On the effect of SNR and superdirective beamforming in speaker diarisation in meetings

This paper examines the effect of sensor performance on speaker diarisation in meetings and investigates the use of more advanced beamforming techniques, beyond the typically employed delay-sum beamformer, for mitigating the effects of poorer sensor performance. We present superdirective beamforming and investigate how different time difference of arrival (TDOA) smoothing and beamforming techniques influence the performance of state-of-the-art diarisation systems. We produced and transcribed a new corpus of meetings recorded in the instrumented meeting room using a high SNR analogue and a newly developed low SNR digital MEMS microphone array (DMMA.2). This research demonstrates that TDOA smoothing has a significant effect on the diarisation error rate and that simple noise reduction and beamforming schemes suffice to overcome audio signal degradation due to the lower SNR of modern MEMS microphones. Index Terms — Speaker diarisation in meetings, digital MEMS microphone array, time difference of arrival (TDOA), superdirective beamforming 1

The Sheffield Wargames Corpus.

Recognition of speech in natural environments is a challenging task, even more so if this involves conversations between sev-eral speakers. Work on meeting recognition has addressed some of the significant challenges, mostly targeting formal, business style meetings where people are mostly in a static position in a room. Only limited data is available that contains high qual-ity near and far field data from real interactions between par-ticipants. In this paper we present a new corpus for research on speech recognition, speaker tracking and diarisation, based on recordings of native speakers of English playing a table-top wargame. The Sheffield Wargames Corpus comprises 7 hours of data from 10 recording sessions, obtained from 96 micro-phones, 3 video cameras and, most importantly, 3D location data provided by a sensor tracking system. The corpus repre-sents a unique resource, that provides for the first time location tracks (1.3Hz) of speakers that are constantly moving and talk-ing. The corpus is available for research purposes, and includes annotated development and evaluation test sets. Baseline results for close-talking and far field sets are included in this paper. 1

Determining the number of speakers in a meeting using microphone array features

The accuracy of speaker diarisation in meetings relies heavily on determining the correct number of speakers. In this paper we present a novel algorithm based on time difference of arrival (TDOA) features that aims to find the correct number of active speakers in a meeting and thus aid the speaker segmentation and clustering process. With our proposed method the microphone array TDOA values and known geometry of the array are used to calculate a speaker matrix from which we determine the correct number of active speakers with the aid of the Bayesian information criterion (BIC). In addition, we analyse several well-known voice activity detection (VAD) algorithms and verified their fitness for meeting recordings. Experiments were performed using the NIST RT06, RT07 and RT09 data sets, and resulted in reduced error rates compared with BIC-based approaches. Index Terms — Speaker diarisation in meetings, microphone array, time difference of arrival (TDOA), speech segmentation and clustering, BIC, voice activity detection (VAD) 1

A multi-channel corpus for distant-speech interaction in presence of known interferences

This paper describes a new corpus of multi-channel audio data designed to study and develop distant-speech recognition systems able to cope with known interfering sounds propagating in an environment. The corpus consists of both real and simulated signals and of a corresponding detailed annotation. An extensive set of speech recognition experiments was conducted using three different Acoustic Echo Cancellation (AEC) techniques to establish baseline results for future reference. The AEC techniques were applied both to single distant microphone input signals and beamformed signals generated using two state-of-the-art beamforming techniques. We show that the speech recognition performance using the different techniques is comparable for both the simulated and real data, demonstrating the usefulness of this corpus for speech research. We also show that a significant improvement in speech recognition performance can be obtained by combining state-of-the-art AEC and beamforming techniques, compared to using a single distant microphone input

Magnetic Bearing Reaction Wheel Micro-vibration Signature Prediction

This article presents an analytical micro-vibration model for magnetic bearing reaction wheels (MBRWs) based on a rotordynamics model combined with the active control loop. This model is validated employing a fullyactive Lorentz-type MBRW demonstrator and a multicomponent dynamometer capable of measuring the exported micro-vibrations. The results show an accurate description of the generated vibration by only considering the unbalance forces as excitation

On-line micro-vibration measurement method for Lorentz-type magnetic-bearing space actuators

A novel, cost-effective, real-time and on-line method for measuring the generated micro-vibrations and iden- tifying the forces in a magnetic bearing space actuator is proposed. For its validation, an actively-controlled electrodynamic (Lorentz-type) magnetic bearing reaction wheel (MBRW) demonstrator is used, where the mag- netic bearing coils’ current is used as a measurable magnitude to identify the exertion of forces to the satellite’s structure. Due to the Lorentz-type magnetic bearing, a linear relation between current and force is considered and a validation campaign is undertaken, taking a micro-vibration test set-up as a reference. The results obtained using the proposed method are comparable, to a sub-newton level, to the micro-vibration amplitude measured us- ing a state-of-the-art piezoelectric-based dynamometric equipment, which is usually employed for reaction wheel on-ground qualification. The proposed method does not rely on any external and costly measurement equipment, as it only employs internal sensors, already required for control purposes in any active magnetic bearing (AMB), and it can be used for control or on-line and in-situ monitoring purposes