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What is 'noise'?

What is 'noise'?


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In both my psychology, biology and neuroscience classes, professors are constantly talking about 'noise'. For instance, our perception is limited due to 'sensory noise' in our neurons. I am utterly confused about this concept. What is 'noise'? Can someone please conceptually describe what is is in laymen's terms?


The termnoisecan mean a number of different (more or les related) things is used in a number of different fields such as signal processing, psychology and statistics.

Outside of its context, it is impossible to say for certitude what you professors were referring to.

The quotations below come from wikipedia > Communication noise, wikipedia > Statistical noise, wikipedia > white noise and wikipedia > noise

Psychological noise

Psychological noise results from preconceived notions we bring to conversations, such as racial stereotypes, reputations, biases, and assumptions. When we come into a conversation with ideas about what the other person is going to say and why, we can easily become blinded to their original message. Most of the time psychological noise is impossible to free ourselves from, and we must simply strive to recognize that it exists and take those distractions into account when we converse with others.

Psychological noise

Physiological noise has to do with distractions from the natural effects of the body, such as being tired or hungry.

Physical noise

Physical noise is any external or environmental stimulus that distracts us from receiving the intended message sent by a communicator (Rothwell 11). Examples of physical noise include: others talking in the background, background music, a startling noise and acknowledging someone outside of the conversation.

Semantic noise

This is noise caused by the sender. i.e., the encoder. This type of noise occurs when grammar or technical language is used that the receiver (the decoder) cannot understand, or cannot understand it clearly. It occurs when the sender of the message uses a word or a phrase that we don't know the meaning of, or which we use in a different way from the speakers. This is usually due to the result that the encoder had failed to practice audience analysis at first. The type of audience is the one that determine the jargon one will use.

Statistical noise

Statistical noise is the colloquialism for recognized amounts of unexplained variation in a sample.

White noise

In signal processing, white noise is a random signal with a constant power spectral density.1 The term is used, with this or similar meanings, in many scientific and technical disciplines, including physics, acoustic engineering, telecommunications, statistical forecasting, and many more. White noise refers to a statistical model for signals and signal sources, rather than to any specific signal.

Noise in its everyday use

Noise is a variety of sound. It means any unwanted sound. Sounds, particularly loud ones, that disturb people or make it difficult to hear wanted sounds, are noise. For example, conversations of other people may be called noise by people not involved in any of them; any unwanted sound such as domesticated dogs barking, neighbours playing loud music, portable mechanical saws, road traffic sounds, or a distant aircraft in quiet countryside, is called noise.


In electronics, there are concepts of signal and noise; what is not signal is noise. Signal is an "intended" or expected impulse or waveform; noise is any other impulse or waveform - unwanted or unintended.

Taking this into a biological context, sensory noise would then be sensory impulses, whatever the cause, which don't convey useful or meaningful information.


Cicadas: Noise, myth and biology

Cicadas compensate for near invisibility by making an enervating noise. Cicadas noise equals the sound effect of an aircraft or a rock concert.

You know summer has come to southern Italy, when you can’t hear your own thoughts for the enervating noise of cicadas.

Noisy Buggers

As I understand it, the small insects have a built-in drum in their abdomen that can produce noise of up to 120 dB at close range. That equals the sound effect of an aircraft or a rock concert. Enough, to disable phone calls and conversation and to drive anyone, who has to live with the sound from dawn to dusk a little crazy.

Cicadas are temperature sensitive animals, so they don’t make a racket until the thermometer has climbed up over 30C. Then they start clicking very loud and very early in the morning and continue till midnight. Fortunately, they have the consideration to turn down the volume around noon, when everyone surrenders to the heat.

To a Scandinavian the idea of singing cicadas seems attractively romantic, but in reality it can be a regular pain in the neck.Some days the situation is so desperate, it almost makes you wish for rain.

A One Tree Cosmos

I suppose, you could forgive the cicadas if the din served a purpose, but from what I have read, these insects live their entire lives within a very small radius. In fact, they prefer to stay put around a specific tree. Female cicadas lay their eggs in the bark, the eggs develop into nymphs that slide down the trunk to draw juice from tree roots. In due course, when the nymphs have grown up, they climb back up the tree, leave their skin and start searching for a mate.

The clicking noise serves as a male point of attraction, but as the love of their life is always just around the nearest branch, they might be a bit more discreet.

A live cicada seeking refuge on a towel.

