Saturday, October 11 9:00 am 12 noon
Session G Instrumentation and Measurement
G-1 Objective Measures of LoudnessGilbert A. Soulodre, Scott G. Norcross, Communications Research Centre, Ottawa, Ontario, Canada
There are numerous applications where it is desirable to have an objective measure of the perceived loudness of typical audio signals. For example, in broadcast applications an objective measure would allow the perceived loudness of the various program materials to be equalized. In the present paper several potential objective loudness measures are examined. The objective measures are evaluated in their ability to predict the results of a database derived from a series of formal subjective tests. Possible metrics for rating the performance of the objective loudness measures are considered.
G-2 Testing for Radio-Frequency Common Impedance Coupling (the 'Pin 1 Problem') in Microphones and Other Audio EquipmentJim Brown, Audio Systems Group, Inc., Chicago, IL, USA
It has been shown that inadequate termination within the microphone of the shield of the microphones output wiring, a fault commonly known as the 'pin 1 problem," is a primary cause of VHF and UHF interference to professional condenser microphones. Tests using only audio frequency test signals generally fail to expose susceptibility to radio frequency (RF) interference. Simple RF tests for pin 1 problems in microphones and other audio equipment are described that correlate well with EMI observed in the field.
G-3 A Novel Method of Testing for Susceptibility of Audio Equipment to Interference from Medium and High Frequency Radio TransmittersJim Brown, Audio Systems Group, Inc., Chicago, IL, USA
It has been shown that radio frequency (RF) current flowing on the shield of balanced audio wiring will be converted to a differential signal on the balanced pair by a cable-related mechanism commonly known as Shield-Current-Induced Noise. This paper investigates the susceptibility of audio input and output circuits to differential signals in the 200 kHz to 2 MHz range, used worldwide for AM broadcasting. Simple laboratory test methods and data are correlated with EMI observed in the field.
G-4 Directional Room Acoustics Measurement Using Large-Scale Microphone ArraysPaul Henderson, Rensselaer Polytechnic Institute, Troy, NY, USA
To fully describe the sound field at a listening position in an acoustical environment, the distribution of energy arriving from varying spatial directions is required, which this research accomplishes through the use of microphone array beamforming. Using the proposed technique, a multimicrophone impulse response measurement may be used to directionally locate any direct, reflected, or scattered energy arriving at the measurement location. This data may be graphically projected onto a sphere surrounding the measurement location or onto a virtual model of the measured environment, revealing the origin of the arriving energy. Preliminary measurements conducted at a prominent concert hall are presented, illustrating the analysis capability of the technique.
G-5 Intelligent Program Loudness Measurement and Control: What Satisfies Listeners?Jeffrey C. Riedmiller, Steve Lyman, Charles Robinson, Dolby Laboratories, Inc., San Francisco, CA, USA
The broadcast, satellite, and cable television industries have been plagued for years by the inability of personnel to accurately interpret and thus consistently control program loudness utilizing traditional measurement devices and methods. As a result, most listeners feel compelled to make adjustments to their television volume controls (in the home). A recent survey of channel-to-channel and/or program-to-program level discrepancies and subjective listening tests confirms that current the practice is unacceptable to listeners. In this paper we describe loudness measurement techniques that improve accuracy, usability, and consistency relative to previous techniques. Accuracy in this application is determined by correlation to listener opinion, with the particular goal of minimizing annoyance resulting from level mismatch. Usability is improved by minimizing the interaction required by the user. Consistency is achieved by minimizing the amount of meter interpretation required. The keys to this method are: providing a single numeric indication of loudness for a given program or segment; and isolating and measuring the portions of the program that are primarily speech, and using speech loudness as the basis for overall program level thereby improving listener satisfaction.
G-6 A Novel Single-Microphone Method of Measuring Acoustical Impedance in a TubeRobert Stevens, HGC Engineering, Mississauga, Ontario, Canada; John Vanderkooy, University of Waterloo, Waterloo, Ontario, Canada
A method is presented, for measuring acoustical properties of materials, which the authors believe to be novel and unique. The method relies on an MLS (maximum length sequence) excitation signal to measure the acoustical impedance of a specimen of material placed at the termination of a long tube. Whereas the traditional methods require that measurements be made at multiple locations within the tube, either using a multichannel data acquisition system, or by physically moving a single microphone from one location to the next, the novel method requires only a single measurement at one location in the tube, using a single microphone. The necessity to conduct only a single measurement makes this method two to four times faster than traditional methods, depending on the desired frequency range of the measurement. Other benefits of this method include the fact that it requires only a single channel data acquisition system and single microphone, and that it has the unique ability to measure the impedance of the source end of the tube (i.e., the loudspeaker) as well as the material specimen at the termination end of the tube.