Browsing by Author "Schlecht, Sebastian"

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  • Aalto University - Acoustics Lab: Lab presentation
    (2021) Lokki, Tapio; Meyer-Kahlen, Nils; Schlecht, Sebastian; Välimäki, Vesa
     Foreword / postscript
    The professor’s and researchers working at the Aalto Acoustics Lab have prepared video presentations and demos in the special facilities of the laboratory. The laboratories were renovated two years ago, so they are now in great shape. Most of the video material is recorded binaurally so that it can be enjoyed well with headphones.
  • Active Acoustics With a Phase Cancelling Modal Reverberator
    (2024-10-15) De Bortoli, Gian; Prawda, Karolina; Schlecht, Sebastian
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Active acoustics (AA) systems are used to electronically modify the acoustics of a room (e.g., in live music venues). AA systems have an inherent feedback component and can suffer from instability and coloration artifacts resulting from too high feedback gains. State-of-the-art methods can improve system stability and coloration, usually at the cost of complex implementations and long parameter-tuning sessions. They can also cause sound artifacts due to time-varying components, limiting the enhancement at low frequencies. This work proposes a time-invariant feedback attenuation method for low frequencies based on a modal reverberator. The attenuation is achieved through destructive acoustic interference, obtained via phase shifts between the input and output signals. The analyzed frequency range is 0–500 Hz, where the room transfer functions are considered highly invariant over time. The results show a gain-before-instability increase of more than 5 dB for a modal reverberator with high mode density in this frequency range. The improvement is also stable for low-magnitude changes in the room transfer functions over time. The proposed method provides a robust AA system with artificial reverberation for the low-frequency range and can be used alongside other established methods.
  • An analysis of empowering the audience in immersive performance -- Take Pipa as an example
    (2021) Wu, Yanran
     School of Arts, Design and Architecture | Master's thesis
  • Assessing Room Acoustic Memory using a Yes/No and a 2-AFC Paradigm
    (2021-11-11) Nastasa, Anamaria Madalina; Meyer-Kahlen, Nils; Schlecht, Sebastian
     A4 Artikkeli konferenssijulkaisussa
    We present a study that tests the ability to remember room acoustics-a cognitive skill that is one of the guiding mechanisms behind plausible virtual acoustics for extended realities. Room acoustic memory was tested by assessing a person's ability to recognise sound samples, convolved with room impulse responses of everyday rooms presented in a preceding training session. To test a common assumption of detection theory, we conducted two listening tests using both a yes/no and a 2AFC paradigm. Results show that subjects can recognise different rooms above chance level, but even with relatively large differences between the rooms, the accuracy is low in general. Furthermore, the relation between the two test paradigms follows the prediction of detection theory when averaging over all participants , but less so for individual participants.
  • Audio Peak Reduction Using Ultra-Short Chirps
    (2022-06) Välimäki, Vesa; Fierro, Leonardo; Schlecht, Sebastian; Backman, Juha
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Two filtering methods for reducing the peak value of audio signals are studied. Both methods essentially warp the signal phase while leaving its magnitude spectrum unchanged. The first technique, originally proposed by Lynch in 1988, consists of a wideband linear chirp. The listening test presented here shows that the chirp must not be longer than 4 ms, so as not to cause any audible change in timbre. The second method, called the phase rotator, put forward in 2001 by Orban and Foti is based on a cascade of second-order all-pass filters. This work proposes extensions to improve the performance of the methods, including rules to choose the parameter values. A comparison with previous methods in terms of achieved peak reduction, using a collection of short audio signals, is presented. The computational load of both methods is sufficiently low for real-time application. The extended phase rotator method is found to be superior to the linear chirp method and comparable to the other search methods. The practical peak reduction obtained with the proposed methods spans from 0 to about 3.5 dB. The signal processing methods presented in this work can increase loudness or save power in audio playback.
