Intro

Video

Video in the Kennedy psychophys suite is relatively simple.

See Kennedy Psychophys Suite for details on the PC, monitors, and other equipment used to provide visual stimuli to participants.

See Participant Monitoring Cameras And TVs for details on participant monitoring equipment.

Audio

Audio is somewhat more complicated, but is kept manageable by the use of an X-Air digital mixer.

What makes our setup complicated is that we, like most psychological researchers, only need a few audio inputs (stimulus PC, researcher microphone, participant microphone), but need to send them to a mix of several outputs (participant headphones, participant speakers, researcher (participant monitoring) speaker, output to BIOPAC system, optionally recording participant speech to computer files). However, most audio mixers are designed for musicians, who need the opposite: many inputs (one mic per singer, guitar, bass, drums, and many more for orchestras or choirs), and few outputs (recording system, monitoring headphones). So, the equipment we need doesn't exist, and we need to make due with hodgepodging together what is available. With the advent of the digital mixer, what we need does exist. And it's relatively easy to control, using an app to set the mixer up instead of the dozens or hundreds of sliders and dials needed on a traditional analog mixer.

The heart of the audio setup is the Behringer X-Air XR18 electronic mixer, which is controller via "scenes" or pre-defined settings. The scenes are defined on a iPad or laptop PC, and can be changed on the fly. Each study would have its own scene that would preset the connections and input and output levels for that study's specific needs.

The XAIR-18 has 18 mono inputs (section 1 on the diagram), 1 stereo MAIN output (section 2 on the diagram), 6 additional mono AUX outputs (section 15 on the diagram), stereo headphone outputs (section 6 on the diagram), plus USB output of all channels (section 9 on the diagram).

The XAIR-18 can connect to the iPad or laptop via ethernet (section 10 on the diagram) or wifi. The connection mode is selected via the mode switch (section 12 on the diagram). We will always use ethernet mode with a cable connected to a computer so that interference with our Bionomadix wireless systems and campus wifi are minimized.

We use the following connections:

XAir Inputs and Outputs

In/Out	Line #	Description
In	1 (section 1)	Researcher mic (mono)
In	2	Participant mic (mono)
In	3, 4	Stimulus PC output (stereo)
Out	MAIN L, R (section 2)	Participant headphones (stereo)
Out	AUX 1 (section 15)	TV / participant monitor (mono)
Out	AUX 2, 3	Participant speakers (stereo)
Out	AUX 4, 5	Researcher speakers (stereo)
Out	AUX 6	BIOPAC A??? (mono)
Out	USB	Optional recording of any channels (to PC)

XAir Power

The XAir doesn't have any controls on it. There is only a small power switch at one end, next to / above the power cable. When the switch is rocked so that the white stripe on it is pressed down, the XAir is on. There are no external status lights or other indicators that the power is on. However, you can look through the vent at the other end of the XAir and see some of the internal red lights are on. 

NOTE: The power cable is a bit loose and can appear to be plugged into the XAir when it is actually not quite connected. If you turn on the XAir with the switch and it doesn't seem to work, visually check the vent end for the red lights, and confirm that the power cable is fully snugged into the XAir's power jack.

XAir Usage

You don't use the XAir directly. Instead, you use an app on an iPad or on a PC to connect to the XAir and program it.

The iPad app connects to the XAir via wifi. Due to the close proximity of the XAir to our BIOPAC amps, we don't use this connection method.

The PC app connects to the XAir via a dedicated ethernet cable. We've installed the app on the stimulus PC AIRBOURNE to control the XAir in the Kennedy psychophys suite.

To use the XAir app, log onto the stimulus PC, and double-click the XAir app on the desktop, or look for it in the Start menu.

When the app first starts it does not automatically connect to the XAir. You need to tell the app to do that. Click on the Setup icon in the upper-right corner of the app window.

