Microphone Array Project ECE5525 – Speech Processing Robert Villmow 12/11/03

Microphone Array Purpose Improves sound reception when interfering sources are located far enough apart spatial separation Capable of determinig the direction a sound is coming from

Background Data sampled at each microphone is different due to different angles of arrival Delay and Sum Algorithm Assume a sound is arriving at a specific angle then calculate when that sound will be sampled by the other microphones Sound arriving from desired angle will be correlated between microphones Sound arriving from other angles will be uncorrelated Summation of the data will attenuate uncorrelated signals

15 Element Microphone Array Low Middle High Low Array 4x spacing as high array Middle Array 2x spacing as high array High Array minimum spacing between microphones

Microphone Sampling Source at 90° Source at 50° Source at 10°

Sampling Summary Sample rate affects performance sampled data differs between microphones algorithm depends on data being correlated between microphonesS Sound sources at 0° are not affected by sample rate sampled by all microphones at the same time

Frequency Responses at 4400 Hz High Array Low Frequency Response Similar to a single microphone High Frequency Response Narrow beam width Frequency Responses at 4400 Hz

Frequency Responses at 800 Hz Low Array Low Frequency Response Good Directional response High Frequency Response Too many Grating lobes Frequency Responses at 800 Hz

Block Diagram     High Freq BP Filter Middle Freq BP Filter 2.5khz – 4.5khz BP Filter Middle Freq  1.5khz – 2.5khz BPFilter Low Freq  300hz – 1.5khz

Array Test Configuration Speaker Radio 45°

CMU Microphone Array Data 15 Channels 16 kHz, 16-bit linear Sampling Files used an101-mtms-arr3A.adc 3 cm spacing in a noisy computer lab Speaker is 1 meter from array an101-mtms-arr4A.adc 4 cm spacing in a noisy computer lab an101-mtms-arrCR1A.adc 4 cm spacing with radio at 45° Speaker at a distance of 1 meters

Arr3A Results High Middle Low Difference – Single Channel vs. Summed signal -100 -80 -60 -40 -20 20 40 60 80 100 2 3 4 5 6 x 10 Maximum Peak Error - Summed vs. Single Channel 0.5 1 1.5 2.5 3.5 7 Mean Squared Error - Summed vs. Single Channel -100 -80 -60 -40 -20 20 40 60 80 100 2.5 3 3.5 4 x 10 Maximum Peak Error - Summed vs. Single Channel 1 1.5 2 7 Mean Squared Error - Summed vs. Single Channel -100 -80 -60 -40 -20 20 40 60 80 100 2.5 3 3.5 4 x 10 Maximum Peak Error - Summed vs. Single Channel 0.5 1 1.5 2 7 Mean Squared Error - Summed vs. Single Channel Mean Squared Error – Single Channel vs. Summed signal High Middle Low

Arr3A – Mean Squared Error Array Max Min High 9.8070 x 106 3.3647 x 107 Middle 1.0517 x 107 3.4093 x 107 Low 7.7878 x 106 3.1970 x 107

Arr4A Results High Middle Low Difference – Single Channel vs. Summed signal -100 -80 -60 -40 -20 20 40 60 80 100 2 2.5 3 3.5 4 x 10 Maximum Peak Error - Summed vs. Single Channel 6 8 7 Mean Squared Error - Summed vs. Single Channel -100 -80 -60 -40 -20 20 40 60 80 100 2 2.5 3 3.5 4 x 10 Maximum Peak Error - Summed vs. Single Channel 6 8 7 Mean Squared Error - Summed vs. Single Channel -100 -80 -60 -40 -20 20 40 60 80 100 1.5 2 2.5 3 3.5 4 x 10 Maximum Peak Error - Summed vs. Single Channel 6 8 7 Mean Squared Error - Summed vs. Single Channel Mean Squared Error – Single Channel vs. Summed signal High Middle Low

Arr4A – Mean Squared Error Array Max Min High 8.1192 x 106 6.7789 x 107 Middle 8.3030 x 106 6.8715 x 107 Low 6.3974 x 106 6.7689 x 107

ArrCR1A Results (Interpolated) Difference – Single Channel vs. Summed signal -100 -80 -60 -40 -20 20 40 60 80 100 2.5 3 3.5 4 4.5 x 10 Maximum Peak Error - Summed vs. Single Channel 6 8 10 12 14 Mean Squared Error - Summed vs. Single Channel -100 -80 -60 -40 -20 20 40 60 80 100 2 2.5 3 3.5 4 4.5 x 10 Maximum Peak Error - Summed vs. Single Channel 6 8 10 12 14 Mean Squared Error - Summed vs. Single Channel -100 -80 -60 -40 -20 20 40 60 80 100 2.5 3 3.5 4 x 10 Maximum Peak Error - Summed vs. Single Channel 6 8 10 12 14 Mean Squared Error - Summed vs. Single Channel Mean Squared Error – Single Channel vs. Summed signal

ArrCR1A – Mean Squared Error Array Max Min High 5.0761 x 106 1.2176 x 107 Middle 5.2716 x 106 1.3283 x 107 Low 4.3089 x 106 1.3238 x 107

Sound Results Sound Files...

Summary Microphone array increases SNR Array Response is best at angles between ±30° Oversampling smoothes array response increased computations decreases performance lost due to sampling