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Line 2: − + − These are measurements of the audio delay in Neurobs Presentation on the Faculty of Social Sciences (DCC and BSI) labcomputer − with three different settings. Note that exclusive mode is most used in experiments and is the mode best comparable with for − instance Linux Alsa. Shared mode is best comparable with Linux Jack. − === Presentation, Exclusive Mode === − === Presentation, Shared Mode === − === Presentation, DirectX Mode === − − == Alternative definitions == − + + Line 26:
Line 19: − + − + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + − === Precision test ===+ − +
no edit summary
For experiments where no distinction is made between systematic and random errors in timing, the audio delay equals the accuracy
For experiments where no distinction is made between systematic and random errors in timing, the audio delay equals the accuracy
of the onset of the audio stimulus.
of the onset of the audio stimulus.
== Neurobs presentation ==
== Ways of measuring / definitions ==
=== Round trip test ===
=== Round trip test ===
This is the definition used above.
This is the definition that we use most often, because it is relatively simple to measure. All you need is a computer with an analog audio output
and a usb-port. The analog output can also be a different device that is controlled by the computer, for instance the Behringer.
# the audio stimulus is prepared
# the audio stimulus is prepared
# a random delay is applied
# a random delay is applied
# the audio stimulus is prepared
# the audio stimulus is prepared
# a random delay is applied
# a random delay is applied
# a trigger is sent to the buttonbox, the trigger show on one channel of the oscilloscope
# a trigger is sent to the buttonbox, the trigger shows on one channel of the oscilloscope
# the audio stimulus is started
# the audio stimulus is started
# the line output of the audio hardware is connected to another channel of the oscilloscope
# the line output of the audio hardware is connected to another channel of the oscilloscope
# the time difference between the onsets on the trigger and the audio signal is measured on the oscilloscope
# the time difference between the onsets on the trigger and the audio signal is measured on the oscilloscope
This is an example of audio delay measured with the oscilloscope test.
=== Precision test ===
This test does not measure the audio delay itself, but only the precision. It can be combined with the previous tests.
The difference is that step 3 and 4 are exchanged. This effectively deducts the time that sending the audio stimulus
takes is deducted from the audio delay. If the audio is made with a synchronous function then this test is similar to
how visual delay is measured.
= Examples =
== Neurobs presentation ==
These are measurements of the audio delay in Neurobs Presentation on the Faculty of Social Sciences (DCC and BSI) labcomputer
with three different settings ([https://gitlab.socsci.ru.nl/tsg/performance-tests/tree/master/Presentation/audio/SoundLatencyTest download the script here]). Note that exclusive mode is most used in experiments and is the mode best comparable with for
instance Linux Alsa. Shared mode is best comparable with Linux Jack.
In exclusive mode the histogram is square. The minimum delay is 15 ms, the maximum delay is 24 ms. This is caused by a single 10 ms buffer.
The maximum error is therefore 24 ms. When a distinction is made between accuracy and precision, the maximum accuracy error is 14 ms,
the maximum precision error is 10 ms.
Note that for most experiments this is more than good enough.
=== Presentation, Exclusive Mode ===
[[File:Exclusive mode.png|border|Exclusive mode delay]]
=== Presentation, Shared Mode ===
[[File:Shared.png|border|Shared mode delay]]
=== Presentation, DirectX Mode ===
[[File:Directx.png|border|DirectX mode delay]]
== Neurobs presentation, precision test ==
Since the audio call in Presentation is semi-synchronous (it waits till the sound starts playing) it is possible to know the audio onset with much
higher precision by noting the time that the call ''ends''. This way a precision of better than 3 ms is possible. If one does not need to ''control''
the moment the audio starts but only needs to ''know'' the moment, this is the value that should be called the onset ''precision''.
== Linux, Alsa, oscilloscope test ==
This is an example of an audio delay of 2 ms measured with the oscilloscope test.
[[File:Alsa.png|border|Example audio delay of about 2ms using the osciloscope test.]]
[[File:Alsa.png|border|Example audio delay of about 2ms using the osciloscope test.]]
This particular test was done on the labcomputer with a python script using ALSA, which is comparable with true exclusive mode, as it existed in MS Windows Xp, where the operating
This test does not measure the audio delay itself, but only the precision. It can be combined with the previous test.
system allows only one program to control the audio hardware.