Main Causes of Low Noise Performance

The main causes of high noise levels in signaling systems are:

If the wanted signal spectrum differs from the noise spectrum, the signal-to-noise ratio can be improved by limiting the system bandwidth.

To improve the noise characteristics of complex complexes, electromagnetic compatibility methods are used.

Measurement

In audio engineering, the signal-to-noise ratio is determined by measuring the noise voltage and the signal at the output of an amplifier or other sound-reproducing device with an RMS millivoltmeter or a spectrum analyzer. Modern amplifiers and other high-quality audio equipment have a signal-to-noise ratio of about 100-120 dB.

In systems with higher requirements, indirect methods of measuring the signal-to-noise ratio are used, implemented on specialized equipment.

In music

Signal-to-noise ratio - the parameter of the active speaker amplifier, shows how much the amplifier makes noise (from 60 to 135.5 dB), if, in the absence of a signal, the volume control is turned to the maximum. The higher the signal to noise ratio, the clearer the sound produced by the speakers. It is desirable that this parameter be at least 75 dB, for powerful speakers with high-quality sound at least 90 dB.

In video

see also

Wikimedia Foundation. 2010 .

• Barricades (PO)
• Larynx

See what "Signal-to-noise ratio" is in other dictionaries:

Signal-to-noise ratio- The signal-to-noise ratio (SNR, SNR, Signal to Noise Ratio) is a dimensionless value equal to the ratio of the useful signal power to the noise power. Usually expressed in decibels. The larger this ratio, the less noticeable the noise. where P is the average ... ... Wikipedia

signal-to-noise ratio- The ratio of the amplitude (or energy) of the signal generated by a defect in the material to the RMS value of the signal (or energy) of the noise. [Non-destructive testing system. Types (methods) and technology of non-destructive testing. Terms and Definitions …

signal-to-noise ratio- — [Ya.N. Luginsky, M.S. Fezi Zhilinskaya, Yu.S. Kabirov. English Russian Dictionary of Electrical Engineering and Power Industry, Moscow, 1999] Topics in electrical engineering, basic concepts EN signal to noise ratioS / N ratio ... Technical Translator's Handbook

signal-to-noise ratio- (ITU T G.691; ITU T G.983.2 G.991.2). Telecommunication topics, basic concepts EN signal to noise ratioSNR ... Technical Translator's Handbook

Signal-to-noise ratio G/s d- value characterizing the change in the G gradient against the background of the optical density of an equally exposed radiographic image. A source …

signal-to-noise ratio- 3.4 signal-to-noise ratio: The ratio of the level of an ultrasonic signal to the level of "background" noise, expressed in decibels (dB). A source … Dictionary-reference book of terms of normative and technical documentation

signal-to-noise ratio- signalo ir triukšmo santykis statusas T sritis automatika atitikmenys: engl. signal to noise ratio vok. Signal/Rausch Verhaltnis, n rus. signal-to-noise ratio, npranc. rapport signal/bruit, m … Automatikos terminų žodynas

signal-to-noise ratio for magnetic testing Technical Translator's Handbook

signal-to-noise ratio in magnetic non-destructive testing- signal-to-noise ratio The ratio of the peak value of the signal of the magnetic transducer, caused by a change in the measured characteristics of the magnetic field, to the root-mean-square value of the noise amplitude, due to the influence of interfering parameters ... ... Technical Translator's Handbook

integrated circuit signal-to-noise ratio- signal-to-noise ratio The ratio of the effective value of the output voltage integrated circuit, containing only low-frequency components corresponding to the frequencies of the modulating voltage, to the effective value of the output voltage at ... Technical Translator's Handbook

The ratio of the pure audio signal to the noise generated by the device itself.

The higher the value (in dB), the better.

The Sound Blaster X-Fi sound card has a signal-to-noise ratio of 118 dB.

Most audio codecs have 80-95 dB.

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Excessive noise is bad for more than just hearing. According to WHO, about 2% of all deaths in the world are caused by diseases associated with excessive noise.

Modern medicine considers loud sounds one of the formidable enemies of human health. In ecology, there is even the concept of "noise pollution". In addition to hearing disorders, cardiovascular diseases, hypertension can occur. Violated metabolism, activity of the thyroid gland, brain. Decreased memory and performance. Noise stress causes insomnia, loss of appetite. High noise levels can cause peptic ulcer disease, gastritis, mental illness.