  • Audiovisual Congruence and Localization Performance in Virtual Reality: 3D Loudspeaker Model vs. Human Avatar
    (2024-10) Hofmann, Anja; Meyer-Kahlen, Nils; Schlecht, Sebastian; Lokki, Tapio
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    This paper investigates audiovisual congruence in virtual reality with both horizontal and vertical offsets between audio and visual rendering. Audiovisual congruence and localization errors are assessed using loudspeaker playback and nonindividualized headphone rendering. To account for the influence of different types of visual information on congruence, presentations of a loudspeaker model and 3D human avatar were compared. Therefore, a new dataset of audiovisual speech was recorded. Results show that human avatar rendering increases perceived congruence, and experienced listeners have an increased tendency to respond with “incongruent” when a loudspeaker model is shown but not when the human avatar is presented. Moreover, a correlation is found between localization precision and audiovisual congruence for horizontally offset stimuli and avatar presentation. For vertical offsets, the angular range of congruence is generally large, and localization errors are high, so no correlation can be observed between the two. The paper contributes congruence ranges for audiovisual speech in virtual reality, which also has implications for augmented reality telepresence use.
  • Autonomous robot twin system for room acoustic measurements
    (2021-04) Götz, Georg; Martinez Ornelas, Abraham; Schlecht, Sebastian; Pulkki, Ville
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    While room acoustic measurements can accurately capture the sound field of real rooms, they are usually time consuming and tedious if many positions need to be measured. Therefore this contribution presents the Autonomous Robot Twin System for Room Acoustic Measurements (ARTSRAM) to autonomously capture large sets of room impulse responses with variable sound source and receiver positions. The proposed implementation of the system consists of two robots, one of which is equipped with a loudspeaker, while the other one is equipped with a microphone array. Each robot contains collision sensors, thus enabling it to move autonomously within the room. The robots move according to a random walk procedure to ensure a big variability between measured positions. A tracking system provides position data matching the respective measurements. After outlining the robot system, this paper presents a validation, in which anechoic responses of the robots are presented and the movement paths resulting from the random walk procedure are investigated. Additionally the quality of the obtained room impulse responses is demonstrated with a sound field visualization. In summary, the evaluation of the robot system indicates that large sets of diverse and high-quality room impulse responses can be captured with the system in an automated way. Such large sets of measurements will benefit research in the fields of room acoustics and acoustic virtual reality.
  • Binaural Dark Velvet Noise Reverberator
    (2024-09-03) Fagerström, Jon; Meyer-Kahlen, Nils; Schlecht, Sebastian; Välimäki, Vesa
     A4 Artikkeli konferenssijulkaisussa
    Binaural late-reverberation modeling necessitates the synthesis of frequency-dependent inter-aural coherence, a crucial aspect of spa- tial auditory perception. Prior studies have explored methodolo- gies such as filtering and cross-mixing two incoherent late rever- beration impulse responses to emulate the coherence observed in measured binaural late reverberation. In this study, we introduce two variants of the binaural dark-velvet-noise reverberator. The first one uses cross-mixing of two incoherent dark-velvet-noise se- quences that can be generated efficiently. The second variant is a novel time-domain jitter-based approach. The methods’ accu- racies are assessed through objective and subjective evaluations, revealing that both methods yield comparable performance and clear improvements over using incoherent sequences. Moreover, the advantages of the jitter-based approach over cross-mixing are highlighted by introducing a parametric width control, based on the jitter-distribution width, into the binaural dark velvet noise reverberator. The jitter-based approach can also introduce time- dependent coherence modifications without additional computa- tional cost.
  • Black-box modeling audio effects with Koopman-based neural networks
    (2024-09-28) Huhtala, Ville
     School of Electrical Engineering | Master's thesis
    In the last few years, neural network-based black-box modeling of non-linear audio effects has improved significantly. Present recurrent and convolutional neural models can model audio effects with long-term dynamics, but they require many parameters, thus increasing the processing time. This thesis presents a Koopman-linearised audio neural network structure that lifts a one-dimensional signal (mono audio) into a high-dimensional approximately linear state-space representation with non-linear mapping, and then uses differentiable biquad filters to predict linearly within the lifted state-space. Two models based on the general structure are compared against state-of-the art recurrent and convolutional models. Results show that the proposed models match the high performance of the state-of-the-art neural models while having a more compact structure, reducing the number of parameters by tenfold, and having interpretable components.