Heard but not seen

Now their discretion is entirely visual. In spite of the noise, it is difficult to catch sight of the cicadas, unless you are satisfied with the dry discarded skin they leave behind on tree trunks and steel wires. I don’t think I have seen live cicadas more than twice, one of which demonstrated an alternative mode of singing every time a wanton 11-year-old poked it with his shoe. The cries of the poor insect were heartbreaking, but also highly entertaining, if you asked the kids.

The Immortal Prince

They are not familiar with Greek myth saying that the cicada is the lover of the Titan dawn goddess Eos. She fell in love with a beautiful prince and Zeus helped her to make the prince immortal. Yet they forgot to grant him eternal youth, so the prince ended up as a shrivelled old corpse. He maintained his powerful voice, however, and he is still using it.


Choosing a White Noise Machine

A white noise machine, also known as a sound machine, can help you create a more relaxing bedroom environment that promotes healthy, high-quality sleep. In addition to white noise and other noise colors, these devices often produce ambient and natural sounds such as chirping birds and crashing waves. Before choosing a machine, here are a few factors to consider:

  • Price: Most white noise machines cost less than $100. Higher-end models typically offer a wider selection of noises and sounds.
  • Size: Sound machines are generally lightweight and compact, though some are exceptionally small and designed for travel.
  • Sleep Timer: Some sound machines have programmable timers that will automatically shut off the device after a certain amount of time.
  • Looping: Some white noise machines loop their sounds at the end and beginning to create a continuous listening experience, while others will stop when the recording is finished.
  • Alarm: Sound machines often feature a built-in alarm to help you wake up at certain times.

If you’d rather not purchase a dedicated sound machine, you can download a white noise app to your smartphone or tablet device instead. These apps are typically very inexpensive, if not free of charge.


Noise in biological circuits

Virginia Commonwealth University, Richmond, VA 23284.

University of Tennessee, Knoxville, TN, USA.

Oak Ridge National Laboratory, Oak Ridge, TN, USA.

University of Tennessee, Knoxville, TN, USA.

Oak Ridge National Laboratory, Oak Ridge, TN, USA.

University of Tennessee, Knoxville, TN, USA.

Oak Ridge National Laboratory, Oak Ridge, TN, USA.Search for more papers by this author

University of Tennessee, Knoxville, TN, USA.

University of North Texas, Denton, TX, USA.

Virginia Commonwealth University, Richmond, VA 23284.

University of Tennessee, Knoxville, TN, USA.

Oak Ridge National Laboratory, Oak Ridge, TN, USA.

University of Tennessee, Knoxville, TN, USA.

Abstract

Noise biology focuses on the sources, processing, and biological consequences of the inherent stochastic fluctuations in molecular transitions or interactions that control cellular behavior. These fluctuations are especially pronounced in small systems where the magnitudes of the fluctuations approach or exceed the mean value of the molecular population. Noise biology is an essential component of nanomedicine where the communication of information is across a boundary that separates small synthetic and biological systems that are bound by their size to reside in environments of large fluctuations. Here we review the fundamentals of the computational, analytical, and experimental approaches to noise biology. We review results that show that the competition between the benefits of low noise and those of low population has resulted in the evolution of genetic system architectures that produce an uneven distribution of stochasticity across the molecular components of cells and, in some cases, use noise to drive biological function. We review the exact and approximate approaches to gene circuit noise analysis and simulation, and review many of the key experimental results obtained using flow cytometry and time-lapse fluorescent microscopy. In addition, we consider the probative value of noise with a discussion of using measured noise properties to elucidate the structure and function of the underlying gene circuit. We conclude with a discussion of the frontiers of and significant future challenges for noise biology. Copyright © 2009 John Wiley & Sons, Inc.


Here’s What Happens In Your Brain When You Hear White Noise

In the popular imagination, white noise usually means television static or the crackling that emerges from white noise machines. It's actually a pretty complicated noise — and researchers have found that white noise has a lot of effects on the brain. White noise is a collection of randomized sounds from every frequency on the acoustic spectrum, all with the same intensity. It's called white noise because it's the auditory equivalent of white light, which contains equal intensities of all kinds of light. Research shows that white noise may help us focus in the short term, but over the long term, it can actually damage our synapses.

"In naturally structured sounds such as speech and music, only a few frequencies occur at a time, with predictable relationships among the combinations and sequences of notes," Dr. Mouna Attarha, Ph.D., a researcher at Posit Science who researched white noise at the University of Iowa, tells Bustle. "Acoustically, white noise is the equivalent of mashing all the keys at once on a thousand untuned pianos — random activation of every frequency at once with absolutely no relationship among the different notes."

