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. Author manuscript; available in PMC: 2009 Aug 30.

Published in final edited form as: J Neurosci Methods. 2008 Jun 17;173(2):235–240. doi: 10.1016/j.jneumeth.2008.06.003

A 60-Hertz sinusoid resulting from ambient noise was amplified and fed into the data acquisition system. (a) The original signal sampled at 1 kHz as logged to memory. (b) The same signal simultaneously sampled by Matlab as fast as software allowed (~1.8 kHz). (c) The same signal split and fed into a second data acquisition board, sampled while that board was left in a non-logging (“free-running”) state. These figures demonstrate that when an acquisition board is set to log data to memory or disk, that data becomes available to Matlab only after it has been uploaded in chunks to motherboard memory. Attempting to simultaneously sample this data, as in (b), results in the retrieval of the last uploaded data point, even that sample is tens of milliseconds old. This produces an aliased image of the signal which is not adequate for real-time behavioral control. Instead, data sampled from a second acquisition board, set not to log data, provides an accurate, immediate record of the signal. In this way, data can both be logged for post-hoc analysis and used for on-line behavioral control. (d) With the DAQ set to acquire data at 1 kHz, the number of samples uploaded to memory is plotted against time for two settings: the result using the default buffer size set by Matlab is depicted by the dotted line, and result using the minimum allowable buffer size is depicted by the solid line. Shrinking the DAQ’s buffer size provided a significant but limited benefit (gaps between uploads still occurred, lasting about 15 ms). Thus, the two-DAQ solution offered the best performance.

A 60-Hertz sinusoid resulting from ambient noise was amplified and fed into the data acquisition system. (a) The original signal sampled at 1 kHz as logged to memory. (b) The same signal simultaneously sampled by Matlab as fast as software allowed (~1.8 kHz). (c) The same signal split and fed into a second data acquisition board, sampled while that board was left in a non-logging (“free-running”) state. These figures demonstrate that when an acquisition board is set to log data to memory or disk, that data becomes available to Matlab only after it has been uploaded in chunks to motherboard memory. Attempting to simultaneously sample this data, as in (b), results in the retrieval of the last uploaded data point, even that sample is tens of milliseconds old. This produces an aliased image of the signal which is not adequate for real-time behavioral control. Instead, data sampled from a second acquisition board, set not to log data, provides an accurate, immediate record of the signal. In this way, data can both be logged for post-hoc analysis and used for on-line behavioral control. (d) With the DAQ set to acquire data at 1 kHz, the number of samples uploaded to memory is plotted against time for two settings: the result using the default buffer size set by Matlab is depicted by the dotted line, and result using the minimum allowable buffer size is depicted by the solid line. Shrinking the DAQ’s buffer size provided a significant but limited benefit (gaps between uploads still occurred, lasting about 15 ms). Thus, the two-DAQ solution offered the best performance.