How to synchronize recordings

See Synchronization and breath timing for how M3Resp uses start times.

Give each recording a start time

Call synchronize_raw_modalities before the processing. Give the start time of each recording in seconds from the start of the reference recording. A negative value means that the recording started earlier than the reference.

session.synchronize_raw_modalities(
    method="manual_offset",
    offset_seconds={"eit": 0.0, "emg": -2.0, "ventilator": 0.0},
    reference_modality="eit",
)

• If you do not set reference_modality, the reference is the ventilator. Without ventilator data, the reference is the EIT, and without EIT, the EMG.

• A single number for offset_seconds is the start time of the EMG.

• A second call replaces the start times. It does not add to them.

M3Resp stores the start times in session.start_times. Each recording keeps all its samples and its own clock.

Synchronize ventilator data

The key "ventilator" sets the start time of a ventilator file that you loaded with source="ventilator". Ventilator data inside an EIT or EMG file always has the start time of that file.

If two separate ventilator recordings started at different times, give each one a name when you load it. Then use the key "ventilator:<name>":

session.load_ventilator("monitor.txt", name="monitor", source="ventilator")
session.synchronize_raw_modalities(
    offset_seconds={"eit": 0.0, "ventilator": 0.0, "ventilator:monitor": 12.5},
)

Use recordings that started together

If one trigger started all devices, the recordings need no start times. Call skip_synchronization to record this choice:

session.skip_synchronization()

M3Resp then stores "none" for each recording in session.sync_methods. link_breaths gives a warning for a recording with no synchronization record, so this call also stops that warning.

Shift the breaths after detection

If you find a better offset after the breath detection, shift the breaths with synchronize_multimodal_breaths. This offset adds to the start times:

session.synchronize_multimodal_breaths(method="manual_offset", offset_seconds={"emg": 0.2})

M3Resp stores the shifted breaths in session.processed["synchronized"]. link_breaths uses these breaths.

Overview of the three calls

Call	What it changes	When
synchronize_raw_modalities	It stores the start time of each recording in session.start_times	Before the processing
synchronize_multimodal_breaths	It shifts the detected breaths by an extra offset	After the breath detection, only if the offset changed
link_breaths	Nothing. It puts the breaths that belong together into a linked breath	Last

The "multimodal" preset runs synchronize_raw_modalities and then synchronize_multimodal_breaths. Run it after the "eit" and "emg" presets.