Is the sample-rate adjustable on a BioSemi system ?
 

The new Active3 system system always transmits all installed channels on the maximum (fixed) sample rate of 16,384 Hz and a bandwidth of 5.4 kHz. Down-sampling to a lower sample-rate (to a minimum of 256 Hz) is performed in software with a 5th order CIC decimation filter to prevent aliasing. Although the output sample rate of the ActiveThree system is fixed at 16 kHz, the ADCs internally operate at a 8x over-sample rate. The 8 x over-sampling allows for optimal operation of the steep anti-aliasing filter integrated in the ADC.


In the ActiveTwo system, there are 4 user selectable sample rate options: 2, 4, 8 or 16 kHz per channel. It has a 10-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). 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. ActiView can always downsample the data in order to reduce the file size. The Analog bandwidth (-3dB) is always 1/5th of the sample rate.
 
PS: You can find out what model AD-box you have by running ActiView and then select the 'About' Tab-page.
 

AD-box models Active2 and Active2.5 with standard firmware:
AD-box switch
Sample-rate
Pin channels + EX channels + Sensor channels
0 (Hyperscanning) Daisy-chain mode (Hyperscanning):
 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+sensors @ 2 kHz, speedmode switch = box number. (0=Box1, 1=Box2, 2=Box3, 3=Box4). Daisy chain mode requires an extra fiber input to be installed on the front of the AD-box. (not standard included in the base system price)
1 (Hyperscanning)
2 (Hyperscanning)
3 (Hyperscanning)
4 2048 (2 kHz)
256+8+7
5 4096 (4 kHz)
128+8+7
6 8192 (8 kHz)
64+8+7
7 16384 (16 kHz)
32+8+7
8 (AIB-mode) 2048 (2 kHz)
256+8+7+32AIB
9 (ABR-mode) 16384 (16 kHz)
5

AD-box models Active2 and Active2.5 with special high-speed firmware "MK2HS High-Speed"
No AIB mode possible, no Daisy-chain possible, ABR is possible. Not compatible with AD-boxes or old receivers with standard firmware. PS: With the 'High'Speed' firmware, the USB receiver will also have another firmware which is not compatible with MK1 or MK2 firmware.
AD-box switch
ActiView displays mode
Sample-rate
Pin channels + EX channels + Sensor channels
0
10
4096 (4 kHz)
256+8+7
1
11
8192 (8 kHz)
128+8+7
2
12
8192 (8 kHz)
256+8+7
3
13
16384 (16 kHz)
128+8+7
4
4
2048 (2 kHz)
256+8+7
5
5
4096 (4 kHz)
128+8+7
6
6
8192 (8 kHz)
64+8+7
7
7
16384 (16 kHz)
32+8+7
8
-
-
-
9 (ABR-mode)
9
16384 (16 kHz)
5

AD-box model Active2 MK1 ActiView will display in the 'About' Tab-page if your Active2 is MK1 (produced until 2002) or MK2 (produced after 2002)
AD-box switch
Sample-rate
Pin channels + EX channels + Sensor channels
0
2048 (2 kHz)
256+0+0
1
4096 (4 kHz)
128+0+0
2
8192 (8 kHz)
64+0+0
3
16384 (16 kHz)
32+0+0
4
2048 (2 kHz)
232+8+7
5
4096 (4 kHz)
104+8+7
6
8192 (8 kHz)
40+8+7
7
16384 (16 kHz)
8+8+7
8 (AIB-mode)
2048 (2 kHz)
AIB-mode
9
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 than 2 kHz are acceptable. Examples:
 
I Want to make a recording of 8 channels at 16 kHz sample rate:
- Select speedmode 7. The AD-box will sample 32 channels at 16 kHz.
- When saving in ActiView, select to save only the 8 'Monopolar displayed channels' so ActiView will save 8 channels at 16 kHz.
 
I Want to make a recording of 64 channels at 256 Hz sample rate:
- Select speedmode 4. The AD-box will sample 256 channels at 2 kHz
- In ActiView (at the right bar) select a decimation of 1/8. so the samplerate will be 2048/8 = 256 Hz.
- When saving in ActiView, select to save only 'A1-B32 (64)' so ActiView will save 64 channels at 2 kHz