more details about LIS2DW problems

docs/macros/axis_tuning.md

@@ -146,17 +146,19 @@ The presence of an unbalanced or poorly running fan can be directly observed in
 | --- | --- | --- |
 | ![](../images/shaper_graphs/fan_notproblematic.png) | ![](../images/shaper_graphs/fan_maybeproblematic.png) | ![](../images/shaper_graphs/fan_problematic.png) |
 
-### Noisy accelerometer
+### Spectrogram lightshow (LIS2DW)
 
-The integration of LIS2DW as a resonance measuring device in Klipper is starting to be more and more common, particularly due to some manufacturers promoting its superiority over the established ADXL345. A critical analysis of their respective datasheets reveals a nuanced reality: the LIS2DW offers a higher sampling rate, but also it tends to exhibit increased noise levels at comparable sensitivity settings compared to the ADXL345. But, given that LIS2DW chips are also 5-10 times cheaper, it definitely makes sense for mass-producing PCBs.
+The integration of LIS2DW as a resonance measuring device in Klipper is becoming more and more common, especially because some manufacturers are promoting its superiority over the established ADXL345. It's indeed a new generation chip that should be better to measure traditional "accelerations". However, a detailed comparison of their datasheets and practical measurements paints a more complex picture: the LIS2DW boasts greater sensitivity, but it has a lower sampling rate and produce significant aliasing that results in a "lightshow" effect on the spectrogram, characterized by multiple spurious resonance lines parallel to the main resonance, accompanied by intersecting interference lines that distort the harmonic profile.
 
-In our use case, this chip manifests aliasing in the spectrogram that can be seen as additional 'ghosting' resonance lines parallel to the main resonance diagonal, with some intersecting interference lines that skew across the harmonics. Fortunately, this apparent lightshow do not distort the overall shape of the top graph and both the resonant frequency and damping ratio remain accurately measured as well as the input shaping filters that are also quite similar. This only makes it more challenging to discern fine details that could be masked, and it doesn't help for diagnosing mechanical issues.
+While, the top resonance graph's overall shape, including resonant frequency and damping ratio, should be close with pretty similar recommendations for input shaping filters, this aliasing complicates the identification of subtle details and hampers mechanical issue diagnostics. It especially introduces a potential misinterpretation of "[binding](#low-frequency-energy)" due to a global offset of the curve.
 
-Finally, please note that LIS2DW are known to add a small offset all over the top graph due to this aliasing. So the curve and peaks might be a bit higher, even at very low frequencies: in this case, this is probably not [#low-frequency-energy] but just some noise and it's not a mechanical problem.
+  > **Note**:
+  >
+  > It seems that some LIS2DW chips are better than others: in some cases aliasing is not a problem, but it can also be very problematic and lead to bad graphs, as seen in the "Extreme Aliasing" example below.
 
-| LIS2DW measurement | ADXL345 measurement |
-| --- | --- |
-| ![](../images/shaper_graphs/chipcomp_s2dw.png) | ![](../images/shaper_graphs/chipcomp_adxl.png) |
+| ADXL345 measurement | LIS2DW measurement | LIS2DW extreme aliasing |
+| --- | --- | --- |
+| ![](../images/shaper_graphs/chipcomp_adxl.png) | ![](../images/shaper_graphs/chipcomp_s2dw.png) | ![](../images/shaper_graphs/chipcomp_s2dw_2.png) |
 
 ### Crazy graphs and miscs
 

docs/macros/belts_tuning.md

@@ -60,7 +60,6 @@ The following graphs show the effect of incorrect or uneven belt tension. Rememb
 | The A belt tension is slightly lower than the B belt tension. This can be quickly remedied by tightening the screw only about one-half to one full turn.                                     | ![](../images/belt_graphs/low_A_tension.png) |
 | B belt tension is significantly lower than the A belt. If you encounter this graph, I recommend going back to the [Voron belt tensioning documentation](https://docs.vorondesign.com/tuning/secondary_printer_tuning.html#belt-tension) for a more solid base. However, you could slightly increase the B tension and decrease the A tension, but exercise caution to avoid diverging from the recommended 110Hz base. | ![](../images/belt_graphs/low_B_tension.png) |
 
