/usr/share/psychtoolbox-3/PsychTests/PsychPortAudioTimingTest.m is in psychtoolbox-3-common 3.0.11.20131230.dfsg1-1build1.
This file is owned by root:root, with mode 0o644.
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% PsychPortAudioTimingTest([exactstart=1][, deviceid=-1][, latbias=0][, waitframes=1][, useDPixx=0][, triggerLevel=0.01])
%
% Test script for sound onset timing reliability and sound onset
% latency of the PsychPortAudio sound driver.
%
% This script configures the driver for low latency and high timing
% precision, then executes ten trials where it tries to emit a beep sound,
% starting in exact sync to a black-white transition on the display.
%
% You'll need measurement equipment to use this: A photo-diode attached to
% the top-left corner of your CRT display, a microphone attached to your
% speakers, some oszillograph to record and measure the signals from the
% diode and microphone.
%
% Some parameters may need tweaking. Make sure you got a setup as described
% in 'help InitializePsychSound' for best results.
%
% Optional parameters:
%
% 'exactstart' = 0 -- Start immediately, measure absolute latency.
% = 1 -- Test accuracy of scheduled sound onset. (Default)
%
% 'deviceid' = -1 -- Auto-select optimal device (Default).
% >=0 -- Select specified output device. See
% PsychPortAudio('GetDevices') for a list of devices.
%
% 'latbias' = Hardware inherent latency bias. To be determined by
% measurement - allows to PA to correct for it if provided.
% Unit is seconds. Defaults to zero.
%
% 'waitframes' = Time to wait (in video refresh intervals) before emitting beep + flash.
% Defaults to a value of 1, may need to be set higher for
% high latency sound hardware (where absolute latency > 1
% video refresh duration).
%
% 'useDPixx' = 1 -- Use DataPixx device to automatically measure the true
% audio onset time wrt. to visual stimulus onset.
% 0 -- Don't use DataPixx. This is the default.
%
% 'triggerLevel' = Sound signal amplitude for DataPixx to detect sound
% onset. Defaults to 0.01 = 1% of max amplitude if
% exactstart == 0, otherwise it is auto-detected by
% calibration. This will likely need tweaking on your
% setup. If the measured audio onset delta by DataPixx is
% much lower (or almost zero) than the expected delta
% reported by PsychPortAudio, then the triggerLevel may be
% too low and you should try if slightly higher thresholds
% help to discriminate signal from noise. Too high values
% may cause a hang of the script. In practice, levels
% between 0.01 and 0.1 should yield good results. Setting
% the 'useDPixx' flag to 2 also plots the waveforms
% captured by DataPixx, which may help in selection of the
% optimal triggerLevel.
%
% Initialize driver, request low-latency preinit:
InitializePsychSound(1);
if ~IsLinux
PsychPortAudio('Verbosity', 10);
end
% Force GetSecs and WaitSecs into memory to avoid latency later on:
GetSecs;
WaitSecs(0.1);
% If 'exactstart' wasn't provided, assume user wants to test exact sync of
% audio and video onset, instead of testing total onset latency:
if nargin < 1
exactstart = [];
end
if isempty(exactstart)
exactstart = 1;
end
if exactstart
fprintf('Will test accuracy of scheduled sound onset, i.e. how well the driver manages to\n');
fprintf('emit sound at exactly the specified "when" deadline. Sound should start in exact\n');
fprintf('sync with display black-white transition (or at least very close - < 1 msec off).\n');
fprintf('The remaining bias can be corrected by providing the bias as "latbias" parameter\n');
fprintf('to this script. Variance of sound onset between trials should be very low, much\n');
fprintf('smaller than 1 millisecond on a well working system.\n\n');
else
fprintf('Well test total latency for immediate start of sound playback, i.e., the "when"\n');
fprintf('parameter is set to zero. The difference between display black-white transition\n');
fprintf('and start of emitted sound will be the total system latency.\n\n');
end
% Default to auto-selected default output device if none specified:
if nargin < 2
deviceid = [];
end
if isempty(deviceid)
deviceid = -1;
end
if deviceid == -1
fprintf('Will use auto-selected default output device. This is the system default output\n');
fprintf('device in "normal" (=reliable but high latency) mode. In low-latency mode its the\n');
fprintf('device with the lowest inherent latency on your system (as determined by some internal\n');
fprintf('heuristic). If you are not satisfied with the results you may query the available devices\n');
fprintf('yourself via a call to devs = PsychPortAudio(''GetDevices''); and provide the device index\n');
fprintf('of a suitable device\n\n');
else
fprintf('Selected the following output device (deviceid=%i) according to your spec:\n', deviceid);
devs = PsychPortAudio('GetDevices');
for idx = 1:length(devs)
if devs(idx).DeviceIndex == deviceid
break;
end
end
disp(devs(idx));
end
% Request latency mode 2, which used to be the best one in our measurement:
% classes 3 and 4 didn't yield any improvements, sometimes they even caused
% problems.
