Howto:Add sound effects to aircraft: Difference between revisions

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Howto:Add sound effects to aircraft (view source)

Revision as of 10:01, 20 June 2015

35 bytes removed ,  20 June 2015
rewriting here and there; +inclusion from aircraft-set.xml; links to related wiki articles, readme and source code; copyedit; etc
(Add Recommended audio formats)
(rewriting here and there; +inclusion from aircraft-set.xml; links to related wiki articles, readme and source code; copyedit; etc)
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Users Guide to FlightGear sound configuration
You can '''add sound effects to aircraft''' by adding the sound samples and configuring the sound effects in XML files.  The sound effects can be conditional and the sound's pitch and volume can depend on properties in the property tree. 


Version 0.9.9, December 15, 2014
Some sound effects are added other ways. For example are sounds from avionics like navigation radio receivers automatically added when you add those radios.


Author: Erik Hofman <erik at ehofman dot com>
== Sound configuration files ==
The sound configuration files are [[PropertyList XML files]].


Minor changes: [[User:Necolatis|Necolatis]] ([[User talk:Necolatis|talk]]) 03:41, 15 December 2014 (UTC)
The top level sound configuration file is composed of a <code>&lt;fx&gt;</code> and a <code>&lt;name&gt;</code> tag, a <code>&lt;path&gt;</code> to a sound sample file and zero or more <code>&lt;volume&gt;</code> and/or <code>&lt;pitch&gt;</code>definitions.
[[User:Chris_blues|chris_blues]] 12:00, 21 February 2015 (UTC)


This document is an attempt to describe the configuration of
Paths are relative to [[$FG_ROOT]], but absolute paths may also be used.
FlightGear flight simulator's aircraft sound in XML.


== Sound Architecture ==
Comments are bracketed with <code>&lt;!-- --&gt;</code>.
All of the sound configuration files are XML-encoded* property lists.
The root element of each file is always named <PropertyList>. Tags are
almost always found in pairs, with the closing tag having a slash
prefixing the tag name, i.e </PropertyList>. The exception is the tag
representing an aliased property. In this case a slash is prepended to
the closing angle bracket.  (see section Aliasing)


The top level sound configuration file is composed of a <fx>, a
=== Example ===
<name>, a <path> sound file and zero or more <volume> and/or <pitch>
This example would define an engine sound effect for a piston engine driven aeroplane.
definitions.


[ Paths are relative to $FG_ROOT (the root of the installed base package .) ]
The sound effect representing the engine is located in <code>$FG_ROOT/Sounds</code> and is named <code>wasp.wav</code>. The effect is started when the property <code>/engines/engine/running</code> becomes non-zero.  
[ Absolute paths may be used. Comments are bracketed with <!-- -->.         ]


A limited sound configuration file would look something like this:
When that happens, the sound will be played looped (see <code>&lt;mode&gt;</code>) until the property returns zero again. As you can see the volume is dependent on the property <code>/engines/engine/mp-osi</code>, and the pitch of the sound depends on the property <code>/engines/engine/rpm</code>.


<source>
<syntaxhighlight lang="xml">
<?xml version="1.0" encoding="UTF-8"?>
<PropertyList>
<PropertyList>
  <fx>
  <fx>
Line 55: Line 47:
  </fx>
  </fx>
</PropertyList>
</PropertyList>
</source>
</syntaxhighlight>


This would define an engine sound event handler for a piston engine driven
=== Inclusion from the aircraft-set.xml file ===
aeroplane. The sound representing the engine is located in $FG_ROOT/Sounds
In order for the sound configuration to be used it has to be included from the [[aircraft-set.xml]] file.
and is named wasp.wav. The event is started when the property
/engines/engine/running becomes non zero.  


When that happens, the sound will be played looped (see <mode>) until the
This can be done by adding the path to the file relative to the aircrafts base path within the <code>&lt;sim&gt;</code> tags.
property returns zero again. As you can see the volume is mp-osi dependent,
and the pitch of the sound depends on the engine rpm.


