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

2. 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

3. 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

4. 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

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

6. 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

7. 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

8. 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

9. 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

10. Array Test Configuration
Speaker
Radio
45°

11. 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

12. 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

13. Arr3A – Mean Squared Error
Array
Max
Min
High
x 106
x 107
Middle
x 107
x 107
Low
x 106
x 107

14. 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

15. Arr4A – Mean Squared Error
Array
Max
Min
High
x 106
x 107
Middle
x 106
x 107
Low
x 106
x 107

16. 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

17. ArrCR1A – Mean Squared Error
Array
Max
Min
High
x 106
x 107
Middle
x 106
x 107
Low
x 106
x 107

18. Sound Results
Sound Files...

19. 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