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Monday, May 16, 2005
OpenAL Basics:
The OpenAL has three fundamental primitives or objects: Buffers, Sources, and a single Listener. Each object can be changed independently, the setting of one object does not affect the setting of others.
Listener AND Source Attributes:
POSITION specifes the current location of the Object in the world coordinate system.
VELOCITY specifies the current velocity (speed and direction) of the
Object, in the world coordinate system.
GAIN denotes a scalar amplitude multiplier. As a Source attribute, it applies to that particular source only. As a Listener attribute, it effectively applies to all Sources in the current Context. The default 1.0 means that the sound is un-attenuated. A GAIN value of 0.5 is equivalent to an attenuation of 6 dB. The value zero equals silence (no output).
Source Attributes:
SOURCE_RELATIVE set to TRUE indicates that the values specifed by POSITION are to be interpreted relative to the listener position.
LOOPING is a flag that indicates that the Source will not be in STOPPED state once it reaches the end of last buffer in the buffer queue.
MIN_GAIN is a scalar amplitude threshold. It indicates the minimal GAIN which is always guaranteed for this Source.
MAX_GAIN denotes a scalar amplitude threshold. It indicates the maximal GAIN permitted for this Source.
REFERENCE_DISTANCE This is used for distance attenuation calculations based on inverse distance with roll off.
ROLLOFF_FACTOR This is used for distance attenuation calculations based on inverse distance with roll off. For distances smaller than MAX_DISTANCE (and, depending on the distance model, larger than REFERENCE_DISTANCE), this will scale the distance attenuation over the applicable range.
MAX_DISTANCE This is used for distance attenuation calculations based on inverse distance with roll off, if the Inverse Clamped Distance Model is used.
PITCH Desired pitch shift, where 1.0 equals identity. Each reduction by 50 percent equals a pitch shift of -12 semitones (one octave reduction). Zero is not a legal value.
Direction and Cone:
Each Source can be directional, depending on the settings for CONE_INNER_ANGLE and CONE_OUTER_ANGLE.
There are three zones denoted: the inner cone, the outside zone, and the transitional zone in between.
The angle-dependent gain for a directional source is constant inside the inner cone, and changes over the transitional zone to the value specified outside the outer cone.
Source GAIN is applied for the inner cone, with an application selectable
CONE_OUTER_GAIN factor to de ne the gain in the outer zone. In the transitional zone implementation-dependent interpolation between GAIN and GAIN TIME.
CONE_OUTER_GAIN is applied.
The OpenAL has three fundamental primitives or objects: Buffers, Sources, and a single Listener. Each object can be changed independently, the setting of one object does not affect the setting of others.
Listener AND Source Attributes:
POSITION specifes the current location of the Object in the world coordinate system.
VELOCITY specifies the current velocity (speed and direction) of the
Object, in the world coordinate system.
GAIN denotes a scalar amplitude multiplier. As a Source attribute, it applies to that particular source only. As a Listener attribute, it effectively applies to all Sources in the current Context. The default 1.0 means that the sound is un-attenuated. A GAIN value of 0.5 is equivalent to an attenuation of 6 dB. The value zero equals silence (no output).
Source Attributes:
SOURCE_RELATIVE set to TRUE indicates that the values specifed by POSITION are to be interpreted relative to the listener position.
LOOPING is a flag that indicates that the Source will not be in STOPPED state once it reaches the end of last buffer in the buffer queue.
MIN_GAIN is a scalar amplitude threshold. It indicates the minimal GAIN which is always guaranteed for this Source.
MAX_GAIN denotes a scalar amplitude threshold. It indicates the maximal GAIN permitted for this Source.
REFERENCE_DISTANCE This is used for distance attenuation calculations based on inverse distance with roll off.
ROLLOFF_FACTOR This is used for distance attenuation calculations based on inverse distance with roll off. For distances smaller than MAX_DISTANCE (and, depending on the distance model, larger than REFERENCE_DISTANCE), this will scale the distance attenuation over the applicable range.
MAX_DISTANCE This is used for distance attenuation calculations based on inverse distance with roll off, if the Inverse Clamped Distance Model is used.
PITCH Desired pitch shift, where 1.0 equals identity. Each reduction by 50 percent equals a pitch shift of -12 semitones (one octave reduction). Zero is not a legal value.
Direction and Cone:
Each Source can be directional, depending on the settings for CONE_INNER_ANGLE and CONE_OUTER_ANGLE.
There are three zones denoted: the inner cone, the outside zone, and the transitional zone in between.
The angle-dependent gain for a directional source is constant inside the inner cone, and changes over the transitional zone to the value specified outside the outer cone.
Source GAIN is applied for the inner cone, with an application selectable
CONE_OUTER_GAIN factor to de ne the gain in the outer zone. In the transitional zone implementation-dependent interpolation between GAIN and GAIN TIME.
CONE_OUTER_GAIN is applied.
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