Audible Spectrum Research Articles

Laser-sound reproduction by pulse amplitude modulation audio streams

Recently, the possibility to reproduce complex continuous acoustic signals via pulsed laser-plasma sound sources was demonstrated. This was achieved by optoacoustic transduction of dense laser pulse trains, modulated via single- or multi-bit Sigma–Delta, in the air or on solid targets. In this work, we extend the laser-sound concept to amplitude modulation techniques. Particularly, we demonstrate the possibility of transcoding audio streams directly into acoustic pulse streams by analog pulsed amplitude modulation. For this purpose, an electro-optic modulator is used to achieve pulse-to-pulse amplitude modulation of the laser radiation, similarly to the multi-level Sigma–Delta method. The modulator is directly driven by the analog input stream through an audio interface. The performance of the system is evaluated at a proof-of-principle level for the reproduction of test audio signals such as single tones, double tones and sine sweeps, within a limited frequency range of the audible spectrum. The results are supported by computational simulations of the reproduced acoustic signals using a linear convolution model that takes as input the audio signal and the laser-generated acoustic pulse profile. The study shows that amplitude modulation allows for significant relaxation of the laser repetition rate requirements compared to the Sigma–Delta-based implementation, albeit at the potential cost of increased distortion of the reproduced sound signal. The nature of the distortions is analyzed and a preliminary experimental and computational investigation for their suppression is presented.

Micro-Electro-Mechanical Systems Microphones: A Brief Review Emphasizing Recent Advances in Audible Spectrum Applications.

The MEMS microphone is a representative device among the MEMS family, which has attracted substantial research interest, and those tailored for human voice have earned distinct success in commercialization. Although sustained development persists, challenges such as residual stress, environmental noise, and structural innovation are posed. To collect and summarize the recent advances in this subject, this paper presents a concise review concerning the transduction mechanism, diverse mechanical structure topologies, and effective methods of noise reduction for high-performance MEMS microphones with a dynamic range akin to the audible spectrum, aiming to provide a comprehensive and adequate analysis of this scope.

Predicting low-frequency noise using its own bandwidth

Soon after A-weighing began, an article of 1938 mentioned that as a metric it didn't represent true low-frequency loudness. In 1952, a method for “guessing” low-frequency energy was proposed and later, Beranek in 1954 recommended that if the dBC level is greater than dBA, an analysis should be performed below 150 Hz. In 1969, Botsford introduced a criterion for predicting the low-frequency level by [(dBC-dBA) > 10 dB], using the entire audible spectrum, so that this condition applies only if the spectrum is “balanced.” The German Standard DIN 45680 of 1997 proposed a similar criterion, limiting this calculation to one-third octave band frequencies from 8 to 100 Hz. Since 1999, the WHO recommends using the Botsford criterion, but warns that it is not valid if the spectrum contains tones or if it is unbalanced. This paper will demonstrate that the correct way to analyze the low-frequency sound levels is to use its own bandwidth, that to have a traceable noise descriptor the ISO low-frequency definition must be used, it means to use the one-third octave band frequencies between 16 and 200 Hz, to calculate the difference (dBC-dBA) in this range to predict its actual low-frequency sound level.

Methodology for the Acoustic Analysis of Acoustic Guitar Top Plates Designs by Additive Manufacturing

Nowadays, tools such as Additive Manufacturing (AM) contribute directly to an increase in the value of Industrial Design through the development of new products focused on customization. Specifically, the acoustic guitar is a good example of this, because it is a complex product to study due to the great variety of possible designs depending on the materials and the way they are obtained, which has repercussions on the final sound of the instrument. Due to the above, this paper develops a methodology for the study of the acoustic response depending on the design of an acoustic guitar using AM with Polylactic Acid (PLA) material. The methodology is divided into two types of tests: an acoustic test to capture the frequencies emitted by transmitting a sweep of frequencies across the audible spectrum to the soundboard, and another to visualize the vibrational patterns at five specific harmonic frequencies of the guitar by analyzing the movement of the soundboard and the influence of the bracing. This second test includes the PLA designed top with a reinforcement structure in its soundboard and a case in order to compare this design with a wooden guitar of the same size whose top has no reinforcement at all. From the tests carried out, it can be seen that the acoustics recorded by a top made of PLA can provide a good acoustic response compared to a wooden guitar, giving the possibility to create customized guitars according to the musician's tastes.

