Steven L. Gay – författare

The ongoing revolution in electronic switching and transport technologies promises a dramatic increase in user satisfaction levels for future telecommunications networks. However, unless there is a corresponding improvement in the technologies of the acoustics of telecommunications, this promise will prove empty. The sense of presence that people feel when together in a room is largely due to the psycho-acoustic cues they sense from the human binaural hearing system evolved over thousands of years. Modern acoustic signal processing is just now beginning to be able to deliver that same experience to users in seperate locations. This includes the ability to communicate in full duplex with wider bandwidths and multiple audio streams (for instance stereo and 3D audio). It also involves locating and separating audio sources, suppressing noise, and using sound to automatically steer video cameras. This text presents digital signal processing techniques for telecommunications acoustics that are both cutting-edge and practical. Each chapter presents concepts as yet unused, but easily realizable with today's technology.To this end, both new theory and new implementation techniques are presented. Topics include new adaptive filtering algorithms, multi-channel acoustic echo cancellation, noise control, virtual sound, sound source localization for camera tracking, source separation, and microphone arrays.

158 2. Wiener Filtering 159 3. Speech Enhancement by Short-Time Spectral Modification 3. 1 Short-Time Fourier Analysis and Synthesis 159 160 3. 2 Short-Time Wiener Filter 161 3. 3 Power Subtraction 3. 4 Magnitude Subtraction 162 3. 5 Parametric Wiener Filtering 163 164 3. 6 Review and Discussion Averaging Techniques for Envelope Estimation 169 4. 169 4. 1 Moving Average 170 4. 2 Single-Pole Recursion 170 4. 3 Two-Sided Single-Pole Recursion 4. 4 Nonlinear Data Processing 171 5. Example Implementation 172 5. 1 Subband Filter Bank Architecture 172 173 5. 2 A-Posteriori-SNR Voice Activity Detector 5. 3 Example 175 6. Conclusion 175 Part IV Microphone Arrays 10 Superdirectional Microphone Arrays 181 Gary W. Elko 1. Introduction 181 2. Differential Microphone Arrays 182 3. Array Directional Gain 192 4. Optimal Arrays for Spherically Isotropic Fields 193 4. 1 Maximum Gain for Omnidirectional Microphones 193 4. 2 Maximum Directivity Index for Differential Microphones 195 4. 3 Maximimum Front-to-Back Ratio 197 4. 4 Minimum Peak Directional Response 200 4. 5 Beamwidth 201 5. Design Examples 201 5. 1 First-Order Designs 202 5. 2 Second-Order Designs 207 5. 3 Third-Order Designs 216 5. 4 Higher-Order designs 221 6. Optimal Arrays for Cylindrically Isotropic Fields 222 6. 1 Maximum Gain for Omnidirectional Microphones 222 6. 2 Optimal Weights for Maximum Directional Gain 224 6. 3 Solution for Optimal Weights for Maximum Front-to-Back Ratio for Cylindrical Noise 225 7. Sensitivity to Microphone Mismatch and Noise 230 8.