Browsing by Author "Pöntynen, Henri"
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- Auditory localization under conflicting dynamic and spectral cues
Sähkötekniikan korkeakoulu | Master's thesis(2015-12-14) Pöntynen, HenriSound localization in humans functions by identifying and comparing different attributes in acoustic signals presented to the two ears. These attributes are largely independent of one another and can thus be manipulated separately to provide the auditory system with conflicting cues to sound source location. While the topic of cue conflict between binaural cues has received a fair amount of attention in the field of psychoacoustics, localization of acoustic stimuli providing discrepant dynamic and spectral cues remains a less explored topic. The experimental part of this thesis consists of the design, implementation and documentation of a psychoacoustic experiment assessing cue conflict. In the implemented listening test, subjects performed horizontal head rotations while being exposed to noise burst sequences presented over loudspeakers in the horizontal plane. Head orientation data gathered via motion tracking cameras was used to move the stimuli in tandem with the subject's head movements to artificially alter the rate of change in the binaural cues during head movements. The resulting binaural cues corresponded to those produced by an overhead source. Subjects were asked to report whether they localized the stimuli to the horizontal direction indicated by the spectral cues or not. The results from the conducted experiment indicate wide intersubject variability in localization performance. In general, subjects exposed to stimuli providing conflicting dynamic and spectral cues either display a preference for one of the two cues or switch the cue they attend to between trials, leading to inconsistent localization performance. Results from some subjects displayed an apparent localization bias towards the rear hemiplane. - Cortical Processing of Binaural Cues as Shown by EEG Responses to Random-Chord Stereograms
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-02) Pöntynen, Henri; Salminen, NelliSpatial hearing facilitates the perceptual organization of complex soundscapes into accurate mental representations of sound sources in the environment. Yet, the role of binaural cues in auditory scene analysis (ASA) has received relatively little attention in recent neuroscientific studies employing novel, spectro-temporally complex stimuli. This may be because a stimulation paradigm that provides binaurally derived grouping cues of sufficient spectro-temporal complexity has not yet been established for neuroscientific ASA experiments. Random-chord stereograms (RCS) are a class of auditory stimuli that exploit spectro-temporal variations in the interaural envelope correlation of noise-like sounds with interaurally coherent fine structure; they evoke salient auditory percepts that emerge only under binaural listening. Here, our aim was to assess the usability of the RCS paradigm for indexing binaural processing in the human brain. To this end, we recorded EEG responses to RCS stimuli from 12 normal-hearing subjects. The stimuli consisted of an initial 3-s noise segment with interaurally uncorrelated envelopes, followed by another 3-s segment, where envelope correlation was modulated periodically according to the RCS paradigm. Modulations were applied either across the entire stimulus bandwidth (wideband stimuli) or in temporally shifting frequency bands (ripple stimulus). Event-related potentials and inter-trial phase coherence analyses of the EEG responses showed that the introduction of the 3- or 5-Hz wideband modulations produced a prominent change-onset complex and ongoing synchronized responses to the RCS modulations. In contrast, the ripple stimulus elicited a change-onset response but no response to ongoing RCS modulation. Frequency-domain analyses revealed increased spectral power at the fundamental frequency and the first harmonic of wideband RCS modulations. RCS stimulation yields robust EEG measures of binaurally driven auditory reorganization and has potential to provide a flexible stimulation paradigm suitable for isolating binaural effects in ASA experiments. - Directional-band-dominant spectral region for the sound localisation in the median plane
A4 Artikkeli konferenssijulkaisussa(2022-10-24) Kim, Taeho; Pöntynen, Henri; Pulkki, VillePrevious studies have reported that the direction of a band-limited sound stimulus in the median plane is localised based on its centre frequency instead of its actual location. The frequency band that determines this localisation is referred to as the directional-band. However, since most relevant studies employed a coarse localisation response scale or a limited range of frequency bands, the precise localisation sensitivity of each frequency band over the whole audible range is not yet clearly established. Therefore, this paper employed a comprehensive approach to the localisation of band-limited stimuli, utilising a continuous response scale within the whole median plane circle and consecutive 1/3-octave frequency bands within 100Hz-16kHz in the listening test. The results show that the `directional-bands' fall exclusively within the spectral region between 2.5kHz and 8kHz. Moreover, a `pitch-height effect' is observed within this spectral region, correlating to the elevation range of around 20 to 90. Although previous studies find directional-bands dispersed over a wide frequency range, not limited to a particular region, the responses in the directional-band-dominant spectral region from this study were statistically distinct against the other spectral regions for all subjects and source directions. - Effects of spatial cue dynamics on the perceptual organization of sound