The brain's reaction to white noise isn't radically different to its reactions to other sounds. "It appears that white noise is processed very similarly to other noises in the brain," Joanna Scanlon, MSc, a researcher at the Mathewson Attention, Perception, and Performance Lab at the University of Alberta, tells Bustle. However, the brain doesn't treat it in quite the same way as speech or song. "One EEG study found that white noise induced brain activity with lower amplitude to that of pure tones, but also higher amplitude to that of clicking sounds," Scanlon says. The study, she says, implies that the brain thinks that the white noise was less worthy of attention than pure tones, but more relevant than random clicking. This is why white noise machines help lull your brain to sleep — it masks the random noise of the street outside or of your radiator tapping to life, but isn't annoying enough to register in your brain.

Scanlon's own research has shown that the brain tends to filter out white noise when it's attempting to focus on another noise. "My research used white noise as a background stimuli for an auditory task, compared to using other background noises," she tells Bustle. "We observed evidence for a mechanism in which the brain 'tunes in' to the relevant sounds (i.e. the auditory task) while it 'filters out' the white noise." The brains studied in the experiment did the same thing when they were exposed to background noises, but showed a stronger reaction. In other words, white noise got the same neurological reaction as dogs barking or traffic noise, but proved easier for your brain to block out.

Scientists have been attempting to figure out how white noise affects concentration, memory and cognition for a while. A 2014 study in Journal of Cognitive Neuroscience found that playing white noise could slightly improve memory if it was played during a memory task, while research published in Nature in 2017 found that it could help adults learn new words. A review of the science around white noise in 2015 noted that white noise isn't a miraculous brain-changer it just affects our concentration, depending on the context. "White noise has no general effect on cognitive functions. Instead, [it has] differential effects on perception and cognition depending on a variety of factors such as task demands and timing of white noise presentation," the review said. Depending on how you use it and where you are, white noise can make the brain's auditory centers focus, which may help concentration and memory.

This is also why white noise may be helpful for sleep in some people. Research in 1990 showed that it could help to induce sleep, while other studies, including one in hospital patients in 2015 and another on people with insomnia in 2017, have shown that it can improve sleep quality and help people with sleep issues fall into deep sleep more quickly.

However, being exposed to white noise over the long term might not be a great idea for brain function, because of the brain's tendency to adapt to what it hears. "Studies have shown that exposure to information-rich signals such as speech or music shapes the brain," Dr. Attarha tells Bustle. "Individual cells become more specialized, for instance, by responding selectively to only a narrow range of sound frequencies. On the other hand, long-term exposure to signals that lack information — such as random white noise — influences the brain in a maladaptive direction." The issue, she tells Bustle, is that white noise exposure can tell our cells to respond to almost anything, which can alter our ability to process speech and music.

Research from 2003 found that long-term exposure to white noise damaged the auditory organization of rat brains, making them less capable of healthy development. Dr. Attarha's own research has shown that white noise usage for long periods, used for sleep or for managing tinnitus, can impair the central auditory system in the brain, and potentially contribute to brain aging. The key to this long-term damage, she tells Bustle, is in the excitatory and inhibitory cells in the nervous system. "Just as the gas and brake pedals in a car are used to 'go' and 'stop' in response to different roadway signals, excitatory and inhibitory cells in the nervous system influence other cells to 'go' or 'stop' in response to different sensory signals," she says.

While noises with lots of complexity and information, like music, encourage these cells to specialize, only sending a "go" signal in response to a particular noise, white noise makes them much less sensitive. "White noise exposure gradually decreases levels of inhibition, resulting in cells that are unable to 'stop' responses to a broad range of sound frequencies," Dr. Attarha tells Bustle. That disruption, she says, can cause problems with memory and decision-making down the line. The more white noise you hear, according to this theory, the less capable you'll be of blocking out irrelevant noises or focusing on sounds in a noisy environment.

These concerns about white noise are part of the reason why pink noise has now become more popular. Pink noise is similar to white noise in that it contains sounds across all frequencies, but it has more variation: low frequencies in pink noise are louder and more intense than high frequencies, even if we can't detect it when we hear it. A study in 2012 in Journal of Theoretical Biology found that pink noise appears to help people reach deep sleep, while another in 2017 published in Frontiers In Human Neuroscience noted that it can help memory in older adults.