== Configuration description ==
<syntaxhighlight lang="xml">
<?xml version="1.0" encoding="UTF-8"?>
<PropertyList>
<!-- ... --->
<sim>
  <!-- ... --->
  <sound>
    <path type="string">My-sound-config.xml</path>
  </sound>
  <!-- ... --->
</sim>
<!-- ... --->
</PropertyList>
</syntaxhighlight>
 
== Configuration tags ==
    
    
<source><fx>
; <code>&lt;fx&gt;</code>
        Named FX subtree living under /sim/sound
: Named FX subtree living under /sim/sound
</source>
 
<source> < ... >
; <code>&lt; ... &gt;</code>
        This is the event separator. The text inside the brackets
: This is the event separator. The text inside the brackets can be anything, but it is advised to give it a meaningful name like: crank, engine, rumble, gear, squeal, flap, wind or stall.
        can be anything. Bit it is advised to give it a meaningful name
        like: crank, engine, rumble, gear, squeal, flap, wind or stall
   
   
        The value can be defined multiple times, thus anything which is
: The value can be defined multiple times, thus anything which is related may have the same name (grouping them together).
        related may have the same name (grouping them together).
 
</source>
; <code>&lt;name&gt;</code>
<source>   <name>
: This defines the name of the event. This name is used internally and, although it can me defined multiple times in the same file, should normally have an unique value.
        This defines the name of the event. This name is used internally
        and, although it can me defined multiple times in the same file,
        should normally have an unique value.
   
   
        Multiple definitions of the same name will allow multiple sections
: Multiple definitions of the same name will allow multiple sections to interfere in the starting and stopping of the sample.
        to interfere in the starting and stopping of the sample.
 
: This method can't be used to control the pitch or volume of the sample, but instead multiple volume or pitch section should be included inside the same event.
 
: The types "raise" and "fall" will stop the playback of the sample regardless of any other event. This means that when the type "raise" is supplied, sample playback will stop when the event turns false. Using the type "fall" will stop playback when the event turns true.


        This method can't be used to control the pitch or volume of the  
: IMPORTANT
        sample, but instead multiple volume or pitch section should be
:: If the trigger is used for anything else but stopping the sound at a certain event, all sections with the same name ''should'' have exactly the same sections for everything but property and type.
        included inside the same event.


        The types "raise" and "fall" will stop the playback of the sample
:: In the case of just stopping the sample at a certain event, the sections for path, volume and pitch may be omitted.
        regardless of any other event. This means that when the type "raise"
        is supplied, sample playback will stop when the event turns false.
        Using the type "fall" will stop playback when the event turns true.


        IMPORTANT:
; <code>&lt;path&gt;</code>
        If the trigger is used for anything else but stopping the sound
: This defined the path to the sound file. The path is relative to the FlightGear root directory but could be specified absolute.
        at a certain event, all sections with the same name *should* have
        exactly the same sections for everything but property and type.


        In the case of just stopping the sample at a certain event, the
: The sound format must be mono.
        sections for path, volume and pitch may be omitted.
 
</source>
; <code>&lt;condition&gt;</code>
<source>    <path>
: Define a condition that triggers the event.
        This defined the path to the sound file. The path is relative to the
 
        FlightGear root directory but could be specified absolute.
: For a complete description of the FlightGear conditions, please read docs-mini/README.conditions
        The sound format must be mono.
 
</source>
: An event should define either a condition or a property.
<source>   <condition>
 
        Define a condition that triggers the event.
; <code>&lt;property&gt;</code>
        For a complete description of the FlightGear conditions,
: Define which property triggers the event, and refers to a node in the FlightGear property tree.
        please read docs-mini/README.conditions
 
: Action is taken when the property is non zero.


        An event should define either a condition or a property.
: A more sophisticated mechanism to trigger the event is described in <condition&gt;</code>
</source>
<source>    <property>
        Define which property triggers the event, and refers to a node
        in the FlightGear property tree. Action is taken when the property
        is non zero.


        A more sophisticated mechanism to trigger the event is described
; <code>&lt;mode&gt;</code>
        in <condition>
: This defines how the sample should be played:
</source>
<source>    <mode>
        This defines how the sample should be played:
   
   
        once:           the sample is played once.
:; once
                        this is the default.
:: The sample is played once. This is the default.
   
   
        looped:         the sample plays continuously,
:; looped
                        until the event turns false.
:: The sample plays continuously, until the event turns false.
 
