User Tutorial:Testing AV Playback Tutorial

Purpose

This tutorial gives you an overview how to make sure that your computer system is able to fulfill the requirements of auditory and visual stimulus playback using BCI2000.

Introduction

BCI2000 comes with an AVTest application module that produces video and audio suited to detect playback glitches. This is intended help you adjust system preferences in order to eliminate or minimize such glitches.

Running AVTest with SignalGenerator

To run the AVTest application module with the SignalGenerator source module, simply double-click on the AVTest_SignalGenerator batch file in the BCI2000 batch directory. Click Config to open the parameter config dialog, and navigate to the Application->Window section. There, enter your second monitor's left and top coordinate, and height and width (for more information about how to configure a dual monitor setup for use with BCI2000, see this description.

Then, after closing the parameter config dialog, click SetConfig. A rotating wheel will appear on the secondary monitor. The wheel is designed to move smoothly into the left direction. Any flicker or tearing will be clearly visible against the background of this movement. Also, in the lower part of the image, text is shown that indicates some data about the visual display. Of special interest is the field "frames lost" which represents the total number of frames for which BCI2000 has missed its rendering deadline. A small number of lost frames is ok, but if the number is rapidly increasing this indicates an issue with vertical blank synchronization (see below).

Once you have inspected the rotating wheel, you may progress to a simple audio playback test. The test consists of a 1kHz permanent sine tone. It should be clearly audible, without any crackling or stuttering. Click Start to enable the audio test, and Suspend to disable it again. If you experience crackling or stuttering, open the parameter config dialog, and locate the Application->Audio Playback section. There, edit the AudioBufferDuration parameter and enter 50ms. Close the parameter config dialog, click SetConfig and Start, and listen to the permanent sine tone again. Crackling and/or stuttering should be gone. You may now try and reduce the AudioBufferDuration parameter to find an optimal setting where latency is smaller but artifacts are still absent.