Re: Solutions for sending triggers in an AEP (EEG) experiment? (Pawel Kusmierek )

Subject: Re: Solutions for sending triggers in an AEP (EEG) experiment?
From:    Pawel Kusmierek  <pawel.kusmierek@xxxxxxxx>
Date:    Sat, 6 Sep 2008 23:51:28 -0400

2008/9/6 Andreas Widmann <widmann@xxxxxxxx>: > Sound is much more difficult with XP and MATLAB: The MATLAB builtin sound > architecture is a nightmare with respect to timing. In our lab we use the > DirectSound implementation provided by Cogent > ( We have best experience with with > some older onboard AC'97 codecs providing (for sure not the best dynamic > range and SNR but) excellent timing, with sub-millisecond jitter and latency > in very low millisecond range. That's very interesting, would you please elaborate a bit more on that? What do you mean by "very low millisecond range"? Do you by-pass the Windows kmixer, whose latency is 30 ms? I thought than only using ASIO drivers or so-called "Kernel Streaming" which is available in certain audio player application can by-pass the kmixer, and sound produced with DirectSound has to have latency of ~30 ms. Daniel, As for "synchronizing" the parallel port with sound onset: I don't know if it will help you, but in my (previous) setup (which was for single unit recordings, actually), I used a feedback solution similar to Daniel's: a square pulse combined with the audio stimulus into a stereo file to be played together. The pulse was then converted to TTL with an optocoupler, and read into the same computer via the printer port, which was also used to read TTL inputs from the spike discriminator. I was able to poll the port frequently enough to have >90% of poll-to-poll periods below 1 ms, and all (or close enough to all) below 2 ms. This was done with a custom-written software under windows XP. So you could basically keep checking your printer port for sound onset and upon detecting it immediately output your 8-bit trigger via output lines of the printer port, if ~1ms accuracy is good enough for you. Pawel -- Pawel Kusmierek PhD Department of Physiology and Biophysics Georgetown University Medical Center The Research Building WP23 3970 Reservoir Road NW Washington, DC 20007 phone: +1 202 687-8851 or 8028, fax: +1 202 687-0617

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