audioChannelFormat - DirectSpeakers

Description

An audioChannelFormat represents a single sequence of audio samples on which some action may be performed, such as movement of an object, which is rendered in a scene. It contains one or more audioBlockFormats, which sub-divide it in the time domain.

The typeDefinition described here is for the 'DirectSpeakers' type, which is used for traditional channel-based audio. Many audioChannelFormat definitions with the 'DirectSpeakers' type are already defined in the Common Definitions, so they do not need to be defined explicitly when generating ADM metadata.

The other types of audioChannelFormats are:

Example

<audioChannelFormat audioChannelFormatID="AC_00010001"
                    audioChannelFormatName="FrontLeft"
                    typeLabel="0001" typeDefinition="DirectSpeakers">
  <audioBlockFormat audioBlockFormatID="AB_00010001_00000001">
    <speakerLabel>urn:itu:bs:2051:0:speaker:M+030</speakerLabel>
    <position coordinate="azimuth">30.0</position>
    <position coordinate="elevation">0.0</position>
    <position coordinate="distance">1.0</position>
  </audioBlockFormat>
</audioChannelFormat>

Attributes

The common audioChannelFormat attributes are used for the typeDefinition 'DirectSpeakers'.

Sub-elements

The common audioChannelFormat sub-elements are used for the typeDefinition 'DirectSpeakers'.

audioBlockFormat

In addition to the common audioBlockFormat attributes the following sub-elements are defined for the audioBlockFormat with typeDefinition 'DirectSpeakers'.

Sub-elements

Polar coordinates

Element	Attributes	Description	Units	Example	Quantity
speakerLabel		A reference to the label of the speaker position	–	M-30	0...*
position	coordinate=“azimuth”	Exact azimuth location of sound	Degrees	−30.0	1
position	coordinate=“azimuth” bound="max"	Max. azimuth location of sound	Degrees	−22.5	0 or 1
position	coordinate=“azimuth” bound="min"	Min. azimuth location of sound	Degrees	−30.0	0 or 1
position	coordinate=“elevation”	Exact elevation location of sound	Degrees	0.0	1
position	coordinate=“elevation” bound="max"	Max. elevation location of sound	Degrees	5.0	0 or 1
position	coordinate=“elevation” bound="min"	Min. elevation location of sound	Degrees	-5.0	0 or 1
position	coordinate=“distance”	Exact normalised distance from origin	Normalised to 1	1.0	0 or 1
position	coordinate=“distance” bound="max"	Max. normalised distance from origin	Normalised to 1	1.0	0 or 1
position	coordinate=“distance” bound="min"	Min. normalised distance from origin	Normalised to 1	0.8	0 or 1

The distance measure is normalised, as absolute speaker distances from the origin are rarely used, but an absolute reference distance is available in audioPackFormat.

Cartesian coordinates

The coordinates are usually based on the polar system, as this is the common way of describing channel and speaker locations. However it is also possible to use the Cartesian coordinate system by using different coordinate attributes (‘X’, ‘Y’ and ‘Z’).

Element	Attributes	Description	Units	Example	Quantity
speakerLabel		A reference to the label of the speaker position	–	M-30	0...*
position	coordinate=“X”	Exact X left to right location of sound	Normalised Units	-0.2	1
position	coordinate=“X” bound="max"	Max. X left to right location of sound	Normalised Units	-0.1	0 or 1
position	coordinate=“X” bound="min"	Min. X left to right location of sound	Normalised Units	-0.3	0 or 1
position	coordinate=“Y”	Exact Y front to back location of sound	Normalised Units	0.1	1
position	coordinate=“Y” bound="max"	Max. Y front to back location of sound	Normalised Units	0.2	0 or 1
position	coordinate=“Y” bound="min"	Min. Y front to back location of sound	Normalised Units	0.0	0 or 1
position	coordinate=“Z”	Exact Z top to bottom location of sound	Normalised Units	-0.5	1
position	coordinate=“Z” bound="max"	Max. Z top to bottom location of sound	Normalised Units	-0.4	0 or 1
position	coordinate=“Z” bound="min"	Min. Z top to bottom location of sound	Normalised Units	-0.6	0 or 1
position	screenEdgeLock	Defines a speaker position at a screen edge	left, right, top, bottom	left	0 … 2

screenEdgeLock attribute

The screenEdgeLock attribute allows a speaker to be positioned on the edge of the screen. The attribute can be used in combination with the coordinate=“elevation” and/or the coordinate=“azimuth” attribute and it is set to a string stating at which edge of the screen to the speaker position should be assumed to be (if screen-size information is available), so it is either “left”, “right”, “top”, “bottom”. The coordinate attribute must still be included so it is clear which dimension is being set, and to provide an alternative position should the screen not exist or no screen-size information be available.

The example XML code below illustrates how a speaker positioned on the right edge of the screen can be defined (with an alternative position of −29.0 degrees should the screen not exist).

<audioBlockFormat ...>
  <speakerLabel>M-SC</speakerLabel>
  <position coordinate="azimuth" screenEdgeLock=”right”>-29.0</position>
  <position coordinate="elevation">0.0</position>
  <position coordinate="distance">1.0</position>
</audioBlockFormat>

If two screenEdgeLock positions are required (for corners of the screen) then the two position ADM elements must be used as shown in the example below. This is because XML does not allow multiple attributes of the same name within the same element.

  <position coordinate="azimuth" screenEdgeLock=”right”>-29.0</position>
  <position coordinate="elevation" screenEdgeLock=”top”>15.0</position>