# Understanding ToF noise under CPU loads

Source: https://forum.modalai.com/topic/1902/understanding-tof-noise-under-cpu-loads
Category: General Questions (https://forum.modalai.com/category/2/general-questions)
Posted: 2023-03-03 14:04:08 UTC by Rowan Dempster
Replies: 1 · Views: 451

## Rowan Dempster · 2023-03-03 14:04:08 UTC

Hi, I've been working with the ToF sensor under [version 0.8.1 of the camera server](https://gitlab.com/voxl-public/voxl-sdk/services/apq8096-camera-server/-/tree/v0.8.1). I've noticed that as I request higher FPS, the noise present in the measurements increases. This makes sense to me from an intuitive perspective, without understanding exactly how the PMD measurement algorithm works. However what confuses me is that at a single FPS mark (10FPS for example), noise is minimal when only the camera-server is running, but once I start other services (e.g. voxl-vision-px4), the noise increases. The only explanation I can think of is large CPU loads throttling the clock time for temperature control.

I would like to understand why increased CPU load / temperature causes increased ToF noise. In my mind, only code running on the VOXL would be impacted by CPU load. Is there post-processing code running on the VOXL, and is that code's performance somehow tied to CPU load? Or is the ToF measurement algorithm itself (the code running on the sensor) also somehow affected by a hotter board? Any light you can shed here is appreciated.

## Reply by Chad Sweet (ModalAI staff) · 2023-03-03 15:25:19 UTC

This doesn't align with anything we have seen. Any chance there is vibration being introduced?