Noise through the conductive paths of the sound analyzer affects various centers of the brain, as a result of which the work of various body systems is disrupted. According to the Austrian scientist Griffith, noise causes premature aging in 30 cases out of 100 and shortens the life of people in large cities by 8-12 years. WHO experts consider a sound of 85 dB safe for health, acting on a person every day for no more than 8 hours.

25-30 decibels

T What noise level is considered comfortable for a person. This is a natural sound background, without which life is impossible.

By the way…

In terms of volume, this is comparable to the rustle of leaves on trees - 5-10 dB, wind noise - 10-20 dB, whisper - 30-40 dB. And also with cooking on the stove - 35-42 dB, filling the bath - 36-58 dB, elevator movement - 34-42 dB, refrigerator noise - 42 dB, air conditioning - 45 dB.

The house should not be too quiet. When there is deathly silence around, we subconsciously experience anxiety. The sound of rain, the rustle of leaves, the chime of bells hanging in the doorway, the ticking of the clock have a calming effect on us and even have a healing effect.

We used to think that silence is the absence of sounds, but as it turned out, our brain clearly hears it and perceives it in the same way as other sounds. This was found out by scientists from the University of Oregon in the USA.

60-80 decibels

Such noise, acting regularly, causes disorders of the autonomic nervous system in a person and tires even with a short exposure.

By the way…

Large store - 60 dB, washing machine- 68 dB, vacuum cleaner - 70 dB, playing the piano - 80 dB, baby crying - 78 dB, car - up to 80 dB.

The noise level is perceived subjectively, addiction is possible. But with regard to developing vegetative reactions of adaptation is not observed.

Continuous traffic noise (65 dB) leads to hearing loss. Street noise disrupts the hearing center in the brain and negatively affects behavior. This conclusion was made by scientists from the University of California in San Francisco.

90-110 decibels

The sound is perceived as painful. Leads to hearing loss. With intense noise exposure of 95 dB or more, vitamin, carbohydrate, protein, cholesterol and water-salt metabolism may be disturbed. With a sound strength of 110 dB, the so-called "noise intoxication" occurs, and aggression develops.

By the way…

Motorcycle, truck engine and Niagara Falls - 90 dB, redevelopment in the apartment - 90-100 dB, lawn mower - 100 dB, concert and disco - 110-120 dB.

According to GOSTs, production with such a noise level is harmful, workers must undergo regular medical examinations. People working in such conditions are 2 times more likely to suffer from hypertension. Workers in noisy professions are advised to take vitamins B and C.

If the player is turned on at full power, then the sound of the order of 110 dB acts on the ears. There is a high risk of developing hearing loss (deafness).

115-120 decibels

This is the “pain threshold”, when the sound as such is practically no longer audible, pain in the ears is felt.

By the way…

The leaders in creating such noise are airports and railway stations. The volume of the freight train during movement is more than 100 dB. When the train approaches the platform, the noise level on the platform is slightly less - 95 dB. Even a kilometer from the runway, the noise level from an airplane taking off or landing is more than 100 dB.

The noise level in the subway can reach 110 dB at the stations and 80-90 dB in the carriages.

Don't get too carried away with karaoke. The level of acoustic load in this case exceeds the permissible limits, reaching 115 dB. After such extreme vocals, hearing is temporarily reduced by 8 dB.

140-150 decibels

The noise is almost unbearable, loss of consciousness is possible, eardrums may burst.

By the way…

When starting aircraft jet engines, the noise level ranges from 120 to 140 dB, the noise of a working drill is 140 dB, a rocket launch is 145 dB, a salute is fired, a rock concert is next to a huge powerful speaker, a car with a “broken” muffler is -120-150 dB .

180 decibels or more

Deadly for humans. Even the metal begins to break down.

By the way…

The shock wave from a supersonic aircraft is 160 dB, a shot from a 122 mm howitzer is 183 dB, an explosion from a powerful volcano is 180 dB.

According to research by American experts, the loudest sound in the animal kingdom is made by the blue whale - 189 dB.

Big city problems

According to experts, up to 70% of the territory of Moscow is subject to excessive noise from various sources. The value of excesses reaches the following values:

• 20-25 dB - near highways;
• up to 30-35 dB - for apartments of houses facing major highways (without soundproof glazing);
• up to 10-20 dB - near railways;
• up to 8-10 dB - in areas subject to periodic effects of aircraft noise;
• up to 30 dB - in case of non-compliance with the established requirements for construction work at night.

