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Amplification with USBamp, real value in microV

Posted: 14 Jul 2010, 12:30
by EliGC
Good Afternoon,

I am using the USBamp with no amplification (gain per channnel=1), BCI2000 by default has as SourceChGain = 0.033. My question is, if I am getting a value of 1 (A/D units) when I analyze my signals in Matlab, then the real value of them will be: 1*0.033=0.033 microVolts?

Thank you so much.

Eliana

Posted: 15 Jul 2010, 08:44
by mellinger
Eliana,

the gUSBamp source module will always store data such that it is consistent with the SourceChGain value specified.
Thus, if you have a SourceChGain value of 1, 1 AD unit will correspond to 1 Microvolt.

Juergen

Posted: 15 Jul 2010, 15:46
by EliGC
Mr. Juergen

Thank you for your answer :) . I am sorry but I am still having the same dude. :? Because one thing is the SourceChGain that you can configure for g.USBamp, but the other thing is the SourceChGain that you can configure in BCI2000. My point is, the SourceChGain that is apply in BCI2000 affects the AD value of them?. As you told me if I defined 1 as SourceChGain I will have direct correpondence to 1 microVolts, but If BCI2000 has as default the value = 0.033 Will I have 0.033*1=0.033 microvolts?.
I insist with my question because the value of my signals are between 0 and 10 units AD. If I multiply them per 0.033, they will fall. :shock:

Thank you so much,

Posted: 16 Jul 2010, 04:47
by mellinger
Eliana,

with the gUSBamp source module, the SourceChGain value indeed affects the AD value. If you specify 2 as the SourceChGain value, AD values will only be half as large as if you specify 1.

Also, there is no such thing as a "BCI2000 default value" for SourceChGain -- every amplifier/digitizer combination has its own SourceChGain value.

Juergen