All values must be divided by 4 for Blackrock data?

1

Hi,
When I read the code of the openNSx.m code provide by blackrock, I found they say (line 962 of openNSx.m)：

disp('The data is in unit of 1/4 uV. This means that 100 in the NSx file equals to 25 uV. All values must be divided by 4.');

So, if i imported the data with BS, shoud i divide the data with 4, before any analysis.

2

Hi @zhangjb39,

In Brainstorm the Blackrock data is read using openNSx.m with the parameter 'uV'

With this, the data is already returned in microVolts, no need to perform the division over 4.

From openNSx help:

%   'uV':         Will read the recording waveforms in unit of uV instead of
%                 raw values. Note that this conversion may lead to loss of
%                 information (e.g. 15/4 = 4) since the data type will
%                 stay in int16. It's recommended to read raw spike
%                 waveforms and then perform the conversion at a later
%                 time.
%                 DEFAULT: will read recording information in raw.

Best,
Raymundo

P.S. @Francois, what do you think of moving the conversion to in_fread_blackrock instead of having it in openNSx?

3

This could make sense in order to convert to double and then to divide by 4 to avoid losing 0.25uV of precision.
But this might not be easy to maintain in the future. If they change the way they handle the units conversions in the library, our code would start causing problems.
Let's keep it simple, and not change anything.

2 Likes
4

Thank you.