Sound trapping and waveguiding in locally resonant viscoelastic phononic crystals

We describe the trapping and absorption of audible sound in centimeter-scale claddings of two-dimensional, locally resonant phononic crystals. In a square lattice of local resonators consisting of steel cores and cellulose shells, embedded in a viscous foam, dual acoustic-range band gaps extending from about 200 to 2850 text { Hz} are achieved. The spectral range consists of a low-frequency, local resonance gap, separated from a higher frequency Bragg resonance gap, by narrow bands of slow-sound modes. We demonstrate that thin claddings of such phononic crystal, of only three unit cells in thickness, can effectively prevent sound transmission, by a combination of reflection and absorption, over much of the audible spectrum. Moreover, frequency-selective sound transmission can be enabled by engineering waveguide channels that transmit sound through the local resonance gap, the Bragg gap, or both. This offers a path to sound-sculpting claddings that can surround a noise-generating source. The viscoelastic foam in our cladding is treated using a fractional Voigt model, capable of describing experimentally observed responses.

Micro-computed tomography shows silent bubbles in squeaky mozzarella

Abstract The sound of food is of influence on how its flavour is perceived. Although rarely studied in psychoacoustics, cheese may have a resonating internal structure in the audible spectrum. It has been speculated that this structure or small bubbles that are formed as a result of fermentation are responsible for creating audible acoustic responses. The purpose of this study was to design a mechanical methodology to create audible acoustics from cheese samples and to quantify bubble presence in a sample. One hundred and two samples of mozzarella cheese with 1.5±0.4-cm3 volumes were subjected to shear from a wetted steel blade, whilst orthogonal force, blade acceleration, and acoustic response were continuously monitored. In addition, micro-computed tomography was performed. It was found that under our measurement conditions, mozzarella was forced to squeak in 10% of the experiments, at fundamental squeak frequencies up to 2 kHz, which indicates that the acoustics come from a resonating porous structure, rather than from resonating bubbles. The micro-computed tomography showed a bubble density of 51 cm−3. This low bubble density may account for the absence of a high-frequency component in the spectra analysed. Our results confirm the presence of small bubbles in squeaky mozzarella, but these generate frequencies much higher than those recorded.

Secure cryptographic communication using ultrasound audio for frictionless payment transactions and secure conversations over a short-range human audible/inaudible spectrum

Background: The aim of the study was to address these challenges by leveraging ultrasound audio as a means for secure cryptographic communication. By utilizing the human audible and inaudible audio spectrum, this approach eliminates the reliance on specialized hardware or traditional network technologies, such as bluetooth, wi-fi, NFC, or RF-based alternatives. Methods: Various mobile phones, tablets, and POS hardware devices with basic microphones and speakers were employed to test the communication channel's performance. The sensitivity of the devices in different environments, such as retail stores or crowded venues like stadiums, was taken into account. Results: The results demonstrated the viability of the proposed secure cryptographic communication using ultrasound audio. Transactions, including payment processing, were successfully conducted without the need for specialized hardware or network connectivity. Conclusions: The proposed solution offers a reliable and cost-effective method for proximity detection, verification, and frictionless transactions. By leveraging the human audible and inaudible audio spectrum, this technology eliminates the need for specialized hardware or traditional network connectivity.

H-Matrix BEM application and validation for space habitat

Acoustic requirements for space habitats are stringent and involve a combination of noise sources minimization and public address and general alarm (PAGA) system validation. Simulation solutions are essential for demonstrating compliance requirement as early as possible and continuously throughout the development cycle of the spacecraft. Space habitats' sound field can be computationally challenging to predict in a deterministic manner for most of the audible spectrum as the volume can be important. For this application, an initial PAGA system design assessment was performed using Ray-Tracing, a geometric statistical method, which must be validated using a deterministic method. For validation purpose, the Boundary Element Method (BEM) was chosen for this application. Given the size of the structure and the desired frequency range, the BEM model was very large, containing over 250,000 wetted nodes, and a standard BEM solver required approximately 200GB of RAM. To limit computing hardware constraints, a newly implemented commercially available H-Matrix BEM solver was used. Pressure maps of a PAGA system simulation on a generic space habitat resulting from the Ray-Tracing and H-Matrix BEM solvers are compared to a standard BEM simulation. Results are compared both in terms of accuracy and computational performance, showing the advantages of using multiple simulation methods at various stages of the design.

