A METHOD FOR THE AUTOMATIC CALIBRATION OF AN OPERATIONAL PASSIVE ACOUSTIC LISTENING SYSTEM

Abstract: The calibration of a listening system during operation is achieved with regard to a clock synchronising of the listening stations included in the listening system, and the receiver characteristics of the microphones located in each listening station. These parameters are automatically adjusted by utilising a method for automatic calibration, using one or more sound generators to transmit special correction signals. The geographic position of each sound generator included in the calibration must be known to the listening system, and be within hearing distance and line of sight of the microphones in the listening system. The invention is a method for the correct calibration of a passive acoustic listening system while such a listening system is used for the determination of the direction to, or the position of the origin of sound signals. The automatic clock synchronising of listening stations is important for accurate determination of the direction to and/or the position of the origin of distinct sound. Long term stability and the accuracy of the listening system is secured by the clock calibration and the adjustment of the microphone characteristics. Microphone characteristics from the microphone producers can support the corrections. The calibration can be utilised for listening systems working in 2 or 3 geographical dimensions, and can be performed either continuous or periodic.

Description: A method for the automatic calibration of an operational passive acoustic listening system. The present invention relates to systems installed for listening purpose, consisting of listening stations with microphones, capable of detecting sound in general or together with a feature for the detection of correct direction to and/or the position of any distinct sound received from a 2 or 3 dimensional geographical field of vision. The present invention is an automatic method to maintain the synchronising of the clocks in each individual station and the correction of the receiver characteristics of the microphones. The synchronising of die clocks for the listening stations is important and necessary for the accuracy of the measurements of the listening system. The quality of the relative time measurement between the individual listening stations are important for the quality in the direction- and position-finding of distinct sound originated within any area of interest. The capabilities of correcting the receiver characteristics of a microphone compensates for the ageing of a microphone, thereby improving the long term quality in identifying signals with the same intensity. No methods have been found, describing the present invention. The present method, described in the following, enables calibration during normal operation for a listening system, utilising one or more sound generators located in known positions within hearing distance and line of sight from one or more microphones, included in the said listening system. The method is of a general nature. It requires knowledge about the relative position of the sound generators. To enable microphone calibration, the said listening system must be designed for the active use of the calibration signals received from the sound generators. This is achieved by methods as described in the following claims. A listening system, prepared for automatic operational calibration, may in its simplest form just detect any environmental sound, while the more sophisticated solutions are used for the direction and/ or position determination of the origin of sound. A specific application determines the minimum amount of listening stations and microphones. For sound detection only, one listening station with one microphone is sufficient. In such a minimum configuration, only calibration of microphone characteristics is required. A listening system, for determination of the direction to the origin of sound, the minimum equipment solution is one listening station with 2 microphones, also requiring only calibration of microphone characteristics. When there are two or more listening stations in the listening system, clock synchronising is necessary due to the long term drift of in internal clocks of the listening stations. Such drift in internal clocks increases the inaccuracy in the determination of the direction- and/or position measurements of the origin of sound. The microphones in the listening system shall be capable of relaying signals, relevant for all available acoustics within the frequency range of the microphones for a further calculation in the listening system. One or more sound generator may at any time be installed in defined positions provided that the listening stations have been installed and initially calibrated, the relative position and the directions between the listening stations have been defined, and that the internal clocks of the listening stations have been synchronised. According to the invention, calibration during operation is made by installing one or more sound generators at known positions within hearing distance and line of sight from one or more microphones mounted at the listening stations. The calibration starts when the sound generators are producing calibration signals. These calibration signals' series are adapted to the features in the listening system. It is a precondition that the listening system is utilising signal intensity, time measurements, phase measurements or combinations thereof for the detection of sound alone or together with features to find the position of and the direction to the origin of the sound. According to the present invention, each of the sound generators may transmit periodic measuring series, or such measuring series may be transmitted when required. Another feature of the present invention is that the calibration can be made without interrupting normal operation, enabling the results of the calibration directly to be used. A final feature of the invention is that a listening station can have producer corrections to the calibration of the microphone characteristics, and that these characteristics can be adjusted and automatically updated during operation.

Claims: Claims 1 . A method for the automatic calibration of an operational passive acoustic listening system, for the detection of sound in general or for the direction- and position- finding of the origin of sound that is distinct from the normal environmental sound, with processing means for the co-ordination of the analysis of sound signals received from listening stations in the said listening system, with one or more microphones for each of the said listening stations, for the calibration of one or more microphone receiver characteristics, and clock synchronising in two or more listening stations, and that said synchronising and said correction of microphone characteristics is made together or independently, when each listening station receives special correction signals from one or more sound generators, when each sound generator produces such said signals from known geographical positions within hearing distance and line of sight of the microphones, characterised in that each involved listening station in the acoustic listening system receives the same correction signals from one or more sound generators, that all the sound generators have known positions and are located within hearing distance and line of sight from one or more microphones, that the said microphones and the said listening stations are included in the automatic operational calibration correction, that clock synchronising is performed in two or more listening stations, that the receiver characteristics of the microphones are determined for the said microphones, that the clocks and the receiver characteristics are adjusted together or independently, and that any of these adjustments are made automatically. 2. A method according to claim 1 , characterised in that the correction signals are transmitted continuos or periodic from one or more sound generators. 3. A method according to claim 1 , characterised in that the automatic calibration can be made during normal operation or in a separate calibration mode. 4. A method according to claim 1 , characterised in that the listening system has available references for the receiver characteristics for one or more microphones in the listening system, and that these references are supplied from the producers of the microphones, independent of the installation and the commissioning of the listening system, and that these references are utilised in the correction of the receiver characteristic of the microphones.

Inventors: ENDRESEN TORE, GUSTAVSEN ARVE, OTTERLEI RAGNVALD, ENDRESEN, TORE, GUSTAVSEN, ARVE, OTTERLEI, RAGNVALD
Applicants: ENDRESEN TORE, GUSTAVSEN ARVE, OTTERLEI RAGNVALD, ENDRESEN, TORE, GUSTAVSEN, ARVE, OTTERLEI, RAGNVALD
Application year: 1996
Main classification: G01S5
IPC codes: G01S3, G01V1, G01V13