BIS EEG¶

The raw EEG from the BIS monitor at 128 Hz.

Stub

Imported from the time-source table; the full page is still to be written.


Name in the dataset	`BIS/EEG1_WAV`
Type	waveform
Device	BIS monitor
Stamped by	Recorder PC clock
Spaced by	BIS clock
Rate	128 Hz
Unit	uV

Measurement space¶

Time side (after sync to the ECG): the true time lies between -0.0498 s and -0.017 s from the stamp: the delay range plus the interval one value describes.

Time¶

From UTC to the stored time stamp¶

The clock path first (UTC to the clock that stamps or spaces the samples), then the signal's own path to its stored time. Each bar: the time shift or error the step introduces (pale) and what is left after the atlas's correction (solid), on a log scale; dashed when estimated or assumed.

UTC

The reference every chain starts from.

Recorder PC clock

sync assumed 3 ms – 900 ms · clock link, parameter

Windows time synchronisation to the hospital's time server every 8–24 h (assumed), drifting a few ppm in between. Not observable in the release: dates are shifted to 2100. No step of 0.5 s or more was found.

BIS clock

clock measured 530 ms – 1.05 s · The stamp sawtooth model for SNUADC and BIS

The BIS monitor stamps its EEG on its own clock; for the same event its stamps sit 0.53–1.05 s off the ECG's. It drifts +25 ppm against the PC and is pulled forward on a fixed 8,192 s timer (median +0.17 s). Drift: +25 ppm against the PC; corrected every 8,192 s.

Synchronised to the ECG

correction measured 530 ms – 1.05 s → 17 ms – 42 ms after correction · The stamp sawtooth model for SNUADC and BIS

The stamp model removes the drift and corrections; one constant per SNUADC mode, from bursts seen in both the ECG and the EEG, removes the offset. With the recording's own bursts the error is about 17 ms, with the mode's constant about 42 ms (whole release).

Stored sample time

stamping measured 7.8 ms

Samples at 128 Hz: one sample is 7.8 ms.

Timing¶

Against the working reference. Delay: from the end of the interval a value describes to its stamp. Interval: how wide that interval is.

Form	Delay	Interval	Clock domain	Status	Evidence
after sync to the ECG (default)	17 ms – 42 ms	7.8 ms	SNUADC stamp-model time (the working reference)	measured	17-42 ms (recording's own constant to the mode's; whole release, 2,710 recordings); loop closes in drift and steps; latency -0.80 s (SD 25 ms) in link K
raw stamps	530 ms – 1.05 s	7.8 ms	BIS clock	measured	offset p5-p95 -1053..-533 ms on the recorded stamps (191-case pilot)

Combine it with other signals in the synchronisation planner.

Value¶

Its value side is still to be described.

Parameters¶

Parameter	Value	Status	From
EEG–ECG timing error after the stamp model	42 ms median, p90 150 ms (17 ms and 79 ms with the recording's own bursts)	measured	The stamp sawtooth model for SNUADC and BIS

Observations¶

Observation	Status	Summary
Eight recordings store whole messages twice	established	In 8 recordings 15–48% of the waveform records are byte-for-byte copies of the record before them, with the same timestamp: case 15, case 364, case 1946, case 3865, case 4857, case 5414, case 5595 and case 5619. SNUADC, Primus and BIS are affected equally, so the recorder, not a device, wrote them twice.
Every time is quantised, and fiducials inherit it	established	A time on a grid of step Δ carries an error of Δ/√12 (1 SD). In VitalDB that is 0.58 ms for a 500 Hz sample, 2.3 ms for BIS EEG, 0.8 ms for the arrhythmia annotations' 1/360 s grid, and up to ±17 ms for PPG fiducials taken on raw samples, which lock to the 33.3 ms frame.
The BIS index is slow	established	The BIS index averages 15–60 s of EEG ending about 3 s before its stamp, with half its weight older than 30 s. It cannot time anything faster than about a minute.
The EEG–ECG offset is fixed by the SNUADC correction mode	established	After the stamp model, BIS EEG still lags the SNUADC ECG by a constant: −804 ms in step mode and −660 ms in frequent-correction mode over the whole release, tight within a port or unit. The mode, a property of the setup, sets the constant.
The BIS EEG carries an averaged cardiac artefact	likely	Averaged on the ECG's R peaks, the BIS EEG shows the heartbeat (median 4.3 µV), near-simultaneous with the R wave. Single beats are too weak to match one by one.
In some recordings two unrelated streams are interleaved in one track	open	In 7 recordings 64–95% of the records alternate between two streams: each record continues the one two before it, not the one before, and the two streams do not match each other. SNUADC and BIS in case 2219, case 2379, case 2640, case 4836, case 5327 and case 5617; SNUADC in case 1939. In case 94, case 945, case 1132, case 3195 and case 5700 4–7% of SNUADC records interleave.
The BIS EEG carries no heartbeat	withdrawn	Claimed after a first search found no consistent cardiac trace in the BIS EEG. The search window was in the wrong place: the BIS stamps sit about 0.8 s off the ECG's.

