Live signal viewer#

The live signal viewer is where you watch EEG in real time. You reach it with Stream, Rec or View on the device card, from the contact check (see Contact check), or by tapping the Streaming bar. The screen stays awake while the viewer is open.

←  BA MAXI 000 · 32 ch            ● 0:32   [rotate] [camera] [ Stop ]
● 45% · 250 Hz
┌────────────┬──────────────────────────────────────────────┐
│ ▮ ● P8     │  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~│~~~~ │
│ ▮ ● O2     │  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~│~~~~ │
│    …       │                                              │
└────────────┴──────────────────────────────────────────────┘
                          window 10 s
[ PSD ] [ Accel ]
[ ● Rec ] [ Marker ▾ ] [ 1–40 Hz ] [ Win 10s ] [ Quality ] [ More ]

Top bar#

Control

What it does

← Back

Leaves the viewer. The stream keeps running (and so does any recording)

Device tabs

Only with more than one headset streaming: tap a tab or swipe the plot sideways to switch device. Each tab shows the device and its worst quality as a coloured dot

● m:ss

Recording indicator and elapsed recording time

Rotate icon

Flips and locks the orientation. Hidden on large screens (about 600 dp and wider), where Android manages orientation itself

Camera icon

Saves a snapshot PNG of the current view. See Recording

Stop

Stops the stream. Hidden while recording — stop the recording first

Status line#

[state · ] battery% · sample rate [ · ⚠ N lost] — the leading dot and the ⚠ N lost counter turn amber if samples were dropped on the Bluetooth link. The state word is omitted while everything is normal.

Channel rail (left edge)#

Starts collapsed in portrait (colour swatch plus quality dot per channel) — tap it to expand, and use the chevron to collapse it again. Expanded, each row shows:

Element

Meaning

Colour swatch

The trace colour for that channel

Name

The electrode label. Dimmed when the channel is hidden

PTP nnn µV

Peak-to-peak amplitude over the visible window, refreshed about once a second

Quality dot

Green = good, amber = check, red = poor, purple = railed. No dot until the channel has been scored

Eye icon

Hide or show that channel

Long-press a row

Solo: hides every other channel. Long-press again to restore

Note

Hidden channels and solo last for the session only; they are not remembered after a restart.

The plot#

  • One trace per visible channel, stacked, top channel first, with a faint separator per channel.

  • Electrodes with no contact are drawn dimmed and flattened to their baseline.

  • Markers appear as amber dashed lines with a label.

  • Stable mode draws a sweep line at the live edge, like a classic oscilloscope; the trace is overwritten in place. Flow mode scrolls right to left. Change it in More → Dynamics.

  • Pinch the plot to change the window length (1–10 s).

  • The caption under the plot shows the window length (Stable) or the time axis (Flow).

Control dock#

Control

What it does

● Rec

Starts recording; turns red and shows the elapsed time. Tap again to stop

Marker ▾

Tap the label to drop a marker with the last-used label; tap the caret (or long-press) to pick another preset or edit the list. See Recording

Filter chip (1–40 Hz / Filter off)

Opens the filter popup (below)

Win Ns

Window length presets: 1 s, 2 s, 5 s, 10 s

Quality

Opens Signal quality. The stream keeps running

More

Opens the settings sheet (below)

Filter popup#

Control

Options

Default

Filter switch

Band-pass on/off

On

Low cutoff (Hz)

0.1, 0.5, 1, 2, 4, or a custom value

1

High cutoff (Hz)

15, 20, 30, 40, 50, 100, or a custom value

40

Notch switch

Mains-hum filter on/off

On

Notch frequency

50 Hz or 60 Hz

50, or auto-detected from your signal the first time (your own choice is never overwritten)

Note

Cutoffs are automatically kept inside the range the sample rate allows, so a value that is too high for the headset is reduced for you.

Important

Filters only change what you see. The band-pass and the notch apply to the display: the trace, the spectrum panel and the peak-to-peak (PTP) numbers. Recorded files and the LSL stream always contain the raw, unfiltered signal in microvolts. Filter freely while monitoring; your data is not altered. If you need filtered data downstream, filter it in your analysis tool.

