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Page Revision: 2012/05/21 11:55

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

Table of Contents [Hide/Show] Description When to use the DirectSound element Stimulus Set Practical Use     Playback modes     Design-time testing Notes Properties     Generic properties

Description ¶

Wave Player is a default element in EventIDE for delivering audio stimuli recorded in the Wave format. The element is recommended for modern sound cards on Vista and Windows 7 OS system, when high temporal accuracy of audio playback is required. For Windows XP and old sound cards the Direct Sound element may produce better results.

The Wave Player element allows to choose one of four audio playback API: DirectSound, WaveOut, ASIO and WSAPI.

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, can start a playback just in 2ms after onset of the parent event)

The Wave Player element allows 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.

When to use the DirectSound 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 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.

Practical Use ¶

1. Add a new Wave Player element into the selected event (where an audio has to be played).
2. Select the element in the Element panel, then its properties will appear in the Property panel at 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.
   

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:

1. 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.

1. Looped playback on event onset
   

In this mode the element starts to play an 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.

1. Manual mode
   

In this mode the element is controlled manually by its IsPlaying property. plays an audio by a manual request made in code snippets at will time. The playback is initiated by assigning true to the IsPlaying property of the element. Later, the same property can be used to monitor if the audio is still currently played. IsPlaying property automatically turns to false when the playback ends. At this moment and later you can initiate a new playback if the parent event is still active.

Design-time testing ¶

While choosing appropriate values for the element's properties, check the content of the [Clip Info] property. It is refreshed after selection of an audio clip should not be empty or contain error messages. If you see an error, the playback is not possible, and you have to select another clip or choose different values for the element's properties. You can also always test an audio playback with the current element settings by clicking the [Test Playback] property.

Notes ¶

1. Due to the nature of ASIO playback protocol a limited number of sound formats (among Wave formats) can be played by ASIO element- a typical playable format is the two-channels, 44.4kHz Wave raw audio. Test every selected audio clip via a special Test playback property of the ASIO element and recode your audio clips if necessary.
2. For better synchronization of the audio playback (in the Once and Loop playback modes), move the ASIO element at the top of the elements list in the parent event. Elements in the list get to work one by one, as soon as the parent event is activated, so the top position in the list will minimize possible delays. )))
   

Properties ¶

Generic properties ¶

Name	Description	Attributes	Value Type
Settings
Test Playback	Use this action at the design time to initiate an testing playback with the current settings.		Design-time action
Is Mixing	If true, the ASIO engine will be able to play multiple audios simultaneously. However, it may increase the playback latencies.		Boolean
Playback mode	Determines the playback mode for the element. If the property is set to None, the playback has to be initiated manually, otherwise it is synchronized with activation of the parent event.		Object
Monitor Playback	Indicates if the element triggers at the end of the each playback and records its start and end times.	D	Boolean
Clip Info	Information about the sound buffer created for the currently selected audio clip. Click to expand all fields.	D	stASIOBufferInfo
Playback
Volume	Volume, from ground (0) to full (100), of the playback of a wave audio		Double
Balance	Stereophonic balance, left (-100) to right (100), of the audio clip.	D,R	Int32
Start position	Defines the start position of the audio playback in percentages (0..100) to the total duration of the currently selected audio clip.	D,R	Double
Position	The current playing position (percentages, 0..100, to the total duration) of the audio. Changes are accepted only if the audio is playing at runtime.	D,R	Double
Runtime info
Start Time	If the playback triggering is on, indicates the actual event time when the last playback has started.	R, Read-Only	UInt64
End Time	If the playback triggering is on, indicates the actual event time when the last playback has reached its end.	R, Read-Only	UInt64
Is triggered	If the playback triggering is on, indicates that the element has been triggered at least once since the parent event is active.	R, Read-Only	Boolean

+=== Properties inherited from clLibraryElement ===

Name	Description	Constraints	Value Type	Upon Runtime Change
Material List
Selected Index	Defines the index of the active item in the material list of the element.		Int32	A change causes the current item to be reloaded and an update of the element.
Selected Item	Defines the name of the active item in the material list of the element. The name matches to a name of item in the Material Library		String	A change causes the current item to be reloaded and an update of the element.
Item Count	Returns the total number of items in the material list of the element.	Status..	Int32
Equalize RGB	The property is only available in the visual element. If the value is true, the average RGB pixel intensity will be equalized across all items in the material list. You can turn on this property, when you need to obtain a luminance-balanced set of visual stimulus.	Design Time..	Boolean

+=== Properties inherited from clElement === Inherited properties of clElement

Name	Description	Constraints	Value Type	Upon Change
Control
Is Enabled	If set to false the element is completely omitted when the experiment is run.	Design Time..	Boolean
Title	Title of the element.	Design Time..	String

The list of Text element properties:

Resource Holder inherited properties

CATEGORY ,Property name	Description	type	Value type
RESOURCE LIST
Resource index	The index of item in the resource list that is currently used by the element. Notice, that index starts from 1.	D,R,*	Int32
Resource count	The number of items loaded in the resource list of the element	D,R,Read-only	Int32