Studies¶

Study	Date	Status	Summary
Gaps and unbroken segments in every waveform	2026-10-19	draft	Every gap and every unbroken segment in the 6,388 recordings, per waveform. The curves are not smooth: a cliff at about 18 s in every device marks the recorder's pauses, SNUADC segments stop at 5 hours, Primus segments at about 2.0 hours and BIS segments at about 2.3 hours (each device's correction cycle), and BIS's short gaps grow with the time since the last one (clock resynchronisations, not lost data).
When each device's clock is corrected, in every recording	2026-10-19	draft	From the steps between records in all 6,388 recordings: the BIS is corrected every 8,192 s and the Primus every 7,230 s, on their own timers (the first correction comes at any time after the device starts); the SNUADC is reset when 0.49 s of drift has built up. With the full rerun of the correction fit, it gives each device's drift against the recorder PC in 4,728 BIS and 2,728 SNUADC recordings, and shows that the Primus's 20–23 s AWP pauses belong to its correction cycle. Every rate here is relative to the recorder PC, whose own clock drifts and is corrected.
Message sizes and the steps between records	2026-10-19	draft	Every record in every waveform: SNUADC writes messages of 100 samples (0.2 s), Primus 30 (0.48 s), BIS 16 (0.125 s), CardioQ no fixed size. Backward steps outnumber gaps by about a hundred to one and come from a few recordings with duplicated or interleaved records. Primus gaps are whole lost messages; most SNUADC and BIS gaps are not.
What each break in the stamps is	2026-10-19	draft	Every step between waveform records in the release, sorted by mechanism: written twice, a SNUADC clock reset, interleaved streams, a pause shared by every device, whole messages, less than a message, or a fraction of a message beyond whole ones. A continuity test with controls shows which classes lose data: shared pauses and most longer SNUADC gaps do; steps under one message, and SNUADC's lone one-message steps, mostly do not.
Value resolution of every signal	2026-10-19	draft	How finely every waveform and numeric track in the release records its values. The SNUADC waveforms are 10-bit codes, though VitalRecorder's documentation describes the SNUADC as 12-bit; Primus waveforms use about 10 bits of 12; BIS EEG is a 16-bit grid of 0.05 µV. Numerics are 32-bit floats on decimal grids of 1, 0.1, 0.01 or 0.001, one per track; settings sit on coarser grids of 10 or 100.
How often each device is corrected	2026-10-17	current	The devices re-synchronise in different ways: SNUADC when its drift reaches about half a second, BIS on a fixed 8,192 s timer, and the Primus by small steps about every two hours that do not keep up with its drift (+104 ppm, measured later by breath matching).
How the BIS index trails its EEG	2026-10-13	current	Modelling the BIS index as a lagged mix of EEG features shows a trailing average starting about 3 s after its EEG window ends: about 16 s long in half the cases (the 15 s smoothing setting) and 32–61 s in most others. Half the response weight is older than 30 s.
Closing loops in the timing graph	2026-10-13	current	Where two independent routes reach the same clock, the offsets around the loop must sum to zero. Three measured loops close within their noise; the BIS loop closes up to a constant latency; the proposed EMR loop is not a loop at all.
What a BIS-mimic project says about the index's smoothing	2026-10-13	current	The openeeg project reproduces the BIS index from the raw EEG and infers each case's smoothing setting: about 80% of its cases come out at 15 s. Its alignment cannot serve as a timing reference.
The cardiac artefact in the BIS EEG	2026-10-12	current	The BIS EEG carries a weak electrical trace of every heartbeat. Too weak for beat-by-beat matching, it shows clearly when averaged on the ECG's R peaks, and gives a second SNUADC–BIS timing reference that agrees with the bursts to about 16 ms.
Shared bursts between the ECG and the EEG	2026-10-12	current	Electrocautery and muscle bursts appear in both the SNUADC ECG and the BIS EEG. Cross-correlating their envelopes gives the offset between the two devices' stamps every 10 minutes: about −0.8 s, in a sawtooth that follows both clocks' corrections.
The stamp sawtooth model for SNUADC and BIS	2026-10-12	current	Fitting each track's record stamps against its sample count as a drift with corrections (a sawtooth) puts SNUADC and BIS on one timeline without any artefact. Checked against shared bursts, the EEG–ECG timing error falls from about 790 ms on the recorded stamps to 33 ms with one constant per SNUADC mode in the pilot, and 42 ms over the whole release.
Clock corrections in every file	2026-10-11	current	A scan of all 6,388 files for the jumps where the recorder re-synchronises a device's stamps. Each device type has its own correction signature; only SNUADC and BIS correct clearly enough to measure their drift.

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