A modulation spectral representation is investigated for non-intrusive quality and intelligibility measurement of reverberant and dereverberated speech. The representation is obtained by means of an auditory-inspired filterbank analysis of critical-band temporal envelopes of the speech signal. Modulation spectral insights are used to develop an adaptive measure termed speech to reverberation modulation energy ratio. Experimental results show the proposed measure outperforming three standard algorithms for tasks involving estimation of multiple dimensions of perceived coloration, as well as quality measurement and intelligibility estimation of reverberant and dereverberated speech.

A Non-Intrusive Quality and Intelligibility Measure of Reverberant and Dereverberated Speech

The first artificial reverberation algorithms were proposed in the early 1960s, and new, improved algorithms are published regularly. These algorithms have been widely used in music production since the 1970s, and now find applications in new fields, such as game audio. This overview article provides a unified review of the various approaches to digital artificial reverberation. The three main categories have been delay networks, convolution-based algorithms, and physical room models. Delay-network and convolution techniques have been competing in popularity in the music technology field, and are often employed to produce a desired perceptual or artistic effect. In applications including virtual reality, predictive acoustic modeling, and computer-aided design of acoustic spaces, accuracy is desired, and physical models have been mainly used, although, due to their computational complexity, they are currently mainly used for simplified geometries or to generate reverberation impulse responses for use with a convolution method. With the increase of computing power, all these approaches will be available in real time. A recent trend in audio technology is the emulation of analog artificial reverberation units, such as spring reverberators, using signal processing algorithms. As a case study we present an improved parametric model for a spring reverberation unit.

Fifty Years of Artificial Reverberation

Presenting sounds in virtual environments requires filtering free-field signals with headrelated transfer functions (HRTF). HRTFs describe the filtering effects of pinna, head, and torso measured in the ear canal of a subject. The measurement of HRTFs for many positions in space is a time-consuming procedure. To speed up the HRTF measurement, the multiple exponential sweep method (MESM) was developed. MESM speeds up the measurement by overlapping sweeps in an optimized way and retrieves the impulse responses of the measured systems. MESM and its parameter optimization are described. As an example of an application of MESM, the measurement duration of an HRTF set with 1550 positions is compared to the unoptimized method. Using MESM, the measurement duration could be reduced by a factor of four without a reduction of the signal-to-noise ratio.

Multiple Exponential Sweep Method for Fast Measurement of Head-Related Transfer Functions

In this and the companion paper Part II, the authors present the Perceptual Objective Listening Quality Assessment (POLQA), the third-generation speech quality measurement algorithm, standardized by the International Telecommunication Union in 2011 as Recommendation P.863. In contrast to the previous standard (P.862 Perceptual Evaluation of Speech Quality), a more complex temporal alignment was developed allowing for the alignment of a wide variety of complex distortions for which P.862 was known to fail, such as multiple delay variations within utterances as well as temporal stretching and compression of the degraded signal. When this new algorithm is used in combination with the advanced perceptual model described in Part II, it provides a new measurement standard for predicting Mean Opinion Scores that outperforms the older PESQ standard, especially for wideband and super wideband speech signals (7 and 14 kHz audio bandwidth). Part I provides the basics of the POLQA approach and outlines the core elements of the temporal alignment.

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Perceptual Objective Listening Quality Assessment (POLQA), The Third Generation ITU-T Standard for End-to-End Speech Quality Measurement Part I-Temporal Alignment

In this article, a systematic overview of various recording and reproduction techniques for spatial audio is presented While binaural recording and rendering is designed to resemble the human two-ear auditory system and reproduce sounds specifically for a listener’s two ears, soundfield recording and reproduction using a large number of microphones and loudspeakers replicate an acoustic scene within a region These two fundamentally different types of techniques are discussed in the paper A recent popular area, multi-zone reproduction, is also briefly reviewed in the paper The paper is concluded with a discussion of the current state of the field and open problems

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Surround by Sound: A Review of Spatial Audio Recording and Reproduction

This paper addresses efficient interpolation of Head-Related Transfer Functions (HRTFs) for binaural generation of moving sound. Aiming at computational complexity reduction, the authors have recently proposed a new method for HRTF interpolation based on auxiliary Inter-positional Transfer Functions (IPTFs). The present paper reviews this IPTF-based method and focuses on IPTF design, which employs tools such as balanced model reduction and spectral smoothing to compute a complete set of reduced-order IPTFs. The interpolation scheme based on these reduced-order IPTFs is computationally more efficient and yields results perceptually comparable to those attainable by the bilinear method, which uses the HRTFs directly. Therefore, the proposed method is promising for real-time generation of spatial sound.

Efficient HRTF Interpolation in 3D Moving Sound

The interpolation of head-related transfer functions (HRTFs) for 3D-sound generation through headphones is addressed. HRTFs, which represent the paths between sound sources and the ears, are usually measured for a finite set of source locations around the listener. Any other virtual position requires interpolation procedures on these measurements. In this work a definition of the interpositional transfer function (IPTF) and an IPTF-based method for HRTF interpolation, recently proposed by the authors, are reviewed in detail. The formulation of the interpolation weights is generalized to cope with azimuth measurement steps which change with elevation. It is shown how to obtain a set of reduced-order IPTFs using tools such as balanced model reduction and spectral smoothing. Detailed comparisons between the accuracy and the efficiency of the IPTF-based and the bilinear interpolation methods (the latter using the HRTFs directly) are provided. A practical set of IPTFs is built and applied to a computationally efficient interpolation scheme, yielding results perceptually similar to those attainable by the bilinear method. Therefore the proposed method is promising for real-time generation of spatial sound.

Interpositional Transfer Function for 3D-Sound Generation*

This paper constitutes an introduction to the field of quality evaluation of sound (speech and audio) signals. The need for such an assessment is inherent to modern communications: VoIP, mobile phone, or teleconference systems require meaningful measures of performance, which may ultimately assure good service or profitable business. A brief survey on subjective and objective evaluation methods is provided. Recent developments as well as new topics to be investigated are also addressed. Experiments are conducted to illustrate how to validate quality assessment methods.

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On the quality assessment of sound signals

Reverberation assessment in audioband speech signals for telepresence systems

Modern telepresence systems constitute a new challenge for quality assessment of multimedia signals. This paper focuses on the evaluation of the reverberation impair ent for audioband speech signals. A review on the reverberation effect is presented, with emphasis given on the mathematical modeling of its components, including early reflections and late reverberation. A subje ctiv test for evaluating the human perception of the reverberation phenomenon is completely described, fro m its conception to the final results. Analyses are provided comparing the average subjective grades to curren t quality-evaluation standards for speech and audio signals. It is observed that the PESQ and PEAQ objective algo rithms constitute interesting starting points for developing an objective method for measuring the reverbera tion effect on speech signals.

Fabio P. Freeland

Papers

Efficient HRTF Interpolation in 3D Moving Sound

Interpositional Transfer Function for 3D-Sound Generation*

On the quality assessment of sound signals

Reverberation assessment in audioband speech signals for telepresence systems

Reverberation Assessment in Audioband Speech Signals for Telepresence Systems.