When performing some experiments, it may be desirable to link a recorded audio file to a recorded data file. For instance, a subject may be speaking, listening to voice commands, or listening to sounds played by a computer's speakers as physiological data are acquired.
Audio can be synchronized with other data types by connecting a sound signal directly to the MP150 system. To do this, the sound signal must be relatively large, such as the line level signals used to drive a set of speakers. Microphone levels would generally be too low and have to be amplified. The audio out from the sound card of a computer would generally suffice. However, this signal would typically be stereo. Inputs to the MP150 system have to be mono. A stereo to dual mono Y-cable could be used to bring the sound out of a computer's soundcard, and then one or both channels could be brought into the MP150 system via CBL100.
If none of the measures of the human subject involve direct electrical connections to that subject — that is, if no ECG, EMG, EEG, etc. signal is recorded from the subject, then the CBL100 can be connected directly to the front of the UIM100C. If electrophysiological recordings from human subjects are part of the experiment, then the output from the sound card must go through an INISO and HLT100C. For more information about the potential safety hazard involved here, please see the Knowledge Base entry on galvanic isolation.
Let us assume the audio is plugged into channel 5 of the UIM100C (or the HLT100C). Make sure this channel is not used by another amplifier. Enable channel 5 in the Acqknowledge software to acquire the sound. The higher the sample rate the better the sound will be captured (for example, a 40 000Hz sample rate would capture the entire range of human hearing.) But even at sample rates lower than 1000 Hz it is possible to pick up the sound as noise which will serve fine as a marker.
It is probably best to use a loud sound as a marker at the beginning of the experiment so that it can be easily recognized in the Acqknowledge recording and in the audio recording. After the data are acquired, it is possible (only for Windows computers) to bind the sound recording (in a .wav file format) to the Acqknowledge recording in the same way that video can be bound to an Acqknowledge recording. Consult the section on Playback under the Video chapter in the Acqknowledge software guide for further details.
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