Noise Cancellation – What is it?
We can lessen the amount of unwanted noise that enters an audio system or signal path by using noise cancellation, also known as active noise control. This is accomplished via a number of techniques, which we’ll look at in this post. The first commercially available headphones with noise-cancellation technology appeared in the late 1980s. It is now a standard feature on many of our devices, such as computers, landlines, and cell phones.
In order to eliminate noise from ducts, the ability to reduce ambient background noise or cancel it out totally was initially created. Later, this technology was incorporated into military and aviation communication systems. It was a ground-breaking development in the business, even if at this point noise removal was only possible over a relatively narrow bandwidth.
We need to understand sound transmission fundamentally and some of the terminology we use to describe it before we can grasp noise cancellation strategies and how it all works.
What Qualifies as “Noise”?
Sound is the audio waves that we receive through our ears and brain. This is accomplished by a procedure called transduction, in which sound waves are transformed into electrical impulses that our brains receive and decode.
The human voice, as well as musical instruments, animals, the wind, machines, and other source “devices,” all transmit sound. When something makes a sound, it causes changes in the surrounding air pressure. These vibrations then pass through the air and reach our ears. A sequence of bones and hairs in the human ear then detects these changes in air pressure, which is eventually turned into electrical signals that the brain can understand as sound.
Frequencies are the building blocks of sound. These are noted in Hertz (Hz). Human hearing can detect frequencies between 20Hz and 20kHz. This range varies from person to person and can alter as we get older and are exposed to various sound pressure levels, which can eventually deteriorate our hearing.
In general, as we get older, we start to lose some of our ability to understand higher frequencies. Rarely do we only hear one frequency at once. We frequently hear a wide variety of frequencies and interpret them by using a sizable portion of our hearing range.
As was previously mentioned, sound acts and is transmitted as a waveform. Higher frequencies complete more cycles per second and have a shorter wavelength, whereas lower frequencies complete fewer cycles per second and have a longer wavelength. Of course, this wave has positive and negative excursions, as may be seen in the illustration below, which shows a 50Hz waveform:
Now that we are familiar with the audio waveform, we can move on to another crucial idea that is essential to the noise-canceling technology: phase.
The link between audio waveforms is known as phase. Phase reinforcement is the process of making a sound louder by combining two identical waveforms. The waveforms interact negatively and the listener can only distinguish the differences between them if one of the waveforms is reversed before the waveforms are played simultaneously.
Another key topic to understand is the perceived volume or level of a sound. Our ears do not respond linearly because of evolution, thus different frequencies must be played louder for us to hear them at the same volume. The frequency range that the human voice resides in has become audible to our ears. This varies across individuals and between males and females. Our voices, both male and female combined, are found in the frequency range from about 85Hz to 255Hz.
A sound’s volume is measured in Decibels (dB), which can be either a positive or negative number. Along with this, we also use two terms:
- Amplification or reinforcement – to make a sound louder.
- Attenuation – to make a sound softer.
We may look at the chart below, which shows common noises, where they sit on the scale, and any effects they might have on our hearing, to get a better grasp of the decibel level.
We can move on to noise-canceling technologies now that we are aware of how different frequencies and pressure levels affect our perception.
Noise cancellation Basics
Noise cancellation can be defined as the process of decreasing (attenuating) undesired noise from a system to the point where it is barely heard, if at all. Anything ambient that you would prefer not to record, such as wind, other artists in the space or on the stage, audio system noise, or outside influences like generators and equipment, falls under the category of unwanted noise. To do this, you can go in either of two directions:
- originating from the source device, such as a microphone
- inside the listening device—such as a set of headphones
Which of these approaches is used and which produces what outcomes depends on the task at hand.
It is standard practice in live music performance recording or concerts, telecommunications, or filming a television show or movie to perform noise cancellation at the source equipment, such as a microphone. Regarding the recording and performing arts, there are several ways to achieve noise cancellation.
When recording a performance of any kind, whether it is a musical instrument or a human voice, microphone placement is crucial. Without delving into too much detail, distinct polarity patterns exist in different microphones. As a result, only sounds that enter this magnetic field will be recorded; sounds from outside the field will not.
