300ms delay in audio file presentation

Dear Cedrus –

I am experiencing an odd delay between the reset of the RT timer and the beginning of the onset of an audio file (.wav)

I have an audio stimulus sound file of a metronomic click, the beginning of which is triggered by “any correct” subject response from a previous event. I previously had been running the experiment on a MacBook Pro Core Duo (OS 10.6.3) with no problems.

Due to catastrophic computer/coffee/gravity failure, I have had to change computers to a MacBook Pro i5 (OS 10.6.3). The experiment has not changed, but the audio file has begun playing about 300ms after the timer starts running, giving me very skewed results.

Do you have any insight as to why this might be going on?

To make matters more confusing, this doesn’t seem to happen every time. Sometimes a reset will fix things, or a safe boot, or a repairing of permissions. It always seems to recur.

Many thanks!

How are you seeing, or measuring the 300 ms? This information will be helpful when we’re trying to duplicate the problem. Also, can you post your experiment as an Experiment Package? This is found under the File menu within SuperLab.

I’m approximating the 300ms.

My experiment plays a click that repeats about every 600ms (actually, 667ms to be precise: i’ll simplify the math below). This means that the clicks should occur at the following intervals:



I compare responses from subjects against these expected values to obtain a differential. For example:

Expected Actual Difference
600 575 -25
1200 1250 +50
1800 1790 -10


Typically, these values had been between +/- 25ms… until the issue I describe above. Now, the events return values that read in this way.

Expected Actual Difference
600 900 +300
1200 1525 +325
1800 2075 +275

No one’s THAT off!

Interestingly; I can avoid the issue by pressing the ‘volume up/down’ buttons on my MacBook Pro immediately before the event is presented. It sometimes takes a moment, and a few repeated keypresses, but it eventually seems to kick in.

Could this be some sort of audio conflict with the mac OS? (The Keyspan Serial USB-to-Serial driver I am using on this machine also seems to possess strange voodoo powers over the OS.)

NewFinalExperiment.zip (985 KB)

Were you also using the USB-to-serial port adapter on the previous Mac? If so, were the USB drivers identical? I’ve ran your question by a developer and he mentioned that a driver on Mac OS can completely deprive other resources of time, even keyboard input might be missed/delayed if a badly written driver takes over.

The driver was the latest version of the Keyspan Serial to USB driver, and it was the same that I had been using on my previous computer.

Does that help?

I tried to find how to obtain the driver version, unfortunately I had no luck. Can you ask Keyspan how to find the exact version of the USB driver?

Keyspan appears to now be owned by Tripp Lite…?

At any rate, the product and its driver are shown and supported here:


This is the driver I have been using.

The question remains whether the two drivers installed on your two Macs are the same or not.

Sorry - that was unclear.

The driver referenced above was the same on both Macs.

I don’t know what it may be. I’ll send you a private message to follow up further.