Most accurate signal generator

[radiolistener]

I only use and familiar with Audacity which uses time scale in horizonal and not sample format. what other popular software uses samples format so i can try them all? tnx

Audacity has pretty poor filtering and FFT functionality and can raise many unexpected artifacts.

I recommend to use Matlab or Octave for such tasks.

[loop123]

I only use and familiar with Audacity which uses time scale in horizonal and not sample format. what other popular software uses samples format so i can try them all? tnx

Audacity has pretty poor filtering and FFT functionality and can raise many unexpected artifacts.

I recommend to use Matlab or Octave for such tasks.

What if I will use Owon HDS242S as replacement for the ADC + Audacity? how good is the adc in the HDS242S?

Also I need display software where it can do automatic real time filtering such as real time high pass filter. What software can do it? Audacity cant. Mathcad cant do real time display and its too complex. Just want to try it with user friendliness like Audacity.

[ebastler]

What if I will use Owon HDS242S as replacement for the ADC + Audacity? how good is the adc in the HDS242S?

It's an 8-bit ADC, and input noise is not even specified in the datasheet -- which means that it is not very good. For signals in the audio range, the Owon's ADC will be far worse than any sound card regarding resolution and noise.

(Of course it can capture signifcantly higher bandwidth signals, but you don't need that capability for your targeted application. And you "pay" for it with more noise.)

[loop123]

What if I will use Owon HDS242S as replacement for the ADC + Audacity? how good is the adc in the HDS242S?

It's an 8-bit ADC, and input noise is not even specified in the datasheet -- which means that it is not very good. For signals in the audio range, the Owon's ADC will be far worse than any sound card regarding resolution and noise.

(Of course it can capture signifcantly higher bandwidth signals, but you don't need that capability for your targeted application. And you "pay" for it with more noise.)

Its good you mentioned it. I nearly ordered it. What other least expensive oscilloscope with superb quality that can do better than E1DA ADC + Audacity combo with ability to interface to pc to capture the output for Mathcad etc processing in computer?

[ebastler]

Its good you mentioned it. I nearly ordered it. What other least expensive oscilloscope with superb quality that can do better than E1DA ADC + Audacity combo with ability to interface to pc to capture the output for Mathcad etc processing in computer?

Which aspect of the E1DA + PC + Audacity combination are you unsatisfied with??

If your frequency range of interest is the audio range or a subset of it, and you want low noise and low distortion, I don't think you can find any oscilloscope which can outperform that solution -- even at ten times your $200 price range and more. Oscilloscopes are designed for significantly higher bandwidth. That drives cost (or limits the number of bits an affordable ADC can provide) and has an adverse effect on noise.

[radiolistener]

Also I need display software where it can do automatic real time filtering such as real time high pass filter. What software can do it? Audacity cant. Mathcad cant do real time display and its too complex. Just want to try it with user friendliness like Audacity.

matlab can do it

[JeremyC]

@loop123
I read both your threads. Are you a bot?
Putting all of your concepts together... it doesn’t’ make sense…

[loop123]

Its good you mentioned it. I nearly ordered it. What other least expensive oscilloscope with superb quality that can do better than E1DA ADC + Audacity combo with ability to interface to pc to capture the output for Mathcad etc processing in computer?

Which aspect of the E1DA + PC + Audacity combination are you unsatisfied with??

If your frequency range of interest is the audio range or a subset of it, and you want low noise and low distortion, I don't think you can find any oscilloscope which can outperform that solution -- even at ten times your $200 price range and more. Oscilloscopes are designed for significantly higher bandwidth. That drives cost (or limits the number of bits an affordable ADC can provide) and has an adverse effect on noise.

Someone told me  "Audio ADC's just aren't well suited to voltage signal measurements.". How true is it? If E1DA ADC is not suitable for voltage signal measurements. Then what good ADC like it that can do that? He said:

"For audio equipment, the dynamic range is highly dependent on the frequency.  At very low frequencies, very little dynamic range is needed.  Audio ADC's just aren't well suited to voltage signal measurements.  Proper (non-audio) voltage ADCs try their best to convert the measured voltage to a digital value, without doing any of the shenanigans audio ADCs do to make the result "sound better" than it would without the shenanigans.  And psychoacoustics gives a TON of useful tricks to do that!  For example, noise shaping is extremely common: it uses filtering techniques to move the noise caused by the entire frontend to frequencies where humans perceive it less (where the equal-loudness contour is highest)."

