Ganglion Raw Data file format

yoosung

Hi,
I was looking into the Raw data file provided by Ganglion and would like to ask a few clarifying questions.
Some insight would be much appreciated

1. Why do every 2 samples have the same index and timestamp?

2. What is the difference between the "timestamp" column and the "timestamp(formatted)" column? Are the formatted values calculated from the "timestamp" values?

3. There are instances where 4 of the timestamp(formatted) values are the same as shown below. Why would this be happening?

4. If I change the filter values such as the start/stop frequency on the Ganglion GUI, does this effect the values being printed onto the raw data files(such as OpenBCI-RAW-2023-03-14_17-50-55.txt)? For example, if the stop frequency of the bandpass filter is changed from 50 to 20 Hz and the respective channel catches a 50Hz signal, is this signal still printed onto the raw data file?

Although I've gotten a ton of help from the forum, it still seems there are numerous aspects of the board I do not understand yet.

Best,
Yoosung

wjcroft

Yoosung, hi.

The Ganglion radio packets arrive, each containing TWO samples. This is why the index and timestamp are identical.

Timestamps are INACCURATE, because they are not generated at the Ganglion, but instead as your laptop receives that packets. Thus they are subject to various buffering delays, CPU loading, usb queueing, other apps, etc.

William

wjcroft

https://docs.openbci.com/Ganglion/GanglionDataFormat/

wjcroft

@yoosung said:
...
4. If I change the filter values such as the start/stop frequency on the Ganglion GUI, does this effect the values being printed onto the raw data files(such as OpenBCI-RAW-2023-03-14_17-50-55.txt)? For example, if the stop frequency of the bandpass filter is changed from 50 to 20 Hz and the respective channel catches a 50Hz signal, is this signal still printed onto the raw data file?

The raw recording files are just that, raw, with no filtering.