, 86, and 80% valid sonotubograms, respectively. Yawning led to only 40% valid sonotubograms. In total, 237/320 (~74%) sonotubograms were classified as valid. The evaluation of the sound level increase during ET openings showed that it was significantly higher in measurements with dry and water swallowing, as well as Toynbee maneuvers (mean 17.1, 19.0 and 17.2 dB, respectively), than with yawning (mean 10.17 dB; P0.0001). Nasal decongestion was found to have little influence on the results (P0.05). Sonotubometry using PSEQ stimuli is a novel sonotubometry methodology that provides valuable information regarding the auditory tube patency. By further technical refinements of the method, a diagnostic tool with high sensitivity and specificity could be developed.

Sonotubometry allows for the detection of the dynamic Eustachian tube function under physiological conditions, whether the eardrum is intact or perforated. Quality and reliability of state-of-the-art sonotubometry have been substantially improved by a new real-time system for otological diagnostics [1]–[4]. Moreover, this diagnostic system provides a time-variant virtual model of the Eustachian tube as a new feature, which opens up entirely new possibilities in monitoring Eustachian tube openings. In this work we investigate the correlation of the virtual model to the human anatomy.

In contrast to most of the clinical examinations, the sonotubometric assessment of the Eustachian tube function allows the registration of the tube opening at the perforated, as well as at the intact eardrum in physiological conditions. In this paper, a new procedure is introduced which performs a measurement of the transmission path nose/ear. With digital signal processing algorithms the generation of a new feature relevant for medical diagnostics is made accessible. The method is based on techniques known from speech processing: the acoustic tube model, the normalized least-mean-square (NLMS) algorithm with so-called perfect sequence (PSEQ) (Luke, 1992 and Luke and Schotten, 1995) excitation and the Levinson-Durbin algorithm. Within the framework of an interdisciplinary cooperation we developed a new real-time acoustic measurement prototype which opens up entirely new possibilities in otological diagnostics.