Synthesis of Spatially Extended Virtual Source with Time-Frequency Decomposition of Mono Signals

In horizontal stereophony, it is known that interchannel correlation relates to the horizontal spread of a phantom auditory image. However, little is known about the perceptual effect of interchannel correlation on vertical image spread (VIS) between two vertically-arranged loudspeakers. The present study investigates this through two subjective experiments: (i) a multiple comparison of relative VIS for stimuli with varying degrees of correlation; and (ii) the absolute measurement of upper and lower VIS boundaries for extreme stimuli conditions. Octave-band (center frequencies: 63 Hz to 16 kHz) and broadband pink noise signals have been decorrelated using two techniques: all-pass filtering and complementary comb-filtering. These stimuli were presented from vertically-spaced loudspeaker pairs at three azimuth angles (0• , ±30• , and ±110 • ), with each angle assessed discretely. Both the relative and absolute test results show no significant effect of vertical correlation on VIS for the 63 Hz, 125 Hz, and 250 Hz bands. For the 500 Hz band and above, there is a general tendency for VIS to increase as correlation decreases, which is observed for both decorrelation methods. This association is strongest at 0• azimuth for the 500 Hz and 1 kHz bands; at ±30• for 8 kHz and Broadband; and at ±110• for 2 kHz, 4 kHz, and 16 kHz. The 8 kHz band at ±30• has the strongest association of all conditions-post-hoc objective analysis indicates a potential relationship between HRTF localization cues (pinna filtering) and VIS perception within this frequency region. Furthermore, the absolute test results suggest that changes of VIS from interchannel decorrelation are fairly slight, with only the Broadband and 16 kHz bands showing a significant increase. The deviations of boundary scores also suggest a difficulty grading absolute VIS and/or potential disagreements among listeners.

Section: Phase-based Decorrelationmentioning

confidence: 99%

The Frequency and Loudspeaker-Azimuth Dependencies of Vertical Interchannel Decorrelation on the Vertical Spread of an Auditory Image

Gribben¹

2018

“…Various methods have been proposed for rendering auditory image spread in horizontal stereo, such as decorrelation techniques based on all-pass filtering [1][2][3] and comb-filtering [4], stereo shuffling [5], and frequencydependent panning [6]. These methods are fundamentally based on the fact that our ears are spaced apart and horizontally arranged.…”

Section: Introductionmentioning

confidence: 99%

Perceptual Band Allocation (PBA) for the Rendering of Vertical Image Spread with a Vertical 2D Loudspeaker Array

Lee

2016

Two subjective experiments were conducted to examine a new vertical image rendering method named "Perceptual Band Allocation (PBA)," using octave bands of pink noise presented from main and height loudspeaker pairs. The PBA attempts to control the perceived degree of vertical image spread (VIS) by a flexible mapping between frequency band and loudspeaker layer based on the desired positioning of the band in the vertical plane. The first experiment measured the perceived vertical location of the phantom image of each octave band stimulus for the main and height loudspeaker layers individually. Results showed significant differences among the frequency bands in perceived image location. Furthermore, the so-called "pitch-height" effect was found for two separate frequency regions, with most bands from the main loudspeaker layer perceived to be elevated from the physical height of the layer. Based on the localization data from the first experiment, six different PBA stimuli were created in such a way that each frequency band was mapped to either the main or height loudspeaker layer depending on the target degree of VIS. The second experiment conducted a listening test to grade the perceived magnitudes of VIS for the six stimuli. The results first indicated that PBA could significantly increase the perceived magnitude of VIS compared to that of a sound presented only from the main layer. It was also found that the different PBA schemes produced various degrees of perceived VIS with statistically significant differences. The paper discusses possible reasons for the obtained results in details based on the localization test results and the frequency-dependent energy weightings of ear-input signals. Implications of the proposed method for the vertical upmixing of horizontal surround content are also discussed.

“…Therefore, a new method that can render vertical image spread would be necessary. In the context of horizontal stereophony, horizontal image spread can be rendered by means of interchannel decorrelation, and many different decorrelation methods have been proposed over the past years [6][7][8][9][10]. Such methods are based on the principle that as the degree of correlation between stereophonic channel signals decreases, that between ear-input signals (interaural crosscorrelation), which has a direct relationship with perceived auditory image spread [4], also decreases.…”

Section: Introductionmentioning

confidence: 99%

2D-to-3D Ambience Upmixing based on Perceptual Band Allocation

Lee

2015

Listening tests were conducted to evaluate the feasibility of a novel 2D-to-3D ambience upmixing technique named "perceptual band allocation" (PBA). Four-channel ambience signals captured in a reverberant concert hall were low-pass and high-pass filtered, which were then routed to lower and upper loudspeaker layers arranged in a 9-channel 3D configuration, respectively. The upmixed stimuli were compared against original 3D recordings made using an 8-channel ambience microphone array in terms of 3D listener envelopment and preference. The results suggest that the perceived quality of the proposed method could be at least comparable to that of an original 3D recording. INTRODUCTIONThree-dimensional multichannel audio systems such as Auro-3D [1], Dolby Atmos [2], and 22.2 [3] employ additional height loudspeakers in order to provide the listener with a three-dimensional (3D) auditory experience. One of the perceptual attributes that could be enhanced by the use of height channels is listener envelopment (LEV). In the context of two-dimensional (2D) surround sound (e.g., 5.1), LEV is widely understood as the subjective impression of being enveloped by reverberant sound [4,5]. With 3D loudspeaker formats, the added height channels could be used to render the "vertical" spread of reverberant sound image as well as the horizontal one, and ultimately the auditory impression of 3D LEV could be achieved.One of the key requirements for 3D multichannel audio applications would be a 2D-to-3D upmixing technique that can add a height dimension to 2D content. Therefore, a new method that can render vertical image spread would be necessary. In the context of horizontal stereophony, horizontal image spread can be rendered by means of interchannel decorrelation, and many different decorrelation methods have been proposed over the past years [6][7][8][9][10]. Such methods are based on the principle that as the degree of correlation between stereophonic channel signals decreases, that between ear-input signals (interaural crosscorrelation), which has a direct relationship with perceived auditory image spread [4], also decreases. However, vertically reproduced stereophonic signals would have no or little influence on interaural cross-correlation. From a recent study by Gribben and Lee [11] it was found that vertically applied interchannel decorrelation was not as effective as horizontal decorrelation in terms of controlling the spread of image.The literature generally suggests that vertical localization relies on spectral cues. A number of researchers [12][13][14] have found that the higher the frequency of a pure tone the higher the perceived image position was regardless of the physical height of the presenting loudspeaker; a phenomenon referred to as the "pitch-height" effect in [15]. In the case of band-pass filtered noise signals, however, this effect was reported to be dependent on the physical height of the loudspeaker that presents the signal. For example, Roffler and Butler [16] found from their experiments using loudspeake...