Degree Of Amplitude Modulation Research Articles

Machine learning for analysis of wind farm noise

Two challenges associated with analyzing acoustical data from wind farms are: 1) separating turbine sounds from environmental sounds and 2) classifying acoustical samples into different types of wind turbine noise based on acoustic characteristics. Machine-learning methods for classifying general environmental sounds have been developed using large human classified databases (e.g., YAMNet), but only a few studies have targeted classification of wind farm noise (WFN) specifically. Techniques for classifying wind farm noise have focused on identification of amplitude modulation (AM) using both traditional methods such as low frequency peak prominence (IOA method) and machine learning methods using both targeted AM acoustics features and more general deep acoustic features. To address these two challenges, we are developing a multi-echelon machine learning framework to identify and classify noise from wind farms using publicly available windfarm data and open-source software. The first echelon provides an automated method for identifying WFN samples that are free of environmental sounds. The second echelon uses machine learning to classify these wind farm noises according to the degree of AM, prominent tones, and other factors that might contribute to the human response and are incorporated in the metrics used or potentially used to assess compliance with regulations.

Acoustic correlates of perceived anger in the Ferguson clear speech database

Previous work has shown that clear speech is perceived as sounding angry significantly more often than conversational speech (Morgan and Ferguson, 2017; Young, 2021). The current study examined possible acoustic correlates of perceived anger in clear speech. A principal component analysis was completed to guide selection of acoustic variables for analysis. The remaining six acoustic measures, fundamental frequency median, fundamental frequency variability, relative mid-frequency energy from 1000 to 3150 Hz, speaking rate, and degree of amplitude modulation at 2 Hz and 16Hz envelopes, were analyzed using mixed effects regression. Results indicated that after controlling for speaking style, fundamental frequency approached significance but did not significantly predict perceived anger. However, speaking rate significantly predicted perceived anger after controlling for speaking style, with slower rates leading to an increase in perceived anger. Further, there was a significant interaction between speaking rate and speaking style, where slower speech was only perceived as angry in the clear speech style. Finally, a decrease in the degree of low-frequency amplitude modulation (i.e., equal emphasis on both content and function words) led to an increase in perceived anger after controlling for speaking style. The results have implications for counseling individuals in the use of clear speech.

Novel underwater soundscape: acoustic repertoire of plainfin midshipman fish.

Toadfishes are among the best-known groups of sound-producing (vocal) fishes and include species commonly known as toadfish and midshipman. Although midshipman have been the subject of extensive investigation of the neural mechanisms of vocalization, this is the first comprehensive, quantitative analysis of the spectro-temporal characters of their acoustic signals and one of the few for fishes in general. Field recordings of territorial, nest-guarding male midshipman during the breeding season identified a diverse vocal repertoire composed of three basic sound types that varied widely in duration, harmonic structure and degree of amplitude modulation (AM): 'hum', 'grunt' and 'growl'. Hum duration varied nearly 1000-fold, lasting for minutes at a time, with stable harmonic stacks and little envelope modulation throughout the sound. By contrast, grunts were brief, ~30-140 ms, broadband signals produced both in isolation and repetitively as a train of up to 200 at intervals of ~0.5-1.0 s. Growls were also produced alone or repetitively, but at variable intervals of the order of seconds with durations between those of grunts and hums, ranging 60-fold from ~200 ms to 12 s. Growls exhibited prominent harmonics with sudden shifts in pulse repetition rate and highly variable AM patterns, unlike the nearly constant AM of grunt trains and flat envelope of hums. Behavioral and neurophysiological studies support the hypothesis that each sound type's unique acoustic signature contributes to signal recognition mechanisms. Nocturnal production of these sounds against a background chorus dominated constantly for hours by a single sound type, the multi-harmonic hum, reveals a novel underwater soundscape for fish.

Time-variant investigation of quadratic phase couplings caused by amplitude modulation in electroencephalic burst-suppression patterns.