  • Breathe in, breathe out : augmented reality murals as a tool for extended storytelling narratives
    (2021) Hiremath, Punit
     School of Arts, Design and Architecture | Master's thesis
  • Building a Dataset of Sauna Room Impulse Response Measurements
    (2023-08-21) Pitkänen, Arttu
     Sähkötekniikan korkeakoulu | Master's thesis
    In room acoustics, impulse responses are used to derive different acoustic parameters of a room. They provide valuable data for acoustics and audio-related applications. No previous research provides specific data about the acoustics of a sauna along with changing atmospheric conditions. This thesis aims to build a dataset of room impulse responses from measurements in a sauna for further processing considering the effect of atmospheric conditions on sound propagation. The acoustic effect of a room can be modeled as a linear and time-invariant system, where the input is an excitation signal, the transfer function is the effect of the room on the propagating signal, and the output is the recorded signal that consists of direct and reflected sound. The impulse response can be extracted from the recorded output with convolution operations. A sine sweep is an excitation signal option that varies in frequency over time. Its qualities differ depending on the shape of the sweep, such as length and rate of the frequency change. Notable atmospheric conditions affecting sound propagation in a room include temperature and humidity. They mostly affect the speed and attenuation of sound, and increased speed of sound is noticeable in higher temperatures and humidity levels. In this thesis, the impulse response data is collected by recording multiple sweeps over time as the atmospheric conditions change and then post-processing the recordings to extract the impulse responses. The measurement setup includes a loudspeaker for excitation signal playback, a microphone in the far field for recording sweeps, and a microphone in the near field for comparison and input monitoring. The measurement equipment is piloted via an audio interface with a Python script. The temperature and humidity are documented using Arduino-driven sensors and integrated meters of the sauna. Matlab scripts are used to post-process the recordings and analyze results. The thesis provides impulse response data under varying atmospheric conditions from the measured sauna. Temperature varies from 22 degrees Celsius to 93 degrees Celsius during the measurements. The results show the difference in the time of arrival of sound, and the atmospheric effect on the frequency response is illustrated. The sensor data shows the distribution of temperature and humidity, and the dominating effect of temperature over humidity in sauna acoustics is demonstrated.
  • Clearly audible room acoustical differences may not reveal where you are in a room
    (2022-08-05) Meyer-Kahlen, Nils; Schlecht, Sebastian; Lokki, Tapio
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A common aim in virtual reality room acoustics simulation is accurate listener position dependent rendering. However, it is unclear whether a mismatch between the acoustics and visual representation of a room influences the experience or is even noticeable. Here, we ask if listeners without any special experience in echolocation are able to identify their position in a room based on the acoustics alone. In a first test, direct comparison between acoustic recordings from the different positions in the room revealed clearly audible differences, which subjects described with various acoustic attributes. The design of the subsequent experiment allows participants to move around and explore the sound within different zones in this room while switching between visual renderings of the zones in a head-mounted display. The results show that identification was only possible in some special cases. In about 74% of all trials, listeners were not able to determine where they were in the room. The results imply that audible position dependent room acoustic rendering in virtual reality may not be noticeable under certain conditions, which highlights the importance of evaluation paradigm choice when assessing virtual acoustics.
  • Colours of Velvet Noise
    (2022-06) Meyer-Kahlen, Nils; Schlecht, Sebastian; Välimäki, Vesa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Velvet noise is a sparse ternary pseudo-random signal containing only a small portion of non-zero values. In this work, the derivation of the spectral properties of velvet noise is presented. In particular, it is shown that the original velvet noise is white, i.e. has a constant power spectrum. For velvet noise variants with altered probability of polarity, the spectral characteristics are analytically derived. Crushed additive velvet noise is shown to have potential in the design of coloured sparse noise sequences, which are useful in acoustic signal processing.
  • A Common-Slopes Late Reverberation Model Based on Acoustic Radiance Transfer
    (2024-09-03) Scerbo, Matteo; Schlecht, Sebastian; Ali, Randall; Savioja, Lauri; De Sena, Enzo
     A4 Artikkeli konferenssijulkaisussa
    In rooms with complex geometry and uneven distribution of energy losses, late reverberation depends on the positions of sound sources and listeners. More precisely, the decay of energy is characterised by a sum of exponential curves with position-dependent amplitudes and position-independent decay rates (hence the name common slopes). The amplitude of different energy decay components is a particularly important perceptual aspect that requires efficient modeling in applications such as virtual reality and video games. Acoustic Radiance Transfer (ART) is a room acoustics model focused on late reverberation, which uses a pre-computed acoustic transfer matrix based on the room geometry and materials, and allows interactive changes to source and listener positions. In this work, we present an efficient common-slopes approximation of the ART model. Our technique extracts common slopes from ART using modal decomposition, retaining only the non-oscillating energy modes. Leveraging the structure of ART, changes to the positions of sound sources and listeners only require minimal processing. Experimental results show that even very few slopes are sufficient to capture the positional dependency of late reverberation, reducing model complexity substantially.
