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Understanding emWave Pro Data Exports

Last Updated: February 2026

Overview

When exporting session data from emWave Pro (to a CSV, text file, or spreadsheet), researchers and users frequently notice two confusing details:

  1. The rawIBI data column seems to stop about halfway down the page compared to the Time Offset column.

  2. The total time of the summed IBI values (e.g., in Kubios or Excel) is slightly shorter than the total recorded session time displayed in the emWave application.

At first glance, this looks like the software stopped recording early or data was lost. However, no data has been lost. This article explains the data formatting, the resampling process, and how session time is calculated.

1. Why the rawIBI Column Appears to Stop Halfway Down

In your exported table, the rawIBI column and the Time Offset column occupy the same spreadsheet, but they are entirely independent of one another. A given row's Time Offset value does not correspond to the rawIBI value in that exact same row.

  • The HeartRate & Time Offset Columns: The HeartRate data is resampled at a strict linear rate of 2 Hz (2 samples per second) using linear interpolation. This is done to create the uniformly spaced Time Offset timeline.

  • The rawIBI Column: The rawIBI values represent your actual, physical heartbeats, which typically occur roughly once per second at a resting heart rate.

Because the HeartRate series is forcing two samples every second, it will produce approximately twice as many rows as your natural heartbeat (rawIBI) series. Therefore, the rawIBI entries will naturally run out and appear to end around the halfway point of the spreadsheet. This is a table layout artefact, not a loss of data.

2. How emWave Constructs the Graph from rawIBI Values

If the Time Offset column doesn't align with the raw IBI values, how does the emWave software draw an accurate, continuous graph for the full session?

The application does not use the uniform Time Offset column to position raw IBI values along the timeline. Instead, it reconstructs the elapsed time by cumulatively summing the raw IBI intervals.

Since each raw IBI value represents the exact number of milliseconds between consecutive heartbeats, adding them together sequentially produces an accurate, beat-by-beat timeline. This is why the visual graph in emWave appears complete and continuous across the entire session, gracefully ignoring any layout gaps seen in the raw spreadsheet.

3. The Discrepancy Between Total Session Time and Summed IBI Time

You may notice a discrepancy of anywhere from a few seconds to a minute between the total recorded session time shown in emWave (e.g., 31 minutes and 30 seconds) and the duration you get when you manually sum the exported raw IBI values (e.g., 30 minutes and 40 seconds).

This difference is expected and is a normal part of the software's data-cleaning design:

  • The Stabilization Period: When you first start a recording, the software intentionally drops a small number of IBIs at the very beginning of the session to allow the hardware signal and algorithms to settle and calibrate.

  • Artifact Trimming: A brief cleaning pass occurs at the end of the session, meaning a few terminal IBI values may be excluded from the final export to ensure data purity.

Therefore, the sum of your exported raw IBIs is the true duration of the clean, analyzable data you recorded, accounting for the slight shortfall compared to the raw clock time of the recording.