ON THE EVALUATION OF THE CREST FACTOR OF BIONIC SIGNALS USED IN HYDROACOUSTIC COMMUNICATION SYSTEMS

In this article, the authors evaluated the crest factor of bionic signals used in hydroacoustic communication systems, using the example of the study of signals based on the use of recordings of sounds of various whale species. The calculations and literature analysis show that the sound recordings of the following whale species have an acceptable crest factor value (p ≤ 4): Blue whale, Alaska humpback whale, Atlantic blue whale and Northeast Pacific blue whale. Recordings of the sounds of these types of whales should be used in the appropriate hydroacoustic communication systems. In contrast, recordings of the sounds of such whale species as Atlantic fin whale, Atlantic minke whale, South Pacific blue whale, and Western Pacific blue whale have an increased crest factor value (p > 4) and without adaptation, it is impractical to use them in appropriate hydroacousticcommunication systems. It is established that bionic signals used in hydroacoustic communication systems, based on the example of the study of signals based on the use of recordings of sounds of various species of whales, can have both an acceptable value of the crest factor or an increased one. It is advisable to pay attention of the de-velopers and manufacturers of the corresponding hydroacoustic communication systems to this conclusion during designing, testing and implementation of such systems.

Experimental investigation of helical gear tooth crack location and depth detection using moving average method on transmission error

Gear systems are the most useful and essential power transmission systems in the high-speed industry due to their accuracy. It is necessary to make sure that these systems work without defects such as tooth cracks. Therefore, detecting the location and depth of cracks in gear systems is very important. In this research, a new approach is proposed to detect the crack location, and accordingly, some statistical indicators are used to estimate the crack depth in the helical gear tooth. To this end, after explaining the helical gear mesh stiffness and tooth-root crack modeling, the helical gear pair dynamic is modeled. Then, the vibration data of a helical gear system is obtained by an experimental test rig, and the moving average method is undertaken to precisely detect the crack location. The crack depth ratio is estimated using the crest factor, impulse factor, clearance factor, and [Formula: see text] and [Formula: see text] which are applied to the simulation results and the experimental signal. According to these results, the crest factor, impulse factor, and clearance factor calculated the crack depth ratio with a good agreement, and the indicators [Formula: see text] and [Formula: see text] estimated it with a more significant error. Also, the average of estimated values is calculated, indicating a better result than each indicator alone.

Waveform Amplitude and Temporal Symmetric/Asymmetric Characteristics of Phoneme and Syllable Segments in the W-1 Spondaic Words Recorded by Four Speakers

Background The amplitude and temporal asymmetry of the speech waveform are mostly associated with voiced speech utterances and are obvious in recent graphic depictions in the literature. The asymmetries are attributed to the presence and interactions of the major formants characteristic of voicing with possible contributions from the unidirectional air flow that accompanies speaking. Purpose This study investigated the amplitude symmetry/asymmetry characteristics (polarity) of speech waveforms that to our knowledge have not been quantified. Study Sample Thirty-six spondaic words spoken by two male speakers and two female speakers were selected because they were multisyllabic words providing a reasonable sampling of speech sounds and four recordings were available that were not related to the topic under study. Research Design Collectively, the words were segmented into phonemes (vowels [130], diphthongs [77], voiced consonants [258], voiceless consonants [219]), syllables (82), and blends (6). For each segment the following were analyzed separately for the positive and negative datum points: peak amplitude, the percent of the total segment datum points, the root-mean-square (rms) amplitude, and the crest factor. Data Collection and Analyses The digitized words (44,100 samples/s; 16-bit) were parsed into 144 files (36 words × 4 speakers), edited, transcribed to numeric values (±1), and stored in a spread sheet in which all analyses were performed with in-house routines. Overall approximately 85% of each waveform was analyzed, which excluded portions of silent intervals, transitions, and diminished waveform endings. Results The vowel, diphthong, and syllable segments had durations (180–220 ms) that were about twice as long as the consonant durations (∼90 ms) and peak and rms amplitudes that were 6 to 12 dB higher than the consonant peak and rms amplitudes. Vowel, diphthong, and syllable segments had 10% more positive datum points (55%) than negative points (45%), which suggested temporal asymmetries within the segments. With voiced consonants, the distribution of positive and negative datum points dropped to 52 and 48% and essentially was equal with the voiceless consonants (50.3 and 49.6%). The mean rms amplitudes of the negative datum points were higher than the rms amplitudes for the positive points by 2 dB (vowels, diphthongs, and syllables), 1 dB (voiced consonants), and 0.1 dB (voiceless consonants). The 144 waveforms and segmentations are illustrated in the Supplementary Material along with the tabularized positive and negative segment characteristics. Conclusions The temporal and amplitude waveform asymmetries were by far most notable in segments that had a voicing component, which included the voiced consonants. These asymmetries were characterized by larger envelopes and more energy in the negative side of the waveform segment than in the positive side. Interestingly, these segments had more positive datum points than negative points, which indicated temporal asymmetry. All aspects of the voiceless consonants were equally divided between the positive and negative domains. There were female/male differences but with these limited samples such differences should not be generalized beyond the speakers in this study. The influence of the temporal and amplitude asymmetries on monaural word-recognition performance is thought to be negligible.

Research on the Influence of Time-Varying Excitation on Vibration Characteristics of the Spiral Bevel Geared Transmission System with Broken Teeth

Due to heavy and alternating loads of working conditions, spiral bevel gears are prone to broken tooth failures. To solve the problem of vibration characteristic of spiral bevel geared transmission with broken tooth failures that is unknown, this study, considering time-varying mesh stiffness and friction excitation, proposed a torsional vibration dynamic model of spiral bevel geared transmission, which has more simple transmission path and the smaller signal attenuation. First, the time-varying excitations of various broken tooth failure are calculated and introduced into the torsional vibration dynamic model. The vibration response of spiral bevel geared transmission with various broken tooth failures is analysed in the time-frequency domain. Then, the sensitivity of the time-domain statistical index and the frequency domain components to different broken tooth failures are studied. Finally, the correctness of the simulation is verified by experiment. The results show that the crest factor is sensitive to minor tooth failure (10–30%), while kurtosis is sensitive to severe failure (30–60%). With the increase of degrees of broken tooth failure, the energy of the low-frequency band increases obviously.

COMBINATION OF SYNTHETIC HIGH-PERFORMANCE RF AMPLIFICATION TECHNIQUES

To amplify modern high crest factor telecommunication radio signals with high efficiency, switching operation modes of transistors and synthetic amplification methods are used. The most common of these are the Kahn method (EER – envelope elimination and restoration) and the outphasing method. However, application of these methods has a number of technological (in terms of element base capabilities) limitations on the bandwidth and dynamic range of amplified signal. To expand high-efficiency RF power amplifiers field of application, the possibilities of combination several different synthetic amplification techniques are being considered. Expressions are obtained for the theoretically achievable efficiency when combining the outphasing method with a bridge power combiner and pulse-step modulation of supply voltage. The dependence of average efficiency on the number of supply voltage levels is determined. RF amplified signal bandwidth and its dynamic range determine the minimum required pulse width of the PWM modulator for the EER amplifier. Variants of these characteristics dependence on the number of supply voltage levels are discussed with combined use of PWM and pulse-step modulation of the supply voltage. Directions for further research are formulated.