sampling rate and bioSemi nyquist

brroach · Post by **brroach** » Wed Dec 27, 2006 4:16 pm

BioSemi Users,

What is the maximum resolvable frequency given a sampling rate of X on the BioSemi system with ActiveView2 software? Is it X/2Hz? I believe it is X/4Hz on neuroscan systems, and I was curious about how bioSemi compares.

If we are sampling at 1024Hz, can we resolve up to 512Hz?

thanks in advance!

Brian

Post by **Coen** » Wed Dec 27, 2006 8:39 pm

In the ActiveTwo, the-3dB point is at approx 1/5th of the sample rate, also see http://www.biosemi.com/faq/adjust_filter.htm. For a selected sample-rate, the ActiView software displays the cutoff frequency in the right sidebar. Competing systems with a 24-bit ADC show exactly the same low-pass response.

Best regards, Coen (BioSemi)

brroach · Post by **brroach** » Tue Jan 23, 2007 12:10 am

Thanks for your response. What about the lowest resolvable frequency - does the system place any restriction on that (something like a high pass filter) or is it only based on the amount of data recorded?

thanks again,
Brian

Post by **Coen** » Tue Jan 23, 2007 1:45 pm

The ActiveTwo system uses DC coupled amplifiers, no high-pass filters are applied. The high dynamic range of the used 24-bit ADCs allowed elimination of all coupling capacitors from the design. So, the above statement is correct: the lowest resolvable frequency is only limited by the duration of the experiment.

Best regards, Coen (BioSemi)