  • Deep Room Impulse Response Completion -- A Multiexponential Decay Approach
    (2024-05-20) Lin, Jackie
     Sähkötekniikan korkeakoulu | Master's thesis
    The acoustics of enclosed spaces, vital for applications like concert hall design, have been studied extensively since the 1960s. Emerging technologies such as augmented reality and virtual reality (AR/VR) have brought new demands on immersive audio, necessitating fast, realistic simulation of acoustics. Room Impulse Responses (RIRs), the acoustic fingerprint of a space, are used in the auralization of virtual spaces. However, generating accurate RIRs in real-time for dynamic AR/VR environments remains challenging. Traditional simulation methods such as geometrical acoustics and wave-based acoustics have known limitations in accuracy and computational cost. Hybrid methods combining geometrical acoustics and wave-based acoustics have been proposed, but they also face challenges, thus motivating the need for new RIR generation paradigms. This thesis introduces RIR completion, a novel RIR generation task to predict the remaining portion of an RIR from its early segment. A lightweight encoder-decoder style deep neural network, Deep Exponential Completion of Room impulse responses (DECOR), is proposed to efficiently complete RIRs. DECOR's highly informed decoder predicts the amplitude values of exponential decay curves within the multiexponential decay reverberation framework. Experimental results demonstrate DECOR's effectiveness and reliability compared to a state-of-the-art model, while achieving fewer audible artifacts and more than thirty-fold model size reduction. While this thesis focuses on deep learning-based implementation, it serves as an initial proof-of-concept for RIR completion, opening avenues for more refined future RIR completion methods.
  • Design with Sound: The Relevance of Sound in VR as an Immersive Design Tool for Landscape Architecture
    (2023) Luoma, Loviisa; Fricker, Pia; Schlecht, Sebastian
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Sound in landscape architecture commonly focuses on noise. In design or planning process sound rarely plays a holistic and essential role. This is partly due to the need for more tools to address the complex topic. This research introduces novel opportunities to explore the importance of sound as an immersive design parameter in landscape architecture and planning within Virtual Reality (VR). The project investigates immersive sound experiences by presenting sonic data in audible form. A VR app was constructed from multiple on-location spatial sound recordings. Within a test case, the application was used by participants, comparing a conventional design approach with the proposed VR methodology. The outcome of the test clearly shows the importance of integrating sound in an audible form to enhance the comprehensive understanding of space. The paper will focus on the discussion of the technical as well as the design-specific components.
  • Differentiable Active Acoustics: Optimizing Stability via Gradient Descent
    (2024-09-03) De Bortoli, Gian; Dal Santo, Gloria; Prawda, Karolina; Lokki, Tapio; Välimäki, Vesa; Schlecht, Sebastian
     A4 Artikkeli konferenssijulkaisussa
    Active acoustics (AA) refers to an electroacoustic system that actively modifies the acoustics of a room. For common use cases, the number of transducers---loudspeakers and microphones---involved in the system is large, resulting in a large number of system parameters. To optimally blend the response of the system into the natural acoustics of the room, the parameters require careful tuning, which is a time-consuming process performed by an expert. In this paper, we present a differentiable AA framework, which allows multi-objective optimization without impairing architecture flexibility. The system is implemented in PyTorch to be easily translated into a machine-learning pipeline, thus automating the tuning process. The objective of the pipeline is to optimize the digital signal processor (DSP) component to evenly distribute the energy in the feedback loop across frequencies. We investigate the effectiveness of DSPs composed of finite impulse response filters, which are unconstrained during the optimization. We study the effect of multiple filter orders, number of transducers, and loss functions on the performance. Different loss functions behave similarly for systems with few transducers and low-order filters. Increasing the number of transducers and the order of the filters improves results and accentuates the difference in the performance of the loss functions.
