User Reference:gUnicornADC

Parameters

SampleBlockSize

Samples per channel per digitized block. Together with the sampling rate, this parameter determines how often per second data are collected, processed, and feedback is updated. For example, at 600 Hz sampling and a SampleBlockSize of 20, the system (e.g., source signal display, signal processing, and stimulus presentation) would be updated 30 times per second.

SourceChList

The list of channels that should be acquired from each device. The total number of channels listed should correspond to SourceCh. For more than one device, SourceChDevices determines how the SourceChList values are mapped to each device. For example if SourceChDevices = '8 8' and SourceChList = '1 2 3 4 13 14 15 16 5 6 7 8 9 10 11 12', then channels 1-4 and 13-16 will be acquired on the first device, and channels 5-12 will be acquired on the second device. These channels will be saved in the data file as 16 contiguous channels. The order of channels does not matter; i.e., '1 2 3 4' is the same as '2 3 1 4'. The channels are always in ascending order on a single device. Channels may not be listed twice on a single device; e.g., entering '1 2 3 4 5 6 7 1' if SourceChDevices = '8' will result in an error. If this parameter is left blank (the default), then all channels are acquired on all devices.

Additional Information

Using 32bit Executables on 64bit Installations

BCI2000 supports compilation of the gUSBamp source module for 64bit targets. The resulting executable will run on 64bit systems, and work with the 64bit version of the gUSBamp drivers. However, the binary distribution of BCI2000 contains 32bit executables. These run fine under 64bit systems, but you will need to perform these additional driver installation steps to install 32bit gUSBamp API DLLs on 64bit systems:

• Execute gtec's 32bit driver installer on your 64bit system.
• After successful installation, execute gtec's 64bit driver installer on your 64bit system.
• You will now have both the 32bit API DLL and the 64bit API DLL installed, such that both 32bit and 64bit executables will be able to connect to a gUSBamp attached to the system's USB ports.

Data Storage

Unlike other systems, the USBamp is a DC amplifier system that digitizes at 24 bit. Bandpass and notch filtering is performed on the digitized samples, resulting in floating point signal samples in units of $\mu V$. BCI2000 currently supports signed 16 bit integers and floating point numbers for its data storage. If SignalType is set to int16, the floating point values have to be converted back into integers before they can be stored and transmitted to Signal Processing. This is done by the following transformation:

${\mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}}_{\mathrm{s}\mathrm{t}\mathrm{o}\mathrm{r}\mathrm{e}\mathrm{d}}\mathrm{(}\mathrm{A}/\mathrm{D}\mathrm{u}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{s}\mathrm{)}=\frac{{\mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}}_{\mathrm{a}\mathrm{c}\mathrm{q}\mathrm{u}\mathrm{i}\mathrm{r}\mathrm{e}\mathrm{d}}(\mu V)}{\mathrm{S}\mathrm{o}\mathrm{u}\mathrm{r}\mathrm{c}\mathrm{e}\mathrm{C}\mathrm{h}\mathrm{G}\mathrm{a}\mathrm{i}\mathrm{n}}$.

(SourceChOffset is assumed (and required) to be zero for all channels.) BCI2000 Signal Processing or any offline analysis routine can derive, as with any other BCI2000 source module, sample values in $\mu V$ by subtracting, from each stored sample, SourceChOffset (i.e., zero), and multiplying it with SourceChGain for each channel. If SignalType is set to float32, data samples are stored in units of $\mu V$. In this case, SourceChGain should be a list of 1's (because the conversion factor between data samples into $\mu V$ is 1.0 for each channel).

Still, when values other than 0 and 1 are specified, a consistent data file will be produced, i.e. values will be transformed before they are written to the file, such that applying SourceChOffset and SourceChGain will reproduce the original values in $\mu V$.

See also

User Reference:DataIOFilter, Programming Reference:GenericADC Class