detecting 150 and 200 Hz in GUI

krupalmistrykrupalmistry Fullerton
edited February 2017 in Software
Hello,

I have using processing files of HexBug experiment from Chip. It was great help from chip by providing the files through GITHUB. I am doing similar kind of stuff. I have few doubts: 
1. If the sample rate is changed from 250 Hz to large frequency, which other files I need to take care?
2. My peak detection frequencies are 60 to 70 Hz and other will be 150 to 200 Hz. What files I need to take care other than EEG_Processing? 
3. Do I need to change the filters in the EEG_Processing file?

Can anyone guide me on this?

Many thanks.

Comments

  • wjcroftwjcroft Mount Shasta, CA
    1. Cyton sample rate is fixed at 250 Hz (8 ch) or 125 Hz (16 ch). It cannot be changed except by using the Wired USB link approach, which is difficult and not applicable in your situation.

    2. Google "nyquist limit". You need at least 2, preferably more samples per sample wave period. 250 Hz can at the most get you 125 hz waves, but better with 3, 4 etc samples. So 80 hz. Even then you'll hit aliasing effects. EEG above 50 hz or so is mostly EMG artifact, not EEG.

    3. Filter coefficients can be changed.

  • krupalmistrykrupalmistry Fullerton
    Thank you wjcroft. I am going to do my peak detection with sampling frequency as 250 Hz. My peak is coming around 60 to 70 Hz. So can I use the Hexbug processing files?
  • krupalmistrykrupalmistry Fullerton
    For peak detection around 60 Hz, how to change the filter coefficients? 

    Thank you wjcroft.
  • wjcroftwjcroft Mount Shasta, CA
    If you are in the U.S., you want to have a notch filter at 60 Hz, to cancel out mains noise. There are tutorials on the web on how to construct the filter coefficients. And also some here,

    http://openbci.com/forum/index.php?p=/search&Search=coefficients

  • krupalmistrykrupalmistry Fullerton
    Thank you wjcroft for guidance and I will post my result here. 
  • krupalmistrykrupalmistry Fullerton
    I got the same co efficient for the 60 Hz notch filter. I have used the sampling rate as 250 Hz and got the peak at the 60 Hz frequency. Thank you wjcroft.  
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