  • Differentiable Feedback Delay Network For Colorless Reverberation
    (2023-09-04) Dal Santo, Gloria; Prawda, Karolina; Schlecht, Sebastian; Välimäki, Vesa
     A4 Artikkeli konferenssijulkaisussa
    Artificial reverberation algorithms often suffer from spectral coloration, usually in the form of metallic ringing, which impairs the perceived quality of sound. This paper proposes a method to reduce the coloration in the feedback delay network (FDN), a popular artificial reverberation algorithm. An optimization framework is employed entailing a differentiable FDN to learn a set of parameters decreasing coloration. The optimization objective is to minimize the spectral loss to obtain a flat magnitude response, with an additional temporal loss term to control the sparseness of the impulse response. The objective evaluation of the method shows a favorable narrower distribution of modal excitation while retaining the impulse response density. The subjective evaluation demonstrates that the proposed method lowers perceptual coloration of late reverberation, and also shows that the suggested optimization improves sound quality for small FDN sizes. The method proposed in this work constitutes an improvement in the design of accurate and high-quality artificial reverberation, simultaneously offering computational savings.
  • Evaluation of Reverberation Time Models with Variable Acoustics
    (2020-06) Prawda, Karolina; Schlecht, Sebastian; Välimäki, Vesa
     A4 Artikkeli konferenssijulkaisussa
    Reverberation time of a room is the most prominent parameter considered when designing the acoustics of physical spaces. Techniques for predicting reverberation of enclosed spaces started emerging over one hundred years ago. Since then, several formulas to estimate the reverberation time in different room types were proposed. Although validations of those models were conducted in the past, they lack testing in a space with a high granularity of controllable absorptive and reflective conditions. The present study discusses the reverberation time estimation techniques by comparing various formulas. Moreover, the reverberation time measurements in a variable acoustic laboratory for different combinations of reflective and absorptive panels are shown. The values calculated with the presented models are compared with the ones obtained via measurements. The results show that all formulas predict reverberation time values inaccurately, with an average error of 16% or larger. Among the analyzed models, Fitzroy's formula gives the smallest error.
  • Exploring narrative possibilities of audio augmented reality with six degrees of freedom
    (2021) Harju, Matias
     School of Arts, Design and Architecture | Master's thesis
    Audio augmented reality (AAR) is gaining momentum with the current renaissance of augmented reality (AR) and mixed reality (MR). Since the 1990s when the term AAR was first introduced, the medium has been researched extensively, and with new technologies and wearable devices, interesting AAR applications are getting available to the wider audiences. However, the narrative possibilities of AAR tend to be still an under-explored territory. This is especially true for AAR that utilises six-degrees-of-freedom (6DoF) positional tracking. In 6DoF AAR the user can freely move in a space while hearing spatially synchronised virtual sounds embedded in the environment. Conceivably, the medium has interesting storytelling potential in, for instance, museums. This thesis explores the narrative possibilities of 6DoF AAR, concentrating on what is arguably characteristic of the medium: use of spatialised virtual audio, interplay between real and virtual, and interactivity based on user’s location and movements. The topic is approached from a content creator’s perspective through oscillation between conceptualisation and practical work. By analysing literature and related AAR experiences, 1) a series of narrative techniques characteristic to 6DoF AAR has been identified, and 2) a prototype of a 6DoF AAR setup has been crafted. The design and creation process of the prototype has been discussed to better understand the possibilities and limitations the technology may set for the narrative use of the medium. Five demonstrative scenes have been created and used to test some of the identified techniques in practice. This thesis presents a proposal for a list of narrative techniques characteristic to 6DoF AAR. The techniques are accounted for being a useful tool set for the author when designing the demonstrative scenes. Further, observations are disclosed on designing and building a 6DoF AAR setup capable of plausible auditory illusions and immersion. Challenges are reported related to, for example, registration errors in tracking and unexpected environmental sounds potentially hindering immersion and disrupting the narrative. For lack of user testing, however, more definite presumptions of the effectiveness of the techniques and the prototyped scenes cannot be made. On the other hand, it is suggested that with off-the-shelf components and authoring tools it is nowadays relatively easy for anyone with knowledge on sound design, programming, and storytelling to create gripping, spatially dynamic AAR experiences.