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Lecture presented at Mikroforum 2022, Karlsruhe, Germany https://mikroforum.schoeps.de/

This paper presents open-access 3D sound recordings of musical performances and room impulse responses made using various 3D microphone arrays simultaneously. The microphone arrays include OCT-3D, 2L-Cube, PCMA-3D, Decca Cuboid, Hamasaki Square with height, First-order and Higher-order Ambisonics microphone systems, providing 256 possible front-rear-height combinations. The sound sources recorded were string quartet, piano trio, piano solo, organ, clarinet solo, vocal group and room impulse responses of a virtual ensemble with 13 source positions captured by all of the microphones. The recordings can be freely downloaded from https://doi.org/10.5281/zenodo.3474285. This paper also objectively analyses the microphone arrays to gain insights into spatial and tonal differences among the arrays, which will serve basis for formal subjective comparison to be conducted in the future.

This paper presents open-access 3D sound recordings of musical performances and room impulse responses made using various 3D microphone arrays simultaneously. The microphone arrays include OCT-3D, 2L-Cube, PCMA-3D, Decca Cuboid, Hamasaki Square with height, First-order and Higher-order Ambisonics microphone systems, providing 256 possible front-rear-height combinations. The sound sources recorded were string quartet, piano trio, piano solo, organ, clarinet solo, vocal group and room impulse responses of a virtual ensemble with 13 source positions captured by all of the microphones. The recordings can be freely downloaded from https://doi.org/10.5281/zenodo.3474285. This paper also objectively analyses the microphone arrays to gain insights into spatial and tonal differences among the arrays, which will serve basis for formal subjective comparison to be conducted in the future.

Paper:https://ieeexplore.ieee.org/document/9610831 Abstract: The effect of direct-to-reverberant ratio (DRR) on front-back confusion in binaural reproduction was investigated. Binaural room impulse responses (BRIRs) of loudspeakers at 0° and 180° azimuths from the listening position were captured in an ITU-R BS.1116-3-compliant listening room (RT=0.25s) using a KU100 dummy head placed 2m away from each loudspeaker. The DRRs of the original BRIRs were manipulated by varying the levels of the reverberant parts (beyond 2.5ms after the direct sound) of the signals, producing BRIRs with DRRs ranging from -12 dB to 12 dB with 4 dB intervals for each source position, as well as a pseudo-anechoic HRIR condition. Five subjects participated in the initial listening test. Each front or back stimulus with a different DRR was presented 20 times in a random order and the subject’s task was to respond either Front or Back. From psychometric functions derived from the data collected, a consistent pattern was observed from all subjects in that a lower DRR (more reverberant) tended to cause a higher rate of front-to-back confusion, whereas a higher DRR produced a higher rate of back-to-front confusion. The DRR thresholds of discrimination were different between the front and rear located sources, and the region between the two thresholds is proposed as a transition region where an extreme chance of confusion can be avoided for both source positions.

Slides from the presentation given at the 150th AES Convention. Related paper: Lee (2020), A Conceptual Model of Immersive Experience in Extended Reality https://psyarxiv.com/sefkh/&nbsp

3D multichannel audio aims to produce an immersive auditory experience by adding the height dimension to the reproduced sound field. In order to use the added height channels most effectively, it is necessary to understand the fundamental psychoacoustic mechanisms of vertical stereophonic perception. This tutorial/demo session will provide sound engineers and researchers with an overview of important psychoacoustic principles to consider for 3D audio recording and reproduction. The talk will first introduce recent research findings on topics such as 3D sound localization, phantom elevation, vertical image spread, and 3D listener envelopment. It will then show how the research has been used to develop new 3D/VR microphone array techniques, 2D–3D upmixing techniques and a new 3D panning technique without using height channels. The talk will be accompanied by 9.1 recording demos of various types of music, including orchestra, choir, organ, EDM, etc.

Presentation slides for the "Goodbye Stereo" workshop session at the AES 148th Virtual Vienna convention, 5 Jun 2020.

This paper investigates the influences of the recording/reproduction format, video and listening position on the quality perception of surround ambience recordings for sport events. Two microphone systems First Order Ambisonics (FOA) and Equal Segment Microphone Array (ESMA) were compared in both 4-channel (2D) and 8- channel (3D) loudspeaker reproductions. One subject group tested audio-only conditions while the other group was presented with video as well as audio. Overall, the ESMA was rated significantly higher than the FOA for all quality attributes tested regardless of the presence of video. The 2D and 3D reproductions did not have a significant difference within each microphone system. Video had a significant interaction with the microphone system and listening position depending on the attribute.

This paper evaluates a perceptually motivated objective model for the measurement of “punch” in musical signals. Punch is a perceptual attribute that is often used to characterize music that conveys a sense of dynamic power or weight. A methodology is employed that combines signal separation, onset detection, and low level parameter measurement to produce a perceptually weighted “punch” score. The model is evaluated against subjective scores derived through a forced pairwise comparison listening test using a wide variety of musical stimuli. The model output indicates a high degree of correlation with the subjective scores. Correlation results are also compared to other objective models such as Crest Factor, Inter-Band-Ratio (IBR), Peak-to-Loudness Ratio (PLR), and Loudness Dynamic Range (LDR).

