Measure a transfer function. Adjust an existing filter to compensate by putting another filter in series.
# Steps
## 1. Load References
- Loading references means using previous measurements and assigning them as references.
- Loaded references are displayed on plots alongside new measurements to be compared visually.
- Pre-CDS diaggui is cumbersome as there is no ability to annotate references. There are several usability issues in the issue tracker related to loading references. In particular, a reference can only be created from a measurement in the existing test file.
- When the file is saved, defined references are saved with it.
## 1. Setup Channels
- The user picks which channels should be measured and which should be excited. The user also configures A/B channels for transfer function calculation.
- This is currently a complicated and error-prone
## 3. Measure transfer functions
This consists in just running the test. Note that this use case dose not really get into the setup of the measurement.
## 4. Fine tune
- Look at the coherence of transfer function.
- Adjust gain filter on output to increase coherence in frequency bands where coherence is too low.
- Re-run transfer function
- PRE-CDS: this involved flipping back and forth between results and a Foton filter window. This is cumbersome as they are on separate tabs and cannot be displayed at the same time.
## 6. Calculate correction
- When coherence is good enough, the results are saved to an xml file.
- The xml file is consumed by a python script or notebook that does a fit on the difference of the transfer function from the expected transfer function, then derives a new filter to correct for the difference.
- There's some attempt to weight the fit based on frequency ranges of interest.