Acoustic animal identification using unsupervised learning

Abstract Passive acoustic monitoring is usually presented as a complementary approach to monitoring wildlife communities and assessing ecosystem conditions. Automatic species detection methods support biodiversity monitoring and analysis by providing information on the presence–absence of species, which allows understanding the ecosystem structure. Therefore, different alternatives have been proposed to identify species. However, the algorithms are parameterized to identify specific species. Analysing multiple species would help to monitor and quantify biodiversity, as it includes the different taxonomic groups present in the soundscape. We present an unsupervised methodology for multi‐species call recognition from ecological soundscapes. The proposal is based on a clustering algorithm, specifically the learning algorithm for multivariate data analysis (LAMDA) 3pi algorithm, which automatically suggests the number of clusters associated with the sonotypes. Emphasis was made on improving the segmentation of the audio to analyse the whole soundscape without parameterizing the algorithm according to each taxonomic group. To estimate the performance of our proposal, we used four datasets from different locations, years and habitats. These datasets contain sounds from the four major taxonomic groups that dominate terrestrial soundscapes (birds, amphibians, mammals and insects) in audible and ultrasonic spectra. The methodology presents performances between 75% and 96% in presence–absence species recognition. Using the clusters proposed by our methodology, the whole soundscape biodiversity was measured and compared with the estimate of four acoustic indices (ACI, NP, SO and BI). Our approach performs biodiversity assessments similar to acoustic indices with the advantage of providing information about acoustic communities without the need for prior knowledge of the species present in the audio recordings.

Metahouse: Noise‐Insulating Chamber Based on Periodic Structures

AbstractNoise pollution remains a challenging problem requiring the development of novel systems for noise insulation. Extensive work in the field of acoustic metamaterials has led to various ventilated structures which, however, are usually demonstrated for rather narrow regions of the audible spectrum. In this work, the idea of metamaterial‐based systems is further extended, developing the concept of a metahouse chamber representing a ventilated structure for multiple band noise insulation. Broad stop‐bands originate from strong coupling between pairs of Helmholtz resonators constituting the structure. The averaged transmission −18.6 dB are demonstrated numerically and experimentally within the spectral range from 1500 to 16 500 Hz. The sparseness of the structure together with the possibility to use optically transparent materials suggest that the chamber may be also characterized by partial optical transparency depending on the mutual position of structural elements. The obtained results are promising for development of novel noise‐insulating structures advancing urban science.

Potential Effects on Human Safety and Health from Infrasound and Audible Frequencies Generated by Vibrations of Diesel Engines Using Biofuel Blends at the Workplaces of Sustainable Engineering Systems

Employees involved in various occupational environments that include vibration machines and any kind of vehicles are adversely subjected to multiple source noise. Thus, the corresponding noise frequencies (and mainly the infrasound ones) present high interest, especially from the viewpoint of sustainability, due to the potential effects on human safety and health (H_S&H) in sustainable engineering projects. Moreover, the occupational safety and health (OSH) visualization (a fact of unveiling the social dimension of sustainability) of occupational workplaces (by evaluating the infrasound and audible noise frequencies generated by diesel engines) could help a safety officer to lessen crucial risk factors in the OSH field and also to protect, more efficiently, the employees by taking the most essential safety measures. This study (i) suggests a technique to determine the infrasound and audible sound frequencies produced due to vibrations of diesel engines, by using biofuels (i.e., sustainable utilization of resources), in order to evaluate potential effects on human safety and health at the workplaces of sustainable engineering projects, and (ii) it ultimately aims to contribute to the improvement of the three “sustainability pillars” (economy, social, and environmental). Therefore, it provides experimental results of the frequency of the noise (regarding the infrasound and audible spectrum) that a diesel motor generates by vibration, in the frame of using different engine rpms (850, 1150, and 2000) and a variety of biofuel mixtures (B20-D80, B40-D60, B60-D40, and B80-D20). The article shows that the fuel blend meaningfully affects the generated noise, and more particularly, the usage of biofuel blends coming from mixing diesel oil with biodiesel (a fact of the emerging environmental dimension of sustainability) can produce various noise frequencies, which are determined in the infrasound and audible spectra (~10–23 Hz). The suggested technique, by ameliorating the OSH situation, doubtless will help enterprises to achieve the finest allocation of limited financial resources (a fact corresponding to the economic dimension of sustainability), allowing financial managers to have more available budget for implementing other risk-reduction projects.