:; in-transit
:: the sample plays continuously, while the property is changing its value.
 
; <code>&lt;type&gt;</code>
: This defines the type os this sample:
 
:; fx
:: This is the default type and doesn't need to be defined.
 
:; avionics
:: Sounds set to this time don't have a position and orientation but are treated as if it's mounted to the aircraft panel.
 
:: It is up to the user to define if it can always be heard or only when in cockpit view.
 
; <code>&lt;volume&gt;</code> / <code>&lt;pitch&gt;</code>
: Volume or Pitch definition.
 
: Currently there may be up to 5 volume and up to 5 pitch definitions defined within one sound event.
 
: Normally all offset values are added together and the results after property calculations will be multiplied.
 
: A special condition occurs when the value of factor is negative, in which case the offset doesn't get added to the other offset values but instead will be used in the multiplication section.
 
; <code>&lt;property&gt;</code>
: Defines which property supplies the value for the calculation.


        in-transit:     the sample plays continuously,
: Either a <property> or an <internal> should be defined.
                        while the property is changing its value.
</source>  
<source>   <type>
        This defines the type os this sample:


        fx:             this is the default type and doesn't need to be defined.
: The value is treated as a floating point number.


        avionics:      sounds set to this time don't have a position and
; <code>&lt;internal&gt;</code>
                        orientation but are treated as if it's mounted to
: Defines which internal variable should be used for the calculation.
                        the aircraft panel. it's up to the user to define
                        if it can always be heard or only when in cockpit
                        view.
</source>
<source>    <volume> / <pitch>
        Volume or Pitch definition. Currently there may be up to 5
        volume and up to 5 pitch definitions defined within one sound
        event. Normally all offset values are added together and the
        results after property calculations will be multiplied.
        A special condition occurs when the value of factor is negative,
        in which case the offset doesn't get added to the other offset values
        but instead will be used in the multiplication section.
</source>
<source>      <property>
        Defines which property supplies the value for the calculation.
        Either a <property> or an <internal> should be defined.
        The value is treated as a floating point number.
</source>  
<source>      <internal>
        Defines which internal variable should be used for the calculation.
        The value is treated as a floating point number.
        The following internals are available at this time:


        dt_play:       the number of seconds since the sound started playing.
: The value is treated as a floating point number.


        dt_stop:       the number of seconds after the sound has stopped.
: The following internals are available at this time:
</source>
<source>      <delay-sec>
        Delay after which the sound starts playing. This is useful to let
        a property start two sounds at the same time, where the second is
        delayed until the first stopped playing.
</source>
<source>      <type>
        Defines the function that should be used upon the property
        before it is used for calculating the net result:


        lin:           linear handling of the property value.
:; dt_play
                        this is the default.
:: The number of seconds since the sound started playing.
 
:; dt_stop
:: The number of seconds after the sound has stopped.
 
; <code>&lt;delay-sec&gt;</code>
: Delay after which the sound starts playing.
 
: This is useful to let a property start two sounds at the same time, where the second is delayed until the first stopped playing.
 
; <code>&lt;type&gt;</code>
: Defines the function that should be used upon the property before it is used for calculating the net result:
 
:; lin
:: Linear handling of the property value. This is the default.
   
   
        ln:             convert the property value to a natural logarithmic
:; ln
                        value before scaling it. Anything below 1 will return
:: Convert the property value to a natural logarithmic value before scaling it.
                        zero.
 
:: Anything below 1 will return zero.
   
   
        log:           convert the property value to a true logarithmic
:; log
                        value before scaling it. Anything below 1 will return
:: convert the property value to a true logarithmic value before scaling it.
                        zero.
 
:: Anything below 1 will return zero.
 
:; inv
:: Inverse linear handling (1/x).
 
:; abs
:: Absolute handling of the value (always positive).
 
:; sqrt
:: Calculate the square root of the absolute value before scaling it.
 
; <code>&lt;factor&gt;</code>
: Defines the multiplication factor for the property value.
 