In the Setup window:

• Click on the CHM_164Mixer in the "Select Mixer from list" list.
• Click on the Connect button.
• If you don't already have a settings file for the Xair created, or if you're not sure, click on the Mixer -> PC "Sync Direction" option.
• Click on the Synchronize button. This will copy the XAir's current built-in settings over to the app.
  • It's very likely that the XAir has already been set up with the correct settings for most studies.
• Close the Setup window.

You should now see that many of the sliders in the app have changed. You can now tweak them, save them to a file, and sync the tweaked settings back to the XAir.

Changing settings in the app is a little non-intuitive. The app only shows the settings for one output channel at a time.

To switch to a different output channel's settings, select the channel from the buttons in the app's lower-right corner by clicking on it's button (Main LR, Bus 1, etc.):

Note that the channel's description is in a colored box just to the upper-right of the selector buttons. (For example, the Main LR's description is PPT PHONES.)

Output Channels

The output channels are:

• Main LR (PPT PHONES - participant headphones), light blue. Main LR corresponds to MAIN L and MAIN R on the XAir's physical connectors. It is the only stereo output; all others are mono.
• Bus 1 (TV - participant monitoring), light green. Bus 1 corresponds to AUX 1 on the XAir's physical connectors.
• Bus 2 (PPTSPK - participant speakers), dark blue. AUX 2.
• Bus 3 (not used), dim yellow. AUX 3.
• Bus 4 (not used), bright yellow. AUX 4.
• Bus 5 (Bionomadix - not currently used, but cabled up for output to a second BIOPAC channel if need be), light blue. AUX 5.
• Bus 6 (BIOPAC - output to the BIOPAC HLT100C in the psychophys participant room), red. AUX 6.
• FX 1 - FX 4 are for sound processing. We don't use them.

Input Channels

The input channels are:

• In 1 (RSCH MIC - researcher microphone), red. This corresponds to IN 1 on the XAir's physical connectors. Mono.
• In 2 (PPT MIC - participant microphone, a small black mic which is hidden in the cable tray behind the table in the participant room), green. IN 2. Mono.
• In 3 and 4 (STIM PC L and STIM PC R - the left and right audio channels coming from the headphone / line out jack on the back of the stimulus PC), yellow. Stereo (2 x mono).
• While the XAir is capable of handling up to 16 input channels, we only need these 4.

XAir Current Settings

These are the settings per output channel used by both the AFCHRON and SCIM studies as of March 2020:

Main LR - PPT PHONES

Participant headphones. The RSCH MIC and STIM PC L and R inputs are turned up; PPT MIC is turned down.

In other words, the participant can hear the researcher mic and the stimulus PC's audio through the participant headphones.

Bus 1 - TV

The TV on the wall of the researcher room, used for monitoring the participant's activity. The RSCH MIC and STIM PC L and R inputs are turned down. PPT MIC is turned up.

The researchers can hear the participant mic through the TV's speaker.

Bus 2 - PPTSPK

The participant speakers on the table in the participant room. The RSCH MIC is turned up; everything else is turned down.

The participant can only hear the researcher mic through the speakers. Note: If your study needs to have the participant hear the stimulus PC audio through the speakers as well, please talk to RSC.

Bus 5 - Bionomadix

Currently not used. STIM PC L and R are turned up; everything else is turned down.

Note: If your study needs to record the participant and / or researcher mics via BIOPAC, please talk to RSC. Due to the low 2000 samples / second rate of the BIOPAC system, the recordings would not be intelligible, but might be useful for noting the timing of when the participant begins speaking, for example.

Bus 6 - BIOPAC

Stimulus PC audio is fed to BIOPAC system to record in parallel with psychophys measures. Used to determine the exact timing of audio stimulus onset and correct for delays in audio stimulus presentation caused by E-Prime and Windows, in relation to timing signals sent from the stimulus PC to BIOPAC DIN lines.

STIM PC L and R are turned up; everything else is turned down.