reqlatencyclass = 2;
% Requested output frequency, may need adaptation on some audio-hw:
freq = 44100; % Must set this. 96khz, 48khz, 44.1khz.
buffersize = 0; % Pointless to set this. Auto-selected to be optimal.
suggestedLatencySecs = [];
if IsWin
% Hack to accomodate bad Windows systems or sound cards. By default,
% the more aggressive default setting of something like 5 msecs can
% cause sound artifacts on cheaper / less pro sound cards:
suggestedLatencySecs = 0.015 %#ok<NOPRT>
fprintf('Choosing a high suggestedLatencySecs setting of 15 msecs to account for shoddy Windows operating system.\n');
fprintf('For low-latency applications, you may want to tweak this to lower values if your system works better than average timing-wise.\n');
end
% Needs to determined via measurement once for each piece of audio
% hardware:
if nargin < 3
latbias = [];
end
if isempty(latbias)
% Unknown system: Assume zero bias. User can override with measured
% values:
fprintf('No "latbias" provided. Assuming zero bias. You''ll need to determine this via measurement for best results...\n');
latbias = 0;
end
if nargin < 4
waitframes = [];
end
if nargin < 5
useDPixx = [];
end
if isempty(useDPixx)
useDPixx = 0;
end
if nargin < 6
% Default triggerLevel is "auto-trigger":
triggerLevel = [];
end
% Open audio device for low-latency output:
pahandle = PsychPortAudio('Open', deviceid, [], reqlatencyclass, freq, 2, buffersize, suggestedLatencySecs);
% Tell driver about hardwares inherent latency, determined via calibration
% once:
prelat = PsychPortAudio('LatencyBias', pahandle, latbias) %#ok<NOPRT,NASGU>
postlat = PsychPortAudio('LatencyBias', pahandle) %#ok<NOPRT,NASGU>
% Generate some beep sound 1000 Hz, 0.1 secs, 50% amplitude:
mynoise(1,:) = 0.5 * MakeBeep(1000, 0.1, freq);
mynoise(2,:) = mynoise(1,:);
% Fill buffer with data:
PsychPortAudio('FillBuffer', pahandle, mynoise);
% Setup display:
screenid = max(Screen('Screens'));
% Shall we use the DataPixx for measurement?
if useDPixx
% Yes!
% Initialize audio capture subsystem of Datapixx:
% 96 KhZ sampling rate, Mono capture: Average across channels (0), Audio
% input is line in (2), Gain is 1.0 (1):
DatapixxAudioKey('Open', 96000, 0, 2, 1);
% Check settings by printing them:
dpixstatus = Datapixx('GetMicrophoneStatus') %#ok<NOPRT,NASGU>
if ~(exactstart && isempty(triggerLevel))
if isempty(triggerLevel)
% Choose a default of 1% of max. signal amplitude:
triggerLevel = 0.01;
end
fprintf('Using a trigger level for DataPixx of %f. This may need tweaking by you...\n', triggerLevel);
DatapixxAudioKey('TriggerLevel', triggerLevel);
end
% DataPixx: Setup Screen imagingpipeline to support measurement via the PSYNC
% video synchronization mode of DataPixx and Screen():
PsychImaging('PrepareConfiguration');
PsychImaging('AddTask', 'General', 'UseDataPixx');
win = PsychImaging('OpenWindow', screenid, 0);
LoadIdentityClut(win);
else
% Default: No need for imaging pipeline:
win = Screen('OpenWindow', screenid, 0);
end
ifi = Screen('GetFlipInterval', win);
% Set waitframes to a good default, if none is provided by user:
if isempty(waitframes)
% We try to choose a waitframes that maximizes the chance of hitting
% the onset deadline. We are conservative in our estimate, because a
% few video refresh cycles hardly matter for this test, but increase
% our chance of success without need for manual tuning by user:
if isempty(suggestedLatencySecs)
% Let's assume 12 msecs on Linux and OSX as a achievable latency by
% default, then double it:
waitframes = ceil((2 * 0.012) / ifi) + 1;
else
% Whatever was provided, then double it:
waitframes = ceil((2 * suggestedLatencySecs) / ifi) + 1;
end
end
fprintf('\n\nWaiting %i video refresh cycles before white-flash.\n', waitframes);
% Auto-Selection of triggerLevel for Datapixx timestamping requested?
if useDPixx && exactstart && isempty(triggerLevel)
% Use auto-trigger mode. Tell the function how long the silence
% interval at start of each trial is expected to be. This will be
% used for calibration: We set it to 75% of the duration of the pause
% between start of Datapixx recording and scheduled sound onset time:
DatapixxAudioKey('AutoTriggerLevel', ifi * waitframes * 0.75);
fprintf('Setting lead time of silence in Datapixx auto-trigger mode to %f msecs.\n', ifi * waitframes * 0.75 * 1000);
end
% Perform one warmup trial, to get the sound hardware fully up and running,
% performing whatever lazy initialization only happens at real first use.