Overall, white noise may be a good short-term solution for helping your sleep or allowing you to concentrate on a task, but it's not a good idea long-term. The best way to help your auditory centers, says Dr. Attarha, is to replace unstructured noises with speech and music. Doing this, she says, "can reinforce the specialized abilities of our cells, and sustain the chemical, structural, and functional health of the brain." It's an argument in favor of listening to Spotify at work rather than miscellaneous background rumblings, and for turning off that white noise machine at night unless you really need it.

Angwin, AH, Wilson, WJ, Arnott, WL et al. White noise enhances new-word learning in healthy adults. Sci Rep 7, 13045 (2017) doi:10.1038/s41598-017-13383-3

Attarha M, Bigelow J, Merzenich MM. (2018) Unintended Consequences of White Noise Therapy for Tinnitus—Otolaryngology's Cobra Effect: A Review. JAMA Otolaryngol Head Neck Surg. 144(10):938–943. doi:10.1001/jamaoto.2018.1856

Chang EF, Merzenich MM. (2003) Environmental noise retards auditory cortical development. Science. 300(5618):498-502.

Farokhnezhad Afshar, P., Bahramnezhad, F., Asgari, P., & Shiri, M. (2016). Effect of White Noise on Sleep in Patients Admitted to a Coronary Care. Journal of caring sciences, 5(2), 103–109. doi:10.15171/jcs.2016.011

Herweg NA, Bunzeck N. (2015) Differential effects of white noise in cognitive and perceptual tasks. Front Psychol. 6:1639. doi: 10.3389/fpsyg.2015.01639.

Papalambros, NA, Santostasi, G, Malkani, RG, et al. (2017) Acoustic Enhancement of Sleep Slow Oscillations and Concomitant Memory Improvement in Older Adults. Frontiers in Human Neuroscience. 11 DOI: 10.3389/fnhum.2017.00109

Rausch VH, Bauch EM, Bunzeck N. (2014) White noise improves learning by modulating activity in dopaminergic midbrain regions and right superior temporal sulcus. J Cogn Neurosci. 26(7):1469-80. doi: 10.1162/jocn_a_00537. Epub 2013 Dec 17. PubMed PMID: 24345178.

Reite, M., Zimmerman, J. T., & Zimmerman, J. E. (1982). MEG and EEG auditory responses to tone, click and white noise stimuli. Electroencephalography and clinical neurophysiology, 53(6), 643-651.

Scanlon, J. E., Cormier, D. L., Townsend, K. A., Kuziek, J. W., & Mathewson, K. E. (2019). The ecological cocktail party: Measuring brain activity during an auditory oddball task with background noise. Psychophysiology, 56(11), e13435.

Spencer JA, Moran DJ, Lee A, Talbert D. (1990) White noise and sleep induction. Arch Dis Child. 65(1):135-7.


Human-generated noise can contribute to deplete Seagrass Posidonia populations

Credit: Universitat Politècnica de Catalunya · BarcelonaTech (UPC)

When exposed to human-made noise, seagrass posidonia reveals permanent severe lesions in their sensory organs that sense gravity, which threatens their survival. This is the main conclusion of a recent study of the Laboratory of Applied Bioacoustics (LAB) of Universitat Politècnica de Catalunya BarcelonaTech (UPC) titled "Seagrass Posidonia is impaired by human-generated noise," which is published in Nature Communications Biology.

These new findings demonstrate that plants have the physiological ability to perceive sounds, and just as importantly, reveal that commonly encountered sources of noise in the ocean can contribute to deplete their populations.

The last 100 years have seen the introduction of many sources of artificial noise in the sea environment, which have shown to negatively affect marine organisms. Many aspects of how noise and other forms of energy may critically impact the natural balance of the oceans are still unstudied. A lot of attention has been devoted to determining the sensitivity to noise of fish and marine mammals, especially cetaceans and pinnipeds, because they are known to possess hearing organs. Recent studies conducted at the Laboratory of Applied Bioacoustics (LAB) of the Universitat Politècnica de Catalunya, Barcelona Tech (UPC) have also shown that cephalopods, anemones and jellyfish, while lacking similar auditory receptors, are also affected by artificial sounds. Indeed, marine invertebrates have sensory organs whose main functions allow these species to maintain equilibrium and sense gravity in the water column. But not a single study has yet addressed the sensitivity to noise of sessile marine organisms like plants or coral reefs, whose immobility makes them highly susceptible to chronic effects since they also have sensory organs specialized in gravity perception, which are essential to find their natural substrate.

Posidonia is already fragilised by mechanical human threats because of the massive use of leisure boats' anchors that literally uproot these unique seagrasses.

