[Eeglablist] EEG amplifier and alternative input

[Frank H Duffy]

There are two major issues, both related to the differences in EEG and 
voice spectral content:

1. EEG amplifiers typically record from 0.5 -100 Hz but may be able to 
open to 500Hz for EP data collection. However, voice typically requires, 
for telephone-like reproduction, a 500 Hz to 3000 Hz band pass. Thus the 
EEG amplifiers would likely reject and/or severly distort audio inputs.
2. As most EEG machines are digital these days, they time sample 
(digitize) EEG signals. As a minimum they must use a rate that is 
slightly more than twice the highest desired input signal, e.g., 200 H 
samplige rate for 100 Hz EEG.  For voice one would require a 
digitization rate of at least 2x 3000Hz; typically one wants a minimum 
of 10000 Hz for voice.  So the EEG devices typical sampling rates of 
200-1024 Hz would not reasonably sample voice signals.

So, no, voice over EEG amplifiers won't work. It would take a complex, 
parallel EEG and separate voice amplifier and A-D converter setups to 
match voice to EEG. This can be done. Indeed some EEG machines match 
both voice and video to EEG. However, there is a lot of engineering to 
make the EEG and voice/video follow the same clock time.

Best of luck.

Frank Duffy, MD  fhd at sover.net
For the above discussion also BSEE and ham (k1moq)
On 8/3/2010 8:10 AM, Marc wrote:
> Hi.
>
> This is not directly related to EEGLab. But I thought someone may be
> able to give some pointers.
>
> We're doing some experiments measuring scalp EEG of participants. One
> of the variables we intend to record is the participant's voice reply.
> We're wondering if it is possible to use the same EEG hardware
> amplifier to record the voice reply? Have anyone tried that before?
> That is, instead of connecting the electrodes to the one of the 64
> channels of the amplifier, we connect a microphone to the input
> channel. I assume we will be able to record as good a signal as any
> audio amplifier? Is there any thing else to watch out for?
>
> Thanks for any advise.
>
> Marc.
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