Recording During Activity

The PiEEG XR mask is made to be worn under a headset while you move. Movement is also the hardest condition for EEG: the brain signal is only tens of microvolts, while movement artifacts can be hundreds of times larger. This page explains why the signal gets noisy, how to set up the mask, and how to confirm the signal is real before you record.

This guide is for the XR mask (dry electrodes, under a headset, while moving). For a lab setup with clip electrodes and a wired board, see Noise elimination.

Why the signal gets noisy

EEG is roughly 10–100 µV. Almost every movement noise source is bigger, so the goal is to control them, not to filter them out afterwards.

Source	What happens	What it looks like
Electrode movement	Each electrode forms a small voltage with the skin. When it slides or lifts, that voltage jumps. Dry electrodes are more prone to this than gel.	Swings from tens of µV to millivolts
Muscle activity (EMG)	Jaw, forehead, neck and scalp muscles fire as you move.	Broadband fuzz, about 20 Hz and up
Cable movement	A swinging cable generates charge and picks up mains and Wi-Fi interference.	Spikes and hum
Sweat	Skin resistance changes as you sweat; sweat can bridge two electrodes.	Slow drift below 1 Hz, sudden steps
Footsteps and pulse	Each step and heartbeat moves the head slightly.	Rhythmic low-frequency wave

⚠️

Most "too noisy during activity" cases are motion + cable + sweat, not a hardware fault. Check the board first with Test 1 in Noise elimination, then follow the steps below.

How to keep the signal clean

Do this every session.

Clean the skin

Wipe the forehead and temples with an alcohol pad to remove oil, sweat and make-up, then let the skin dry. Clean skin lowers resistance and helps dry electrodes stay steady.

Fit the mask firmly and evenly

Use the PiEEG XR mask, or your headset's original mask with the PiEEG XR silicone insert, and adjust it until it sits firmly with no gaps or bending. Every electrode needs steady, even pressure. A mask that shifts under the headset is the fastest way to lose the signal.

Add a little gel (optional)

The electrodes work dry, but a small amount of conductive gel or saline steadies the contact and is the most effective way to cut motion artifacts during activity.

Stay wireless

PiEEG XR streams over Bluetooth LE, so there is no data cable to swing. Keep the power cable short and fixed to the strap.

Check reference and bias

Make sure the reference and bias electrodes (centre of the forehead) are firmly in contact. A loose reference makes the whole trace drift or rail: it looks like huge noise but is really one bad contact.

Before you record: confirm the signal is real

Don't start recording until you've confirmed live data. These checks take under a minute.

Confirm data is streaming

The device is connected and the app shows a live, scrolling signal.
Every channel is moving. A perfectly flat line means that electrode has no skin contact.
The sample counter advances with no big gaps. Many dropped packets mean a weak Bluetooth link: move the receiver closer.
Let the filter settle. For the first few seconds the trace swings widely. Wait until it calms down.

Read the baseline

Sitting still with the mask on, each channel should be a fairly flat line that wanders within a few µV to a few tens of µV.

What you see	What it means	Fix
Gentle line, small wander, reacts to blinks	Good, real signal	Go on to the tests below
Perfectly flat line	No contact on that electrode	Reseat the mask, add a little gel
Stuck at the top or bottom (railed)	Saturated, usually a bad reference	Check the reference and bias contact
Thick, constant fuzzy band	50/60 Hz mains hum	Battery power only, move away from chargers, use a notch filter
Large, slow rolling wander	Drift (sweat, movement, filter settling)	Wait, dry the skin, steady the mask
All channels identical	Reference or common-mode problem	Fix the reference contact

Run the functional tests

These prove the signal comes from you, not from the room.

Test	What to do	What you should see	Confirms
Blink	Blink hard 3–5 times	Large, sharp spikes, strongest on the forehead channels	Good contact and real biosignal
Eye movement	Look left, then right	Slower swings, opposite directions on the left and right channels	Contact and correct channel order
Jaw clench	Clench your teeth briefly	A burst of high-frequency fuzz that stops when you relax	Responsive electrodes; shows what muscle noise looks like
Alpha (academic version only)	Sit still, close your eyes for 10 s, then open	Smooth 8–12 Hz waves on the back-of-head channels while the eyes are closed	Real brain activity

⚠️

Always do the blink test. If blinking shows nothing on the forehead channels, those electrodes aren't touching. Stop and fix the fit before going further.

Record a still baseline

Once blinks show clearly, record 20–30 seconds standing still. This gives you a clean stretch to compare the moving data against later.

During the session

Warm up before recording the real data, so sweat and contact have settled.
Keep the jaw and forehead relaxed where the activity allows. Clenching adds strong EMG.
Note the times of big movements, so you can match them to spikes later.
If the trace suddenly rails, reseat the mask. It's usually a shifted electrode or a loose reference.

Cleaning the signal in software

Band-pass filter of about 1–40 Hz removes slow drift and most muscle noise.
Notch filter at 50 or 60 Hz (your region's mains frequency) removes hum.
Reject the time windows around big movements instead of trying to rescue them.
ICA can separate and remove muscle and cable components when you need the higher bands.

Filtering can't recover a channel that was fully saturated by movement. Getting the fit and contact right is always worth more than processing afterwards.

Quick checklist

Software Signals & Projects