Several studies suggest that parameters derived from bispectral analysis of the EEG can be used to characterize specific cortical activation states represented by non linear interaction between brain electrical oscillations. For example, it was shown that so-called bispectral indices can be used to assess the depth of sedation. The methods applied so far are based on interval-related procedures of bispectral analysis. Consequently, the use of the resulting parameters for on-line monitoring or investigations of signal properties during transition periods, e.g., when entering burst-suppression periods, is restricted. The objective of this paper is to provide the methodological basis for a time-continuous (on-line) investigation of quadratic phase coupling induced by amplitude modulation. To accomplish this aim an algorithm is presented which enables the analysis of the temporal development in the degree of amplitude modulation (DAM), e.g., during the transition to burst-suppression periods in patients with severe neurological diseases. It was found that these periods are associated with increasing DAM compared with the baseline conditions.

Horizontal oscillations of a cylinder beneath a free surface: vortex formation and loading

The patterns of vortex formation from a cylinder oscillating in a horizontal plane, located at various depths of submergence beneath a free surface, are characterized using high-image-density particle image velocimetry (PIV). Instantaneous representations of the velocity field, streamline topology and vorticity patterns are referenced to the instantaneous velocity of the cylinder. In turn, these features are related to the magnitude and phase of the instantaneous transverse force, which can exhibit highly nonlinear, spike-like fluctuations. When a finite gap is maintained between the free surface and the cylinder, the patterns of vorticity concentrations are altered in such a fashion that both the peak magnitude and the degree of amplitude modulation of the negative transverse force spikes are attenuated, but shifted little in phase, relative to the case of the fully submerged cylinder. On the other hand, when the cylinder is sufficiently close to the free surface such that the gap region is eliminated, the patterns of vorticity concentrations are fundamentally different and the negative transverse force spikes are remarkably more pronounced and consistent than for deeper submergence.

Lunar terms in the geomagnetic spectrum at Hermanus

An analysis of Hermanus H component data (1933–1972) by the maximum entropy method (MEM) has confirmed most of the minor lunar terms found by Gupta and Chapman (1969). After re-examining earlier spectrum analyses we conclude that, although many are probably generated by lunar tides, these lines are significantly affected in both amplitude and frequency by the amplitude modulation mechanism proposed by Black (1970). The degree of amplitude modulation seems to be dependent on latitude.

Third-order distortion and cross modulation in a grounded emitter transistor amplifier

The nonlinear modulation characteristic of a transistor is approached by the first terms of a Taylor-series formula and the output voltage is calculated for a suitably-chosen ac-input voltage. For higher frequencies and different working points, the influence of the diffusion capacity and the emitter admittance are illustrated by experimental results. It is shown that--as in electronic tubes-the third-order distortions (harmonic distortion, distortion of modulation, alteration of the degree of amplitude modulation, degree of cross modulation) are closely connected, but unlikethe situation in electronic tubes, the distortions disappear at a special working point. The influence of the base resistance and the internal resistance of the signal source are discussed in relation to the appearance of this zero point and the frequency dependence. In an RF amplifier a transistor is modulated, for example, only by a part of the resonant circuit voltage because of the low input resistance in a grounded emitter circuit. Although this voltage transformation is accounted for, the transistor is inferior to the electronic tube with respect to cross modulation. To reduce the cross modulation in a transistor RF stage, two possibilities are described for correcting the distortions with a fixed or controlled working point using a predistortion or a push-pull modulation. In this case the different influences of a resistance in the base lead, or of a resistance blocked for HF but not for LF in the emitter lead, are discussed.

Some Notes on the Practical Measurement of the Degree of Amplitude Modulation

Some questions met with when measuring the degree of amplitude modulation (AM) are discussed. The degree of modulation is defined as the ratio of certain amplitude quantities, a clear distinction being made between what are defined as "up" and "down" values. The difference between the unmodulated carrier amplitude and the "mean amplitude during modulation" is stressed. It is shown that for an arbitrary amplitude modulation the effective value of the modulated current is dependent only on the amplitude of the harmonics, whereas the degree of modulation depends largely on the phase as well. From this it follows that any "effective" method of modulation degree measurement must be rejected as being not in accordance with the definition of the quantity to be measured. The effects of nonlinearity in a class B amplifier and of overmodulation in a class C amplifier are discussed, noting the rise of "mean high-frequency amplitude", the formation of harmonics, and the resulting degrees of modulation. After a short critical review of some existing methods, general requirements are proposed for a measuring device, and a description of the principle and performance of a direct reading modulation meter is given. A "ripple meter" constructed to measure exceedingly small degrees of modulation, and developed along lines similar to the modulation meter, is also briefly described with attention to its principle and its capabilities.