# noises at different frequencies

#### Gpand

Joined Dec 11, 2023
82
If a circuit has say less than 2 microVolt peak-to-peak noise at DC to 100 Hz with 10,000 Ohm source.

How would the noise increase at 1000 Hz? Would it become 8 microVolt or 30 microVolt? For a 1-10 mV signal. What must be the minimum noises in microVolt to make it produce good signal?

Also does input impedance change with frequency, like becoming 100 Ohm from 10,000 Ohm?

Please give actual example of other amplifier to see how the noise behavior changes with frequency.

Thank you.

#### wayneh

Joined Sep 9, 2010
17,498
If a circuit has say less than 2 microVolt peak-to-peak noise at DC to 100 Hz with 10,000 Ohm source.

How would the noise increase at 1000 Hz? Would it become 8 microVolt or 30 microVolt? For a 1-10 mV signal. What must be the minimum noises in microVolt to make it produce good signal?
There's nowhere near enough information given to answer the questions. Do you have a specific device or schematic you're talking about?

Also does input impedance change with frequency, like becoming 100 Ohm from 10,000 Ohm?
In general, yes, real devices have input impedances that change with frequency. A better answer requires more detail.

Please give actual example of other amplifier to see how the noise behavior changes with frequency.
Uh oh, this question sounds like homework. Is that true? It can get moved to the homework area for more attention there.

#### Ian0

Joined Aug 7, 2020
9,844
What sort of noise?

#### joeyd999

Joined Jun 6, 2011
5,287
For a 1-10 mV signal. What must be the minimum noises in microVolt to make it produce good signal?
How much time do you have?

#### sparky 1

Joined Nov 3, 2018
759
An example could be an attenuated audio generator signal into a circuit approaching a resonance point.
I had to build my own equipment for measuring very small audio signals.
I tried to amplify the small signal. I could rely on the signal generator while switching the level of attenuation.
I never did get high level of accuracy like some of the equipment today. The audio AC to DC uV to mV worked ok.
Using a true RMS converter chip dedicated to the application was helpful and made calibration go faster.
The pc oscilloscope may have some advantage over a standard digital oscilloscope for certain applications
by sampling and working with the data the software can give you more ways to analyze and display results.

Measuring the frequency response using software PC oscilloscope usually the application involves a higher amplitude.
such as speakers but there may be some who are listening to small insects that would also rely on the quality of the microphone as a sensor.
Some of the mems devices are showing an advance in that field and would be interesting to get a sample to test.

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#### Gpand

Joined Dec 11, 2023
82
I initially plan to build this but will just decide to buy one.

It's for measuring Biopotential. Does anyone know a system which can measures 1mV to 10 mV with 2 microVolt noise at 1000 Hz?

What is the maximum noises in 1mV before the signal is no longer clear? How is it connected to Nyquist theorem?

#### MrChips

Joined Oct 2, 2009
30,823
Is this a school related project?

You need to define what you mean by noise. There are different types of noise with characteristic frequency spectra, and pdf (probability density function). There is white, pink, red, purple, grey, shot, thermal, Gaussian noise.

What is generating 1000Hz? Is this your signal or is this "noise"?

#### Gpand

Joined Dec 11, 2023
82
I'm a medical student.

1000 Hz is generated deep in the muscles and nerve centers.

Have you seen a Bioamplifier kit that can measure 1mV-10mV at 1000 Hz and less than 2 microVolt of noise? Such kit may have noises of hundreds of microVolt or even a milliVolt. Is it not? That is why I plan to buy a readily commercial one. But not easy to find a 1 channel of good noise profile.

Can some of you construct this kit for me?

#### Ian0

Joined Aug 7, 2020
9,844
The noise is proportional to the square root of the bandwidth, if you are talking about Johnson noise from resistances, and voltage- and current-noise from op-amps. But what about interference?

#### Gpand

Joined Dec 11, 2023
82
The noise is proportional to the square root of the bandwidth, if you are talking about Johnson noise from resistances, and voltage- and current-noise from op-amps. But what about interference?
What are the possible interferences at 1000 Hz? And if the amplifier circuit didn't handle it in chip, is it possible to pass the output to a post processing module or even software based?