Seagrasses are considered as an equivalent of primary forests in their ecological functions. They are higher plants adapted to marine environments, developing vital ecosystems consisting of complex networks that are thousands of years old, anchored in soft bottom areas. They have significant effects on both biodiversity and ecosystem functions, minimizing hydrodynamic forces, influencing hosted species (invertebrates and fishes) and promoting microbiome and bacteria growth. Seagrasses present starch grains in its roots that function as invertebrate statocysts, which are sensory organs responsible of sensing gravity and processing sound vibration. In addition, its rhizomes, which act as storage organs, provide a considerable amount of starch grains, a guarantee of energy provision to the plants.

This study, lead by Marta Solé, a senior researcher at the LAB-UPC, reports morphological and ultrastructural changes in seagrass after exposure to sounds in a controlled environment. These changes are new to aquatic plants pathology. Low-frequency sounds produced alterations in posidonia oceanica root and rhizome statocysts, and the nutritional processes of the plant were affected by a decrease in the number of rhizome starch grains. In addition, a degradation in the specific fungal symbionts of posidonia roots was observed. Fungus improves the nutrient status of the plant (e.g. mineral nutrition, water absorption) in exchange for carbon provided by posidonia, which is necessary for fungal growth and reproduction.

This sensitivity to artificial sounds revealed how sound can potentially affect the health status of posidonia. Moreover, these findings address the question of how much the increase of ocean noise pollution may contribute in the future to the depletion of seagrass populations and to biodiversity loss.


Difference Between Signal and Noise

Signal and noise are two terms used in electrical engineering and communications. Signal is a time or space varying quantity carrying some information, and noise is an unwanted effect on signal which reduces the visibility of that information. Signal to noise (S/N) ratio is a widely used parameter to measure the quality of signals. The higher the S/N ratio, better the signal in quality.

A signal is an information carrier. It is a time or space varying quantity and used to send information. Many things can be considered as signals. For example, pixels of an image, a written line of text, and color of the sky are all some sort of signals. However, electrical signals are the most studied and used type of signals.

Signals can be categorized as analog and digital. Analog signals can take any value, whereas in digital signals, it is restricted to certain values. Information content of a signal is an important parameter, and it is called the ‘entropy’. Usually signals are analyzed in frequency domain for the convenience.

Noise is an unwanted effect on signals. Noise is added on to signal due to many natural reasons as it travels through a medium. Noise can randomly fluctuate the value of signals, and it disturbs the process of revealing the information sent through a signal.

Noise can occur due to natural or artificial reasons. There are many types of noise such as thermal noise, shot noise, flicker noise, burst noise, and avalanche noise in electronics. White noise and Gaussian noise are statistically defined noise types. Some of the noise are unavoidable and only the effect of them on signals can be minimized.

Effect of noise on a signal is measured using a parameter known as signal to noise (S/N) ratio. If the S/N ratio is small, effect of the noise is higher. If the S/N ratio is less than one and very low, revealing the information held in the signal is difficult.

What is the difference between Signal and Noise?

1. Usually signal is a wanted part, and noise is an unwanted part,which should be eliminated.

2. For a signal to be high in quality, signal to noise ratio should be a high value


Understanding and Eliminating 1/f Noise

This article explains what 1/f noise is and how to reduce or eliminate it in precision measurement applications. 1/f noise cannot be filtered out and can be a limit to achieving the best performance in precision measurement applications.

What Is 1/f Noise?

1/f noise is low frequency noise for which the noise power is inversely proportional to the frequency. 1/f noise has been observed not only in electronics, but also in music, biology, and even economics. 1 The sources of 1/f noise are still widely debated and much research is still being done in this area. 2

Looking at the voltage noise spectral density of the ADA4622-2 op amp shown in Figure 1, we can see that there are two distinct regions visible in the graph. On the left of Figure 1 we can see the 1/f noise region and on the right of Figure 1 we can see the broadband noise region. The crossover point between the 1/f noise and the broadband noise is called the 1/f corner.

Figure 1. ADA4622-2 voltage noise spectral density.

How Do We Measure and Specify 1/f Noise?

After comparing the noise density graphs of a number of op amps, it becomes apparent that the 1/f corner can vary for each product. To easily compare components, we need to use the same bandwidth when measuring the noise of each component. For low frequency voltage noise, the standard specification is 0.1 Hz to 10 Hz peak-to-peak noise. For op amps, the 0.1 Hz to 10 Hz noise can be measured using the circuit shown in Figure 2.

Figure 2. Low frequency noise measurement.

