Data Viewing And Acquisition; Sample Rate And Amplifier Bandwidth Selection - NeuroNexus SmartBox Instruction Manual

SOFTWARE

Data Viewing and Acquisition

Amplifiers connected to other ports may be viewed by selecting the appropriate radio button in the "Ports" box. The eight ADCs and 16 digital inputs on
the SmartBox may also be observed, although these channels are disabled by default and must be enabled for viewing. The "Run" and "Stop" buttons
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at the top of the window start and stop data viewing. After a base filename and directory are selected, the "Record" button may be used instead of
"Run" to stream data to disk. Data files may grow quite large (watch the status bar at the bottom of the window for file size estimates in MB/minutes). If
the "Traditional Intan File Format" is selected, new data files are created at a time interval specified by the user (one minute intervals are recommend-
ed) with date and time stamps added to the base filename in year-month-day and hour-minute-second format (e.g., "mydatafile_130301_093500.rhd").

Sample Rate and Amplifier Bandwidth Selection

The "Bandwidth" tab in the lower-left corner of the main window contains buttons for selecting the amplifier sampling rate and bandwidth (see FIG. 21
on the following page). The amplifier sampling rate may be set to one of the following values: 1.0, 1.25, 1.5, 2.0, 2.5, 3.0, 3.33, 4.0, 5.0, 6.25, 8.0, 10, 12.5,
20, 25, or 30 kS/s. Higher sampling rates will produce larger saved data files. Saved data files may be imported into MATLAB using an m-file available
at neuronexus.com. Also provided is an m-file that upsamples amplifier data by a factor of two (using cubic spline fitting), so higher effective sampling
rates may be approximated. See the "Importing Recorded Data into MATLAB" section on p.22 for more information on these m-files.
The "Change Bandwidth" button brings up an amplifier bandwidth selection dialog (see Figure 22) that allows users to select upper and lower cutoff
frequencies for the amplifier chips connected to the SmartBox . The software automatically calculates SmartProbe register values that produce
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actual bandwidth settings as close as possible to the desired bandwidth settings selected by the user. See the RHD2000 series datasheet (available at
neuronexus.com) for more details on the mechanisms of bandwidth selection and the operation of the DSP offset removal filter.
The general recommendation for best linearity is to set the DSP cutoff frequency to the desired low-frequency cutoff and to set the amplifier lower
bandwidth 2x to 10x lower than this frequency. Note that the DSP cutoff frequency has a limited frequency resolution (stepping in powers of two), so if
a precise value of low-frequency cutoff is required, the amplifier lower bandwidth could be used to define this and the DSP cutoff frequency set 2x to
10x below this point. If both the DSP cutoff frequency and the amplifier lower bandwidth are set to the same (or similar) frequencies, the actual 3-dB
cutoff frequency will be higher than either frequency due to the combined effect of the two filters.
The software adds an optional software high-pass filter that is only applied to displayed data; this filter is not applied to data saved to disk. This filter
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