09-08-2012, 03:57 PM
NOISE CANCELLATION BY ADAPTIVE FILTERING
APPLICATIONS
Noise cancellation almost requires the sound to be cancelled at a source, such as from a loud speaker. That is why the effect works well with headsets, since you can contain the original sound and the canceling sound in an area near your ear. In applications where the sound comes from many areas, such as in a room, it is difficult to cancel the sound from each area. But, scientists and engineers are working on solutions.
Noise cancellation is a method to reduce or completely cancel out undesirable sound, such that you can't hear it. It is often called Active Noise Cancellation because the electronics involved actively cause the noise cancellation in real time.
a.) HEADSETS
One obvious application is that people working near aircraft or in noisy factories can now wear these electronic noise cancellation headsets to protect their hearing. Noise cancellation makes it possible to enjoy music without raising the volume excessively.
Noise-cancelling headphones typically use ANC to cancel the lower-frequency portions of the noise; they depend on more traditional methods such as soundproofing to prevent higher-frequency noise from reaching the ear. This approach is preferred because it reduces the demand for complicated electronic circuitry that would be required for noise cancellation at higher frequencies, where active cancellation is less effective. To truly cancel high frequency components (coming at the ear from all directions), the sensor and emitter for the cancelling waveform would have to be adjacent to the user's eardrum, which is not technically feasible.
b.) SPACE SATELLITE ANTENNA
Some space satellites have long antennas. If such an antenna would start to vibrate wildly, it could throw the satellite out of orbit and out of control. By detecting the waveform or any vibration in the antenna, it can be suppressed in the same way that noise is suppressed.
A piezoelectric device creates an electrical signal when it detects a vibration. It also will vibrate according to an electrical signal it receives. Putting piezoelectric devices on the antenna can result in vibrating the antenna in an opposite phase, thus eliminating the dangerous motion.
c.) USE IN APARTMENTS
One cool idea is to suppress unwanted noise from another apartment by vibrating your wall out of phase with the sound from next door. For example, suppose the person in the next apartment has his stereo on real loud. In some cases, you can even feel the wall vibrate. By placing devices on the wall, you can detect the wall vibrations and generate vibrations in an opposite phase. Thus would completely cancel out the noise coming from the other apartment.
d.) HONDA CARS
Honda is now using noise-cancellation technology in their Japan-only Accord station wagon.
The way it works is that a microphone connected to the car stereo system picks up all the sound inside the car, including music or such from the stereo. Then the noise-cancellation system subtracts the sound of the music coming from the stereo and produces noise-canceling sound waves that match the frequency of unwanted sound.
The noise-canceling sound waves are also sent through the stereo speakers, along with the music. This technique greatly reduces the low frequency vibration noises in the car, without dampening the car's audio system.
e.) IN DIGITAL CAMERAS
NEC just injected a little Bose up in some digital cameras, adding what it calls "noise suppression technologies" to Casio's new EX-ZR10 and promising that it will be deployed "throughout the digital camera and video camera markets" soon. The tech is designed to combat the evil intrusion of noise from optical zoom motors, working with a recording of what the zoom motor sounds like inside the camera. The shooter's internal circuitry then subtracts that noise from what's being recorded and NEC indicates a camera's microphone still captures other, desirable ambient noise without issue and that this tech allows the use of faster, more powerful motors for faster, more powerful zooming.
APPLICATIONS
Noise cancellation almost requires the sound to be cancelled at a source, such as from a loud speaker. That is why the effect works well with headsets, since you can contain the original sound and the canceling sound in an area near your ear. In applications where the sound comes from many areas, such as in a room, it is difficult to cancel the sound from each area. But, scientists and engineers are working on solutions.
Noise cancellation is a method to reduce or completely cancel out undesirable sound, such that you can't hear it. It is often called Active Noise Cancellation because the electronics involved actively cause the noise cancellation in real time.
a.) HEADSETS
One obvious application is that people working near aircraft or in noisy factories can now wear these electronic noise cancellation headsets to protect their hearing. Noise cancellation makes it possible to enjoy music without raising the volume excessively.
Noise-cancelling headphones typically use ANC to cancel the lower-frequency portions of the noise; they depend on more traditional methods such as soundproofing to prevent higher-frequency noise from reaching the ear. This approach is preferred because it reduces the demand for complicated electronic circuitry that would be required for noise cancellation at higher frequencies, where active cancellation is less effective. To truly cancel high frequency components (coming at the ear from all directions), the sensor and emitter for the cancelling waveform would have to be adjacent to the user's eardrum, which is not technically feasible.
b.) SPACE SATELLITE ANTENNA
Some space satellites have long antennas. If such an antenna would start to vibrate wildly, it could throw the satellite out of orbit and out of control. By detecting the waveform or any vibration in the antenna, it can be suppressed in the same way that noise is suppressed.
A piezoelectric device creates an electrical signal when it detects a vibration. It also will vibrate according to an electrical signal it receives. Putting piezoelectric devices on the antenna can result in vibrating the antenna in an opposite phase, thus eliminating the dangerous motion.
c.) USE IN APARTMENTS
One cool idea is to suppress unwanted noise from another apartment by vibrating your wall out of phase with the sound from next door. For example, suppose the person in the next apartment has his stereo on real loud. In some cases, you can even feel the wall vibrate. By placing devices on the wall, you can detect the wall vibrations and generate vibrations in an opposite phase. Thus would completely cancel out the noise coming from the other apartment.
d.) HONDA CARS
Honda is now using noise-cancellation technology in their Japan-only Accord station wagon.
The way it works is that a microphone connected to the car stereo system picks up all the sound inside the car, including music or such from the stereo. Then the noise-cancellation system subtracts the sound of the music coming from the stereo and produces noise-canceling sound waves that match the frequency of unwanted sound.
The noise-canceling sound waves are also sent through the stereo speakers, along with the music. This technique greatly reduces the low frequency vibration noises in the car, without dampening the car's audio system.
e.) IN DIGITAL CAMERAS
NEC just injected a little Bose up in some digital cameras, adding what it calls "noise suppression technologies" to Casio's new EX-ZR10 and promising that it will be deployed "throughout the digital camera and video camera markets" soon. The tech is designed to combat the evil intrusion of noise from optical zoom motors, working with a recording of what the zoom motor sounds like inside the camera. The shooter's internal circuitry then subtracts that noise from what's being recorded and NEC indicates a camera's microphone still captures other, desirable ambient noise without issue and that this tech allows the use of faster, more powerful motors for faster, more powerful zooming.