The op amp gain is set to 100 with the noninverting input grounded. The op amp is powered from a split supply to allow for the input and the output to be at the ground.

The active filter block limits the bandwidth of the noise that is measured while simultaneously providing a gain of 10,000 to the noise from the op amp. This ensures that the noise from the device under test is the dominant source of noise. The offset of the op amp is not important, as the input to the filter is ac-coupled.

The output of the filter is connected to an oscilloscope and the peak-to-peak voltage is measured for 10 seconds to ensure we capture the full 0.1 Hz to 10 Hz bandwidth (1/10 seconds = 0.1 Hz). The results shown on the scope are then divided by the gain of 1,000,000 to calculate the 0.1 Hz to 10 Hz noise. Figure 3 shows the 0.1 Hz to 10 Hz noise for the ADA4622-2. The ADA4622-2 has a very low, 0.1 Hz to 10 Hz noise of just 0.75 µV p-p typical.

Figure 3. 0.1 Hz to 10 Hz noise, VSY = ±15 V, G = 1,000,000.

What Impact Does 1/f Noise Have in My Circuit?

The total noise in a system is the combined 1/f noise and broadband noise from each component in the system. Passive components have 1/f noise and current noise also has a 1/f noise component. However, for low resistances the 1/f noise and current noise are usually too small to be considered. This article will focus on voltage noise only.

To calculate the total system noise we calculate the 1/f noise and the broadband noise, and then combine them. If we use the 0.1 Hz to 10 Hz noise specification to calculate the 1/f noise, then we are assuming that the 1/f corner is below 10 Hz. If the 1/f corner is above 10 Hz then we can estimate the 1/f noise using the following formula 3 :

en1Hzis the noise density at 1 Hz,

fh is the 1/f noise corner frequency,

For example, if we want to estimate the 1/f noise for the ADA4622-2, then f h is about 60 Hz. We set flto be equal to 1/aperture time. Aperture time is the total measurement time. If we set the aperture time or measurement time to be 10 seconds, then flis 0.1 Hz. The noise density at 1 Hz, en1Hz, is approximately 55 nV&radicHz. This gives us a result of 139 nV rms between 0.1 Hz and 60 Hz. To convert this to peak-to-peak we should multiply by 6.6, which will give us approximately 0.92 µV p-p. 4 This is about 23% higher than the 0.1 Hz to 10 Hz specification.

The broadband noise can be calculated using the following formula:

enis the noise density at 1 kHz,

NEBW is the noise equivalent bandwidth.

The noise equivalent bandwidth takes into account the additional noise beyond the filter cutoff frequency due to the gradual roll-off of the filter. The noise equivalent bandwidth is dependent on the number of poles in the filter and the filter type. For a simple one pole, low-pass Butterworth filter, the NEBW is 1.57 × filter cutoff.

The wideband noise density for the ADA4622-2 is just 12 nV/&radicHz at 1 kHz. Using a simple RC filter on the output with a cutoff frequency of 1 kHz, the wideband rms noise is approximately 475.5 nV rms and can be calculated as follows:

Note that a simple low-pass RC filter has the same transfer function as a single-pole, low-pass Butterworth filter.

To get the total noise, we must add the 1/f noise and the broadband noise together. To do this we can use the root sum square method as the noise sources are uncorrelated.

Using this equation, we can calculate the ADA4622-2 total rms noise with a simple 1 kHz, low-pass RC filter on the output to be 495.4 nV rms. This is just over 4% higher noise than the broadband noise alone. It&rsquos clear from this example that 1/f noise affects systems that measure from dc up to very low bandwidth only. Once you go beyond the 1/f corner by about a decade or more, the contribution of the 1/f noise to the total noise becomes almost too small to worry about.

Since noise adds together as a root sum square, we can decide to ignore the smaller noise source if it is below about 1/5 th of the larger noise source, since below a ratio of 1/5 th the noise contribution is about a 1% increase in the total noise. 5

How Do We Remove or Mitigate 1/f Noise?

Chopper stabilization, or chopping, is a technique to reduce amplifier offset voltage. However, since 1/f noise is near dc low frequency noise, it is also effectively reduced by this technique. Chopper stabilization works by alternating or chopping the input signals at the input stage and then chopping the signals again at the output stage. This is the equivalent to modulation using a square wave.

Figure 4. ADA4522 architecture block diagram.

