The sensor locations depend on your head size. Interaxon updated their documents to state that the front two sensors are closer to AF7 and AF8. So the four locations are AF7, AF8, TP9 and TP10.
The “sampling rate” and the “maximum recorded frequency” are two separate things.
Sampling rate, is the rate at which data is sent out from the system. For the Emotive headset this is 128Hz.
For the Muse, the sampling rate is set via the preset value when you connect to the device, the documentation for the presets is in the developer docs here.
- The MU-01 (2014 Muse with two USB ports) has RAW EEG rates of 220Hz and 500Hz available.
- The MU-02 (2016 Bluetooth LE Muse with one USB port) has a RAW EEG rate of 256Hz.
Regarding the maximum frequency that can be recorded, this is talking about the frequency data which is calculated from the RAW EEG data. The name of this calculation is a Fast Fourier Transform, so you will often see this referred to as just “FFT data”.
The Emotive SDK outputs pre-calculated FFT data, which has been filtered for background noise and electrical noise. They output these FFTs up to a maximum of 43Hz.
The Muse SDK does not output pre-calculated FFT data, instead it outputs individual brainwaves (Alpha, Delta etc), and more importantly RAW EEG. From the RAW EEG data, you can do you own FFT calculations without any of the limits of the Emotive SDK, but on the downside, you have to do your own noise filtering.
FFTs are very easy to calculate and if you want to see the real time FFT output from the Muse, this is available in my Muse Monitor app and looks like this:
In this screenshot the colored bands represent the areas of the five brainwaves.
As you can see here, Gamma (represented by the greek letter γ) is from 30Hz to 44Hz, so this is likely why Emotive cut off their FFT data at 43Hz.