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Most accurate signal generator
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loop123:

--- Quote from: gf on April 01, 2024, 12:16:58 pm ---
--- Quote from: loop123 on March 31, 2024, 10:53:58 pm ---I figured out the sine waves noises don't merge into one another because they don't affect the past. And at 1kHz amplifier setting. The noises of 50Hz vs 900Hz is identical because making it pulse faster (higher frequency below 1kHz) doesn't produce more noise. And I want to test this.

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Sorry, I can't follow your thoughts. What do you mean with "noises of 50HZ vs. 900Hz"? You have noise, and you have your wanted signal. Just consider them as two independent signals. At the end, noise and wanted signal simply add up. The noise does not change if your wanted signal changes. You don't get a "different noise" if your wanted signal is 50Hz or 900Hz.

Nevertheless keep in mind that your noise is not white, but your amplifier also suffers from 1/f noise at low frequencies, and that you deal with bandwidth-limited noise (~1kHz). Both imply that your noise is not independent and identically distributed, but it is autocorrelated. So the deformation of the waveform due to noise (if you zoom-in) will definitively look different for a 50Hz sine wave signal and for a 900Hz sine wave signal. I have attached example plots for 1kHz-bandlimited (2nd order Butterworth) white noise and 12dB SNR. Note that for the 900Hz signal, the noise mostly affects the envelope. Keep in mind that these plots are still not represenative for the noise of your amplifier.
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Unless what you mean by bandwidth-limited noise (~1kHz)  is simply noise at bandwidth of 1kHz?  If so, then why did the jag lines disappear at 9kHz when you zoom them the same size? Remember they are supposed to have similar noise. If you produce these solely by software generator and out. What software is that? I'd like to try them.



nctnico:
Regarding the bottom picture: The noise is there but the sampling frequency and/or bandwidth is too low to make noise appear as jagged edges. Run an FFT on both signals (using equal record lengths and sampling frequencies).
loop123:

--- Quote from: nctnico on April 02, 2024, 08:49:57 am ---Regarding the bottom picture: The noise is there but the sampling frequency and/or bandwidth is too low to make noise appear as jagged edges. Run an FFT on both signals (using equal record lengths and sampling frequencies).

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Why did gf make the sampling frequency unequal causing confusion. Please make them equal gf so they can be compared equally.
ebastler:

--- Quote from: loop123 on April 02, 2024, 08:57:21 am ---
--- Quote from: nctnico on April 02, 2024, 08:49:57 am ---Regarding the bottom picture: The noise is there but the sampling frequency and/or bandwidth is too low to make noise appear as jagged edges. Run an FFT on both signals (using equal record lengths and sampling frequencies).

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Why did gf make the sampling frequency unequal causing confusion. Please make them equal gf so they can be compared equally.

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Jeesh, mate. The sampling rate obviously is the same in both diagrams: For the 50 Hz signal, one period takes about 1000 sample points. For the 900 Hz signal, on period takes about 56 sample points. What else do you want?

The plot for the 900 Hz signal is zoomed in on the horizontal axis, to fully resolve the 900 Hz signal. You see some added low-frequency noise, which causes the signal to wobble up and down. The higher-frequency noise, in the same rough range as the 900 Hz, is not as visible, and appears more like a phase jitter. There is obviously no noise at much higher frequencies than the 900 Hz, since the noise is bandwidth-limited to 1 kHz.
gf:

--- Quote from: nctnico on April 02, 2024, 08:49:57 am ---Regarding the bottom picture: The noise is there but the sampling frequency and/or bandwidth is too low to make noise appear as jagged edges. Run an FFT on both signals (using equal record lengths and sampling frequencies).

--- End quote ---

It is the same noise in both plots. Therefore the spectrum of the noise floor is the same as well. Flat up to ~1kHz, then rolling off with 12dB/octave. The first plots adds a 50Hz sine wave to the noise, and the 2nd plot adds a 900Hz sine wave to the noise. However, time/div is different in both plots in order to fit 10 signal periods of 50Hz or 900Hz into the screen width.

[ The units of the x-axis are samples, at a sample rate of 48kSa/s, in both plots. ]
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