I can not hear

The human ear can only hear vibrations whose frequency is from 16 to 20,000 Hz. Oscillations with a frequency of up to 16 Hz are called infrasound, more than 20,000 Hz - ultrasound, and the human ear does not perceive them. The highest sensitivity of the ear to sounds is in the frequency range of 1000-4000 Hz. The higher the tone of the sound or noise, the stronger its adverse effect on the organ of hearing. Infra- and ultrasound can harm human health. However, the degree of their influence depends on the frequency and time of exposure.

Let's sleep!

Hearing sensitivity during sleep increases by 10-14 dB. According to WHO guidelines, cardiovascular disease can occur if a person is constantly exposed to noise at a volume of 50 dB or more at night. 42 dB of noise is enough to cause insomnia, 35 dB of noise is enough to just become irritable.

In the last article, we touched on the topic of cleaning the ears. cotton buds. It turned out that, despite the prevalence of such a procedure, self-cleaning of the ears can lead to perforation (rupture) of the eardrum and a significant decrease in hearing, up to complete deafness. However, improper ear cleaning is not the only thing that can damage our hearing. Excessive noise that exceeds sanitary standards, as well as barotrauma (pressure-related injuries) can also lead to hearing loss.

To have an idea of ​​the danger that noise poses to hearing, it is necessary to familiarize yourself with the permissible noise standards for different times of the day, as well as find out what level of noise in decibels certain sounds produce. In this way, you can begin to understand what is safe for hearing and what is dangerous. And with understanding comes the ability to avoid the harmful effects of sound on hearing.

According to sanitary standards, the permissible noise level, which does not harm hearing even with prolonged exposure to the hearing aid, is considered to be: 55 decibels (dB) during the day and 40 decibels (dB) at night. Such values ​​are normal for our ear, but, unfortunately, they are very often violated, especially within large cities.

Noise level in decibels (dB)

Indeed, often the normal noise level is significantly exceeded. Here are examples of just some of the sounds we encounter in our lives and how many decibels (dB) these sounds actually contain:

• Spoken speech ranges from 45 decibels (dB) to 60 decibels (dB), depending on the volume of the voice;
• Car horn reaches 120 decibels (dB);
• Heavy traffic noise - up to 80 decibels (dB);
• Baby crying - 80 decibels (dB);
• The noise of a variety of office equipment, a vacuum cleaner - 80 decibels (dB);
• Noise of a running motorcycle, train - 90 decibels (dB);
• The sound of dance music in a nightclub - 110 decibels (dB));
• Airplane noise - 140 decibels (dB);
• Repair work noise - up to 100 decibels (dB);
• Cooking on a stove - 40 decibels (dB);
• Forest noise 10 to 24 decibels (dB);
• Lethal noise level for a person, the sound of an explosion is 200 decibels (dB).

As you can see, most of the noises that we encounter literally every day significantly exceed the acceptable threshold of the norm. And these are just natural noises that we can't do anything about. But there is also the noise from the TV, loud music, which we ourselves expose our hearing aid to. And with our own hands we cause great harm to our hearing.

What level of noise is harmful?

If the noise level reaches 70-90 decibels (dB) and lasts for quite a long time, then such noise with prolonged exposure can lead to diseases of the central nervous system. And prolonged exposure to noise levels of more than 100 decibels (dB) can lead to significant hearing loss up to complete deafness. Therefore, we get much more harm from loud music than pleasure and benefit.

What happens to hearing when exposed to noise?

Aggressive and prolonged noise exposure to the hearing aid can lead to perforation (rupture) of the eardrum. The consequence of this is a decrease in hearing and, as an extreme case, complete deafness. And although perforation (rupture) of the eardrum is a reversible disease (i.e., the eardrum can recover), but the recovery process is long and depends on the severity of the perforation. In any case, the treatment of perforation of the tympanic membrane takes place under the supervision of a doctor who chooses a treatment regimen after an examination.

2014-03-08T21:22

2014-03-08T21:22

Audiophile's Software

Introduction

Noise is usually much more audible when using headphones than when using speakers, and is a popular topic of complaint among headphone wearers.

There are many misconceptions about where noise comes from, its characteristics and how it compares.

What is noise?