THE SOUND DIMENSION IN THE UPPER BASIN OF THE MIÑO RIVER (GALICIA, NW IBERIAN PENINSULA)

The sound spectrum of water configures representative marks of various environments, which define a sound heritage with scientific, cultural, emotional, sensorial and educational value. From this perspective, river environments comprise a wide spectrum of sonic resonances. This study, contextualized within the field of geo-sonority research, considers the recording and analysis of water through several samples from the upper basin of the Miño River. The objectives are to advocate for the role of sonority as part of the intangible heritage, to explore its character in the fluvial environment of inland Galicia, and to contribute to the preservation of the sonic marks of water as sounds inherent to the identity of an area. The methodology applied consists of phases of field recording, the creation of databases and of phonic analysis. Water in its sound form, from the drop rhythmically repeating to the roar of a waterfall, fills an audible sound spectrum that characterizes soundscapes. By registering, documenting, and analyzing the sounds of the water, we advance in the knowledge of the diversity of the sound environments in the river basin of the Miño River.

Liquid Applied Sound Damping for High Frequency Vibrations

<div class="section abstract"><div class="htmlview paragraph">The automotive industry is rapidly changing as electric vehicles (EVs) have gained share in the market, bringing new challenges to ensure passenger comfort through noise, vibration, and harshness (NVH) management. Automotive acoustics engineers employ a variety of materials to reduce NVH across the audible frequency spectrum. In general, these materials have been tailored to address vibrations related to internal combustion engines (ICE). For example, liquid applied sound damping (LASD) coatings are widely employed to reduce structural vibrations due to their ease of application and light weight. LASD coatings are typically applied to the vehicle body to reduce structural vibrations at frequencies <1000 Hz, since ICE vehicles tend to exhibit vibrational modes primarily at these frequencies. However, EVs are known to also excite higher frequency vibrational modes up to 3000 Hz. Additionally, the lack of masking noise from the engine may lead these noises to be more noticeable to the passengers than in previous vehicles. Consequently, it is anticipated that damping materials and their specifications may need to be adjusted to better mitigate these high frequency vibrations. Herein, we will examine the effects of LASD design on damping up to 3200 Hz, including formulation, polymer/filler interactions, and coating thickness. These results will guide design of next-generation LASD materials.</div></div>

The Importance of Reverberation for the Design of Neonatal Incubators.

Low frequency noises are predominant in neonatal intensive care units (NICUs). Some studies affirm that neonates can perceive noises from 113 Hz, and can therefore be affected by sound sources with high spectral content at low frequencies (e.g., incubator engine, air fan). Other studies suggest that reverberation amplifies noise within incubators. In this paper, the reverberation time (T, T30) within an incubator with standard dimensions was measured in one-third octave bands. To get reliable results, the T was measured in 15 positions at the neonate's ear height, in a room with low T values (to reduce the influence of the room in the results), using an impulsive sound method. Results show a heterogeneous T distribution at the neonate's ear height, with maximum average T differences between positions of 1.07 s. The highest average T of all microphone positions is 2.27 s at 125 Hz, an extremely high mean value for such a small space. As the frequency of electrical devices in America is 60 Hz, some harmonics lay within the one-third octave band of 125 Hz, and therefore may create a very reverberant and inappropriate acoustic environment within the audible spectrum of neonates. As the acoustic environment of the incubator and the room are coupled, it is expected that the results are higher in the NICUs than in the room where the measurements were conducted, as NICUs are more reverberant. Therefore, it is recommended that the T will be limited in the international standards, and that incubator designers take it into account.

METHODS OF MUSIC THERAPY AND EXPERIMENTAL STUDY OF BIOELECTRICAL ACTIVITY OF STUDENTS' BRAINS WHILE LISTENING TO THE MUSICAL COMPOSITION OF THE AUDIBLE FREQUENCY SPECTRUM

The object of the study. Experimental research of music therapy methods. The problem to be solved. Determining the influence of selected musical composition of the audible frequency spectrum on the bioelectrical activity of students' brains, in particular alpha-, beta- and theta-rhythms. Main scientific results. The dependence of the influence on the bioelectrical activity of the brain of the compositions of the three frequency bands both individually and the composition as a whole is revealed. The dependence of alpha, beta and theta rhythms is shown. The area of ​​practical use of the research results. Medical institutions specializing in the treatment of disorders of the central nervous system, organic brain damage, stress, and its effective psychological rehabilitation. An innovative technological product. A technique of music therapy that allows to determine how different frequency ranges affect the bioelectrical activity of the human brain. The area of application of an innovative technological product. Clinical practice of using a music therapy.