Referring to the ADA4522-2 architecture block diagram shown in Figure 4, the input signal is modulated to the chopping frequency at the CHOPIN stage. At the CHOPOUT stage, the input signal is synchronously demodulated back to its original frequency and simultaneously the offset and 1/f noise of the amplifier input stage are modulated to the chopping frequency. In addition to reducing the initial offset voltage, the change in offset vs. common-mode voltage is reduced, which results in very good dc linearity and a high common-mode rejection ratio (CMRR). Chopping also reduces the offset voltage drift vs. temperature. For this reason, amplifiers that use chopping are often referred to as zero-drift amplifiers. One key thing to note is that zero-drift amplifiers only remove the 1/f noise of the amplifier. Any 1/f noise from other sources, such as the sensor, will pass through unaffected.

The trade-off for using chopping is that it introduces switching artifacts into the output and increases the input bias current. Glitches and ripple are visible on the output of the amplifier when viewed on an oscilloscope and noise spikes are visible in the noise spectral density when viewed using a spectrum analyzer. The newest zero-drift amplifiers from Analog Devices&mdashsuch as the ADA4522 55 V zero-drift amplifier family&mdashuse a patented offset and ripple correction loop circuit to minimize switching artifacts 6 .

Figure 5. Output voltage noise in the time domain. 6

Chopping can also be applied to instrumentation amplifiers and ADCs. Products such as the AD8237 true rail-to-rail, zero-drift instrumentation amplifier, the new AD7124-4 low noise and low power, 24-bit &Sigma-&Delta ADC, and the recently released AD7177-2 ultralow noise, 32-bit &Sigma-&Delta ADC, use chopping to eliminate 1/f noise and minimize drift vs. temperature.

One disadvantage to using square wave modulation is that square waves contain many harmonics. Noise at each harmonic will be demodulated back to dc. If sine wave modulation is used instead, then this approach is much less susceptible to noise and can recover very small signals in the present of large noise or interference. This is the approach used by lock-in amplifiers. 7

Figure 6. Measuring surface contamination with a lock-in amplifier. 7

In the example shown in Figure 6, the sensor output is modulated by using a sine wave to control a light source. A photodetector circuit is used to detect the signal. Once the signal passes through the signal conditioning stage, it can be demodulated. The same sine wave is used to modulate and demodulate the signal. The demodulation returns the sensor output to dc, but also shifts the 1/f noise of the signal conditioning stage to the modulation frequency. The demodulation can be done in either the analog or digital domain after ADC conversion. A very narrow low-pass filter&mdashfor example, 0.01 Hz&mdashis used to reject the noise above dc and we are left with only the original sensor output with extremely low noise. This relies on the sensor output being at exactly dc, so the precision and fidelity of the sine wave is important. This approach eliminates the 1/f noise of the signal conditioning circuitry, but does not eliminate the 1/f noise of the sensor.

If a sensor requires an excitation signal, then it is possible to eliminate the 1/f noise from the sensor using ac excitation. AC excitation works by alternating the sensor excitation source to produce a square wave output from the sensor and then subtracting the output from each phase of the excitation. This approach not only allows us to eliminate the 1/f noise of the sensor, but also eliminates offset drift in the sensor and eliminates unwanted parasitic thermocouple effects. 8

Figure 7. AC excitation of a bridge sensor. 8

AC excitation can be done using discrete switches and controlling them with a microcontroller. The AD7195 low noise, low drift, 24-bit &Sigma-&Delta ADC with internal PGA included drivers to implement ac excitation of the sensor. The ADC manages the ac excitation transparently by synchronizing the sensor excitation with the ADC conversions, making ac excitation easier to use.

Figure 8. CN-0155&mdashPrecision weigh scale design using a 24-bit &Sigma-&Delta ADC with internal PGA and ac excitation.

Implementation

When using zero-drift amplifiers and zero-drift ADCs, it is very important to be aware of the chopping frequency of each component and the potential for intermodulation distortion (IMD) to occur. When two signals are combined, the resulting waveform will contain the original two signals, as well as the sum and difference of these two signals.

For example, if we consider a simple circuit using the ADA4522-2 zero-drift amplifier and the AD7177-2 &Sigma-&Delta ADC, the chopping frequencies of each part will mix and create sum and difference signals. The ADA4522-2 has a switching frequency of 800 kHz, while the AD7177-2 has a switching frequency of 250 kHz. The mixing of these two switching frequencies will cause additional switching artifacts at 550 kHz and 1050 kHz. In this case, the AD7177-2 maximum corner frequency of the digital filter, 2.6 kHz, is much lower than the lowest artifact and will remove all of these IMD artifacts. However, if two identical zero-drift amplifiers are used in series, the IMD created will be the difference in the internal clock frequency of the parts. This difference could be small and, therefore, the IMD would appear at much closer to dc and be more likely to fall inside the bandwidth of interest.