The chip used in the E1DA is the following:

[JeremyC]

Someone told me  "Audio ADC's just aren't well suited to voltage signal measurements.". How true is it?

It's not possible to make measurements with sub uV (micro volt) accuracy in average room environment, even in majority of university labs.
You're talking about using 8 bit scope to measuring 100dB dynamic range , and on the other hand you are providing equations about noise level in nV/sqrt... come on!

[loop123]

Someone told me  "Audio ADC's just aren't well suited to voltage signal measurements.". How true is it?

It's not possible to make measurements with sub uV (micro volt) accuracy in average room environment, even in majority of university labs.
You're talking about using 8 bit scope to measuring 100dB dynamic range , and on the other hand you are providing equations about noise level in nV/sqrt... come on!

im only familiar with analog noises. i dont know how to relate ADC bits to dynamic range to nV/Sqrt. any definite equations that can convert  one to another?

I need to build a Faraday Cage bench size. Im building a lab.

[JeremyC]

Someone told me  "Audio ADC's just aren't well suited to voltage signal measurements.". How true is it?

It's not possible to make measurements with sub uV (micro volt) accuracy in average room environment, even in majority of university labs.
You're talking about using 8 bit scope to measuring 100dB dynamic range , and on the other hand you are providing equations about noise level in nV/sqrt... come on!

im only familiar with analog noises. i dont know how to relate ADC bits to dynamic range to nV/Sqrt. any definite equations that can convert  one to another?

I need to build a Faraday Cage bench size. Im building a lab.

Well noise is noise...
Agreed, you should build GOOD Faraday cage in order to isolate yourself from people with common sense.

[loop123]

Someone told me  "Audio ADC's just aren't well suited to voltage signal measurements.". How true is it?

It's not possible to make measurements with sub uV (micro volt) accuracy in average room environment, even in majority of university labs.
You're talking about using 8 bit scope to measuring 100dB dynamic range , and on the other hand you are providing equations about noise level in nV/sqrt... come on!

im only familiar with analog noises. i dont know how to relate ADC bits to dynamic range to nV/Sqrt. any definite equations that can convert  one to another?

I need to build a Faraday Cage bench size. Im building a lab.

Well noise is noise...
Agreed, you should build GOOD Faraday cage in order to isolate yourself from people with common sense.

But isnt it when the signal of 10uV is amplified with gain of 50000 in my main amp. The output of 0.5V can easily be viewed even with 8 bit scope?? Its not like the entire 10uV being directly put on the ADC.

Is it not if Audio ADC is used. It can bias the output to make it musical. Actually one participant here at EEVblog told me: "Proper (non-audio) voltage ADCs try their best to convert the measured voltage to a digital value, without doing any of the shenanigans audio ADCs do to make the result "sound better" than it would without the shenanigans."

I guess it doesnt apply to 0.5V signal or would it also pull a shenanigans trick to make the say 50Hz or 900Hz signal or combination sound musical?

[radiolistener]

There is no requirement to keep stable reference voltage for audio DAC/ADC, and this is the reason why it is not good for precise voltage measurements. Your calibration can drift a lot, for audio this is not an issue, but for measurement it is a problem.

Also, some DAC/ADC has decoupling capacitor on it's output/input, which will prevent you DC and low frequency measurements.

[loop123]

There is no requirement to keep stable reference voltage for audio DAC/ADC, and this is the reason why it is not good for precise voltage measurements. Your calibration can drift a lot, for audio this is not an issue, but for measurement it is a problem.

Also, some DAC/ADC has decoupling capacitor on it's output/input, which will prevent you DC and low frequency measurements.