% This "useless" warmup will allow for lower latency for start of playback
% during actual use of the audio driver in the real trials:
PsychPortAudio('Start', pahandle, 1, 0, 1);
PsychPortAudio('Stop', pahandle, 1);
% Ok, now the audio hardware is fully initialized and our driver is on
% hot-standby, ready to start playback of any sound with minimal latency.
% Wait for keypress.
KbStrokeWait;
% Realtime scheduling: Can be used if otherwise timing is not good enough.
% Priority(MaxPriority(win));
% Ten measurement trials:
for i=1:10
if useDPixx
% Schedule start of audio capture on DataPixx at next Screen('Flip'):
DatapixxAudioKey('CaptureAtFlip');
end
% This flip clears the display to black and returns timestamp of black onset:
% It also triggers start of audio recording by the DataPixx, if it is
% used, so the DataPixx gets some lead-time before actual audio onset.
[vbl1 visonset1]= Screen('Flip', win);
% Prepare black white transition:
Screen('FillRect', win, 255);
Screen('DrawingFinished', win);
if exactstart
% Schedule start of audio at exactly the predicted visual stimulus
% onset caused by the next flip command.
PsychPortAudio('Start', pahandle, 1, visonset1 + waitframes * ifi, 0);
end
% Ok, the next flip will do a black-white transition...
[vbl visual_onset t1] = Screen('Flip', win, vbl1 + (waitframes - 0.5) * ifi);
if ~exactstart
% No test of scheduling, but of absolute latency: Start audio
% playback immediately:
PsychPortAudio('Start', pahandle, 1, 0, 0);
end
t2 = GetSecs;
% Spin-Wait until hw reports the first sample is played...
offset = 0;
while offset == 0
status = PsychPortAudio('GetStatus', pahandle);
offset = status.PositionSecs;
t3=GetSecs;
plat = status.PredictedLatency;
fprintf('Predicted Latency: %6.6f msecs.\n', plat*1000);
if offset>0
break;
end
WaitSecs('YieldSecs', 0.001);
end
audio_onset = status.StartTime;
%fprintf('Expected visual onset at %6.6f secs.\n', visual_onset);
%fprintf('Sound started between %6.6f and %6.6f\n', t1, t2);
%fprintf('Expected latency sound - visual = %6.6f\n', t2 - visual_onset);
%fprintf('First sound buffer played at %6.6f\n', t3);
fprintf('Flip delay = %6.6f secs. Flipend vs. VBL %6.6f\n', vbl - vbl1, t1-vbl);
fprintf('Delay start vs. played: %6.6f secs, offset %f\n', t3 - t2, offset);
fprintf('Buffersize %i, xruns = %i, playpos = %6.6f secs.\n', status.BufferSize, status.XRuns, status.PositionSecs);
fprintf('Screen expects visual onset at %6.6f secs.\n', visual_onset);
fprintf('PortAudio expects audio onset at %6.6f secs.\n', audio_onset);
fprintf('Expected audio-visual delay is %6.6f msecs.\n', (audio_onset - visual_onset)*1000.0);
if useDPixx
% 'visonset1' is the GetSecs() time of start of capture on
% DataPixx. 'audio_onset' is reported GetSecs() audio onset time
% according to PsychPortAudio.
%
% 'expectedAudioDelta' is therefore the expected delay for the
% measured audio onset by DataPixx:
expectedAudioDelta = audio_onset - visonset1;
% Retrieve true delay from DataPixx measurement and stop recording
% on the device:
[audiodata, measuredAudioDelta] = DatapixxAudioKey('GetResponse', [], [], 1);
fprintf('DPixx: Expected audio onset delta is %6.6f secs.\n', expectedAudioDelta);
fprintf('DPixx: Measured audio onset delta is %6.6f secs.\n', measuredAudioDelta);
fprintf('DPixx: PsychPortAudio measured onset error is therefore %6.6f msecs.\n', 1000 * (measuredAudioDelta - expectedAudioDelta));
if useDPixx > 1
figure;
plot(audiodata);
end
end
% Stop playback:
PsychPortAudio('Stop', pahandle, 1);
% Wait a bit...
WaitSecs(0.3);
Screen('FillRect', win, 0);
telapsed = Screen('Flip', win) - visual_onset; %#ok<NASGU>
WaitSecs(0.6);
end
% Done, close driver and display:
Priority(0);
if useDPixx
% Close Datapixx audio subsystem:
DatapixxAudioKey('Close');
end
PsychPortAudio('Close');
Screen('CloseAll');
% Done. Bye.
return;
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