#### MrChips

Joined Oct 2, 2009
30,823
It's for measuring Biopotential. Does anyone know a system which can measures 1mV to 10 mV with 2 microVolt noise at 1000 Hz?
Your statement as written implies that the noise is at 1000Hz.
If the signal is at 1000Hz, digital cross-correlation techniques can be used to extract signals buried in noise.

#### sparky 1

Joined Nov 3, 2018
759
There have been advances in understanding how the nerve derives energy which involves a pumping action.
A percussion wave is very different on the onset, it is longitudinal. The L wave compression and rarefaction
is not converted accurately with an electromagnetic sensor however it is best to use what is available.
It is not outside the field of electricity but those with specialized education will grasp some of the numerous bioelectric mechanisms.
I wonder how far beyond matlab some of the schools have gotten having the newer Ai and 3D subscriptions.
It must be overwhelming to see and frustrating to not ask how can all this could have come about by itself.

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#### MisterBill2

Joined Jan 23, 2018
18,585
The noise voltage produced by a circuit depends quite a bit on what components comprise the circuit.

#### Gpand

Joined Dec 11, 2023
82
For manufacturer who will build one unit per request per customer. What kinds of electronics are usually used? Do they use 0603 size components or bigger ones?

#### MrChips

Joined Oct 2, 2009
30,823
For manufacturer who will build one unit per request per customer. What kinds of electronics are usually used? Do they use 0603 size components or bigger ones?
Make a list of all the important requirements and specifications of the device. Now put the list in order of priority. Is SMD 0603 size in your list of priorities?

#### ronald01

Joined Dec 15, 2023
1
Noises at different frequencies can refer to sounds or signals that vary in pitch or tone. Sound is a wave, and its frequency is the number of oscillations or cycles it completes in a second, measured in Hertz (Hz). Different frequencies produce different perceptions of pitch. Here are some common classifications of noises based on their frequencies:
1. Low-Frequency Noise (LFN):
• Frequencies below 200 Hz are generally considered low-frequency. Examples include the rumble of thunder, the low hum of machinery, or the bass in music.
2. Mid-Frequency Noise (MFN):
• Frequencies between 200 Hz and 2 kHz fall into the mid-frequency range. This includes most human speech sounds and some background noises like traffic.
3. High-Frequency Noise (HFN):
• Frequencies above 2 kHz are considered high-frequency. Examples include the high-pitched chirping of birds, the sound of breaking glass, or the hiss of steam.
4. White Noise:
• White noise contains all frequencies in the audible spectrum with equal intensity. It is often used for masking other sounds, promoting relaxation, or improving concentration.
5. Pink Noise:
• Pink noise has equal energy per octave and is often used in audio engineering and testing.
6. Impulse Noise:
• Short bursts of high-intensity noise, like the sound of a gunshot or a handclap, contain a wide range of frequencies.
Understanding the frequency characteristics of different noises is essential in various fields such as acoustics, audio engineering, and environmental science. It allows for the identification, analysis, and mitigation of unwanted or harmful sounds.

#### sparky 1

Joined Nov 3, 2018
759
Personally I prefer RN55 low noise metal oxide resistor. If the unit warms up in 15 minets, a change in the
enclosure's ambient temperature is slowed by the mass of the larger package size and given thermal coefficient.
You may never know until you build it and sometimes it helps to experiment before ordering by specifications.
Sometimes an attenuator is mounted in a mini enclosure having a bnc connector. I prefer a flexible coax figuring in
whatever small resistance it has. Then you have an approximation because the entire test set up could have issues at 2uV.

#### Gpand

Joined Dec 11, 2023
82
There are many cheap \$20 biopotential modules. And some you can change the frequency cutoffs by altering the capacitor values. But how exactly do you test the level of noise at different frequencies? Let's say the noise is at 20 microVolt. Are you supposed to just look at the signal at microVolt to see the noise floor?

#### Ian0

Joined Aug 7, 2020
9,844
But how exactly do you test the level of noise at different frequencies?
Spectrum analyser