javax.microedition.amms.control.audio3d
Interface DopplerControl

All Superinterfaces:

javax.microedition.media.Control

public interface DopplerControl
extends javax.microedition.media.Control

DopplerControl is an interface for manipulating the settings of an effect called Doppler. It can be obtained either for the Spectator (in which case it specifies the listener's velocity) or a SoundSource3D (in which cases it specifies a sound source's velocity). The DopplerControl must be enabled before it has any effect.

Please see the section below on Synthesizing Doppler with PitchControl if DopplerControl is not supported.

Doppler

Doppler is the change in frequency perceived by a listener in the sound emitted from a sound source when the distance between them is rapidly increasing or decreasing. The frequency shift is defined by the following formula:

where:

• f_l is the frequency perceived by the listener,
• f_s is the frequency emitted by the source,
• c is the speed of sound (which must be expressed in the same units as the other speeds), about 330 or 340 m/s (meters per second),
• u_ls is the speed of the listener relative to the propagation medium in the direction from listener to sound source, and
• v_ls is the speed of the source relative to the propagation medium in the direction from listener to sound source.

NOTE: All of these quantities are scalar values (not vectors).

Illustration

The following diagram illustrates how v_ls changes during a simple scenario in which the listener is stationary (u_ls = 0) while a sound source (whose position relative to the listener at any point in time is denoted by the vector p) flies by at a constant velocity v:

• When the sound source is in position A, v_ls is negative; therefore the frequency of the source is increased.
• When the sound source is in position B, the position vector p is perpendicular to the source's velocity v, so v_ls is zero; therefore there is no Doppler pitch shift.
• When the sound source is in position C, v_ls is positive; therefore the frequency of the source is decreased.

Usage

The application need only specify the absolute velocity of the Spectator and each SoundSource3D via the setVelocityCartesian or setVelocitySpherical method of each of their DopplerControls. There is normally no need to calculate the Doppler frequency shift, because it is calculated automatically by the implementation when the DopplerControl is enabled.

The velocity specified using these methods is used for Doppler purposes only and does not actually move the object. This allows a decoupling between position and velocity information, which can be useful in variable frame rate applications or when the CPU resources are low, to allow the actual positions of the objects to "catch up" with their theoretically projected positions while preserving their theoretical velocity, giving a continuous frequency shift curve. This is also useful in server-controlled or peer-to-peer applications such as multi-player games where sometimes only limited information is available about the other objects in the system.

NOTE: Specifying speeds in excess of 50 m/s may give unexpected results, as implementations may use an approximation to the Doppler formula which gives inaccurate answers at these high velocities.

Default Values

The default values for the properties of all Doppler controls (whether the application has obtained them or not) are:

velocity = 0
enabled = false

DopplerControl from Spectator is an exception. It has

enabled = true

as a default.

Synthesizing Doppler with PitchControl

If the implementation does not support DopplerControl but does support javax.microedition.media.control.PitchControl for the content type being played, the application can use the following formula to manually calculate the Doppler pitch shift P_Doppler (in millisemitones) in a form suitable to pass as the argument to PitchControl.setPitch:

where:

• P_Doppler is the Doppler pitch shift in millisemitones (positive values raise the pitch),
• c is the speed of sound (which must be expressed in the same units as the other speeds), about 330 or 340 m/s (meters per second),
• u_ls is the speed of the listener relative to the propagation medium in the direction from listener to sound source, and
• v_ls is the speed of the source relative to the propagation medium in the direction from listener to sound source.

In this way, the Doppler effect can be approximated with the PitchControl.

The next section describes how u_ls and v_ls may be calculated.

Calculation of Velocities

Let p be the position of the sound source relative to the position of the listener, defined in terms of the source's position p_s and the listener's position p_l:

If u is the velocity of the listener in the medium, then u_ls (the speed of the listener in the direction from listener to sound source) can be calculated as follows:

Similarly, if v is the velocity of the sound source in the medium, then v_ls (the speed of the sound source in the direction from listener to sound source) can be calculated as follows:

See Also:

LocationControl, PitchControl

Method Summary

int[]	getVelocityCartesian() Returns the current velocity, used in calculations for the Doppler effect.
boolean	isEnabled() Returns whether this Doppler effect is currently active.
void	setEnabled(boolean dopplerEnabled) Specifies if this Doppler effect is active or ignored.
void	setVelocityCartesian(int x, int y, int z) Sets the velocity, used in calculations for the Doppler effect.
void	setVelocitySpherical(int azimuth, int elevation, int radius) Sets the velocity, used in calculations for the Doppler effect.

Method Detail

setEnabled

void setEnabled(boolean dopplerEnabled)

Specifies if this Doppler effect is active or ignored. If the DopplerControl was fetched from the Spectator, this method has no effect.

Parameters:

dopplerEnabled - a boolean specifying if this Doppler effect is to be applied

isEnabled

boolean isEnabled()

Returns whether this Doppler effect is currently active. If the DopplerControl was fetched from the Spectator, this method always returns true.

Returns:

true if Doppler is being applied

setVelocityCartesian

void setVelocityCartesian(int x,
                          int y,
                          int z)

Sets the velocity, used in calculations for the Doppler effect.

The velocity is specified using right-handed cartesian components in millimeters per second (mm/s).

Parameters:

x - the x component of the new velocity in mm/s

y - the y component of the new velocity in mm/s

z - the z component of the new velocity in mm/s

See Also:

setVelocitySpherical(int, int, int)

getVelocityCartesian

int[] getVelocityCartesian()

Returns the current velocity, used in calculations for the Doppler effect.

The velocity is specified using right-handed cartesian components in millimeters per second (mm/s).

Returns:

an int array containing the x, y and z components of the current velocity in mm/s

See Also:

setVelocityCartesian(int, int, int)

setVelocitySpherical

void setVelocitySpherical(int azimuth,
                          int elevation,
                          int radius)

Sets the velocity, used in calculations for the Doppler effect.

The velocity is specified using spherical components. The radius component is specified millimeters per second (mm/s).

Parameters:

azimuth - the azimuth angle of the new velocity in degrees. The azimuth is measured from the negative z-axis in the direction of the x-axis.

elevation - the elevation angle of the new velocity in degrees. The elevation is measured from the x-z-plane in the direction of the y-axis.

radius - the magnitude of the new velocity (namely the speed) in mm/s

See Also:

setVelocityCartesian(int, int, int)