In Pulsar, exact aligned of the onset of the audio with the corresponding triggers is an absolute necessity for reproducible auditory evoked potentials. High-speed microprocessors in Pulsar control the generation of the audio and the timing of the trigger events. Testing the time-sync of the audio and triggers can be done quite easily. The audio and trigger output of Pulsar is connected to an audio recording device and recorded. The left audio channel is recorded at the left channel, while the triggers are recorded in the right channel. The result is a stereo audio file with on the left channel the original auditory stimulation and on the right the triggers.
The image shows the alignment of the audio onset and the trigger. It is time-synced with the onset of the audio, exactly at the start of the “rise” of the tone. The 1000Hz tone had a length of 50 ms with a rise and fall time of 5 ms. The trigger is send for 25 ms to make sure it is detected by all EEG systems, even at low sampling rates (for ERP’s a sampling rate of at least 500Hz is recommended).