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Most accurate signal generator
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JeremyC:

--- Quote from: loop123 on April 03, 2024, 11:35:48 pm ---
--- Quote from: JeremyC on April 03, 2024, 11:18:56 pm ---
--- Quote from: loop123 on April 03, 2024, 10:51:53 pm ---Someone told me  "Audio ADC's just aren't well suited to voltage signal measurements.". How true is it?

--- End quote ---

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!

--- End quote ---

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.

--- End quote ---

Well noise is noise...
Agreed, you should build GOOD Faraday cage in order to isolate yourself from people with common sense.
loop123:

--- Quote from: JeremyC on April 03, 2024, 11:50:09 pm ---
--- Quote from: loop123 on April 03, 2024, 11:35:48 pm ---
--- Quote from: JeremyC on April 03, 2024, 11:18:56 pm ---
--- Quote from: loop123 on April 03, 2024, 10:51:53 pm ---Someone told me  "Audio ADC's just aren't well suited to voltage signal measurements.". How true is it?

--- End quote ---

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!

--- End quote ---

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.

--- End quote ---

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

--- End quote ---

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:

--- Quote from: radiolistener on April 04, 2024, 01:16:25 am ---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.

--- End quote ---

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:

--- Quote from: loop123 on April 04, 2024, 01:24:59 am ---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?

--- End quote ---

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.
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