For direct 10uV mapping into the ADC like in the case of the g.USBamp which doesnt have amplifier. It may be true but when the output is 0.5V (after 10uV x 50000 gain in main amp). What would be wrong for the 0.5V at audio Adc? would it make it like 0.4V or 0.6V?? How about the chip shown in spec in my last 2 messages used by the E1DA? does it keep stable reference voltage?

[ebastler]

For direct 10uV mapping into the ADC like in the case of the g.USBamp which doesnt have amplifier. It may be true but when the output is 0.5V (after 10uV x 50000 gain in main amp). What would be wrong for the 0.5V at audio Adc? would it make it like 0.4V or 0.6V?? How about the chip shown in spec in my last 2 messages used by the E1DA? does it keep stable reference voltage?

It would be really helpful if you clarify for us -- and for yourself! -- what your requirements are.

• What frequency range do you need to capture (lower and upper limit)?
  

• Do you need to capture only low-level signals, say in the 10 µV range -- in which case you could and should use an analog pre-amplifier, and then can work with an ADC with low resolution?
  

• Or do you need to pick out a 10 µV signal sitting on a 1 V background, as implied by your original questions in this thread -- in which case you need an ADC with correspondingly high resolution, if you want to use digital signal processing techniques to pick out the weak signal?
  

• Why do you think precise, absolute voltage levels are so critical for you to control or measure? I understand that you intend to study some EEG-like brain/computer interface -- won't the physiological differences and drifts, day-to-day and run-to-run variations of contacting the electrodes etc. be dominant by far? 

Given your limited budget, there is no room for an approach like "I'd rather get something that covers all the bases and all potential future needs". If there is any chance to establish a solution for $200, it will need to be tailored to your specific needs. Hence, until you have a clear and consistent picture of what your signals are and how you need to control and measure them, there is not much point in equipment discussions.

[loop123]

For direct 10uV mapping into the ADC like in the case of the g.USBamp which doesnt have amplifier. It may be true but when the output is 0.5V (after 10uV x 50000 gain in main amp). What would be wrong for the 0.5V at audio Adc? would it make it like 0.4V or 0.6V?? How about the chip shown in spec in my last 2 messages used by the E1DA? does it keep stable reference voltage?

It would be really helpful if you clarify for us -- and for yourself! -- what your requirements are.

• What frequency range do you need to capture (lower and upper limit)?
  

• Do you need to capture only low-level signals, say in the 10 µV range -- in which case you could and should use an analog pre-amplifier, and then can work with an ADC with low resolution?
  

• Or do you need to pick out a 10 µV signal sitting on a 1 V background, as implied by your original questions in this thread -- in which case you need an ADC with correspondingly high resolution, if you want to use digital signal processing techniques to pick out the weak signal?
  

• Why do you think precise, absolute voltage levels are so critical for you to control or measure? I understand that you intend to study some EEG-like brain/computer interface -- won't the physiological differences and drifts, day-to-day and run-to-run variations of contacting the electrodes etc. be dominant by far? 

Given your limited budget, there is no room for an approach like "I'd rather get something that covers all the bases and all potential future needs". If there is any chance to establish a solution for $200, it will need to be tailored to your specific needs. Hence, until you have a clear and consistent picture of what your signals are and how you need to control and measure them, there is not much point in equipment discussions.

I already have a 50,000 gain amplifier to work with 10uV (100Hz to 2400Hz) signal. The CWE BMA-200. Since the output of the amplifier is 0.5V to 2 V. Then even audio ADC can work with it, right?  When you talk about stable reference voltage. Can it make the output vary between say 0.5V to become 0..4V or does it only occur in micro or millivolt signal?

