Does SRBOX/Microphone setup effect RTs?

Fri Aug 1 07:45:57 UTC 2014

Hi,
Wouldn't the use of two (perhaps even taped together) microphones make a lot
more sense? Given that these do very different things: record onset of audio
vs record audio, I can think of few reasons why these would need to be very
exactly synchronised - apart from that warm feeling we all get from hyper
precise timing, obviously! Anyway, the benefit would be that the audio
microphone can then be a very good, studio quality, microphone, rather than
the SRBox voicekey one which I don't think was really built for audio
analysis. Second, it makes from an audio engineer's point of view some sense
to direct microphone's different (e.g. a little underneath the mouth).
Third, you could use the onset of the SRBox voicekey as a trigger to start
an audio input object. Finally: you could always try to sync the data
offline if you send out a tone (e.g. at >20 Khz) at the onset of your
critical stimulus, then write a bit* of matlab code to calculate the
distance between beeps and first human vocal range (0.5<KHz<4), and save the
chunk as data - it has certain benefits, since you will be more sure that
it's not just some subject's sigh that triggers the voicekey. 
Anyway, just some ideas, maybe one helps.
Best,
Michiel

* That sounds like it's little work - obviously, it's not, but maybe there
are toolboxes out there already.
PS: Many audio interfaces (cards) do provide line level inputs, I've
previously recommended M-Audio Fast Track USB before as a cheap one (also
comes with dedicated ASIO drivers and such which might help E-Prime 2 audio
out latency)
------------

Dr. Michiel Spapé
Helsinki Institute for Information Technology HIIT
Aalto University & University of Helsinki
Finland

-----Original Message-----
From: e-prime at googlegroups.com [mailto:e-prime at googlegroups.com] On Behalf
Of David McFarlane
Sent: 31 July 2014 18:58
To: e-prime at googlegroups.com
Subject: Re: Does SRBOX/Microphone setup effect RTs?

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 trained
staff (and other support facilities) at https://support.pstnet.com .  3) If
you do get an answer from PST staff, please extend the courtesy of posting
their reply back here for the sake of others.
\----

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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