| Vol 32 No 2 | CONTENTS |
August 2004 |
Low-bitrate Coding, of Sound and Implications for Hiqh-Quality Digital Audio
A.J.M Houtsma
Acoustical Features of Musical Sounds
H. F. Pollard
The Sonar of Dolphins
W. Au
Designing and Making a Ceremonial Dinner Gong
N. Fletcher
Research at MARCS Auditory Laboratories, University of Western Sydney
D. Burnham, K. Stevens, B. DiBase, J. Buchholz, C. Kitamura, S. Malloch, M. Wiggins
Interlude
Book Reviews
News
New Products
Meeting Reports
Future Conferences
Obituary
New Members
FASTS
Sustaining Members
Diary
Acoustics Australia Information
Australian Acoustical Society Information
Advertisers Index
Vol. 32, No. 2 pp 49 - 54 (2004)
ABSTRACT: The Compact Disc launched in the early 1980s has set a worldwide standard for high-quality digital audio. Its sampling rate of 44.1 kHz and 16-bit word size appeared to provide enough bandwidth and dynamic range to capture every sound feature perceivable by the human ear. Although digital technology today is capable of delivering an even larger dynamic and spectral range at relatively little cost, there has been an ever-increasing need to produce digital sound of CD-equivalent quality at much lower bitrates than the CD's 1411 kbit/s. Examples of instances requiring lower bitrates are digital audio broadcast, fixed-head digital tape recorders, recordable mini-disc, multi-channel cinema sound, and internet audio. The original bit-compression schemes of transform and subband coding developed in the late 1980s, both exploiting the known perceptual limitations of the human auditory system, have now mostly been merged into a number of standardized complex coding systems that combine the best elements of the original schemes. Other techniques have been developed such as model-based parametric coding where not the waveform but rather the controlling parameters of a waveform-generating model are encoded and transmitted. Synthesis of the intended sound wave is then accomplished at the decoder end. This technique leads to additional bit savings and gives the end-user control over playback conditions like the positioning of sound sources. This feature is not only potentially useful for music playback in the home, but also for live electronic concerts, teleconferencing, and multi-user voice communication systems.
Vol. 32, No. 2 pp 55 - 59 (2004)
ABSTRACT: In searching for significant features of musical sounds, it is necessary to convert basic physical spectral data into psychophysical measures. Preliminary analysis and organisation of the data takes place in the cochlea where incoming acoustic waves are filtered and converted into digital nerve impulses. These impulses are passed on to the brain where they are processed in a number of stages of increasing sophistication. Time and frequency analysis occurs simultaneously allowing continuous assessment of both the characteristics of the starting transient and the eventual 'steady' sound. The tristimulus method of analysis emulates this process by measuring the changes that occur with respect to both time and frequency.
Vol. 32, No. 2 pp 61 - 63 (2004)
ABSTRACT: The sonar of dolphins has undergone evolutionary re-finement for millions of years and has evolved to be the premier sonar system for short range applications. It far surpasses the capability of technological sonar, i.e. the only sonar system the US Navy has to detect buried mines is a dolphin system. Echolocation experiments with captive animals have revealed much of the basic parameters of the dolphin sonar. Features such as signal characteristics, transmission and reception beam patterns, hearing and internal filtering properties will be discussed. Sonar detection range and discrimination capabilities will also be included. Recent measurements of echolocation signals used by wild dolphins have expanded our understanding of their sonar system and their utilization in the field. A capability to perform time-varying gain has been recently uncovered which is very different than that of a technological sonar. A model of killer whale foraging on chinook salmon will be examined in order to gain an understanding of the effectiveness of the sonar system in nature. The model will examine foraging in both quiet and noisy environments and will show that the echo levels are more than sufficient for prey detection at relatively long ranges.
Vol. 32, No. 2 pp 65 - 68 (2004)
ABSTRACT: The acoustic and aesthetic design of a ceremonial dinner gong for the fiftieth anniversary of University House at the Australian National University is described. The gong is made from polished stainless steel with a walnut frame constructed from the same timber used in building the Great Hall, and the shape of the frame echoes the slightly sloping walls of the Hall in which it will be housed and used.
Vol. 32, No. 2 pp 69 - 73 (2004)
ABSTRACT: MARCS Auditory Laboratories is a University Research Centre at the University of Western Sydney. MARCS specialises in research on speech, music, and auditory processes. This paper elaborates particular research strands in MARCS - Auditory Processes and Speech Technology, the Baby Lab, Cormnunicative Musicality, Human Factors and Performance, Music Cognition, Second Language Acquisition, and Speech and Language. and describe current projects in each of these strands. This is followed by a brief history of the Centre and its role at UWS.