I already have the E1DA ADC as well as a 16 channel amp that doesn't have any amplifier inside. The 16 channel g.USBAmp has this description I shared earlier. My question concerns its last sentence.

https://www.gtec.at/product/gusbamp-research/

"g.USBamp uses wide-range DC-coupled amplifier technology in combination with 24-bit sampling. The result is an input voltage range of +/- 250 mV with a resolution of < 85,7 nV! This means that any physiological signal can be recorded directly, without additional hardware. Neither high electrode offset voltage nor large artifacts resulting from electrical or magnetic stimulation will saturate the amplifier inputs. This feature is an important requisite for various artifact treatment and correction techniques"

"Each of the 16 analog to digital converters operates at 2.4576 MHz. Oversampling 64 times yields the internal sampling rate of 38,400 Hz (per channel and for all channels!). In addition, a powerful floating point Digital Signal Processor performs oversampling and real-time filtering of the biosignal data (between 0 Hz – 2,400 Hz). Therefore, a typical sampling frequency of 256 Hz yields an oversampling rate of 9,600. This results in a very high signal to noise ratio, which is especially critical when recording evoked potentials (EP) in the EEG or identifying small amplitude changes in high-resolution ECG recordings. You are measuring far below the noise-range of conventional amplifiers.""


Today due to JeremyC comments that I only knew about nV/Sqrt(Hz) noise formulas. I researched for hours about bits, how to compute for dynamic range in dB and even to relate to nV/Sqrt(Hz). Now I know. But I still can't totally comprehend the above description "You are measuring far below the noise-range of conventional amplifiers."? How so? What is typical noise-range of conventional amplifiers and how could it be measuring far below? Please give actual figure as examples. Thank you.

[gf]

It may be true but when the output is 0.5V (after 10uV x 50000 gain in main amp). What would be wrong for the 0.5V at audio Adc?

My understanding of the problem is that you consider your BMA-200 pre-amplifier too noisy, so you are looking for an alternative solution. And as far as I understood (in the other thread), one of your requirements is a high input impedance, which is not particularly helpful either if you want low noise on the other hand.

You are measuring far below the noise-range of conventional amplifiers

This is just meaningless marketing
Do you have numbers? E.g. plot of the (input referred) noise spectral density up to 1 kHz (which seems to be your ROI)? Did you ask the manufacturer to provide some data?

[ebastler]

...

You claim to respond to my post, but have not really answered a single of my questions, right? 

If you need to capture low-level signals only, rather than small signals sitting on top of a large fluctuating signal, then the CWE BMA-200 looks like a pretty capable pre-amplifier. And the g.USBAMP looks like a very plausible AD-converter -- probably a better choice than an audio amplifier since it is DC-coupled. (It better be good, given that it costs closer to $20000 than $200...)

What functionality do you find lacking in your current setup?

[loop123]

It may be true but when the output is 0.5V (after 10uV x 50000 gain in main amp). What would be wrong for the 0.5V at audio Adc?

My understanding of the problem is that you consider your BMA-200 pre-amplifier too noisy, so you are looking for an alternative solution. And as far as I understood (in the other thread), one of your requirements is a high input impedance, which is not particularly helpful either if you want low noise on the other hand.

You are measuring far below the noise-range of conventional amplifiers

This is just meaningless marketing
Do you have numbers? E.g. plot of the (input referred) noise spectral density up to 1 kHz (which seems to be your ROI)? Did you ask the manufacturer to provide some data?

The following is the noise spec of my BMA-200. Noise Wideband Referred to Input <7uV P-P, < 3uV RMS, Wideband is 50kHz



The following is the noise spec of my USBamp.



Noise mentioned is 0.4uV RMS at 1 to 30 Hz. about 2.64uV Peak to Peak? According to Netech. Their simulator output is 10uV peak to peak. If you will extrapolate it. At 1000Hz. The g.USBamp will be so noisy the noise can reach 10uV? 

I mean if at 1 to 30Hz, the g.USBamp has noise of 2.64uV P-P, what is your estimate of the noise at 1000Hz? How do you compute the estimate? However their demo software still has the Netech simulator 10uV, 50Hz resolvable (see below). Shouldn't it be one big blur? 




I still haven't bought the software of the g.USBamp which costs more than $3000. Note major R&D centers used the g.USBamp. Including one with sigma 5 result I'm trying to replicate, one with the potential to produce 5 times the revolution caused by the discovery of DNA by Watson, etc. and will advance humanity a century ahead.