Exploiting the complementary strengths of Orbitless and Planetary drives

An Orbitless drive is a novel fixed-ratio epi-cyclic drive which includes a second carrier in place of a ring gear. This fundamental difference has been shown to have superior efficiency to a Planetary drive, and is shown here to produce less vibration in the audible frequency spectrum at the expense of reduced torque capacity. A similar trade-off has made a plastic primary stage a standard approach for reducing noise in a multi-stage drive unit. A prototype 16 mm Orbitless drive is constructed and compared to an off-the-shelf Planetary drive to demonstrate the predicted audible outputs. Frequency spikes that appears around the tooth engagement frequency of the Planetary drive are absent from the FFT of the Orbitless drive. A high quality 32 mm Orbitless drive is constructed to evaluate it in a multi-stage environment. Sound levels are measured and analyzed for both stand-alone Orbitless and multi-stage Orbitless/Planetary configurations. Improvements in both amplitude and sound quality are demonstrated and it is verified that the primary stage is the dominant noise source. It is concluded that an Orbitless primary stage is a new opportunity that may be used in conjunction with plastic gears and other conventional techniques to minimize NVH levels in multi-stage gear drives.

A Self-Consistent Sonification Method to Translate Amino Acid Sequences into Musical Compositions and Application in Protein Design Using Artificial Intelligence.

We report a self-consistent method to translate amino acid sequences into audible sound, use the representation in the musical space to train a neural network, and then apply it to generate protein designs using artificial intelligence (AI). The sonification method proposed here uses the normal mode vibrations of the amino acid building blocks of proteins to compute an audible representation of each of the 20 natural amino acids, which is fully defined by the overlay of its respective natural vibrations. The vibrational frequencies are transposed to the audible spectrum following the musical concept of transpositional equivalence, playing or writing music in a way that makes it sound higher or lower in pitch while retaining the relationships between tones or chords played. This transposition method ensures that the relative values of the vibrational frequencies within each amino acid and among different amino acids are retained. The characteristic frequency spectrum and sound associated with each of the amino acids represents a type of musical scale that consists of 20 tones, the "amino acid scale". To create a playable instrument, each tone associated with the amino acids is assigned to a specific key on a piano roll, which allows us to map the sequence of amino acids in proteins into a musical score. To reflect higher-order structural details of proteins, the volume and duration of the notes associated with each amino acid are defined by the secondary structure of proteins, computed using DSSP and thereby introducing musical rhythm. We then train a recurrent neural network based on a large set of musical scores generated by this sonification method and use AI to generate musical compositions, capturing the innate relationships between amino acid sequence and protein structure. We then translate the de novo musical data generated by AI into protein sequences, thereby obtaining de novo protein designs that feature specific design characteristics. We illustrate the approach in several examples that reflect the sonification of protein sequences, including multihour audible representations of natural proteins and protein-based musical compositions solely generated by AI. The approach proposed here may provide an avenue for understanding sequence patterns, variations, and mutations and offers an outreach mechanism to explain the significance of protein sequences. The method may also offer insight into protein folding and understanding the context of the amino acid sequence in defining the secondary and higher-order folded structure of proteins and could hence be used to detect the effects of mutations through sound.

Individual Reliability of the Standard Clinical Method vs Patient-Centered Tinnitus Likeness Rating for Assessment of Tinnitus Pitch and Loudness Matching

