Using the Sensimetrics Audio Presentation System

Introduction

This page provides basic instruction on how to us the audio presentation system associated with the Siemens Vida MRI scanner in HDB.

Admonition

Please do not change the cable configuration of the audio presentation system. This configuration has been designed and tested to work for the vast majority of needs. If this system does not do what you need, please consult with IRC staff, and we will make accommodations as necessary. You should not change anything yourself.

Basic Description

The heart of the audio system is the Rolls MX-122 mixer. There is an 1/8" plug audio interface cable provided in the bundle of video cables intended to be used with the headphone output jack on stimulus laptops. But, other inputs can be used, too, if/when the need arises. There is also a benchtop microphone with a push-to-talk button that feeds its own input on the mixer. This microphone and each input has its own level control knob and these levels are mixed into a single audio stream that is controlled by the master level. That master feed then goes to the monitor speakers on the shelf and the Senimetrics s15 headphones. The headphones have their own volume adjustment. This configuration is depicted in the figure on the right. The light red arrows show which logical control physically resides on the mixer.

Audio presentation system wiring diagram

Mixing Procedure

The first time you set up this audio system for a particular experiment, you should run through this type of recommended procedure to set all the audio levels. Once you have these levels balanced the way you need, make note of each knob's position. This should be reproducible for each session of your experiment. The only thing you'll need to tweak every time is the headphone volume to match your subject's comfort level.

Set your laptop's headphone output to about 50% maximum level, and then plug in the 1/8" audio cable to the headphone jack on your laptop.
Set the mic level, laptop input level, and master level to 50% of maximum.
Set the headphone output level to about 25% maximum.
Play a sample of the audio you plan to us in your experiment, listening for distortion on the monitor speakers. If there is distortion, turn down your laptop's headphone output level until the distortion goes away. Don't worry about the speaker volume at this point. Just get clear reproduction of the audio.
Speak into the microphone. Listen for distortion. Adjust the microphone level down until you don't hear any.
Adjust the master volume until the level is comfortable for you out of the monitor speakers. Play your the audio from your laptop again, and adjust the mixer's input level from your laptop until it's level is how you want it compared to the microphone level. Iterate between the mic input level and the laptop input levels on the mixer until the two are balanced the way you need.
Make a note of all the mixer knobs as well as your laptop's headphone volume. The next time you run the same experiment, you can simply dial in those values and be reasonably certain they're going to work again, and you can simply skip to step 8.
Have your subject put the earbuds in their ears correctly, and adjust the headphone volume until it is comfortable for them. This step should be done before every single session.

Safety

It is imperative that the cable feeding the Sensimetrics earbuds NOT touch any bare skin (including hands and legs) and NOT have any loops. Both could potentially cause serious burns. Please refer to the S15-Safety-Statement-2018.pdf provided by the manufacturer for additional notes.

Safety diagram for Sensimetrics Cables