BioSemi.nl

Hello All

I would like to know if low pass filter in ActiView software during signal acquisition is digital filter? or analog hardware filter? If it is digital filter so what is the order of it?

Another question, is BioSemi acquires signal at maximum sampling frequency and than down-samples it before or after filtering?


Thanks

Boris

The filters controlled in the left sidebar only apply to the on-line displayed signals, and not to the data streamed to BDF file. The filters are implemented in software (LabVIEW). The high-pass filters are 1st order, the low-pass filters are 2nd order Bessel.

The hardware sample-rate is determined by the speedmode setting (rotary switch on the AD-box front-panel), see http://www.biosemi.com/faq/adjust_samplerate.htm. The data can be downsampled in ActiView, with the DECIMATE control in the right sidebar. The resultant sample rate and anaolg bandwidth of the data streamed to file is indicated in the right sidebar. Decimation is performed with a 5th order sinc filter to prevent aliasing. This is actually the same filter characteristic as applied in the analog-to-digital converters, see http://www.biosemi.com/faq/adjust_filter.htm and viewtopic.php?t=351. No high-pass filtering is applied to the data streamed to file (fully DC coupled).

Best regards, Coen

Hi Coen!

I have a hard time understanding your answer.

"The filters controlled in the left sidebar only apply to the on-line displayed signals, and not to the data streamed to BDF file."
Does it mean that the filters we apply on the left-hand panel only have a visual effect and do not affect data?

"The filters are implemented in software (LabVIEW)."
Which filters are these? The ones we put on the left panel? If not, where do we see and edit those filters?

Quote: Does it mean that the filters we apply on the left-hand panel only have a visual effect and do not affect data?

Answer: Yes

Quote: Which filters are these? The ones we put on the left panel?

Answer: Yes