Cheah Heng Tan

Real-time Voice Activity Detector Using Gammatone Filter and Modified Long-Term Signal Variability

In this paper, a real-time robust voice activity detector (VAD) is proposed. The proposed VAD adopts the gammatone filter and modify the existing long-term signal variability (LTSV) measure, i.e. known as GMLTSV in short. The proposed VAD is an improved version of existing VAD which used gammatone filter and entropy. The LTSV measure is modified to adapt to the amplitude envelopes extracted using gammatone filter by swapping entropy and variance used in LTSV measure to reduce noise effect in the extracted temporal envelopes and improve discriminative power of the extracted feature. The proposed algorithm also implements an adaptive threshold that is computed using a nonlinear filter to track short-term trend of the extracted feature in real-time. The proposed VAD using GMLTSV feature is tested against clean speech signals from TIMIT test corpus which are degraded at SNR ranged from -10dB to 20dB by non-stationary noise, eg. airport noise, babble noise, exhibition noise from Aurora-2 database, and stationary noise, eg. additive white Gaussian noise. Based on the evaluation, it is proven that the proposed GMLTSV-based VAD is robust in speech and non-speech detection even at low signal-to-noise ratio (SNR) and outperformed other existing voice activity detectors which are compared in the evaluation. The proposed VAD achieved satisfactory accuracy when compared to the impractical single frequency filtering based VAD while implementing real-time scheme for practical application.

Prediction of wind induced noise over bodies and small cavity

The problem with wind induced noise exists in any electronic device used in the outdoor that incorporates microphone components mounted underneath small opened cavities within its body. Due to the complexity nature of the problem, efforts in trying to experimentally understand the flow induced noise problem has lengthened product development cycle time. In this paper, a CFD approach using the SST k-omega turbulence model were utilized as an initial model to assist in understanding the phenomenon. Several instances of experimentation using actual prototype models were conducted for the correlation study. The experimentally perceived noise from the output of the microphone was found to be fundamentally correlated to the numerical analysis as evidenced from the flow velocity vectors, profiles, and vortex core inside the cavity region. It is also shown that by following the principle of nonlinear theory of cavity resonances and Rossiter’s Theory, the understanding of the phenomenon can be further strengthened...

Wind noise analysis of a two-way radio

This paper describes the wind induced noise measurement of a two-way radio inside a wind tunnel by measuring the sound pressure level transmitted to a receiver unit placed inside the anechoic chamber. Anechoic chamber was used to isolate receiver from other outside noise. The transmitted wind noise was delivered by the receiver unit speaker and measured using the microphone which measures the sound pressure level and it was analyzed using the LMS Test Xpress software. The effect of wind flow direction, wind speed (2-6 m/s) and angle of attack (0-45 degrees) were presented. The results show that the increased of the flow speed brought about an increase of the wind noise for both direction of wind flow with more dominant effect for the left-to-right flow. There is a critical angle of attack of the wind which generated significant noise for the left-to right flow where the highest wind noise level is produced.

Sound quality analysis for two-way radio under wind noise

Noise generated from wind flow over a two-way radio could jeopardize communication effectiveness. A pair of two-way radio was studied where a unit (a transmitter)was placed inside a wind tunnel and the other unit (a receiver)was placed inside the anechoic chamber in order to isolate it from external noise. A speaker was located at a distance near the transmitter to give an audio input to the radio while the wind was flowing towards the radio. Sound quality parameters of roughness, sharpness, loudness and articulation index were used to measure the effect of wind noise on the sound quality at wind speed of 2 and 6m/s. In order to measure the effect of wind noise on the intelligibility of the message output from the speaker, the articulation index was calculated for 0,2 and 6 m/s wind speed. The results show that the roughness and loudness of the wind noise increase with the speed and the sharpness decreases with the wind speed. The articulation index also decreases with the wind speed.

Acoustic frequency response inside a rectangular cavity.

In any closed or partly closed regions of space, standing waves exist and the normal modes and natural frequencies associated with these standing waves determine the acoustic behavior of this enclosed air cavity. Also, there are many systems of practical interest in which a structure is in contact with this contained air. One of the practical examples considered in this study is the loudspeaker enclosures. The vibration behavior of the flexible membrane of loudspeaker is significantly affected by the modal contribution of the contained fluid and subsequently changes the frequency response of the speaker system. Thus, the objective of this paper is to study the acoustic behavior, which refers to the normal modes and natural frequencies of a rectangular air cavity and the coupled acoustic behavior of a force excitation source placed within this cavity. This study is then extended to an arbitrary cavity system. The second objective of this study is to locate the placement of the excitation source within the ...