General > General Technical Chat
FFT and 60 Notch filter software
tggzzz:
It is always good to check and verify your understanding by experiment.
You can do this yourself...
Apply a since wave signal to the input, and monitor how that appears in your .wav file and audacity.
Tweak the amplitude until the magnitude is full scale peak to peak without clipping.
Measure the input signal, not forgetting the standard RMS to peak-peak conversion.R
Sanity check: reduce the input signal by a factor of 10, and verify the numbers seen in audacity match that.
Summary: do the bloody experiment yourself, and stop asking us to guess about your setup.
loop123:
--- Quote from: tggzzz on March 14, 2024, 11:48:40 pm ---It is always good to check and verify your understanding by experiment.
You can do this yourself...
Apply a since wave signal to the input, and monitor how that appears in your .wav file and audacity.
Tweak the amplitude until the magnitude is full scale peak to peak without clipping.
Measure the input signal, not forgetting the standard RMS to peak-peak conversion.R
Sanity check: reduce the input signal by a factor of 10, and verify the numbers seen in audacity match that.
Summary: do the bloody experiment yourself, and stop asking us to guess about your setup.
--- End quote ---
Did it. The error is 0.001 or about 0.1%.. from 0.926 (5V) to 0.0922 (0.5V).
Why, does other ADC or typical sound card show more error? The E1DA was marketed to measure distortions (not for general playing music) so it is super accurate. And their technical team said it hasn't got any form of automatic gain control or clipping protection.
Super accurate $800 Netech 2.5mV output and BMA set to 2000 gain for 5V.
Super accurate $800 Netech 2.5mV output and BMA set to 200 gain for 0.5V.
loop123:
--- Quote from: Andy Chee on March 14, 2024, 09:46:18 am ---Assuming your equipment is portable and battery powered, how about going into the middle of a nature park reserve, which is a long distance away from any powerlines, TVs, power supplies, and any other electrical equipment.
You should be able to at least establish the noise floor performance of your equipment. My suggestion is at least 1000m distance in all directions from any electrical device, but I don't know whether you have a location that size.
This is for testing your equipment only, I'm not suggesting you perform your actual experiments in the middle of nowhere!
--- End quote ---
Everytime there is interference, some frequencies can be determined, right? In the case of my 10uV input and 1000 bandwidth switched selected in the amp. Many here concluded it is wideband noise or already the noise floor. So it can't be interference. Well before I try to spend days going to the mountain in the middle of nowhere. I need first to figure out how a 5nV/sqrt (Hz) in the AMP01 becomes 1000nV/sqrt (Hz). Because at 5nV/sqrt(Hz) and with bandwidth of 1000Hz, the noise is only 0.158uV and 10uV signal should look very good. How the AMP01 in the BMA-200 get noise of 2uV at 1000Hz (instead of 0.158uV) is a big mystery I'm trying to figure out. Any ideas guys? Have you encountered any amplifier with noise over 1000 worse than in datasheet? The broadband noise or even noise floor has no particular frequencies so many here concluded they are not interferences.
loop123:
--- Quote from: WatchfulEye on March 13, 2024, 03:50:12 pm ---Only the 60 Hz noise is powerline.
There is a mystery 78 Hz noise.
The main noise is broadband noise - which looks like noise floor, but by my calculations it is about 100-150 nV/sqrt Hz - much higher than specified noise of the AMP01. It could be noise from the waveform generator.
However, note that BMA-200 specifies 7uV noise - and your recording shows less noise than this.
You could try measuring the noise directly by using a 1 kohm resistor instead of the waveform generator. It would be interesting to have a series of recordings with different waveforms and 1 with just a resistor - all settings left exactly the same.
--- End quote ---
The BMA-200 has this noise spec "Wideband noise, RTI <7µV P-P". I figured the wideband noise has full 50kHz selected so for the AMP01 5nV/sqrt(Hz) * sqrt (50000) = 1118nV rms or 7000nV P-P. I know Referred to input means the output is measured that includes all the components including the ADC noise. But still.. 1118nV is good estimate for noise at 50000Hz. But for noise at 1000Hz. It is only 0.158uV rms. So where do you think the 100-150nV/Sqrt (Hz) broadband noise came from in the 10uV signal? You asked me to use 1 k Ohm resistor. I did it and here is the result:
1k resistor, all same setting
10uV, 50Hz all same setting
So the broadband noises don't come from the Netech simulator because the resistor also made those noises. So what do you think is the origin of the broadband noise at your estimated 100-150nV/Sqrt (Hz)? I have 2 units BMA and it can't be both AMP01 were damaged. Or maybe they are? What is your other theory WatchfulEye? I am clueless now. Thanks.
loop123:
I decide to initiate bypass operation to tap directly into the +IN and -IN of the AMP01. I will cut into some part of the pcb. I have 2 sets and one will be sacrifice. Each costs $1595 so don't want to destroy much. So to tap into the +IN and -IN, i'll directly connect the Netech output into them without using any other components? Because I think somewhere en route to it is the source of the broadband noise analyzed by some of you.
BMA front and back (xray mode)
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