Technically, noise is everything but the useful signal. Usually we are only interested in noise in the range from 20 Hz to 20 kHz. Within this range, the ear is more sensitive to some frequencies than others. The most common audible noise is completely random in nature and is perceived as broadband hiss. A low-pitched hum at mains frequencies (50 or 60 Hz) can also occasionally be heard. Everything digital devices especially computers and mobile phones, can create noise at certain frequencies, perceived as squeaks, clicks, hum, etc.

Noise sources

Audible noise can, and often does, occur in the signal path, starting with the microphones used in recording. Here are the most common sources:

• sound recording- Mic preamps and other equipment used during recording often introduce audible noise. But there are many technologies used to reduce their audibility. Noise gate, for example, is used to eliminate noise when there is no useful signal (from a microphone or instrument). Virtually all recordings made prior to the early 80s were mastered using analog tape, which introduces a significant amount of hiss. And even digital recordings can contain noise introduced by electronics during signal transmission and processing. Also, of course, high level noise possesses vinyl.


• DAC- a theoretically ideal 16-bit DAC has a signal-to-noise ratio of 96 dB, but some DACs do not reach the maximum performance of a 16-bit format. 24-bit DACs usually have an accuracy corresponding to only 16 bits, the best of them barely reach 21 bits (effective number of bits).This is especially true for DACs built into PCs.Some DACs also introduce a large amount of their own noise - intermodulation, quantization noise (although these can be considered as distortions, since they take place only if there is a useful signal).


• Amplifier- Even a netbook or portable player has a built-in headphone power amplifier (in some cases it is already included in the DAC chip). Any amplifier introduces noise, the only question is whether this noise is heard or not. Even the most expensive external headphone amplifiers can introduce a significant amount of noise. In addition, of course, the noise entering the amplifier input along with the signal is amplified.


• Noises accumulate- While a primary source of noise is sometimes obvious, noise can also be contributed equally by multiple components. In this case, the noise is summed up.

Noise measurements

Example

• Noise in dBV at 100% volume- -112 dBV unweighted and -115 dBV A-Weighted


• Signal/noise vs. maximum output- 130 dBr unweighted and -133 dBr A-Weighted with respect to 7 V RMS maximum. These figures are impressive, but far from reality, since it is unlikely that anyone will need an output value close to 7 V.

Headphone sensitivity

Headphones differ significantly in sensitivity. Many people think that a 10 dB increase in sensitivity will also degrade the signal-to-noise ratio by 10 dB, but this is often not true. Since headphones are more sensitive, less gain and/or less volume is needed. In both cases, the noise level is also reduced, because ratio signal and noise present at the input of the amplifier remains unchanged. Only fixed noise is directly related to the sensitivity of the headphones. Volume control thermal noise can also complicate matters somewhat, but as headphone sensitivity increases, fixed noise level becomes more important (see marginal conditions above).

Sometimes you can see the spectral analysis of the noise. The average noise threshold in these graphs is much less than the noise specified in the specifications. In the figure on the right, the total noise is about -112 dBV, but in the graph, the noise lies at -150 dBV. The reason for this large difference is that –112 dBV is the sum of the noise components in the 20 Hz to 20 kHz range. Imagine that you spilled a glass of sugar on the floor. This will slightly change the level of the floor. But if you collect all the sugar in a measuring container, you can determine how much sugar is in total - the indicators in the windows in the figure work the same way.

Noise frequency range. Weighing

Typically, noise is the sum of the powers in the audio frequency band. Ideally, the bandwidth is specified for unweighted measurements. A-weighting is often used to adapt the results to the characteristics of human hearing (different hearing sensitivity at different frequencies), and it also limits the frequency band. Another weighing standard is ITU-R 468. For equipment that tends to produce a lot of ultrasonic noise, such as Class D amplifiers and digital equipment, additional broadband noise measurements, down to 100 kHz, can sometimes be useful.

Comparison of noise readings

You can only directly compare readings in dBu, dBV or dBr, at the same level. All measurements must use the same frequency range and the same type of weighting. Otherwise, you won't be able to compare results without doing some extra calculations, or they won't be comparable at all. Here are some examples:

• RMAA- Unfortunately, the concept of RightMark Audio Analyzer lacks the concept of absolute values. Therefore, the program cannot calculate the noise level relative to some given value. She tries to figure dynamic range in dBFS, but these results are subjective and may vary depending on device settings (volume, recording level, etc.), calibration, etc. In general, RMAA noise measurements are rarely accurate, and PC hardware noise is often greater than what you want to measure. Some of the parameters analyzed by RMAA are, in fact, present there “for show”, and this is one of them.