School of Electrical Engineering | Doctoral dissertation (article-based)(2021) Pöntynen, HenriThe auditory system is constantly analyzing the mixture of sounds arriving at the ears to form mental representations of the sound sources present in the environment - a process known as the perceptual organization of sound. This process relies on heuristics derived from the statistical properties of sounds heard in natural environments, including those of their perceived directional properties. Auditory percepts have a salient spatial dimension that reveals the locations of sound sources with remarkable accuracy despite the fact that the sensory receptors of the auditory organs are not sensitive to sound direction. Rather, directional hearing is an inherently computational process wherein implicit spatial cues are extracted neurally from the acoustic waves arriving at the ears. While the vast majority of spatial hearing research has focused on the perception of individual point-like sources under conditions where both the listener and the source remain static, natural listening scenarios are rarely this simplistic. Instead, when sounds are heard outside of laboratory conditions, the spatial cues available to listeners are constantly changing due to the combination of listener and source movements as well as acoustic interference between concurrently active sound sources. Yet, the role of spatial cue dynamics in the perceptual organization of sound remains an unexplored topic in many fields of auditory research. The experiments included in this thesis address various auditory phenomena associated with dynamically varying spatial cues. Publications I, II, and IV document behavioral studies where the perceptual effects of spatial cue dynamics arising from the combination of listener and source motion (PI), listener motion alone (PII), or from acoustic-domain interference of multiple concurrently active sources (PIV) were assessed. The results of these studies show that cue dynamics can both enhance and degrade the accuracy of auditory perception. Publication III documents a neuroscientific experiment where electroencephalography was used to assess the cortical responses evoked by random-chord stereograms — a type of auditory stimulus capable of evoking binaurally driven auditory illusions. The results show that these stimuli evoke robust cortical responses as indicated by various time-, frequency- and time-frequency-domain measures. Random-chord stereograms could therefore potentially provide a flexible research tool for neuroscientific experiments seeking to isolate binaurally driven processes in the perceptual organization of sound. Overall, the results provide new insights into the role of spatial cue dynamics in auditory perceptual organization. The results are informative for the design of novel audio processing algorithms for binaural audio devices as well as for improving the ecological validity of auditory experiments across disciplines. - Kriittisen kaistan määrittäminen
Sähkötekniikan korkeakoulu | Bachelor's thesis(2014-05-06) Pöntynen, Henri - Perception of vertically separated sound sources in the median plane
Sähkötekniikan korkeakoulu | Master's thesis(2017-12-11) Kim, TaeThe ability of human listeners to segregate two sound sources was examined by conducting an experiment when the sources are concurrently presented from different directions in the median plane. A high-pass filtered pink noise was utilized as a sound stimulus in a free-field condition and presented as either a pair of incoherent sound sources or a single-source. Subjects responded whether they perceived sound from one or two directions. Listening tests were conducted with different directions and separation angles of sound sources. These tests consisted of two sessions: a monaural session when only the right ear was made audible, and a binaural session when both ears were audible. The results indicated that the percentage of responding "two directions" for pairwise stimuli exceeded 50% above 33.75 deg. separation angle and reached above 70% at 67.5 deg. separation for both sessions. However, the perceived separation showed weak correlation to the degree of separation although it increased in the binaural session. The ability to discriminate pairwise stimuli to each of two corresponding sound sources showed high statistical significance. The difference between a monaural hearing and binaural hearing was not statistically significant for the segregation of sound sources in the median plane. - Resolving front-back ambiguity with head rotation: the role of level dynamics
