In This Section
Journal of the AES
2014 April - Volume 62 Number 4
Beamforming Regularization, Scaling Matrices, and Inverse Problems for Sound Field Extrapolation and Characterization: Part II – Experiments
Part I of this paper in last month’s Journal (pp. 77–98) described the theory of sound field extrapolation (SFE) and sound field characterization (SFC) for predicting the sound field using microphone arrays. This paper describes experimental results when the SFE method was tested in more realistic situations with real sound fields and microphones, including unknown measurement noise and imprecision and difference between microphones. Environments also included both a hemi-anechoic room and a reverberation chamber. The SFC method was first evaluated by means of a comparison between various fields and the scalar metrics for three archetypical sound fields: source in nearly free field, low-frequency standing wave in reverberation chamber, and diffuse sound in reverberation chamber. Although the SFC and classification methods correctly identified the sound fields, the distinction between a standing wave at 54.5 Hz and the diffuse sound field at 600 Hz were the most difficult.
The coupled perception of sound and vibration is a well-known phenomenon during live rock and pop concerts. Measurements in concert halls and churches have confirmed that sound can excite perceivable vibrations on the surface of the body even during classical performances. This research explores if vibrations have an influence on the quality of the listening experiences. Therefore, sound and seat vibrations were controlled separately in an audio reproduction scenario. Vibrations were generated from audio recordings using various approaches. Different parameters during this process were examined in relation to their perceptual consequences. It can be concluded that vibrations play a significant role in the perception of music. Real concert halls might benefit from amplifying the vibrations (passively or actively) in the auditorium.
Momentary Quality of Experience: Users’ Audio Quality Preferences Measured Under Different Presentation Conditions
Subjective evaluation of audio, video, and audiovisual material is typically performed in a static manner, after the sample has finished. This way, the possible temporal variability of the stimulus quality and its impact on quality perception are ignored. In this study, a new technique for momentary quality assessment was used in order to investigate the effect of content coherence/continuity as well as the influence of video stream on audio quality preferences. Obtained results show that the quality requirements are lower when the presented material is played in a continuous manner than when the same clip is cut into segments that are reproduced in a random order with short pauses in between. This may mean that subjective studies that use short audio stimuli extracted from long-duration content generate results that exaggerate the actual quality needs of consumers. Moreover, it has been shown that subjects’ quality preferences are higher when audio is played without the presence of an accompanying visual stimulus.
Various types of noise and other forms of degradation in the acoustic signal are typical of speech recordings used in forensic speaker recognition. The results of this study suggest that certain speech enhancement algorithms can be a useful tool for preprocessing speech samples before attempting automated recognition. This is particularly true for additive noise such as instrumental music and noise inside of a moving car. Comparing equal-error rates of identification experiments for ten male speakers based on the original, degraded, and enhanced voice signals, the performance of the speaker recognition system was most affected by pop music in both single-channel and 2-channel recordings. In contrast, road traffic and restaurant noise do not markedly degrade recognition performance.
In contrast to the conventional microphone with a moving diagram, this study explores the use of plasmas to create a diaphragmless ionic microphone. By performing FM demodulation of the shift in oscillating frequency of a high-temperature plasma, a useful audio signal was obtained. Increased output levels were observed with a decrease in the sound wave frequency. It was difficult to maintain consistent performance because the discharges in the air led to wearing of the electrode tip as well as adhesions of the discharge products. Results showed that the stability of the discharge corresponded to the nonuniform electric field, which was dependent on the formation shape of the high-temperature plasma, the shape of the discharge electrode, and the use of inert gas to protect the needle electrode. The authors review the experimental outcome of two ionic methods.
Standards and Information Documents
AES Standards Committee News
AES Patent Policy
53rd Conference Report, London
54th Conference Preview, London
54th Conference Preliminary Program
Handling of emotional content, source separation and classification, and intelligent audio production were among the key themes of papers presented at the 53rd International Conference on Semantic Audio held recently in London. We summarize some of the trends and advances in this research.
56th Conference, London, Call for Papers
Special Issue on Sound Field Control, Call for Papers