: A special condition is when scale is defined as a negative value. In this case the result of |<scale>| * <property) will be subtracted from &lt;default&gt;
 
; <code>&lt;offset&gt;</code>
: The initial value for this sound.
 
: This value is also used as an offset value for calculating the end result.
 
; <code>&lt;min&gt;</code>
: Minimum allowed value.
 
: This is useful if sounds start to sound funny. Anything lower will be truncated to this value.
 
; <code>&lt;max&gt;</code>
: Maximum allowed value.
 
: This is useful if sounds gets to loud. Anything higher will be truncated to this value.
 
; <code>&lt;position&gt;</code>
: Specify the position of the sounds source relative to the aircraft center.
 
: The coordinate system used is a left hand coordinate system where +Y = left, -Y = right, -Z = down, +Z = up, -X = forward, +X = aft.  Distances are in meters.
 
: The volume calculation due to distance and orientation of the sounds source ONLY work on mono samples!
 
: Also take notice that the values should not be 0.0, since that can produce sound artifacts on some sound cards.
 
; <code>&lt;x&gt;</code>
: X dimension offset
 
; <code>&lt;y&gt;</code>
: Y dimension offset
 
; <code>&lt;z&gt;</code>
: Z dimension offset
 
; <code>&lt;orientation&gt;</code>
: Specify the orientation of the sounds source.
 
: The zero vector is default, indicating that a Source is not directional.
 
: Specifying a non-zero vector will make the Source directional in the X,Y,Z direction
 
; <code>&lt;x&gt;</code>
: X dimension
 
; <code>&lt;y&gt;</code>
: Y dimension
 
; <code>&lt;z&gt;</code>
: Z dimension
 
; <code>&lt;inner-angle&gt;</code>
: The inner edge of the audio cone in degrees (0.0 - 180.0).
 
: Any sound withing that angle will be played at the current gain.
 
; <code>&lt;outer-angle&gt;</code>
: The outer edge of the audio cone in degrees (0.0 - 180.0).
 
: Any sound beyond the outer cone will be played at "outer-gain" volume.
 
; <code>&lt;outer-gain&gt;</code>
: The gain at the outer edge of the cone.


        inv:           inverse linear handling (1/x).
; <code>&lt;reference-dist&gt;</code>
: Set a reference distance of sound in meters. This is the distance where the volume is at its maximum.


        abs:           absolute handling of the value (always positive).
: Volume is clamped to this maximum for any distance below.


        sqrt:           calculate the square root of the absolute value
: Volume is attenuated for any distance above.
                        before scaling it.
</source>
<source>      <factor>
        Defines the multiplication factor for the property value.
        A special condition is when scale is defined as a negative
        value. In this case the result of |<scale>| * <property) will be
        subtracted from <default>
</source>
<source>      <offset>
        The initial value for this sound. This value is also used as an
        offset value for calculating the end result.
</source>
<source>      <min>
        Minimum allowed value.
        This is useful if sounds start to sound funny. Anything lower
        will be truncated to this value.
</source>
<source>      <max>
        Maximum allowed value.
        This is useful if sounds gets to loud. Anything higher will be
        truncated to this value.
</source>
<source>    <position>
        Specify the position of the sounds source relative to the
        aircraft center.  The coordinate system used is a left hand
        coordinate system where +Y = left, -Y = right, -Z = down, +Z =
        up, -X = forward, +X = aft.  Distances are in meters.
        The volume calculation due to distance and orientation of the
        sounds source ONLY work on mono samples!
        Also take notice that the values should not be 0.0, since that can produce
        sound artifacts on some sound cards.
</source>
<source>      <x>
        X dimension offset
</source>
<source>      <y>
        Y dimension offset
</source>
<source>      <z>
        Z dimension offset


</source>
: Attenuation depends on reference and maximum distance. See OpenAL specification on "AL_INVERSE_DISTANCE_CLAMPED" mode for details on exact computation.
<source>    <orientation>
        Specify the orientation of the sounds source.


