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Session N Tuesday, May 15 8:30 - 13:00 hr Room C/D

Psychoacoustics, Perception and Listening Tests, Part 1

Chair: Nick Zacharov, Nokia Research Center, Tampere, Finland

8:30 hr N-1
An Investigation of Interaural Time Difference Fluctuations. Part 1: The Subjective Spatial Effect of Fluctuations Delivered over Headphones
Russell Mason, Bart de Bruyn & Francis Rumsey
University of Surrey, Guildford, UK

The subjective spatial effect of noise signals with sinusoidal ITD fluctuations was investigated. Both verbal and non-verbal elicitation experiments were carried out to examine the subjective effect of the ITD fluctuations with a number of fluctuation frequencies and fluctuation magnitudes. It was found that the predominant effect of increasing the fluctuation magnitude was an increase in the perceived width of the sound.
Paper 5383

9:00 hr N-2
A New Listener Training Software Application
Sean Olive
Harman International, Northridge, CA, USA

A new computer-based listener training application is described that trains listeners how to detect, classify and rate linear distortions added to program material. All signal processing is performed natively on the computer eliminating the need for expensive external hardware or large sound file libraries of pre-processed signals. The software adapts to the listeners' ability and performs automatic statistical analysis and storage of the results on a database server. It provides a useful tool for selecting the most discriminating and consistent listeners for listening tests and product evaluation.
Paper 5384

9:30 hr N-3
Active Listening Room Simulator: Part 1
Amber Naqvi & Francis Rumsey
University of Surrey, Guildford, UK

The main objective of the 'active listening room' project is to design a critical listening environment where the key acoustic features of the room can be actively modified. The aim is to create a truly variable listening condition in a reference listening room by means of active simulation of key acoustic parameters such as the early reflection pattern, early decay time and reverberation time. These parameters are likely to affect the subjective assessment of reproduced sound quality in a listening environment. Aims of the project are described, together with results of preliminary experiments.
Paper 5385

10:00 hr N-4
Evaluation of Five Commercial Stereo Enhancement 3D Audio Software Plug-ins
Sean Olive
Harman International, Northridge, CA, USA

Objective and subjective measurements were conducted on five commercial software-based plug-ins intended to provide spatial enhancement of stereo reproduction at the computer workstation. Listeners rated the sound quality of each using several different scales such as preference, timbral balance, three different spatial attributes, audible distortion, in addition to giving comments. Regular stereo (no enhancement) was included as a hidden reference. The listening test results revealed clear winners and losers. Stereo was preferred over three of the five plug-ins tested. The subjective results tend to correlate with their measured frequency response.
Paper 5386

10:30 hr N-5
Perceptual and Semantic Scaling for User-Centered Control over Distortion-Based Guitar Effects
William Martens & Atsushi Marui
University of Aizu, Aizu-Wakamatsu, Japan

Multidimensional perceptual and semantic differential analyses were performed for a set of stimuli that were generated by submitting a pre-recorded guitar performance to a popular multi-effects processor. Within three nominal types of distortion effect (Overdrive, Distortion and Fuzz), the �drive� setting of the effect was varied between minimum and maximum levels while adjusting the volume of the resulting sounds to maintain constant loudness. As the meaning of the �drive� parameter varies across these effects, changing the tone color for some, while changing only the loudness for others, the loudness of the processor outputs was equalized prior to subjective rating sessions in order to determine what perceptual attributes the �drive� parameter affects besides loudness.
Paper 5387

11:00 hr N-6
Graphical Elicitation Techniques for Subjective Assessment of the Spatial Attributes of Loudspeaker Reproduction - a Pilot Investigation
Natanya Ford, Francis Rumsey & Bart de Bruyn
University of Surrey, Guildford, UK

Non-verbal elicitation techniques may be used in addition to verbal methods in order to obtain meaningful subjective responses about the spatial attributes of reproduced sound. By analyzing results from a preliminary graphical investigation, the provision of such responses has been appraised and practical considerations highlighted. Data analysis indicates that non-verbal responses uphold conventional expectations with respect to the effect of loudspeaker and listener location on perceived sound images. With this in mind, it is suggested that the technique be used to assess variables which have not been subject to such intensive study, or be employed in situations where a verbal language may not be appropriate. Further investigations are therefore proposed with respect to the findings of this paper.
Paper 5388

11:30 hr N-7
An Investigation of Interaural Time Difference Fluctuations. Part 2: Dependence of the
Subjective Spatial Effect on Audio Frequency
Russell Mason, Francis Rumsey & Bart de Bruyn
University of Surrey, Guildford, UK

The effect of the audio frequency of narrow-band noise signals with a sinusoidal ITD fluctuation was investigated. To examine this, a subjective experiment was carried out using a match to sample method and stimuli delivered over headphones. It was found that the magnitude of the subjective effect is dependent on audio frequency and that the relationship between the audio frequency and a constant subjective effect appears to be based on equal maximum phase difference fluctuations.
Paper 5389

12:00 hr N-8
A Jitter Simulator on Digital Data
Shogo Kiryu & Kaoru Ashihara
Electrotechnical Laboratory, Tsukuba, Japan

A simulator is proposed to examine detection threshold of the distortion due to time jitter. Signals with artificial time jitter are simulated on digital data using over-sampling, interpolation, and decimation. With this method, quantitatively controlled distortion is added to musical signals and the signals can be presented to human subjects through a conventional DA converter. The amount of the distortion hardly depends on the equipment. We are examining detection threshold of time jitter. Preliminary results show that some subjects can detect jitter of several hundreds nanoseconds.
Paper 5390

12:30 hr N-9
Variance of Sweet Spot Size with Head Location for Virtual Audio
John Rose, Boaz Rafaely, Takashi Takeuchi & Philip Nelson
University of Southampton, Southampton, UK

3D audio systems are effective when the listener�s head location is close to the head location assumed when the system was designed. In order to accommodate head movement, it is possible to design 3D sound systems that continuously select appropriate virtual audio filters that correspond to a listener�s varying head position. The required spatial resolution of the audio filters depends on the size of the sweet spot. Here the size of the sweet spot of a two speaker 3D audio system is evaluated subjectively at symmetric and asymmetric head locations.
Paper 5391


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