Audio delay - Revision history

Wilbert.vanham at 08:33, 7 March 2019

2019-03-07T08:33:27Z

Wilbert.vanham: rewrote

2019-03-07T08:32:34Z

rewrote

H.voogd at 09:28, 17 December 2018

2018-12-17T09:28:46Z

Wilbert.vanham: /* Neurobs presentation */

2018-12-17T09:18:00Z

Neurobs presentation

Wilbert.vanham: /* Neurobs presentation */

2018-12-17T09:17:35Z

Neurobs presentation

Wilbert.vanham: /* Oscilloscope test */

2018-12-17T08:58:54Z

Oscilloscope test

Wilbert.vanham at 08:56, 17 December 2018

2018-12-17T08:56:58Z

Wilbert.vanham: /* Precision test */

2018-12-17T08:29:32Z

Precision test

Wilbert.vanham at 08:29, 17 December 2018

2018-12-17T08:29:00Z

Wilbert.vanham: Created page with "Audio delay is the time between the moment the experimenter want the audio to be played and the start of the audio playing. For experiments where no distinction is made betwe..."

2018-12-17T08:27:32Z

Created page with "Audio delay is the time between the moment the experimenter want the audio to be played and the start of the audio playing. For experiments where no distinction is made betwe..."

New page

Audio delay is the time between the moment the experimenter want the audio to be played and the start of the audio playing.
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.
== 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. 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 ==
=== Round trip test ===
This is the definition used above.
# the audio stimulus is prepared
# a random delay is applied
# the virtual stopwatch is started
# the audio stimulus is started immediately after the stopwatch
# the line output of the audio hardware is connected to the sound or voice detector of the buttonbox
# the buttonbox reports receiving the audio, the virtual stopwatch is stopped
This loop is repeated a number of times to get a good estimate of the statistical distribution of the delay.

=== Oscilloscope test ===
This test more accurately measures the delay, since no loop back to the computer is needed. The test is
more work to perform and therefore less useful for determining the statistical distribution of the delay.
# the audio stimulus is prepared
# a random delay is applied
# a trigger is sent to the buttonbox, the trigger show on one channel of the oscilloscope
# the audio stimulus is started
# 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

This
[[File:Alsa.png|frame|Example audio delay of about 2ms using the osciloscope test.]]

=== Precision test ===
This test does not measure the audio delay itself, but only the precision. It can be combined with the previous test

@@ Line 61: / Line 61: @@
 [[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 where the operating
+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
 system allows only one program to control the audio hardware.

@@ Line 2: / Line 2: @@
 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.
 == 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.
@@ Line 15: / Line 43: @@
 Note that for most experiments this is more than good enough.
 === Presentation, Exclusive Mode ===
 [[File:Exclusive mode.png|border|Exclusive mode delay]]
@@ Line 24: / Line 50: @@
 [[File:Directx.png|border|DirectX mode delay]]
-== Alternative definitions ==
+== Neurobs presentation, precision test ==
-=== Round trip 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
-This is the definition used above.
+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 audio stimulus is prepared
+the moment the audio starts but only needs to ''know'' the moment, this is the value that should be called the onset ''precision''.
-This is an example of audio delay of 2 ms measured with the oscilloscope test.
+== Linux, Alsa, oscilloscope test ==
 [[File:Alsa.png|border|Example audio delay of about 2ms using the osciloscope test.]]
-=== Precision test ===
+This particular test was done on the labcomputer with a python script using ALSA, which is comparable with true exclusive mode where the operating
-This test does not measure the audio delay itself, but only the precision. It can be combined with the previous tests.
+system allows only one program to control the audio hardware.

@@ Line 14: / Line 14: @@
 Note that for most experiments this is more than good enough.
-Since the audio call in Presentation is semi-synchronous (it waits till the sound starts playing) it is possible to know the audio oneset with much
+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.
 === Presentation, Exclusive Mode ===

@@ Line 13: / Line 13: @@
 Note that for most experiments this is more than good enough.
 === Presentation, Exclusive Mode ===
 [[File:Exclusive mode.png|border|Exclusive mode delay]]

@@ Line 41: / Line 41: @@
 # 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.
+This is an example of audio delay of 2 ms measured with the oscilloscope test.
 [[File:Alsa.png|border|Example audio delay of about 2ms using the osciloscope test.]]

@@ Line 6: / Line 6: @@
 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 36: / Line 46: @@
 === Precision test ===
-This test does not measure the audio delay itself, but only the precision. It can be combined with the previous test.
+This test does not measure the audio delay itself, but only the precision. It can be combined with the previous tests.

← Older revision		Revision as of 08:29, 17 December 2018
Line 36:		Line 36:

	=== Precision test ===		=== Precision test ===
−	This test does not measure the audio delay itself, but only the precision. It can be combined with the previous test	+	This test does not measure the audio delay itself, but only the precision. It can be combined with the previous test.