Journal of the Audio Engineering Society

2015 March - Volume 63 Number 3


Evaluating the Impact of Sound Events’ Rhythm Characteristics to Listener’s Valence

Authors: Drossos, Konstantinos; Floros, Andreas; Kermanidis, Katia L.

While modern sound researchers generally focus on speech and music, mammalian hearing arose from the need to sense those events in the environment that produced sound waves. Such unorganized sound stimuli, referred to as Sound Events (SEs), can also produce an affective and emotional response. In this research, the investigators explore valence recognition of SEs utilizing rhythm-related acoustics cues. A well-known data set with emotionally annotated SEs was employed; various rhythm-related attributes were then extracted and several machine-learning experiments were conducted. The results portray that the rhythm of a SE can affect the listener’s valence up to an extent and, combined with previous works on SEs, could lead to a comprehensive recognition of the rhythm’s effect on the emotional state of the listener.

The moving coil transducer’s tendency to generate DC displacement and unstable rest position increases in smaller loudspeakers, which have less energy and hardware resources. A nonlinear motor structure optimized for highest force factor at the rest position provides maximum overall efficiency for common audio signals having bell-shaped probability density function of the voice coil displacement. A new control technique for electrodynamic transducers is presented that stabilizes the voice coil position, compensates for nonlinear distortion, and generates a desired transfer response by preprocessing the electrical input signal. The control law is derived from transducer modeling using lumped elements and identifies all free parameters of the model by monitoring the electrical signals at the transducer terminals. Although the adaptive control algorithm has been illustrated for moving coil transducers, the same approach can also be applied to other transduction structures such as the balance armature transducer in hearing aids and in-ear phones.

Methods for estimating the reverberation time in room acoustics have always been considered an important problem. A common approach uses Schröder’s backward integration method because it reduces variability, which is interpreted as meaning that it produces a more accurate estimate. This article analyzes this assumption in contexts applicable to both blind and nonblind estimation. Expressions for the estimation bias and variance of the reverberation decay rate are derived and verified using Monte Carlo simulations. The results confirm that backward integration does indeed significantly reduce the variance of decay rate estimates but at a cost of an increased and possibly large bias, which reduces the accuracy of the result. Prudence is therefore required when using backward integration for automated decay rate estimation tasks.

Engineering reports

Evaluating the quality of voice recordings invokes two different aspects of preference: the appeal of the speaker’s voice characteristics and the perceived degradation of the actual recording. Subjective experiments where no reference ideal is provided, called absolute category ratings, fuse together both components. This research investigates if voice postprocessing (timbre optimization, loudness compensations, de-essing, room reverberation, and noise suppression) can improve perceived quality. The results show that none of these processing methods significantly improve the perceived quality and mostly give rise to a quality degradation. The voice preference is a very significant factor in the perceived quality. The subjective results are used to validate ITU-T Recommendation P.863 (POLQA) in the high quality region.

Contemporary high-quality condenser microphones offer noise performance close to the theoretical limit. Because large-diaphragm capsules and transformerless electronics have a high sensitivity, only modest gain from the preamplifier is required. Yet, designers of microphone preamplifiers have traditionally focused on the noise performance at highest gain, where the equivalent input noise (EIN) is at a minimum. At lower gain settings this figure worsens by an amount that depends on the detailed implementation, and may dominate the noise of the microphone. The EIN at highest gain is an insufficient and possibly even misleading criterion. The author presents a detailed noise analysis of the classic current-feedback instrumentation amplifier topology. The collector load resistors and the voltage noise of the operational amplifiers were identified as significant noise sources at low-gain settings. Connecting the collector load resistors to a higher supply rail is an effective technique for reducing the magnitude of the noise sources. Practical verification was found to be in excellent agreement with the predicted performance.

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[Feature] Recent research in transducer technology involves monitoring and controlling the displacement of loudspeaker drivers to ensure that they can be driven as hard as possible with the best sound quality. The requirements for designs to be used with so-called smart amplifiers are also outlined. Alternatives to the conventional moving-coil driver are still being explored and some of the criteria for new transducers are introduced. Graphene appears to be an interesting and useful material that may find a role in the microphones of the future, while moving magnet subwoofers seem to have a number of desirable properties that could enable high outputs with minimal power compression and low distortion.

[Feature] One of the functions of the Technical Council and its committees is to track new, important research and technology trends in audio and report them to the Board of Governors and the Society’s membership. This information helps the governing bodies of the AES to focus on items of high priority. Supplying this information puts our technical expertise to a greater use for the Society. Last month we published a comprehensive report from many of the Technical Committees. This month we add a report from the TC on Semantic Audio Analysis.

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