P17347: Active Noise Cancellation
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Preliminary Detailed Design

Table of Contents

Team Vision for Preliminary Detailed Design Phase

Prototyping, Engineering Analysis, Simulation

The preliminary design phase was driven by an engineering analysis. As our design was broken into more detailed pieces, and the preliminary setup had begun on both the code base and the materials had begun, more questions came up on how we should approach certain problems.


Problem: What is our programming solution? How do go about bringing our preliminary design into the real world?

Solution: Use an Object-Oriented approach in C# to design and represent each physical entity in the process. In our programming solution, we will be able to use an object oriented approach to the system design.


Problem: What does noise cancellation look like from a normal users perspective?

Solution: Sound from all sources come in the form of waves. Below is a sample taken from Gleason on the 4th floor just after announcements. The human hearing can range from 0Hz to 20kHz.

Spectral Analysis of Room Noise

Spectral Analysis of Room Noise

We can analyze sound by establishing an example waveform. Most waveforms in the workplace and other areas are far more complex than the waveform displayed below, but for the idea of simplicity we should stick to looking at this particular waveform.

Audio Waveform

Audio Waveform

We need to take in a signal as shown above. The signal ranges frequencies from 0Hz to 20kHz. The signal can be split into multiple frequencies using a Fast Fourier Transform. A Fast Fourier Transform (FFT) is a means of converting a function from the time domain into the frequency domain. In so doing we determine the discrete fourier transform and convert all the signal into its discrete factors.

Individual Waveforms

Individual Waveforms

We can then follow this up by manipulating each individual signal (typically bying doing a 180 degree phase shift) and then re-summing the signals together into an anti-signal.

Below the red graph demonstrates one of these waveforms (for example, a 7kHz signal) is shown by itself. We should be able to simply change the sign of the equation (or do a phase shift of pi) and reach an anti-signal.

Individual Waveform

Individual Waveform

We can then transform the signal by inverting it: either through flipping the sign or doing a phase shift.

Inverted Waveform

Inverted Waveform

There are multiple reasons that an ideal solution is extremely difficult to incorporate. First, even the best technology in microphones cannot 100% perfectly capture a sound in any normal environment. The second issue is that to produce a FFT fast enough for our project there will need to be a 'close enough' answer that will be imperfect. Thus, our anti-sound wouldn't even be able to completely nullify the signal because of the near real-time nature of this design. With the non-ideal circumstances, the noise floor should still be reached just fine. As a result, we may get a result that looks similar to this design here.

Combined Waveform

Combined Waveform

Our solution now needs to take into account that the speakers will be a distance X meters away from the listener and the sound source will be Y meters away from the listener. Both sound sources will be a different coordinate position away from one another. We are keeping the listener, speaker and sound sources on the same 'z plane' to ensure a simple model. As a result, the amplitude and phase may need to be altered.


Problem: Common laptop speakers have difficulty reaching frequencies below 1kHz. It was established earlier on in the project that cancelling noise above 1kHz is difficult without the use of a direct headphone solution.

Temporary Solution: Work with speakers that can handle lower than 1kHz frequencies temporarily. The reason why laptop speakers have a hard time keeping up at lower frequencies is due to their inability to produce high enough air pressure to produce the low frequencies. They are just not equipped with the right tools to perform this task and thus a different speaker solution is needed for these lower frequencies. How different speakers work with different air pressures is not something that can be manipulated in the scope of this project.

Feasibility: Prototyping, Analysis, Simulation

Functional Decomposition

Functional Decomposition

Memory Allocation:

Sound Frequency Cancelling:

Spectral Analysis of Room Noise

Spectral Analysis of Room Noise

USB vs. Analog:

Networking:

Drawings, Schematics, Flow Charts, Simulations

Overall System Flowchart

Overall System Flowchart

Initialization Flowchart

Initialization Flowchart

Microphone Normalization Subsystem

Microphone Normalization Subsystem

Noise Detection and Location Subsystem

Noise Detection and Location Subsystem

Anti-Noise Subsystem

Anti-Noise Subsystem

Bill of Material (BOM)

Quantity Unit Price Item URL Total Cost
5 20.99 Microphone https://goo.gl/DV0HMS 104.95
1 27.99 USB Hub https://goo.gl/ZYT6pZ 27.99
1 6.99 USB Stereo Adapter https://goo.gl/QzwCVo 6.99
1 13.99 USB Powered Speaker https://goo.gl/XLbiS9 13.99
153.92

Test Plans

Engineering Requirements:

Subsystems:

Whiteboard Work

public/Photo Gallery/Phase 3 - Whiteboard Work/Anti-Noise Subsystem 2.jpg public/Photo Gallery/Phase 3 - Whiteboard Work/Anti-Noise Subsystem.jpg public/Photo Gallery/Phase 3 - Whiteboard Work/Class Breakdown.jpg public/Photo Gallery/Phase 3 - Whiteboard Work/Frequency Diagram.jpg public/Photo Gallery/Phase 3 - Whiteboard Work/Functional Decomp.jpg public/Photo Gallery/Phase 3 - Whiteboard Work/Initialization.jpg public/Photo Gallery/Phase 3 - Whiteboard Work/Normalization.jpg public/Photo Gallery/Phase 3 - Whiteboard Work/Overall Flowchart.jpg public/Photo Gallery/Phase 3 - Whiteboard Work/Waveform Cancellation 2.jpg public/Photo Gallery/Phase 3 - Whiteboard Work/Waveform Cancellation.jpg public/Photo Gallery/Phase 3 - Whiteboard Work/Work to due.jpg

Risk Assessment

Risks within the Preliminary Detailed Design

Plans for next phase


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