Current individualized sound therapies for tinnitus rely on tinnitus pitch assessment, which is commonly derived from the standard clinical 2-alternative forced-choice (2-AFC) approach driven by the examiner. However, this method is limited by lack of individual test-retest reliability and focuses on a single rather than multiple tinnitus frequencies. To assess individual test-retest reliability of the 2-AFC, with a single final frequency (and corresponding loudness), and the tinnitus likeness rating (TLR), with the participant exposed to the entire audible frequency spectrum, from which 3 dominant frequencies and corresponding loudness were extracted. In this case series, participants with tinnitus underwent testing twice with both methods at a 1-month interval by experienced clinicians from January 6 through March 17, 2017. Each clinician tested each patient only once at visit 1 or 2 in a university audiology training setting with standardized equipment and was blind to previous assessment. Participants with bilateral or unilateral chronic tinnitus for longer than 6 months, in good health, without total deafness in either ear, and without cerumen in the ear canal were recruited through advertisements (community and clinics) and word of mouth (volunteer sample). The audiologists were likewise participants in the planned comparison between TLR and 2-AFC in the test-retest measures. Test-retest concordance with 95% CIs for each method, calculated as the proportion of participants with the same final frequency between the 2 visits (2-AFC) or with at least 1 concordant dominant frequency (TLR) as well as loudness differences of no greater than 10 dB. The study sample included 31 participants (55% men; mean [SD] age, 50.7 [13.7] years). For TLR, 26 of 31 participants had at least 1 concordant dominant frequency between the 2 visits (proportion, 0.84; 95% CI, 0.66-0.95), whereas for 2-AFC, 7 of 31 participants had a concordant final tinnitus pitch in either ear (proportion, 0.23; 95% CI, 0.10-0.41). Loudness reliability followed the same pattern, with more concordant loudness levels in the TLR (proportion, 0.73; 95% CI, 0.52-0.88) than in the 2-AFC (proportion, 0.40; 95% CI, 0.05-0.85). Mean time taken to complete the tests was less than 15 minutes, and general appreciation by participants with tinnitus and audiologists were overall similar for both. Superior test-retest concordance can be demonstrated at the individual level using the several dominant frequencies extracted from the patient-centered TLR.

Effect of structural vibration and room acoustic modes on low frequency impact noise in apartment house with floating floor

In today’s apartment houses, adoption of floating floor has vastly improved structure-borne floor impact noise by isolating vibration components well in excess of the major structural vibration resonant frequencies. For 20–200 Hz frequency region encompassing major structural vibratory and room acoustic modes, however, impact noise attenuation is much harder to achieve, and the problem can be exacerbated for small rooms where these modes are sparsely placed in audible frequency range. Experimental and numerical investigation of the effect of structural vibration and room acoustics on impact noise for the frequency region is undertaken. Structural vibration modes of the room with floating floor correlate well with the spectral characteristics of the impact noise, with various structural parts making different contributions in the frequency domain. For the low end of the impact noise spectrum, low density of high-energy axial room acoustic modes arising from small room size causes sound field in the room to show notable variation with measurement locations. For the mock-up typical of a small-sized living room considered in the present study, one of the vibrational mode of floor slab excites an overlapping fundamental room acoustic mode that further amplifies the impact noise. A room design that avoids overlapping of major structural and acoustic resonance modes at low end of the audible spectrum could be crucial in abating an echo commonly encountered in bare apartment rooms.

Adaptive Sojourn Time HSMM for Heart Sound Segmentation.

Heart sounds are difficult to interpret due to events with very short temporal onset between them (tens of milliseconds) and dominant frequencies that are out of the human audible spectrum. Computer-assisted decision systems may help but they require robust signal processing algorithms. In this paper, we propose a new algorithm for heart sound segmentation using a hidden semi-Markov model. The proposed algorithm infers more suitable sojourn time parameters than those currently suggested by the state of the art, through a maximum likelihood approach. We test our approach over three different datasets, including the publicly available PhysioNet and Pascal datasets. We also release a pediatric dataset composed of 29 heart sounds. In contrast with any other dataset available online, the annotations of the heart sounds in the released dataset contain information about the beginning and the ending of each heart sound event. Annotations were made by two cardiopulmonologists. The proposed algorithm is compared with the current state of the art. The results show a significant increase in segmentation performance, regardless the dataset or the methodology presented. For example, when using the PhysioNet dataset to train and to evaluate the HSMMs, our algorithm achieved average an F-score of [Formula: see text] compared to [Formula: see text] achieved by the algorithm described in [D.B. Springer, L. Tarassenko, and G. D. Clifford, "Logistic regressionHSMM-based heart sound segmentation," IEEE Transactions on Biomedical Engineering, vol. 63, no. 4, pp.822-832, 2016]. In this sense, the proposed approach to adapt sojourn time parameters represents an effective solution for heart sound segmentation problems, even when the training data does not perfectly express the variability of the testing data.