Signal-quality scores are not affected by your filter settings. Quality is always computed from the raw signal over a fixed four-second window, so a channel cannot be made to look clean by narrowing the band. The one thing that does change quality is electrode contact: a channel the headset reports as disconnected is scored as unusable rather than being judged on its floating noise (this is also why such a channel is drawn flat and its PTP reads 0 µV).

Note

The notch removes the mains fundamental only (50 or 60 Hz), not its harmonics, so a 100/120 Hz harmonic can still be visible when the band-pass high cutoff sits above it.

The filter chip describes the band-pass only. With the band-pass switched off and the notch left on, the chip reads Filter off while the mains notch is still applied to the display.

The time axis shows the configured window length immediately, so during the first seconds of a stream — before the window has filled — the visible data spans less time than the axis suggests.

Settings sheet (More)#

Display

Setting

Range

Default

Dynamics

Stable / Flow

Stable

Normalization

Individual (each channel scaled to itself) / Common (all channels share one scale, so amplitudes are comparable)

Individual

Window

1–10 s

10 s

Sensitivity

0–2. Above 0, extreme samples are clipped out of the scaling so one noisy spike stops flattening everything else

0

Scale

0.1–3 amplitude multiplier

1

Trace width

0.5–3

1.2

Monochrome

All traces grey instead of colour-coded

Off

Output

Setting

Notes

Session label (next recording)

Up to 48 characters. Added to the next recording’s filename and stored in its header. Cleared when the app restarts

LSL outlet

Live streaming to a computer, off by default. Turn it on here (More → Output → LSL outlet); the choice is then remembered. Turning it on publishes the raw EEG to every LSL client on the joined network. See Streaming to a computer (LSL)

Recording format

BDF (default) or CSV. Cannot be changed while recording

Reset to default restores the display and filter settings. Done closes the sheet.

PSD and Accel panels#

Above the dock, two chips open one panel at a time (tap again to close):

  • PSD — power spectrum, one line per channel, drawn from the filtered display data. Header shows the frequency range and the decibel range in use. While a band-pass is active the x-axis covers the pass band, otherwise it covers the full usable range so you can see the mains dip. Reads Computing… until the first spectrum is ready.

  • Accel — accelerometer X, Y and Z (blue, amber, green). Only offered on headsets that have an accelerometer (MINI, MIDI, MAXI, EXG8), and shows Waiting for accelerometer… until data arrives. Values are in m/s² (gravity reads as about 9.8 on the axis pointing down); each axis is auto-scaled around its own mean for display, so a still headset draws flat lines.

Landscape (immersive mode)#

Rotating gives a full-screen dark plot with no chrome. Overlay buttons: Back and the snapshot camera, a Controls button that reveals the dock on demand, and the recording indicator at the top centre.

What keeps running when you leave#

Leaving the viewer (Back, or another screen) does not stop anything. Streaming, recording and LSL continue, and an ongoing notification appears:

BrainAccess Mobile
Streaming 1 device · REC          [ Marker ]   [ Stop ]

That notification is what keeps the session alive with the screen off. Marker drops a marker on every running stream; Stop ends all streams (finishing any recordings cleanly). Tapping the notification body reopens the app.

Quick recipes#

  • Mains hum (50/60 Hz): open the filter chip and turn on Notch, then pick 50 Hz or 60 Hz for your region — it also auto-detects the first time and never overwrites your own choice.

  • Drifting baseline: open the filter chip, turn Filter on and raise the Low cutoff to 1 Hz (or higher).

  • Traces too small: in More, raise Scale (0.1–3) or Sensitivity (0–2) so one spike stops flattening the rest, or switch Normalization to Common so amplitudes are comparable.

  • A flat channel: a channel drawn dimmed and flattened has lost electrode contact and its PTP reads 0 µV — re-seat the electrode (see Contact check), or hide it with the eye toggle. Check Signal quality for per-electrode guidance.

  • Where is my data going? Recorded files and the LSL stream always hold the raw, unfiltered signal — filters and display settings never touch them. Set the Recording format (BDF/CSV) and Session label in More → Output, and find the file later under Recordings (Recordings and review). The LSL outlet is off by default; turn it on in More → Output → LSL outlet (Streaming to a computer (LSL)).