Audio Engineering Society

Chicago Section

Meeting Review, November 14, 2006

other meeting reports

11/14/06 Meeting Highlights
by Nick Kettman

David Clark was recently invited to speak to the Chicago Section on the topic of subjective and objective evaluations of automotive audio systems.  Mr. Clark founded the company DLC Design in 1977, and is currently the Director of Research at Alpine Electronics.  His presentation included discussion of two techniques he uses to assess audio system performance: Listening Technology (LiT), which is a subjective method used to predict a person's perception of the system, and Perceptual Transfer Function (PTF), which is an objective method capable of linking subjective traits to measurable data.

The two goals of LiT are prediction and analysis.  Predicting the performance of a system can assist in determining, for example, the long term user satisfaction.  Analysis of a system results in an absolute numerical ranking which can be used for comparing different audio systems.  The LiT technique is based on comparisons between the system under test and an agreed-upon reference which embodies what most people consider "good sound."  In most cases, the reference is the sound produced by the playback system in the recording studio.  By choosing this reference, the goal of an automotive audio sysetm becomes the reproduction of sound as the artist intended it to be heard.  A complete system evaluation is divided into smaller tasks which include multiple performance categories, such as tonal balance, spatial reproduction, distortion, clarity, and multiple listening modes, such as foreground, background, maximum impact.

During the second half of his presentation, Mr. Clark discussed the virtues of the PTF method.  The PTF is treated as a black box, with music as its input and listener opinion as its output.  Unlike traditional, often ambiguous links between perception and measurement, the attributes of PTF provide a way to get directly at the things which people hear and describe when evaluating a system.  For example, the PTF method links the perceptual attribute of "stage" (width, depth, balance, etc.) to the measurable attribute of precedence (inter-aural time delay, interaural level difference, etc.).

Mr. Clark concluded his presentation with a short demonstration of the PTF method.  Using a special foam "head," various measurements were taken around the room to show the effects of inter-aural level differences and time delays.