[loop123]

For direct 10uV mapping into the ADC like in the case of the g.USBamp which doesnt have amplifier. It may be true but when the output is 0.5V (after 10uV x 50000 gain in main amp). What would be wrong for the 0.5V at audio Adc? would it make it like 0.4V or 0.6V?? How about the chip shown in spec in my last 2 messages used by the E1DA? does it keep stable reference voltage?

It would be really helpful if you clarify for us -- and for yourself! -- what your requirements are.

• What frequency range do you need to capture (lower and upper limit)?
  

• Do you need to capture only low-level signals, say in the 10 µV range -- in which case you could and should use an analog pre-amplifier, and then can work with an ADC with low resolution?
  

• Or do you need to pick out a 10 µV signal sitting on a 1 V background, as implied by your original questions in this thread -- in which case you need an ADC with correspondingly high resolution, if you want to use digital signal processing techniques to pick out the weak signal?
  

• Why do you think precise, absolute voltage levels are so critical for you to control or measure? I understand that you intend to study some EEG-like brain/computer interface -- won't the physiological differences and drifts, day-to-day and run-to-run variations of contacting the electrodes etc. be dominant by far? 

Given your limited budget, there is no room for an approach like "I'd rather get something that covers all the bases and all potential future needs". If there is any chance to establish a solution for $200, it will need to be tailored to your specific needs. Hence, until you have a clear and consistent picture of what your signals are and how you need to control and measure them, there is not much point in equipment discussions.

In my last message to you. I answered the 1st and 2nd question. About the third. It's small signal sitting on top of others. You said "Or do you need to pick out a 10 µV signal sitting on a 1 V background, as implied by your original questions in this thread -- in which case you need an ADC with correspondingly high resolution, if you want to use digital signal processing techniques to pick out the weak signal?".

But digital filters using oversampling with moving averages can only do brick wall filter above the cutoff frequency. How can digital signal processing techniques pick up the weak signal among the noises??  Is it not both the BMA-100 and USBamp outputs need to be pass through intensive Mathcad analysis?  Or can digital signal processing somehow remove further noises below the cutoff? if not, how can it pick up the weak signal? What techniques is this called?

[ebastler]

In my last message to you. I answered the 1st and 2nd question.

I don't think you did; or I did not get your point. You told us what equipment you have and what its specs are. But you (still) have not told me what signals you need to measure, and where you find your current equipment to be lacking in its capabilities.

About the third. It's small signal sitting on top of others.

OK. What is the level and the frequency (range) of the signal of interest, and ditto for the background?

You said "Or do you need to pick out a 10 µV signal sitting on a 1 V background, as implied by your original questions in this thread -- in which case you need an ADC with correspondingly high resolution, if you want to use digital signal processing techniques to pick out the weak signal?".

But digital filters using oversampling with moving averages can only do brick wall filter above the cutoff frequency. How can digital signal processing techniques pick up the weak signal among the noises??  Is it not both the BMA-100 and USBamp outputs need to be pass through intensive Mathcad analysis?  Or can digital signal processing somehow remove further noises below the cutoff? if not, how can it pick up the weak signal? What techniques is this called?

If you know the frequency (range) of interest, you can use bandpass filters to isolate the signal from the background. If there is a specific undesired background frequency, you can use a notch filter to suppress it. If you are looking for signals with characteristic frequencies, but you don't know the actual frequencies in advance, you can use FFT (Fast Fourier Transformation) to see all spectral components, of the signal and the background. Or you can use auto-correlation to find characteristic frequencies in the time domain (rather in the frequency domain as FFT does).

[gf]

But digital filters using oversampling with moving averages can only do brick wall filter above the cutoff frequency. How can digital signal processing techniques pick up the weak signal among the noises??  Is it not both the BMA-100 and USBamp outputs need to be pass through intensive Mathcad analysis?  Or can digital signal processing somehow remove further noises below the cutoff? if not, how can it pick up the weak signal? What techniques is this called?