• dBV and dBr- If device A has a noise level of -100 dBV and device B has -108 dBr (reference level 10 V), at first glance it seems that the noise of device B is 8 dB less. But for A, the value is given with respect to 1 V, and for B, with respect to 10 V. The difference is 20*Log(10/1) = 20 dB. So in reality for B in relation to 1 V the level will be 20 dB higher, i.e. -88 dBV. See basic transformations below.


• dBu to dBV- These values ​​are similar. To convert from dBV to dBu, decrease the magnitude of the value by 2.2 dB. For reverse conversion, increase the modulus by 2.2 dB.


• dBr (400 mV) to dBv- I updated my own measurements by converting dBr referenced at 400mV to dBV (referenced at 1V). For such a conversion, the modulus of the value must be increased by 8 dB (for the reverse - reduced).


• Basic transformations- The bottom line is to add or subtract 20 * Log(Vref1 / Vref2) dB. The lower the reference level, the larger the relative noise figure will be. Also, the level can be set in relation to power (instead of voltage). In this case, the value is calculated as 10 * Log(Pref1 / Pref2).
  • dBV to Volts - 10^(dBV / 20)
  • -96 dB to Volts - 10^(-96/20) = 16 µV (0.000016 V)
  • Volts to dBV = 20 * log (V)


• Various types of weighing- It is not possible to accurately compare values ​​obtained using different weightings, as they depend on the frequency distribution of the noise. For example, an amplifier with significant hum will have a lower weighted noise value than an amplifier with evenly distributed noise. In most cases, however, type A weighting should be expected to give a noise level 3 to 6 dB lower than unweighted.

Source impedance

Thermal noise is often the main source of noise in preamplifiers and headphone amplifiers. And they are proportional to the impedance of the input circuit, which also includes the source. The higher the source impedance, the more noise. So, for example, a headphone amp works fine with a 100 ohm impedance source, but using a 10 k ohm impedance source can easily lead to audible noise. IN this case the noise you hear is actually produced by the input device, not the amplifier..

Noise measurement

Since the noise level value is the sum of the components in the range audio frequencies, and is also usually very low, it is very problematic to measure it accurately. The best high-end PC hardware can have a fairly low noise floor, but at the same time rarely allows you to take measurements at the maximum output of the device. And, more importantly, the PC audio hardware does not allow you to set the absolute value - in V, dBV, etc. Only a few DMMs have sufficient resolution and low enough noise level for measurements with an accuracy of up to µV in the range of 20-20000 Hz . Theoretically, you can temporarily calibrate the 24-bit sound card using an accurate measuring instrument and appropriate test signals. But there are many nuances here, depending on the software used. Source impedance is also an issue. Designers prefer to short the input contacts of the device during measurements to get the best noise readings, however, closer to the real results can be obtained by connecting a shunt resistance to the input that is close in value to the impedance of a typical source. If you try to use a real source, its noise will be included in the measurement result (as is the case with RMAA). When testing the DAC, it is necessary to use very low level signals, because if nothing is applied to the DAC at all, it will turn off completely and show results that are not true. Almost any quality audio analyzer will be able to eliminate this low-level signal from the results, leaving only noise.

Measurements with RMAA

Even if you managed to calibrate the levels, you still don't know what conversions are going on inside the RMAA program. It's a magical "black box" without any credible documentation describing how the program calculates the output values. What frequency range was used? Is the result weighted or unweighted? Plus, the results include an unknown level of noise from the equipment used. In summary, the best way to measure noise is to use Audio Precision and Prism Sound analyzers.

Conclusion

Noise levels of –105 dBV (relative to 1 V) are almost always inaudible. Noise levels in the region of -95 dBV are acceptable for most listeners. Noise levels given in other quantities must first be converted to dBV or similar units before they can be compared. Results obtained using RMAA are usually uninformative because absolute values ​​cannot be determined from them. RMAA can only determine the dynamic range, and not always, because it is often difficult to correctly set the levels without special equipment.

Original article in English: Noise & Dynamic Range

What is noise, how to measure it, in what quantities. What is dynamic range and how does it differ from noise floor.