Journal of the Audio Engineering Society

2006 January/February - Volume 54 Number 1/2

Papers


A Hybrid Time–Frequency Domain Approach to Audio Time-Scale Modification

Authors: Dorran, David; Lawlor, Robert; Coyle, Eugene

Frequency-domain approaches to audio time-scale modification introduce a reverberant or phasy artifact into the time-scaled output. Such artifacts are generally not present within time-domain implementations. However, high-quality time scaling in the time domain is typically limited to quasi-periodic signals such as speech. A hybrid method of time scaling is presented, which draws upon appealing aspects of both time-domain and frequency-domain implementations. The technique described can be applied successfully to a wide range of audio and is both robust and efficient. Subjective testing demonstrates that the technique reduces the presence of phasiness significantly.

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Spatial impulse response rendering (SIRR) is a method for reproducing room impulse responses over multichannel loudspeaker setups. The applied analysis and synthesis methods were introduced in a companion paper. Time–frequency analysis is used to obtain directional and diffuseness information from the recorded sound field. Nondiffuse sound is then reproduced as pointlike virtual sources, and diffuse sound is synthesized with a decorrelation technique. The proposed synthesis methods for diffuse sound are examined in more detail and a hybrid method is derived. The relationship between diffuseness and interaural coherence is also studied. In addition, results of two listening tests are presented. It is shown that with a large loudspeaker setup under anechoic conditions, SIRR reproduction is at best indistinguishable from the original sample. Furthermore, in a listening test conducted in a standard listening room with real measured responses, SIRR reproduction is evaluated as the most natural one of the systems studied.

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Effects of Headtracker Latency in Virtual Audio Displays

Authors: Brungart, Douglas; Kordik, Alex J.; Simpson, Brian D.

A critical parameter for the design of interactive virtual audio displays is the maximum acceptable amount of delay between the movement of the listener’s head and the corresponding change in the spatialized signal presented to the listener’s ears. Two studies that used a low-latency virtual audio display to evaluate the effects of headtracker latency on auditory localization are presented. The first study examined the effects of headtracker delay on the localization on broad-band sounds. The results show that latency values in excess of 73 ms result in increased localization errors for brief sounds and increased localization response times for continuous sound sources. The second study measured how well listeners could detect the presence of headtracker latency in a virtual sound. The results show that the best listeners can detect latency values of 60–70 ms for isolated sounds, and that their detection thresholds are 25 ms lower for sounds presented in conjunction with a low-latency reference tone. These results suggest that headtracker latency values lower than 60 ms are likely to be adequate for most virtual audio applications, and that delays of less than 30 ms are difficult to detect even in very demanding virtual auditory environments.

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[Engineering Report] Two all-pass crossover networks are described. One is a three-way network with filter sections (high-pass, band-pass, and low-pass) of order four, the other is a four-way network with filter sections of order six. The two crossover networks are realized as active filters using only equal resistors and equal capacitors. This configuration ensures that even though the available standard components may differ from the theoretical values, the pass-band amplification and the quality factor are kept constant. All filter sections have identical crossover frequencies and phase responses. Transient response and polar response for the two filters are examined.

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Audio Forensics

Authors: Staff, AES

[Feature Article] Last summer, Denver played host to the first AES conference on audio forensics, emphasizing the way that this specialized field has adapted to the digital age. In the September 2005 Journal (p. 838) we provided a detailed report of the proceedings of that conference, and now in this article we review in greater depth some of the work presented there in the fields of voice identification, spectrographic analysis, and signal-enhancement techniques.

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A Look Back at the 1952 Parkin-Taylor Paper: Speech Reinforcement in St. Paul’s Cathedral

Authors: Parkin, P. H.; Taylor, J. H.; Klepper, David L.; Eargle, John

[Feature Article] The Parkin-Taylor paper and the work it represents heralded a revolution in speech-reinforcement system design. The accepted wisdom at the time of its publication (1952) was that low reverberation time was essential for high speech intelligibility in large spaces. This frequently involved the sacrifice of much of the beauty that long reverberation time provides for specific classes of music, including organ, choral, and congregational singing. The distributed-column loudspeaker system at London’s St. Paul’s Cathedral proved that a different approach was possible, and similar systems now exist in possibly a majority of Western European cathedrals and large churches, as well as in similar spaces in North America.

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[Feature Article] The first audio network was installed in Hartford, Connecticut in 1877 by the Bell Telephone Company. In 1948, Claude Shannon published “A Mathematic Theory of Communication,” the theoretical basis for digital audio. Finally, in 1962, the development of the integrated circuit allowed the telephone companies to begin the transition to digital audio networking.

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Standards and Information Documents


AES Standards Committee News

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Features


Audio Forensics

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Audio Networking: Applications and Requirements

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29th Conference, Seoul, Call for Papers

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121st Convention, San Francisco, Call for Papers

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Departments


News of the Sections

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Sound Track

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Upcoming Meetings

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New Products and Developments

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Available Literature

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Membership Information

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Advertiser Internet Directory

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Sections Contacts Directory

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AES Conventions and Conferences

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Extras


Cover & Sustaining Members List

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AES Officers, Committees, Offices & Journal Staff

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