It is not possible to separate an arbitrary, unknown signal from random noise. If a separation, or partial separation, is possible at all, then only if you have some a priori knowledge about the signal. The a priori knowledge could be as trivial as knowing that the signal is a sine wave, then you can easily dig it out from the noise floor with a narrow-band filter. But the a priori knowledge could also be a very complex statistical property of the signal, then you need a complex statistical analysis far beyond traditional DSP methods. So you should ask yourself the question: What do you already know about the signal you are looking for?

[loop123]

In my last message to you. I answered the 1st and 2nd question.

I don't think you did; or I did not get your point. You told us what equipment you have and what its specs are. But you (still) have not told me what signals you need to measure, and where you find your current equipment to be lacking in its capabilities.

About the third. It's small signal sitting on top of others.

OK. What is the level and the frequency (range) of the signal of interest, and ditto for the background?

The range of frequency is 300Hz to 10000Hz, the level or amplitude I'm not sure. It's from at least 10uV upward to maybe below 0.5mV or between them. Background is human body potential and countless interferences.

I'm not even sure what it is i'm measuring. I'm just trying to repeat the experiments of some physicists/scientists. The signal is from another realm, not of this world. It needs to use mini-portal or Rosen Einstein bridge to tunnel the signal into this world. You know the brain is the most complex thing in the universe. Our body is also equally complex and tied up with new physics. Again I'm not sure whether the signal from another brane, a dark matter subsector, parallel universe or higher aspect of the universe. I'm still discussing with CERN scientists at other forums.

I know this message would be met with disbelief or I'd be ignored from now on. But I got most information I need already. I'll just study what you wrote below and discuss with digital signal processing experts as well as Mathcad experts from now on. I don't know how to use Mathcad. So it all boils down to signal analysis and I'll talk with other forums that deal with it. The days ahead would be harder I know. 

You said "Or do you need to pick out a 10 µV signal sitting on a 1 V background, as implied by your original questions in this thread -- in which case you need an ADC with correspondingly high resolution, if you want to use digital signal processing techniques to pick out the weak signal?".

But digital filters using oversampling with moving averages can only do brick wall filter above the cutoff frequency. How can digital signal processing techniques pick up the weak signal among the noises??  Is it not both the BMA-100 and USBamp outputs need to be pass through intensive Mathcad analysis?  Or can digital signal processing somehow remove further noises below the cutoff? if not, how can it pick up the weak signal? What techniques is this called?

If you know the frequency (range) of interest, you can use bandpass filters to isolate the signal from the background. If there is a specific undesired background frequency, you can use a notch filter to suppress it. If you are looking for signals with characteristic frequencies, but you don't know the actual frequencies in advance, you can use FFT (Fast Fourier Transformation) to see all spectral components, of the signal and the background. Or you can use auto-correlation to find characteristic frequencies in the time domain (rather in the frequency domain as FFT does).

[ebastler]

I'm not even sure what it is i'm measuring. I'm just trying to repeat the experiments of some physicists/scientists. The signal is from another realm, not of this world. It needs to use mini-portal or Rosen Einstein bridge to tunnel the signal into this world. You know the brain is the most complex thing in the universe. Our body is also equally complex and tied up with new physics. Again I'm not sure whether the signal from another brane, a dark matter subsector, parallel universe or higher aspect of the universe. I'm still discussing with CERN scientists at other forums.

I know this message would be met with disbelief or I'd be ignored from now on. But I got most information I need already. I'll just study what you wrote below and discuss with digital signal processing experts as well as Mathcad experts from now on. I don't know how to use Mathcad. So it all boils down to signal analysis and I'll talk with other forums that deal with it. The days ahead would be harder I know.

Good luck with your endeavors, but I think signal processing is the least of your worries. Better don't tell those CERN scientists and Matchcad experts about the signals which are not of this world. 

[shapirus]

This world or not, but if the signal exists and it is not a natural background noise, then you will be able to detect and measure it, given the right methodology and instruments.

The problem here is that the right methodology requires education and/or training and/or rich experience. The right instuments may require a lot of money.

If you don't know precisely what you're looking for, you may have to look for everything in many small isolated areas one by one until you spot something of interest -- see e.g. the bandpass filter suggestions above.