Environmental noise monitoring

• US 20030039369A1
• Filed: 07/02/2002
• Published: 02/27/2003
• Est. Priority Date: 07/04/2001
• Status: Active Grant

• Current Assignee: Soundscience Pty Limited
• Original Assignee: Soundscience Pty Limited
• Inventors: Bullen, Robert Bruce
• Granted Patent: US 7,308,105 B2
• Time in Patent Office: Days
• US Class Current: 381/71.12
• CPC Class Codes: G01H 3/125 for representing acoustic field distribution using optical means G01H9/002; sonar systems for imaging G01S7/56, G01S15/89; acoustic holography G03H3/00
• CPC Class Codes: G01S 3/8083 determining direction of source

Abstract

This invention concerns environmental noise monitoring, and more particularly a system and method for environmental noise monitoring. The environmental noise monitoring system comprises three or more sound level transducers arranged apart from each other in an environment containing one or more noise sources. Each transducer is arranged to pick up sounds arriving from all directions and to transduce the sounds into electrical signals. The sound level and direction measuring equipment includes signal samplers connected to respective transducers to receive electrical signals representing environmental sounds and to sample the electrical signals. A computer processor is further provided to perform cross correlation calculations to generate a cross correlation function for each pair of sampled signals. The processor identifies local maxima in the cross correlation functions, estimates the angle of arrival of the sound associated with a local maximum and the sound pressure level associated with the maximum, and uses the estimates of the angles from all cross correlation functions to identify a source of noise in a particular direction and the level of noise from that source, and then identifies additional sources of noise in different directions and the levels of noise from those sources. Noise levels from sources in particular directions may be accumulated, displayed and saved for reference.

Claims

1. An environmental noise monitoring system, comprising:

three or more sound level transducers arranged apart from each other in an environment containing one or more noise sources, each transducer is arranged to pick up sounds arriving from all directions and to transduce the sounds into electrical signals;

sound level and direction measuring equipment, including;

signal samplers connected to respective transducers to receive electrical signals representing environmental sounds and to sample the electrical signals; and

a computer processor to;

perform cross correlation calculations to generate a cross correlation function for each pair of sampled signals,

identify local maxima in the cross correlation functions, to estimate the angle of arrival of the sound associated with a local maximum and the sound pressure level associated with the maximum, and

use the estimates of the angles from all cross correlation functions to identify a source of noise in a particular direction and the level of noise from that source, and then to identify additional sources of noise in different directions and the levels of noise from those sources.

2. A system according to claim 1, where the sound transducers are microphones, and three microphones are arranged in a triangular configuration.

3. A system according to claim 2, where the microphones are arranged between 0.5 meters and 10 meters apart.

4. A system according to claim 1, where the electrical signals are received simultaneously and sampled over a period between 200 ms and 1 second.

5. A system according to claim 1, where the signal samplers sample at a rate of at least 44,100 Hz and with at least 24 bit resolution.

6. A system according to claim 1, where the results of the cross correlation calculations are saved or displayed while the sound signals produced by the next period are collected.

7. A system according to claim 1, where the arrival angles corresponding to each local maximum are determined in relation to a fixed directional system.

8. A system according to claim 7, where the arrival angles are pre-computed and stored for faster real-time processing.

9. A system according to claim 1, where the sound transducers comprise a three dimensional array arranged in a tetrahedral configuration.

10. A method of monitoring environmental noise, the method comprising the steps of:

using each of three or more sound level transducers arranged apart from each other in an environment containing one or more noise sources, to pick up sounds arriving from all directions;

transducing the sounds into electrical signals;

sampling the electrical signals;

performing cross correlation calculations to generate a cross correlation function for each pair of sampled signals;

identifying local maxima in the cross correlation functions, and estimating the angle of arrival of the sound associated with a maximum and the sound pressure level associated with the maximum;

using the estimates of the angles from all cross correlation functions to identify a source of noise in a particular direction and the level of noise from that source; and

then identifying additional sources of noise in different directions and the levels of noise from those sources.

11. A method according to claim 10, where the electrical signals are sampled over a period between 200 ms and 1 second.

12. A method according to claim 10 where the electrical signals are sampled at a rate of at least 44,100 Hz, with at least 24 bit resolution.

13. A method according to claim 10, where the step of identifying local maxima in the cross correlation functions includes saving and displaying the results of identified maxima while the electrical signals produced during the next period are recorded.

14. A method according to claim 10, where the step of identifying a source of noise includes comparing the arrival angles in each of the cross correlation functions when there are local maxima in all cross correlation functions for which one of the two possible arrival angles match to within a pre-determined tolerance.

15. A method according to claim 14, which further includes:

determining all matches within the predetermined tolerance;

sorting the matches in order of the sound pressure level;

assigning each match as a noise source to a sound pressure level; and

when a local maximum in any cross correlation function has been assigned to a source, removing all lower-order matches containing this local maximum.

16. A method according to claim 15, where the predetermined tolerance is between 5 and 10 degrees.

17. A method according to claim 10, where the directions and sound pressure levels of identified noise sources are stored and/or displayed for each sample period.

18. A method according to claim 17, where the noise levels associated with identified sources within specified ranges of angle are accumulated over a period of time.

19. A method according to claim 18, where the period of time is five minutes.

20. A method according to claim 10, where the arrival angles are determined in relation to a fixed directional system.

21. A method according to claim 20, where the arrival angles are pre-computed.

22. A method according to claim 10, where there are three transducers arranged in a triangular configuration.

23. A method according to claim 22, where the transducers are arranged between 0.5 meters and 10 meters apart.

24. A method according to claim 10, where the sound transducers comprise a three dimensional array arranged in a tetrahedral configuration.

25. Sound level and direction measuring equipment, the equipment including:

signal samplers connected to respective transducers to receive electrical signals representing environmental sounds from and to sample the electrical signals; and

a computer processor to;

perform cross correlation calculations to generate a cross correlation function for each pair of sampled signals;

identify local maxima in the cross correlation functions, to estimate the angle of arrival of the sound associated with a maximum and the sound pressure level associated with the maximum; and

use the estimates of the angles from all cross correlation functions to identify a source of noise in a particular direction and the level of noise from that source, and then to identify additional sources of noise in different directions and the levels of noise from those sources.

26. Equipment according to claim 25, where the signal samplers sample electrical signals over a period between 200 ms and 1 second.

27. Equipment according to claim 25 where the signal samplers sample electrical signals at a rate of at least 44,100 Hz, with at least 24 bit resolution.

28. Equipment according to claim 25, where the cross correlation functions are saved or displayed while the sound signals produced by the next period are collected.

29. A system according to claim 25, where the arrival angles corresponding to each maximum are determined in relation to a fixed directional system.

30. A system according to claim 25, where the arrival angles are pre-computed and stored for faster real-time processing.