Does SRBOX/Microphone setup effect RTs?

[David McFarlane]

David,

I dearly hope that you get simultaneous voice key and sound recording 
to work with a single microphone, and then report back here on how to 
do it.  I never got that to work here, we gave up and used two 
microphones, one for the voice key (SRBox) and one for sound 
recording through the computer's mic input.  Some details ...

In short, when we used any sort of Y splitter to connect one mic to 
both SRBox and cmoputer mic input, we had trouble getting the voice 
key to respond, and the recorded sound contained a high-pitched 
whine.  I worked on this with PST Support, and they could not do much 
better themselves -- in their own tests using a splitter, either the 
voice key did not work, or the audio quality was degraded (e.g., low volume).

In case it helps, the SRBox uses a dynamic microphone (see 
http://en.wikipedia.org/wiki/Microphone ), with a 3.5mm unbalanced TS 
(tip-sleeve) connector.  Computer mic inputs typically use a 
condenser mic, with a 3.5mm TRS (tip-ring-sleeve) connector where the 
computer may supply power to the mic through the ring.  So things get 
complicated already right there.  Beyond that, I suspect that each 
device connected to the microphone presents an additional load, and 
the microphone simply cannot handle the load of two input devices, 
which would account for the loss in volume.

What we need, of course, is a device that presents a low load to the 
microphone, and can drive multiple loads for the next 
stage.  Ordinarily, that device would be a preamp that supplies 
line-level signals to the next stage.  Unfortunately, in our case a 
line-level signal will likely overload our inputs -- the SRBox can 
take only a mic-level signal, and many computer sound devices no 
longer provide a line-level input, they provide mic-level input 
only.  If you can find a device that takes a mic-level input and then 
buffers that to provide output to multiple mic-level inputs, that 
would be great, but I asked around and could not find such a 
device.  One other option might be to use a preamp, as mentioned 
above, and then attentuate the preamp output using something like a 
series resistor to the mic-level inputs.  I have not yet tried this 
myself, so if you get this to work please write back.  (Even if this 
works, it just seems twisted -- I mean, first we would boost the 
signal from the mic, then attenuate the boosted signal back down to 
mic level so that we could feed it into another mic input that then 
boosts it yet again -- sheesh!)

So in sum, splitting a microphone between the SRBox voice key and the 
computer sound card is not as straightforwared as you might think, 
and in the end using two microphones still seems the best solution.

But to answer your question, I cannot think of any reason that using 
a splitter would affect the measured reaction time, the electric 
signal should travel at the same rate with or without a splitter.  Of 
course, that should be tested empirically (and no one should just 
take my work for any of this :) ), but I would be very surprised if 
it made any difference.  But note that, even with a splitter, as a 
result of latencies in sound recording you will almost certainly find 
a discrepancy between RT measured by voice key vs. sound recording, 
see thread at https://groups.google.com/d/topic/e-prime/DcKdgNJKAlM .

-----
David McFarlane
E-Prime training 
online:  http://psychology.msu.edu/Workshops_Courses/eprime.aspx
Twitter:  @EPrimeMaster (https://twitter.com/EPrimeMaster)

/----
Stock reminder:  1) I do not work for PST.  2) You may reach PST's 
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staff, please extend the courtesy of posting their reply back here 
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\----


At 7/31/2014 10:54 AM Thursday, David Ruvolo wrote:
>I have a question regarding using a microphone for measuring RT and 
>audio input for a battery I am working on.
>
>I am debating on whether using a audio splitter (a y cable) to send 
>the signal to the SRBOX and the computer's recording device vs. 
>using two microphones. If I choose to use two microphones, this 
>creates extra environmental stimuli, would make positioning the 
>microphones and testing the setup in the middle of data collection 
>very time consumming (I am using non SRBOX tasks and SRBOX tasks 
>that have a set order), this might create inconsistencies with data 
>collection (each individual has a slightly different positioning, 
>sound doesn't capture, etc), and the whole experience might be 
>overwhelming for the participant. On the other hand, using the 
>splitter would eliminate this issue, but I am not sure if there 
>would result in differences in RT logged by E-Prime (this would be 
>in ms and could make or break our outcomes).
>
>Does setup (using a splitter vs. two microphones) effect reaction 
>time? I would be interested to know if anyone has looked into this, 
>had any experience using either setup, or measured this.  Feel free 
>to let me know or tell me I am overthinking this.
>
>Thanks,
>
>David

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