Requirements Specification

Selective Voice Tapping System (SVTS)

Background:

There are lots of companies, in the market, which make surveillance cameras for monitoring, but most of the surveillance cameras cannot capture the audio signals with video signals. There are only some surveillance cameras which can capture both audio and video signals, but their range of capturing audio signals is not long and most of them cannot separate and select one audio signal in presence of more than one audio signal.

There are very few surveillance cameras in the market which can selectively monitor by picking a selected individual’s voice in a conference room, but they are very expensive. Our team wants to build a cheap SVTS using eight microphones, a multi channel analog to digital converter, a computer and MATLAB software. The SVTS will be inexpensive, so that monitoring will be done efficiently by listening to what an individual is saying, but yet economical. When it comes to the purchasing decision, buyers have the following options:

Buy an expensive surveillance camera for audio and video monitoring.
Buy an in-expensive surveillance camera for video monitoring and our in-expensive SVTS for audio monitoring.

This document is the required specification for the SVTS to aid monitoring. The SVTS is easy to use and in-expensive, so when used with an in-expensive surveillance camera will provide an effective monitoring.

The Deliverables:

The deliverables are listed below:

• The working prototype of the circuit.
• The following work and setup:
• Wiring artwork.
• Parts list.
• Assembly drawings and, assembly instructions.
• Bill of materials.
• An analysis report.
• User’s manual
• .System specification, including:
• the design concept
• block diagram, and functional description of the blocks
• a system description and any analysis done during the design procedure
• Schematics and circuit diagrams.
  

Special Restrictions:

• The analog to digital converter, that will be used, should have eight channels.
• MATLAB should support the analog to digital converter that will be used in design.
• The analog to digital converter should have a sample rate in the range of 48 kilo samples per second to 250 kilo samples per second.
  

Principle of Operation:

The user will enter the location or the angle at which the desired individual is, then using the eight microphones and an eight channel analog to digital converter, delaying the signal at each microphone accordingly, the signal is fed into the computer and after certain manipulations the voice of the desired individual is heard through the speakers at the computer.

The user also has the option to use an electronic bug. The bug is utilized to track a certain target on which it is installed. The bug will generate a signal with a frequency much higher than that of human voice. This signal is detected by the SVTS and is used to locate the target. The user will be able to listen to/record the voice signals coming from the target’s position.

User Interface:

The user interface consists of a computer monitor, keyboard and speakers. The input location or the angle of the desired individual is entered through the keyboard, which can be seen on the computer monitor, and the individual’s voice is heard through the speakers connected to the computer.

Input:

There are two modes of operation for the SVTS, Mode One and Mode Two. Mode One requires the user to specify a direction to which the user intends to listen. The location will be specified by measuring the amount of degrees the desired location is away from the axis along the array of microphones. Mode Two of operation will allow the user to bug an individual. Once the bug is installed, the SVTS will be able to detect and listen to the person.

In Mode One, the user will input the desired location through the user interface. A program such a Visual Basic will provide the user with the appropriate prompts. If an invalid angle (i.e. any angle outside 0o-180o range) is entered the user will be notified and told to try again. Once the desired location is specified, the eight microphones aligned in an array will pick up voice signals. The voice signals received by each microphone will be amplified and inputted into an eight channel A/D converter. The inputted signals will fall in between the frequency range of 20 Hz to 20 KHz, and the A/D converter must be able to sample at least twice this frequency. The A/D converter will be synchronized with MATLAB. MATLAB then performs the necessary calculations to apply the proper signal delays to the signal received by each microphone. The amount of delay required will be different for each channel depending upon the geometry of the location.

In Mode Two of operation, the bug placed on an individual will be emitting a signal with frequency of roughly 30 kHz, which is above the audible range of humans. The SVTS will then scan the surrounding area until it finds a location where a frequency of 30 kHz is located. Once this frequency is detected the SVTS will track the bug around the room. By locating where the 30 kHz signal is being emitted from the proper delay signals can be added accordingly.

Output:

The output will be an audio signal sent to a set of speakers in range of the user. The audio signal will be the summation of eight synchronized individual microphone signals. The audio signals are able to be added by applying the appropriate signal delay to each channel through MATLAB. When the SVTS is in Mode Two of operation, a low pass filter will be applied to only allow frequencies of 20 Hz to 20 KHz to be outputted through the speakers.

The User’s Manual:

The SVTS operates in two modes.

When operating on Mode One, a specific angle is inputted through the user interface. This angle corresponds to the direction to which the user intends to listen. Once the angle is inputted to the system, the SVTS will filter out the noise from all directions and will allow only the voice signals that are coming from the selected direction.

When operating on Mode Two, an electronic bug is utilized to track a certain target on which it is placed. The bug will generate a signal with a frequency much higher than that of human voice. This signal is detected by SVTS and is used to locate the target. The user will be able to listen to/record the voice signals coming from the target’s position.

For correct operation of the SVTS, the user should follow the instructions below:

1. Turn on the computer, microphones, and the circuit board.
2. Start the SVTS User Interface located on the computer desktop.
3. Choose Mode One or Mode Two:

   • Mode One
     1. Enter the desired angle (in degrees) from which the audible sound is to be recorded.
     2. Choose between “play and record” or “play only” options on the user interface.
   • Mode Two:
     1. Turn on the electronic bug and install on the target
     2. Press the “Scan” button on the user interface
     3. Once “Scanning is Complete” message is displayed, choose between “play and record” or “play only” options on the user interface.
     4. Press the “Stop” button to stop recording.
     5. Open the “Recorded Voice” folder on the desktop and double click on the audio file to listen to the recorded voice.

Acceptance Tests:

The acceptance tests will be done on both Mode One and Mode Two as follows:

Acceptance Test for Mode One:
1. Place the speaker at a pre-determined location in a noisy environment.

2. Input the angle (in degrees) that corresponds to this location in the SVTS user interface.

3. Choose “play only” option.

4. Verify that the speaker’s voice is detectable with the least amount of noise from undesired locations.

5. Press the “Stop” button to stop playing.

6. Choose “play and record” option.

7. Verify that the speaker’s voice is detectable with the least amount of noise from undesired locations.

8. Press the “Stop” button on the user interface

9. Open the “Recorded Voice” folder on the desktop and double click on the audio file.

10. Verify that the speaker’s voice has been recorded properly.

Acceptance Test for Mode Two:

1. Install the electronic bug on a speaker placed at a pre-determined location in a noisy environment

2. Press the “Scan” button on the user interface

3. Once “Scanning is Complete” message is displayed, choose “play only” option on the user interface

4. Verify that the speaker’s voice is detectable with the least amount of noise from undesired locations.

5. Repeat steps 1 and 2.

6. Once “Scanning is Complete” message is displayed, choose “play and record” option on the user interface.

7. Verify that the speaker’s voice is detectable with the least amount of noise from undesired locations Press the “Stop” button on the user interface

8. Open the “Recorded Voice” folder on the desktop and double click on the audio file to listen to the recorded voice.

9. Verify that the speaker’s voice has been recorded properly.

Product Cost:

The cost of building the entire system is simply the sum of the cost for each component. The cost for each microphone will be about $25. The Analog to Digital Converter will cost approximately $50. The necessary circuitry will be built using components provided by UMass Laboratory.