Friedemann Köster

Changes of vigilance caused by varying bit rate conditions

Quality aspects of media content are usually assessed by using subjective rating methods where subjects provide active feedback towards the perceived quality. The process how this judgment is being formed and the long-term influences of accompanying physiological processes are not represented by these methods. In this paper we used the electroencephalogram (EEG) to assess the cognitive state (vigilance) of listeners measured by the alpha frequency band power with respect to varying bit rate conditions. We show that stimuli with varying and constant bit rate cause a state of reduced vigilance. In addition we show the potential tendency that an interval of high bit rate audio inserted into a low bit rate stimulus increased the vigilance of listeners at the timescale of minutes. The results show that the perception of degraded media has long-term influences on physiological processes at the time scale of minutes which may influence customer behavior even though it probably stays undetected using purely standard subjective test methods.

Non-intrusive Estimation of Noisiness as a Perceptual Quality Dimension of Transmitted Speech

This article presents a new approach to the non-intrusive quality estimation of transmitted speech. Traditional estimation methods exhibit limitations to providing diagnostic information and for practical monitoring purposes. The new approach merges solutions to overcome the existing limitations and intends to provide a new user-friendly estimator. We present an overview and the planned structure of the proposed model. In order to provide diagnostic information, the method of assessing perceptual quality-relevant dimensions is applied. One of these quality dimensions is Noisiness, which describes degradations like background noise, circuit noise, or coding noise. As a fundamental component of the proposed model, a non-intrusive parametric Noisiness estimator is presented. The estimator is based on nine different features extracted from the output signal only. Using a linear regression, the features are mapped onto the Noisiness. The Noisiness estimator is trained on two and tested on three individual subjective databases. In addition, the performance of the resulting estimator is compared to the diagnostic intrusive estimator DIAL (Diagnostic Intrusive Assessment of Listening quality). The results prove that the presented estimator provides high reliability and indicate the applicability and value for non-intrusive diagnostic quality estimation.

Comparison of transmission quality dimensions of narrowband, wideband, and super-wideband speech channels

It is commonly acknowledged that the introduction of wideband and super-wideband speech transmission in Voice-over-IP leads to an improved overall quality compared to traditional narrowband telephony. However, beyond overall quality, dimensions such as coloration, continuity, noisiness, loudness, human speaker identification ability, as well as automatic speech and speaker identification performance may benefit from the augmented speech transmission bandwidth. In this paper, we review data on all of these quality and performance dimensions and classify them along a recommended “transmission rating scale” into eight service quality classes which are useful for transmission network planning. Applications of the results are discussed for different human-to-human and human-machine application scenarios.

Identifying Speech Quality Dimensions in a Telephone Conversation

Speech telecommunication services are traditionally used for communication between two interlocutors interacting in a conversation. Thus, the quality of transmitted speech in a conversational situation, as perceived by the end-users, is the important indicator for service providers to evaluate their systems. In this context, it is not enough to only provide information about the overall quality but also to indicate reasons and sources for quality losses. In this article, we present an approach towards analyzing speech quality in a conversational situation by dividing a conversation into three separate phases and identifying corresponding quality-relevant perceptual dimensions, as perceived by the system users. The identified dimensions can be combined for the overall quality assessment and may separately be used to diagnose the technical reasons of quality degradations. For this, four separate subjective experiments to uncover the underlying dimensions in each conversational phase are conducted. The resulting quality-profile, consisting of seven perceptual dimensions, is then validated in an extensive conversational experiment triggering all three phases of a conversation using a new proposed test-paradigm. This allows deeply analyzing conversational speech quality for diagnosis and optimization of telecommunication systems and provides the fundamentals for instrumental diagnostic conversational speech quality measures.

Analyzing the Relation Between Overall Quality and the Quality of Individual Phases in a Telephone Conversation.

Assessing and analyzing the quality of transmitted speech in a conversational situation is an important topic in current research. For this, a conversation has been separated into three individual conversational phases (listening, speaking, and interaction), and for each phase corresponding quality-relevant perceptual dimensions have been identified. The dimensions can be used to determine the quality of each phase, and the qualities of all phases, in turn, can be be combined for overall conversational quality estimation. In this article we present the work that has been conducted to identify the weights of the individual phases for the overall quality. For this, we conducted an experiment that allows the participants to perceive each phase separately and to gather the overall quality as well as the quality ratings for each individual phase. The results enable to create a linear model to predict the overall quality on the basis of the three phases. This allows to draw first conclusions regarding the relation between the individual phases and the overall quality and provides a major landmark towards a diagnostic assessment of conversational quality.

Instrumental Diagnostic Conversational Quality Modeling

The work presented in this book, so far, was conducted with the final goal to develop an instrumental diagnostic conversational quality model.

Speech Quality in a Telephone Conversation

The previous chapter introduced the fundamentals of speech communication, the perceived speech quality, the concept of diagnosing speech quality, as well as subjective and instrumental quality assessment methods.

Perceptual Quality Space in a Telephone Conversation

The approach of the work presented in this book is to combine the advantages of considering all possible user situations in a conversation and of diagnosing the quality of transmitted speech on the basis of perceptual dimensions.

Conversational Validation Experiments

In the two previous chapters, the perceptual quality space in a telephone conversation (Chap. 4) and a new test method for directly scaling the identified perceptual quality dimensions in a conversational situation (Chap. 5) were presented.

Direct Scaling of Perceptual Dimensions in a Conversational Situation

In the previous chapter, the perceptual quality spaces of two conversational phases, namely the Speaking and the Interaction Phase, have been explored and identified. These phases have not been part of multidimensional research in the related literature, yet.