-
 ### Belt path problem
 
 If there's an issue within the belt path, aligning and overlaying the curve might be unachievable even with proper belt tension. Begin by verifying that each belt has **the exact same number of teeth**. Then, inspect the belt paths, bearings, any signs of wear (like belt dust), and ensure the belt aligns correctly on all bearing flanges during motion.
@@ -70,3 +69,13 @@ If there's an issue within the belt path, aligning and overlaying the curve migh
 | On this chart, there are two peaks. The first pair of peaks seems nearly aligned, but the second peak appears solely on the B belt, significantly deviating from the A belt. This suggests an issue with the belt path, likely with the B belt. | ![](../images/belt_graphs/beltpath_problem1.png) |
 | This chart is quite complex, displaying 3 peaks. While all the pairs seem well-aligned and tension ok, there are more than just two total peaks because `[1]` is split in two smaller peaks. This could be an issue, but it's not certain. It's recommended to generate the [Axis Input Shaper Graphs](./axis_tuning.md) to determine its impact. | ![](../images/belt_graphs/beltpath_problem2.png) |
 | This graph might indicate too low belt tension, but also potential binding, friction or something impeding the toolhead's smooth movement. Indeed, the signal strength is considerably low (with a peak around 300k, compared to the typical ~1M) and is primarily filled with noise. Start by going back [here](https://docs.vorondesign.com/tuning/secondary_printer_tuning.html#belt-tension) to establish a robust tension foundation. Next, produce the [Axis Input Shaper Graphs](./axis_tuning.md) to identify any binding and address the issue. | ![](../images/belt_graphs/beltpath_problem3.png) |
+
+### Spectrogram lightshow (LIS2DW)
+
+The integration of LIS2DW as a resonance measuring device in Klipper is becoming more and more common, especially because some manufacturers are promoting its superiority over the established ADXL345. It's indeed a new generation chip that should be better to measure traditional "accelerations". However, a detailed comparison of their datasheets and practical measurements paints a more complex picture: the LIS2DW boasts greater sensitivity, but it has a lower sampling rate and produce significant aliasing that results in a "lightshow" effect on the spectrogram, characterized by multiple spurious resonance lines parallel to the main resonance, accompanied by intersecting interference lines that distort the harmonic profile.
+
+For the belt graph, this can be problematic because it can introduce a lot of noise into the results and make them difficult to interpret, and it will probably tell you that there is a mechanical problem when there isn't.
+
+| ADXL345 measurement | LIS2DW measurement |
+| --- | --- |
+| ![](../images/belt_graphs/chipcomp_adxl.png) | ![](../images/belt_graphs/chipcomp_s2dw.png) |

docs/macros/vibrations_tuning.md

@@ -49,3 +49,13 @@ For reference, the default settings used in Klipper are:
 #driver_HEND: 0
 #driver_HSTRT: 5
 ```
+
+### Semi-blank spectrogram (LIS2DW)
+
+The integration of LIS2DW as a resonance measuring device in Klipper is becoming more and more common, especially because some manufacturers are promoting its superiority over the established ADXL345. It's indeed a new generation chip that should be better to measure traditional "accelerations". However, a detailed comparison of their datasheets and practical measurements paints a more complex picture: the LIS2DW boasts greater sensitivity, but it has a lower sampling rate and produce significant aliasing.
+
+This lower sampling rate is problematic for the vibration graph because it only records data up to 200 Hz, which is too low to produce an accurate graph. This will be seen as a small low frequency band on the spectrogram with a blank area for higher frequencies and incorrect data printed in the speed profile and motor frequency profile.
+
+| LIS2DW vibration measurement |
+| --- |
+| ![](../images/vibrations_graphs/sd2w_spectrogram.png) |