2D Spectrogram

The 2D Spectrogram window shows the frequency content of a device’s EEG channels. Each chart shows the current spectrum, averaged over a short interval. It does not show a history over time. Open it with Windows > Add > 2D Spectrogram. You can open more than one, each with its own settings. It is also part of the Default, Experience Player and EEG layouts.

In 1.7.3: The window has three settings and no display filters, its charts look different, and the Experience Player layout does not include it. See the callouts below and What changed since 1.7.3.

What the window reads

The window reads raw device channels, not classifier output. Filters in your classifier do not change what you see here. The settings in this window do not change the classifier, feedback or other windows.

The charts draw frequencies up to about 60 Hz, or up to half the sample rate if that is lower.

The window’s own display filters are on by default. They can hide real signal, so read the next section before you judge signal quality from this window.

Display filters hide real signal

The window has three display filters: High-Pass (Hz), Notch 50 Hz and Notch 60 Hz. They are there because nothing removes electrode drift or mains pickup from a raw channel before it reaches this window.

Each filter sets the frequency bins in its range to zero, with a hard edge:

Filter	Bins set to zero
High-Pass (Hz)	Below the set frequency
Notch 50 Hz	48 to 52 Hz
Notch 60 Hz	58 to 62 Hz

This has three effects:

• An empty range does not mean the device sent no signal there. Real signal in these ranges still reaches your classifier.
• Mains pickup is hidden, so a clean-looking chart does not show that the mains level is low.
• Auto Scale ignores zeroed bins, so a hidden peak does not change the scale.

The notches do not read NMStudio > Settings > Devices > Local Power Line Frequency. Set them here.

To turn the display filters off:

1. Click the gear button on the window’s toolbar.
2. Set High-Pass (Hz) to 0.
3. Clear Notch 50 Hz and Notch 60 Hz.
4. If drift or mains peaks flatten the other bands, clear Auto Scale and set Max Amplitude.

In 1.7.3: These filters do not exist. Drift and mains pickup are always shown, and they set the scale.

Settings

Click the gear button on the window’s toolbar to open the settings panel. There are nine settings. Defaults can vary by build, so check the values in the panel.

Setting	Default	Range	What it does
Multi View	On		On: one chart per channel. Off: all channels in one chart, each in its own colour.
Show 0Hz Bin	Off		Includes the 0 Hz bin. Studio subtracts each FFT window’s mean first, and any high-pass above 0 zeroes this bin.
Average Interval	1.0	0 to 10	Seconds of spectra to average. 0 uses only the latest spectrum.
Horizontal View	On		Two columns of horizontal bars. Available only when Multi View is on.
Auto Scale	On		The amplitude scale follows the peak. All charts share one scale.
Max Amplitude	25	1 to 200	Fixes the top of the amplitude scale. Used only when Auto Scale is off. Taller peaks are clipped.
High-Pass (Hz)	0.75	0 to 10	Zeroes bins below this frequency. 0 turns it off.
Notch 50 Hz	On		Zeroes 48 to 52 Hz.
Notch 60 Hz	On		Zeroes 58 to 62 Hz.

In 1.7.3: Only Multi View (on), Show 0Hz Bin (off) and Average Interval (1.0, range 0 to 10) exist. The scale always follows the peak, and Studio does not subtract the mean, so the 0 Hz bin carries any signal offset.

The predefined layouts set some of these values. Settings they do not set keep their defaults.

Layout	Multi View	Show 0Hz Bin	Average Interval	Horizontal View
Default	Off	On	1.0	Default
Experience Player	On	Off	1.0	On
EEG	On	On	10.0	Default

In 1.7.3: The Experience Player layout does not include the 2D Spectrogram window.

Reading the charts

Horizontal View draws each channel’s spectrum as horizontal bars, with frequency on the vertical axis and the lowest frequency at the bottom. Channels fill the left column and then the right column of each row. The two columns are mirrored, so the bars of a pair start from the centre. Bar colour shows the frequency band:

Band	Range	Colour
Delta	Below 4 Hz	Red
Theta	4 to 8 Hz	Orange
Alpha	8 to 13 Hz	Yellow
SMR	13 to 15 Hz	Turquoise
Beta	15 to 30 Hz	Blue
Gamma	30 Hz and above	Purple

With Horizontal View off, Multi View arranges vertical bars in a grid, in each channel’s colour.

In 1.7.3: Horizontal View does not exist. Multi View always uses the grid.

Odd channel counts

With Multi View and Horizontal View both on, the code draws charts in pairs. If an odd number of channels is selected, the last channel gets no chart. With one channel selected, including on a one-channel device, no chart is drawn. Both settings are on by default, and in the Experience Player and EEG layouts.

To see every selected channel, do one of these:

• Clear Horizontal View. All channels appear in the grid.
• Clear Multi View. All channels appear in one chart.
• Select an even number of channels.

In 1.7.3: Every selected channel is drawn.

Choosing channels

The toolbar has a device list, with Use Active Device as the first entry, and a checkbox for each EEG channel of that device. By default the first eight channels are checked. REF and GND are not.

If the active classifier has a Select Channels node with Quick Config on, that node sets these checkboxes on every update, so changes you make here do not stay. Change the selection in the node instead. See Nodes.

In 1.7.3: The checkboxes do not follow the classifier. You choose channels here.

FFT settings

The window takes its FFT settings from the Spectrum Analyzer Settings window: FFT Order, Shift and Window Function. The defaults are order 9 (a 512-point FFT), a shift of 8 samples and a Hann window. These settings apply to every 2D Spectrogram window. They don’t change FFT nodes in a classifier, because each FFT node has its own settings. See Windows, menus and shortcuts.

In 1.7.3: The default FFT order is 7 (a 128-point FFT), so each bar covers a wider frequency range. The default window is Rectangular.