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| Is the sample-rate adjustable on a BioSemi system ? |
| Yes, the new ActiveTwo system has 4, user selectable sample rate options: 2, 4, 8 or 16 kHz per channel. However, the total throughput remains constant at 1.5 MByte per second. So, on sample rates higher than 2 kHz, less than the full 256 channels are available. Below follow details, and examples |
| Analog bandwidth (-3dB) is always 1/5th of the sample rate. The system has a 4-way rotary switch on the front panel to select 2 kHz (400 Hz bandwidth), 4 kHz (800 Hz), 8 kHz (1600 Hz) or 16 kHz sample rate (3200 Hz bandwidth). On the 2 kHz setting you can use all 256 channels, on the 4 kHz setting you can only use channels 1-128, on the 8 kHz setting you can only use channels 1-64, on the 16 kHz setting you can only use channels 1-32. The sample-rate/NR-of-channels setting is selected in the front-end, the front-end determines which channels at which sample rate are sent to the PC. |
| Speed
mode |
Sample-rate |
AD-box
Mk1
|
AD-box
Mk2
|
||
| Pin
+ TP channels |
Sensors |
Pin
+ TP channels |
Sensors |
||
| 0 |
2048
(2 kHz) |
256+0 |
No |
Multi
box use: In speedmode 0 to 3, the AD-boxes work as up to 4 optical fiber 'daisy chained' boxes, each with a maximum of 128+8 channels @ 2 kHz, speedmode switch = box number. (0=Box1, 1=Box2, 2=Box3, 3=Box4). Daisy chain possibilities are not standard included in the base system price. |
|
| 1 |
4096
(4 kHz) |
128+0 |
No |
||
| 2 |
8192
(8 kHz) |
64+0 |
No |
||
| 3 |
16384
(16 kHz) |
32+0 |
No |
||
| 4 |
2048
(2 kHz) |
232+8 |
Yes |
256+8 |
Yes |
| 5 |
4096
(4 kHz) |
104+8 |
Yes |
128+8 |
Yes |
| 6 |
8192
(8 kHz) |
40+8 |
Yes |
64+8 |
Yes |
| 7 |
16384
(16 kHz) |
8+8 |
Yes |
32+8 |
Yes |
| 8 |
AIB-mode |
AIB-mode |
Yes |
AIB-mode |
Yes |
| 9 |
Reserved |
Reserved |
Reserved |
Reserved |
Reserved |
| Note: When an AIB is connected, the AD-Box should always be on SpeedMode 4 and the AIB always on SpeedMode 8. |
| The number of modules (hardware channels) which are installed in the system determine which EEG channels are able to display signals (upgrading to more channels is always possible at a later stage by simply inserting additional 8-channel modules). |
| So, if a customer buys the system with for example 96 channels, he will have : |
| - 96 operational channels on 2 kHz |
| - 96 operational channels on 4 kHz |
| - 64 operational channels on 8 kHz (channels 65-96 displayed as flat liners) |
| - 32 operational channels on 16 kHz (channels 33-96 displayed as flat liners) |
| The BioSemi acquisition software (ActiView) can display and save a subgroup of the available channels at a given sample rate. |
| Also, the incoming data can be downsampled in software to reduce the file size in situations where sample rates less then 2 kHz are acceptable. Examples: |
| I Want to make a recording of 8 channels at 16 kHz sample rate: |
| - The ActiveTwo will sample 32 channels at 16 kHz. |
| - ActiView will display and save 8 channels at 16 kHz. |
| I Want to make a recording of 80 channels at 256 Hz sample rate: |
| - The ActiveTwo will sample 256 channels at 2 kHz. |
| - ActiView will display and save 80 channels at 256 Hz. |