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-06-01) Pöntynen, Henri; Salminen, NelliMaking small head movements facilitates spatial hearing by resolving front-back confusions, otherwise common in free field sound source localization. The changes in interaural time difference (ITD) in response to head rotation provide a robust front-back cue, but whether interaural level difference (ILD) can be used as a dynamic cue is not clear. Therefore, the purpose of the present study was to assess the usefulness of dynamic ILD as a localization cue. The results show that human listeners were capable of correctly indicating the front-back dimension of high-frequency sinusoids based on level dynamics in free field conditions, but only if a wide movement range was allowed (±40∘). When the free field conditions were replaced by simplistic headphone stimulation, front-back responses were in agreement with the simulated source directions even with relatively small movement ranges (±5∘), whenever monaural sound level and ILD changed monotonically in response to head rotation. In conclusion, human listeners can use level dynamics as a front-back localization cue when the dynamics are monotonic. However, in free field conditions and particularly for narrowband target signals, this is often not the case. Therefore, the primary limiting factor in the use of dynamic level cues resides in the acoustic domain behavior of the cue itself, rather than in potential processing limitations or strategies of the human auditory system. - Vertical Direction Control Using Difference-Spectrum Filters in Stereophonic Loudspeaker Reproduction
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-03-08) Kim, Taeho; Pöntynen, Henri; Pulkki, VilleThis paper introduces difference-spectrum filters that can be used to control the perceived vertical direction of a sound source presented from ear-level loudspeakers. The difference-spectrum filter was designed to mimic the macroscopic changes in the spectral envelope of head-related transfer functions (HRTFs) between a target elevation angle and the ear-level elevation, where the HRTF envelopes were obtained from averaging an extensive collection of individual HRTFs in a database. Localization tests were conducted to evaluate the effectiveness of difference-spectrum filters on elevation perception, which showed a promising result in the two-channel stereophonic condition for the virtual sound source. The perceived elevation correlated well with the target elevation angle of difference-spectrum filters in the stereophonic condition, although a weak correlation was observed in the monophonic condition. Thus, the test results show that difference-spectrum filters can create robust illusory elevation perception and enable vertical direction control over a wide range of elevation angles in stereophonic loudspeaker reproduction. - Virtual analog Buchla 259 wavefolder
A4 Artikkeli konferenssijulkaisussa(2017) Esqueda, Fabián; Pöntynen, Henri; Välimäki, Vesa; Parker, Julian D.An antialiased digital model of the wavefolding circuit inside the Buchla 259 Complex Waveform Generator is presented. Wave-folding is a type of nonlinear waveshaping used to generate complex harmonically-rich sounds from simple periodic waveforms. Unlike other analog wavefolder designs, Buchla's design features five op-amp-based folding stages arranged in parallel alongside a direct signal path. The nonlinear behavior of the system is accurately modeled in the digital domain using memoryless mappings of the input-output voltage relationships inside the circuit. We pay special attention to suppressing the aliasing introduced by the nonlinear frequency-expanding behavior of the wavefolder. For this, we propose using the bandlimited ramp (BLAMP) method with eight times oversampling. Results obtained are validated against SPICE simulations and a highly oversampled digital model. The proposed virtual analog wavefolder retains the salient features of the original circuit and is applicable to digital sound synthesis. - Virtual Analog Model of the Lockhart Wavefolder
A4 Artikkeli konferenssijulkaisussa(2017) Esqueda Flores, Fabian; Pöntynen, Henri; Parker, Julian; Bilbao, Stefan - Virtual analog models of the Lockhart and Serge wavefolders
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2017-12-20) Esqueda, Fabián; Pöntynen, Henri; Parker, Julian D.; Bilbao, StefanWavefolders are a particular class of nonlinear waveshaping circuits, and a staple of the "West Coast" tradition of analog sound synthesis. In this paper, we present analyses of two popular wavefolding circuits-the Lockhart and Serge wavefolders-and show that they achieve a very similar audio effect. We digitally model the input-output relationship of both circuits using the Lambert-W function, and examine their time- and frequency-domain behavior. To ameliorate the issue of aliasing distortion introduced by the nonlinear nature of wavefolding, we propose the use of the first-order antiderivative method. This method allows us to implement the proposed digital models in real-time without having to resort to high oversampling factors. The practical synthesis usage of both circuits is discussed by considering the case of multiple wavefolder stages arranged in series. - Waveshaping with Norton amplifiers: modeling the Serge triple waveshaper
A4 Artikkeli konferenssijulkaisussa(2018) Gormond, Geoffrey; Esqueda Flores, Fabian; Pöntynen, Henri; Parker, JulianThe Serge Triple Waveshaper (TWS) is a synthesizer module designed in 1973 by Serge Tcherepnin, founder of Serge Modular Music Systems. It contains three identical waveshaping circuits that can be used to convert sawtooth waveforms into sine waves. However, its sonic capabilities extend well beyond this particular application. Each processing section in the Serge TWS is built around what is known as a Norton amplifier. These devices, unlike traditional operational amplifiers, operate on a current differencing principle and are featured in a handful of iconic musical circuits. This work provides an overview of Norton amplifiers within the context of virtual analog modeling and presents a digital model of the Serge TWS based on an analysis of the original circuit. Results obtained show the proposed model closely emulates the salient features of the original device and can be used to generate the complex waveforms that characterize “West Coast” synthesis.