1

OnePlus X E1001, E1003 don't need root, just install Boldbeast Recorder and go.
Please use these settings to record calls:

- Record Mode: 5
- Record Format: WAV
- Tune Audio Effect: No
- Tune Audio Route: Group3

Calls are recorded crystal clear in two directions, confirmed by OnePlus X E1003 Android 5.1.1.

2

OnePlus 6: OnePlus 6 Call Recorder
OnePlus 5, 5T: OnePlus 5 Call Recorder
OnePlus 3, 3T: OnePlus 3 Call Recorder
OnePlus 2: OnePlus Two Call Recorder
OnePlus X: OnePlus X Call Recorder
OnePlus One: OnePlus One Call Recorder