        The zero vector is default, indicating that a Source is not directional.
; <code>&lt;max-dist&gt;</code>
        Specifying a non-zero vector will make the Source directional in
: Set the maximum audible distance for the sound in meters.
        the X,Y,Z direction
</source>  
<source>      <x>
        X dimension
</source>  
<source>      <y>
        Y dimension
</source>
<source>      <z>
        Z dimension
</source>
<source>      <inner-angle>
        The inner edge of the audio cone in degrees (0.0 - 180.0).
        Any sound withing that angle will be played at the current gain.
</source>
<source>      <outer-angle>
        The outer edge of the audio cone in degrees (0.0 - 180.0).
        Any sound beyond the outer cone will be played at "outer-gain" volume.
</source>
<source>      <outer-gain>
        The gain at the outer edge of the cone.


</source>
: Sound is cut-off above this distance.
<source>    <reference-dist>
        Set a reference distance of sound in meters. This is the
        distance where the volume is at its maximum.
        Volume is clamped to this maximum for any distance below.
        Volume is attenuated for any distance above.
        Attenuation depends on reference and maximum distance. See
        OpenAL specification on "AL_INVERSE_DISTANCE_CLAMPED" mode
        for details on exact computation.
</source>
<source>    <max-dist>
        Set the maximum audible distance for the sound in meters.
        Sound is cut-off above this distance.
</source>


== Creating a configuration file ==
== Creating a configuration file ==
Line 315: Line 311:
</source>
</source>
where function can be one of: lin, ln, log, inv, abs or sqrt
where function can be one of: lin, ln, log, inv, abs or sqrt
== Multiplayer sound ==
The multiplayer sound file works just as the normal sound file, except it should reside in <code>/sim/model/sound</code> instead of <code>/sim/sound</code>. Make sure it depends on properties that are [[Howto:Transmit_properties_over_MP|transmitted over MP]].
== Recommended audio file formats ==
{{note|The sound sample '''must be in mono''' format.  This is because it can not be put in a 3D context otherwise. Also, as of at least June 2015 '''stereo samples will not be played'''.}}
There some considerations on the quality to the audio files. As a rule of thumb, any computer is able to playback sounds in DVD-quality (48 kHz/24 bits).
Macs still has trouble reading 32 bit files. Most standard sound cards also can't playback 32 bit files.
From a listeners point of view, anything above 44.1 kHz and 24 bits is only useful for high end music. Personally, I would think that 44.1 kHz with 16 bits should be more than enough to play engine sounds and alarms from the cockpit. Consider the disk-space against the gain in audio quality!


== Preventing sounds from playing when sim starts ==
== Preventing sounds from playing when sim starts ==
Line 323: Line 330:
* None of the position coordinates must not be 0.0 as described above.
* None of the position coordinates must not be 0.0 as described above.


== Multiplay sound ==
== Related content ==
The multiplay sound file works just as the normal sound file, except it should recide in /sim/model/sound instead of /sim/sound. Make sure it depends on properties that are [[Howto:Transmit_properties_over_MP|transmitted over MP]].
=== Wiki articles ===
 
* [[Conditions]]
== Recommended audio file formats ==
* [[Expressions]]
There some considerations on the quality to the audio files. As a rule of thumb, any computer is able to playback sounds in DVD-quality (48kHz/24bits).
* [[Howto:Reload sound config without restarting FG]]
Mac still has trouble reading 32bit files. Most standard soundcards also can't playback 32bit files.


From a listeners point of view, anything above 44.1kHz and 24bits is onyl useful for high end music. Personally, I would think that 44.1kHz with 16bits should be more than enough to play engine sounds and alarms from the cockpit. Consider the disk-space against the gain in audio quality!
=== Readme file ===
* {{readme file|xmlsound}}


And don't forget: In order to put the sound in a 3d context it needs to be mono!
=== Source code ===
* {{repo link
| site  = sf
| proj  = flightgear/flightgear
| path  = src/Sound/fg_fx.hxx
| text  = flightgear/src/Sound/fg_fx.hxx
}}
* {{repo link
| site  = sf
| proj  = flightgear/flightgear
| path  = src/Sound/fg_fx.cxx
| text  = flightgear/src/Sound/fg_fx.cxx
}}


[[Category:Aircraft enhancement]]
[[Category:Aircraft enhancement]]
Retrieved from "https://wiki.flightgear.org/Special:MobileDiff/85679"

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