Engineers can place microphones, instruments, and performers in precise directions by using this knowledge to minimize the amount of undesired noise that enters the microphone’s field and maximize the amount of the desired material that does. You can also implement noise reduction by using extra equipment, such as noise gates, as well as better cables and equipment.
When making a phone call or recording a voice note, several of these techniques are employed on our telephones to limit unwanted sounds from accessing the microphones. Phase can be used to reduce background noise and enhance voice quality on mobile phones, gaming headsets, and laptops with onboard microphones because modern phones have more than one onboard microphone.
By inverting one of the audio channels, phase cancellation techniques are used to clear the audio signal heard on the other end of your phone conversation by filtering out all except your voice from the system.
On the listening or receiving end of the audio stream, noise cancellation works in the opposite direction. Here, we’ll use the example of noise-canceling headphones.
The two forms of noise-cancellation technologies used by noise-canceling headsets are passive noise cancellation and active noise cancellation.
Passive Noise Cancellation
The physical characteristics of the headset, such as the extra-thick padding utilized around the ears to improve the level of isolation between the listener and their surroundings, enable passive noise cancellation. This is frequently seen on construction sites as workers use it to protect their hearing while working all day around loud machines and noises.
Most over-ear headphones have passive noise cancellation, which is kind of always there but can really help when used to block out light to medium-intensity sounds like background office chatter or traffic noise. These headphones shield your surroundings from an excessive amount of music.
Active Noise Cancellation
The same phase cancellation strategies we previously mentioned are used by active noise cancellation on headphones and another noise reduction technique is frequently used as well. When you are wearing your noise-canceling headphones in settings where there is a background noise that is constant, such as in a car, train, airline, or an environment with air conditioners or power generators. The headphones analyze these sounds using a built-in microphone and generate a phase-reversed version of them to effectively blank them out.
Modern noise-canceling headphones frequently combine active and passive noise-control techniques to minimize unwanted sounds and produce a relaxing and distraction-free listening environment. Along with the ways already described, the following additional noise-cancellation features can be found on noise-canceling headphones and other audio equipment, which you can use instead of, or in conjunction with, the methods already mentioned:
Adaptive Noise Cancellation
The onboard microphones are used in a similar manner to how normal active noise cancellation does, in order to use this type of noise reduction technology. However, this approach enables the device to dynamically adapt to your surroundings as they change.
Adjustable Active Noise Cancellation
The level of noise cancellation applied to the incoming audio signal is freely adjustable in this case, allowing the listener to regulate the amount of background noise that is let into the system. This is quite helpful if you want to be able to hear just enough background noise to stay alert when wearing noise-canceling headphones in a noisy place.
Transparency Modes
With the flip of a switch, the user is able to swiftly and effortlessly disable all noise-canceling features and change noise-canceling headphones into a conventional pair, all without taking off the headphones or pausing the music.
Adjustable Transparency Modes
Similar to the mode described above, this one enables the user to regulate how much ambient noise is amplified and supplied into the audio system.
Benefits of Noise Cancellation
Hearing Protection
Noise-canceling devices can provide a protective barrier for our hearing. By eliminating the need to raise audio volumes in noisy environments, they help prevent potential damage to our ears.
Stress Reduction
Unwanted noise has been linked to increased stress levels. Noise cancellation technology promotes a calmer environment, contributing to reduced stress and improved mental well-being.
Enhanced Sound Quality
Noise cancellation not only removes external disturbances but also enhances the clarity of the audio you want to hear. This is especially valuable for audiophiles and those who demand high-quality sound.
Conclusion
As we’ve seen, noise-canceling technology has a wide range of applications. There are many different types of noise cancellation headphones, in-ear earbuds, and other technologies on the market as it rises in popularity, whether you wish to reduce background noise in your headphones or just eliminate the ambient noise of your surroundings to acquire a quieter environment.
Software that uses the same noise-canceling techniques is also available for smartphones and laptops, and it is intended for people who spend a lot of time studying, instructing, or taking part in meetings online or over video or voice conversations.
