BSL PRO Software Guide - Biopac

217ResampleThis function resamples the entire data file to another rate, which can be used to “compress” data files by savingthe data at a lower sampling rate.The minimum rate is based on the total number of samples.The highest sampling rate that a channel can be resampled to is the file acquisition rate (as established under MPUNIT>Setup Acquisition) TIP A good rule of thumb is to select a sampling rate at least four times the highestfrequency of interest for the signal. For example, the alpha component of an EEG signal has a frequency signature of 8-13Hz, so(assuming you have isolated the alpha component using a band pass filter) you wouldprobably want to sample the data (in this case, isolated alpha waves) at a rate of at least52Hz. The acquisition sample rates are limited and you should choose the next highestoption, or in this case 100 Hz.Resampling data maintains the time scale but reduces the number of samples per second. Wheneverdata is resampled to a lower rate, information is lost.For instance, a 4-channel data file sampled at 250 samples per second for 15 minutes takes up about1.8 MB of disk space. Resampling to 100 samples per second reduces the file size to about 720 KB ofdisk space, a considerable reduction.If data is resampled to a lower rate and then resampled again at a higher rate, the waveform will maintain theresolution of the lower sampling rate, only with more data points.Resampling and…Interval You can use Resample to increase the number of sample points per interval (usually samples persecond). When this is done, the BSL PRO software will interpolate between sample points to adjust to the newrate. This will add data points — but not necessarily more information.Exporting If you plan to export resampled data, you should use this method of resampling:Select Find peak from the Transform menu.Select User defined interval and enter a time period for the new sample rate.Set First cursor to Peak.Check the Paste measurements to journal option.Set the measurements for the channel you want to resample.For example, if you set the Value and Time measurements, the software will take those measurements and pastethe Value and Time results from the resampled channel into the Journal.Select OK and place the cursor at the beginning of the data file.Select Find all peaks from the Transform menu.Bias Resampling the data may cause a bias, unless the data was filtered to remove all frequency componentsthat are more than 0.5 the resampling rate.