AES Vienna 2007: Poster Session P26

P26 - Instrumentation and Measurement

Tuesday, May 8, 13:30 — 15:00

P26-1 A Wireless PDA-Based Acoustics Measurement Platform—Petros Alexandridis, Nicolas-Alexander Tatlas, Panos Hatziantoniou, John Mourjopoulos, University of Patras - Patras, Greece
The proposed platform allows acoustic measurements via a flexible, portable system, based on commercially available hardware, such as a personal digital assistant (PDA) equipped with a wireless adapter and a digital audio capture card as well as a personal computer (PC) interconnected with off-the-shelf wireless networking hardware. Using this hardware, three software applications were implemented: (i) a device driver that handles the communication of the digital audio capture card with the PDA; (ii) a PDA application that realizes the WiFi connection with the personal computer, also incorporating a recording function that captures data and presents the user with their analysis; and (iii) the personal computer application that initiates the playback sequence as dictated by the connected PDA. The system can assist the fast measurement of large spaces. Room Impulse Response (RIR) measurement tests were conducted in a laboratory room, in order to evaluate the effectiveness and functionality of the measurement system.
Convention Paper 7148 (Purchase now)

P26-2 Nonlinear Cross Talk in Personal Computer-Based Audio Systems—R. Allan Belcher, Jonathon Chambers, Cardiff University - Cardiff, Wales, UK
International Electrotechnical Commission (IEC) and AES standards provide comprehensive tests for the performance of audio analog to digital (ADC) and digital to analog (DAC) converters for both consumer and professional applications. It is usually assumed that the ADC is more likely to degrade audio sound quality than the DAC. Tests on two samples of a professional quality PC-based audio system are presented that show that a stereo DAC can introduce unexpected nonlinear effects. These results suggest that a future revision of the standards should include a measure of interchannel nonlinear cross talk in the stereo DAC. Results are presented and an intermodulation distortion (IMD) loop test proposed to enable this measurement to be made with precision.
Convention Paper 7149 (Purchase now)

P26-3 A Low-Distortion Fast-Settling Audio Oscillator: A Tribute to the Late Peter J. Baxandall, Analog Audio Expert—John Vanderkooy, University of Waterloo - Waterloo, Ontario, Canada
This paper is dedicated to the memory of Peter Baxandall, well-known for his work in audio and electronics. It is an exposition and analysis of a low-distortion fast-settling audio oscillator that he designed and built. Normal oscillators are shown to suffer from amplitude instability when the thermally-variable controlling resistance has a long time constant. The genius of the present two-integrator design is that it derives its amplitude stability from the cancellation of two square wave signals, of which one is fixed in amplitude, the other proportional to the oscillator output, with a threshold. A detailed analysis of the oscillator is presented. The result is an oscillator with a distortion below 0.01 percent and settling times of approximately 1 oscillation period. It is particularly useful in automated test equipment.
Convention Paper 7150 (Purchase now)

P26-4 Direct Current Offset and Balance for Audio Transformers Used with Paralleled Tubes or Solid State Devices—Aristide Polisois, Pierre Touzelet, S.E.R.E.M.E. S.A. - Bondoufle Cedex, France
In May 2005 (118th AES Convention, Barcelona, Spain, Paper 6346), I described a self compensated transformer for SE audio amplifiers, designed as SC-OPT and based on the principle that an auxiliary winding (tertiary), crossed by the same current as the primary winding, opposes a magnetic flux that reduces the overall flux, produced by the direct current, to almost zero, thus leaving the whole magnetic headroom in the core, for alternating current purposes. The opposed alternating current built in the tertiary was short-circuited with a suitable capacitor. Subsequently, a dedicated auxiliary magnetic core was added to the tertiary, acting as a flux escape, to reduce the antagonism of the tertiary on the primary, which is responsible for the loss of primary inductance. An improved layout to obtain the same result was achieved with the SC-SCC-SET (Split Core-Stereo Common Circuit-Single Ended Transformer), invented by Polisois and Mariani (120th AES Convention, Paris, France, Paper 6831). This model allows significantly improving the bass range. However, to achieve the DC generated flux cancellation, it needs an external balancing device of the DC flowing in the two primaries (left and right channel), situated on the same magnetic core. The transformer described hereafter named 4x4 SC-SCC-SET (4x4 Self Compensated-Single Common Circuit-Single Ended Transformer), overcomes this requirement. It also has many novel features, proceeding from the adopted arrangement of the windings.
Convention Paper 7151 (Purchase now)

P26-5 Acoustical Issues and Proposed Improvements for NASA Spacesuits—Durand R. Begault, James L. Hieronymus, NASA Ames Research Center - Moffett Field, CA, USA
This paper reviews current acoustical issues relevant to the design of future NASA spacesuits, based on measurements conducted in the current Mark III advanced prototype surface suit and proposes solutions for improving voice communications. Methods for mitigating problems including noise from the air supply, structure-borne noise from the suit, and detrimental acoustical reflections are reviewed.
Convention Paper 7152 (Purchase now)

P26-6 Design, Construction, and Qualification of the New Anechoic Chamber at Laboratorio de Sonido, Universidad Politécnica de Madrid—Juan José Gómez-Alfageme, José Luis Sánchez-Bote, Elena Blanco-Martin, Universidad Politécnica de Madrid - Madrid, Spain
The year 2005 has seen the design and construction of a new anechoic chamber at Laboratorio de Sonido of the Universidad Politécnica de Madrid. This new chamber has a free volume of 70 cubic meters and is built with rock wool wedges covered with a porous cotton cloth. The chamber cutoff frequency is 150 Hz. The chamber has been qualified according to that established in the ISO 3745 standard for the determination of the maximum distance between the sound source and the measurement position where the inverse square law is observed, within some tolerance. For the qualification, different types of excitation signals have been used as pure tones, broadband noise, narrow band noise, and pseudorandom sequences MLS.
Convention Paper 7153 (Purchase now)