Early studies found that, when identical signals were presented from two loudspeakers equidistant from the listener, the resulting phantom image was elevated in the median plane and the degree of the elevation increased with the loudspeaker base angle. However, sound sources used in such studies were either unknown or limited to noise signals. In order to investigate the dependencies of the elevation effect on sound source and loudspeaker base angle in details, the present study conducted listening tests using eleven natural sources and four noise sources with different spectral and temporal characteristics for seven loudspeaker base angles between 0° and 360°. The elevation effect was found to be significantly dependent on the sound source and base angle. Results generally suggest that the effect is stronger for sources with transient nature and a flat frequency spectrum than for continuous and low-frequency-dominant sources. Theoretical reasons for the effect are also discussed based on head-related transfer function measurements. It is proposed that the perceived degree of elevation would be determined by a relative cue related to the spectral energy distribution at high frequencies, but by an absolute cue associated with the acoustic crosstalk and torso reflections at low frequencies.

3D multichannel audio systems employ additional elevated loudspeakers in order to provide listeners with a vertical dimension to their auditory experience. Listening tests were conducted to evaluate the feasibility of a novel vertical upmixing technique called “perceptual band allocation (PBA),” which is based on a psychoacoustic principle of vertical sound localization, the “pitch height” effect. The practical feasibility of the method was investigated using 4-channel ambience signals recorded in a reverberant concert hall using the Hamasaki-Square microphone technique. Results showed that the PBA-upmixed 3D stimuli were significantly stronger than or similar to 9-channel 3D stimuli in 3D listener-envelopment (LEV), depending on the sound source and the crossover frequency of PBA. They also significantly produced greater 3D LEV than the 7-channel 3D stimuli. For the preference tests, the PBA stimuli were significantly preferred over the original 9-channel stimuli.

Listening tests were conducted in order to analyse the localisation of band-limited stimuli in vertical stereophony. The test stimuli were seven octave bands of pink noise, with centre frequencies ranging from 125–8000Hz, as well as broadband pink noise. Stimuli were presented from vertically arranged loudspeakers either monophonically or as vertical phantom images, created with the upper loudspeaker delayed with respect to the lower by 0, 0.5, 1, 5 and 10ms (i.e. interchannel time difference). The experimental data obtained showed that localisation under the aforementioned conditions is generally governed by the so-called “pitch-height” effect, with the high frequency stimuli generally being localised significantly higher than the low frequency stimuli for all conditions. The effect of interchannel time difference was found to be significant on localisation judgments for both the 1000-4000Hz octave bands and the broadband pink noise; it is suggested that this was related to the effects of comb filtering. Additionally, no evidence could be found to support the existence of the precedence effect in vertical stereophony.

This paper presents recent research findings in the psychoacoustics of 3D multichannel sound recording and\ud rendering. The addition of height channels in new reproduction formats such as Auro-3D, Dolby Atmos and 22.2,\ud etc. enhances the perceived spatial impression in reproduction. To achieve optimal acoustic recording and signal\ud processing for such formats, it is first important to understand the fundamental principles of how we perceive sounds\ud reproduced from vertically oriented stereophonic loudspeakers. Recent studies by the authors in this field provide\ud insights into how such principles can be applied for practical 3D recording and upmixing. Topics that are discussed\ud in this paper include the interchannel level and time difference relationships in terms of vertically induced\ud interchannel crosstalk, the effectiveness of the precedence effect in the vertical plane, the aspect of tonal coloration\ud resulting from vertical stereophonic reproduction, the effect of vertical microphone spacing on envelopment, the\ud effect of interchannel decorrelation, and the use of spectral cues for extending vertical image spread.

Even though the significance of interchannel crosstalk in multichannel microphone technique has been an issue of much debate in the field of sound recording, any effects on the perception of reproduced phantom images have not been investigated systematically. There is consequently no experimental data to which sound engineers can refer when attempting to control interchannel crosstalk in the design and application of multichannel microphone technique. It was therefore necessary to investigate the effects of such interchannel crosstalk in both the perceptual and the physical domains.\ud \ud Extant multichannel microphone techniques were reviewed, concentrating on their crosstalk characteristics. Findings from concert hall and room acoustics studies relating to the effects of early reflections, which might be the basis for understanding the perceptual effects of interchannel crosstalk, were also studied.\ud \ud The effects of interchannel time and intensity relationship and sound source type on the perception of stereophonic phantom image attributes were first examined in the context of two-channel stereophonic reproduction. The perceptual attributes of phantom sources affected by interchannel crosstalk in three- channel microphone technique were then elicited, and the effects of interchannel time and intensity relationship, sound source type and acoustic condition on the perception of those attributes were investigated. The effects of interchannel crosstalk on sound quality preference were also examined in both controlled and practical manners. Finally, following objective measurements of experimental stimuli, relationships were established between the perceptual and objectively measured effects of interchannel crosstalk.\ud \ud It was found that the most salient perceptual effects of interchannel crosstalk were an increase in source width and a decrease in locatedness. The relationship between interchannel time and intensity differences involved in the crosstalk signal was significant for both effects. The type of sound source was significant only for the source width effect whereas the acoustic condition was significant only for the locatedness effect. The source width increase was mainly influenced by the middle frequencies of crosstalk signals in a region of the spectrum around 1000Hz, at the onsets of the signal envelopes. The results of listener preference experiments suggested that the preference for interchannel crosstalk would depend on the spectral and temporal characteristics of sound source to be recorded rather than on the magnitude of interchannel crosstalk.