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Page Revision: 2015/01/01 20:07

The element is capable of playing audio clips in the Waveform Audio File Format (WAV) with high temporal accuracy.

Table of Contents [Hide/Show] Synchronized Internal Actions Properties     Generic properties Snapshots Element Demo When to use the Wave Player element Stimulus Set Practical Use Playback modes    Single playback on event onset    Looped playback on event onset    Manual mode Triggering at the end of the playback Notes

Wave Player is the default element in EventIDE for delivering audio stimuli that is stored in Wave format. It is recommended to use this element for modern sound cards on Windows Vista, Windows 7 & 8, when high temporal accuracy of audio playback is required. For Windows XP and old sound cards the Direct Sound element may produce more accurate results.

The Wave Player element allows one to select one of four audio playback API: DirectSound, WaveOut (also known asWaveform Audio API), ASIO and WASAPI.

In the most cases, WSAPI in the exclusive mode delivers the best temporal accuracy and fidelity of audio playback. (for example, the mid-range Creative SB X-Fi Titanium Professional card, used in Windows 7 & 8, allows to start a playback just in 2ms after onset of the parent event)

The Wave Player element allows the selection of the output sound device when multiple sound cards installed on a computer.

For some professional sound cards another low-level sound API,Audio Stream Input/Output ASIO, can be recommended. Using ASIO API and compatible sound hardware and drivers (the last two are essential) may also help to achieve perfect temporal precision and fidelity.

Wave Player element supports the majority of resolutions and encodings used in the Wave format. The element automatically converts input wave clips into uncompressed PCM data streams before a playback. Since the conversion takes some time, using the uncompressed PCM wave clips is recommended for faster processing of audio stimuli.

Snapshots ¶

Wave Player element is used in the 'media player' demo made with EventIDE

Element Demo ¶

The 'WaveAudioPlayer' demo for the Wave Player element can be found online in the Experiment Gallery

When to use the Wave Player element ¶

EventIDE provides several elements for delivering auditory stimuli. The audio elements have similar functionality and a choice depends on design demands and the used sound hardware. A guidance on selecting an audio element is available in Auditory stimuli article.

In short, the Wave Player element is the simplest and most recommended audio element, especially if Windows Vista/7/8 system and modern sound card is used.

Stimulus Set ¶

The element can be easily adapted to make up an audio stimulus set that contains multiple audio clips. Then one of these clips can be selected to be played in the given trial. To make a stimulus set, load selected audio clips from Material Library directly into the element (e.g. by drag and drop). Then use the Item Index property to select an audio clip for playback. It's recommended to change the Item Index property before the onset of the parent event because preparing the clip for playback takes some time.

Practical Use ¶

1. Add a new Wave Player element into the selected event (where audio has to be played).
2. Select the element in the Element Panel, then its properties will appear in the Property panel on the right.
3. Load selected audio clips from the Material Library to the item list of the element and select the current clip via Item Index property.
4. Browse to the Hardware Settings group in the element properties and select Playback API and Sound Device in the corresponding properties.
5. Select a playback mode for the element in the Playback Setting group. The most common mode for presentation of auditory stimulus is "Single playback on onset of the parent event"
6. Test, if an audio is played by clicking over the Test Playback property.
7. Make sure that duration of the parent event is greater or equal to duration of the selected audio clip- an audio playback is always aborted on offset of the parent event.
   

There are two typical scenario of using the element for presenting audio stimuli in multiple trials:

• If you want to present a random audio clip in each trial, use the 'Single playback' mode and add a proxy linked to the Item Index property. With that proxy you can select an audio clip from the element's list in code snippets (normally before onset of the parent event).
• If you want to chose whether an audio clip has to be played or not in each trial, select 'Manual' mode add a proxy linked to the Is Playing property. Setting that proxy to true/false in code snippets will allow to turn on/off audio playback on the onset of the parent event (the proxy has to be set before the onset).
  

Playback modes ¶

At runtime the element can work in 3 different playback modes, which define how playback process starts and stops. The mode has to be selected at design-time and cannot be changed. However, it's possible to use multiple elements working in different modes in parallel. The available modes are:

Single playback on event onset¶

In this mode the element starts to play an audio synchronously with activation of the parent event. The audio is played once. When the playback stops you can initiate a new one manually if the parent event is still active.

Looped playback on event onset¶

In this mode the element starts to play audio synchronously with activation of the parent event and automatically restarts the playback as soon as the end of the audio clip is reached. This playback loop lasts until deactivation of the parent event.

Manual mode¶

In this mode the playback is controlled solely by element's IsPlaying property, which can be changed in snippets. If IsPlaying is set to true before onset of the parent event, the playback behaviour will be similar to 'Single playback on event onset' mode. If the parent event is active, the playback starts/stops on a change of the IsPlaying property. The Is Playing property automatically turns to false when the playback ends.

Triggering at the end of the playback ¶

In some experimental scenarios it can be reasonable to end the parent event immediately after finishing a playback of the current audio. Since the same Wave Player element can switch between multiple audio clips of different durations, the duration of the parent event can not be set to a fixed value. The Wave Player elements offers an easy solution - the element monitors a playback process and gets triggered at the end of each audio clip. Triggering is followed by a call of the OnTriggered snippet, which can contain user programmed actions. In addition, the element has a boolean status property, called Is Triggered, which can be used directly to control the event flow in EventIDE.

Notes ¶

1. The Wave Player element is optimized to deliver the best timing accuracy and fidelity of audio playback. However, it's always recommended to measure empirically the timing of the actual playback when high accuracy is required. The measurements can be done with oscilloscope connected to the output of the sound card and photo-diode on a monitor. Probing different settings of the element in such testing can help to achieve the optimal results.
2. Slightly better onset of the audio playback can be achieved if the element is placed at the top of the elements list in the parent event. Elements in the list get activated one by one on the onset of the parent event, so the top position in the list will minimize the onset delay.