In any case, it is important to consider IMD when designing a system that uses zero-drift or chopped parts. It should be noted that most zero-drift amplifiers have much lower switching frequencies than the ADA4522-2. In fact, the high switching frequency is a key benefit to using the ADA4522 family when designing precision signal chains.

Conclusion

1/f noise can limit performance in any precision dc signal chain. However, it can be removed by using techniques such as chopping and ac excitation. There are some trade-offs to using these techniques, but modern amplifiers and &Sigma-&Delta converters have addressed these issues, making zero-drift products easier to use across a broader range of end applications.


REPRODUCTIVE HEALTH AND THE WORKPLACE

Working in a noisy job when you&rsquore pregnant can affect your hearing and increase your stress levels. When the noise level is very high, like a jackhammer or at a rock concert, it may increase your chances of having a baby with hearing problems. Here, you can learn more about noise at work and what you can do to reduce your exposure for a healthier pregnancy.

Why should I be concerned about noise?

  • Increased noise levels can cause stress. This can cause changes in a pregnant woman&rsquos body that can affect her developing baby.
  • Sound can travel through your body and reach your baby. Although this sound will be muffled in the womb, very loud noises may still be able to damage your baby&rsquos hearing.
  • Hearing protectors (ear plugs or earmuffs) can protect your hearing, but if you&rsquore pregnant the only way to protect your baby&rsquos hearing is to stay away from the loud noise as much as possible.

Who works in noisy jobs?

Many women work in noisy jobs, especially women who work with machines, guns, loud music, crowds of people, sirens, trucks, or airplanes.


Urban traffic noise causes song learning deficits in birds

Traffic noise leads to inaccuracies and delays in the development of song learning in young birds. They also suffer from a suppressed immune system, which is an indicator of chronic stress. A new study by researchers of the Max Planck Institute for Ornithology and colleagues shows that young zebra finches, just like children, are particularly vulnerable to the effects of noise because of its potential to interfere with learning at a critical developmental stage.

Traffic noise is a pervasive pollutant that adversely affects the health and well-being of millions of people. In addition to severe noise-induced diseases in adults, traffic noise has also been linked to learning impairments and language deficits in children. In order to analyse the causal mechanisms connecting chronic noise exposure to cognitive deficiencies, researchers of the Max Planck Institute for Ornithology with colleagues at the University of Paris Nanterre and the Manchester Metropolitan University studied the song learning and immune function of young zebra finches exposed to traffic noise. Like children, songbirds must learn their vocalizations from adult tutors during a sensitive period early in life. Under normal conditions, the songs of the finches become stable and stereotyped at an age of around 90 days, and remain the same for the rest of their adult life, a process called "crystallization".

For the study, the researchers raised male zebra finch chicks in two groups. During their sensitive song learning period, the chicks in both groups were tutored with recorded song of adult males. In one group, the birds were additionally exposed to traffic noise that had been recorded in bird habitats close to busy roads in the city of Munich, Germany. The scientists monitored the singing activity of each male and compared their song development and learning success. Furthermore, they measured the immune responses of the chicks while they grew up.

Noise weakens immune response

The researchers found that juvenile zebra finches exposed to realistic levels of city noise had weaker immune responses than chicks from quiet nests, suggesting that noise was a source of chronic stress in these young birds. Furthermore, the birds in the noise treatment were significantly delayed in their vocal development - crystallizing their songs more than 30% later than controls, and with significantly lower accuracy in their song learning. "Our findings indicate that young songbirds, just like human children, are particularly vulnerable to the effects of noise because of its potential to interfere with learning at a critical developmental stage", says Henrik Brumm, who led the international research project.

The results of the study suggest that traffic noise even has the potential to affect the cultural evolution of bird song since noise-induced copying errors are likely to accumulate as song passes from one bird to another. "Our paper marks a breakthrough in the study of the effects of anthropogenic noise," Sue Anne Zollinger of the research team concludes, "it establishes bird song as an experimental paradigm for future studies on noise-related cognitive and developmental impairments, especially in regard to vocal learning deficiencies and speech development".

Henrik Brumm, Wolfgang Goymann, Sébastien Derégnaucourt, Nicole Geberzahn, Sue Anne Zollinger (2021)
Traffic noise disrupts vocal development and suppresses immune function
Science Advances 12 May 2021: Vol. 7, no. 20, eabe2405

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