godot-docs/tutorials/audio/audio_streams.rst

.. _doc_audio_streams:

Audio streams
=============

Introduction
------------

As you might have already read in :ref:`doc_audio_buses`, sound is sent to
each bus via an AudioStreamPlayer node. There are different kinds
of AudioStreamPlayers. Each one loads an AudioStream and plays it back.

AudioStream
-----------

An audio stream is an abstract object that emits sound. The sound can come from
many places, but is most commonly loaded from the filesystem. Audio files such
as WAV (``.wav``) or Ogg Vorbis (``.ogg``) can be loaded as AudioStreams and
placed inside an AudioStreamPlayer.

Here is a comparison of the two file types to help you choose the one that fits
your use case best:

- WAV files are quite large, but use little CPU power to play back.
  Hundreds of them can be played simultaneously with little impact
  on performance. This format is usually best for short sound effects.
- Ogg Vorbis files are much smaller, but use considerably more CPU power
  to play back, so only a few can be played back at once (especially on mobile).
  This format works well for music, long sound effect sequences, and voice
  at relatively low bitrates.

Keep in mind that while WAV files may contain looping information in their metadata,
Ogg Vorbis files do not. If looping an Ogg Vorbis file is desired, 
it must be set up using the import options:

.. image:: img/audio_stream_import.png

There are other types of AudioStreamPlayer, such as AudioStreamRandomPitch.
This one makes a random adjustment to the sound's pitch every time it's
played back. This can be helpful for adding variation to sounds that are
played back often.

AudioStreamPlayer
-----------------

This is the standard, non-positional stream player. It can play to any bus.
In 5.1 sound setups, it can send audio to stereo mix or front speakers.

AudioStreamPlayer2D
-------------------

This is a variant of AudioStreamPlayer, but emits sound in a 2D positional
environment. When close to the left of the screen, the panning will go left.
When close to the right side, it will go right.

.. note::

    Area2Ds can be used to divert sound from any AudioStreamPlayer2Ds they
    contain to specific buses. This makes it possible to create buses with
    different reverb or sound qualities to handle action happening in a
    particular parts of your game world.

.. image:: img/audio_stream_2d_area.png

AudioStreamPlayer3D
-------------------

This is a variant of AudioStreamPlayer, but emits sound in a 3D positional
environment. Depending on the location of the player relative to the screen,
it can position sound in stereo, 5.1 or 7.1 depending on the chosen audio setup.

Similar to AudioStreamPlayer2D, an Area can divert the sound to an audio bus.

.. image:: img/audio_stream_3d_area.png

Unlike for 2D, the 3D version of AudioStreamPlayer has a few more advanced options:

.. _doc_audio_streams_reverb_buses:

Reverb buses
~~~~~~~~~~~~

Godot allows for 3D audio streams that enter a specific Area node to send dry
and wet audio to separate buses. This is useful when you have several reverb
configurations for different types of rooms. This is done by enabling this type
of reverb in the **Reverb Bus** section of the Area's properties:

.. image:: img/audio_stream_reverb_bus.png

At the same time, a special bus layout is created where each area receives the
reverb info from each area. A Reverb effect needs to be created and configured
in each reverb bus to complete the setup for the desired effect:

.. image:: img/audio_stream_reverb_bus2.png

The Area's **Reverb Bus** section also has a parameter named **Uniformity**.
Some types of rooms bounce sounds more than others (like a warehouse), so
reverberation can be heard almost uniformly across the room even though the
source may be far away. Playing around with this parameter can simulate
that effect.

Doppler
~~~~~~~

When the relative velocity between an emitter and listener changes, this is
perceived as an increase or decrease in the pitch of the emitted sound.
Godot can track velocity changes in the AudioStreamPlayer3D and Camera nodes.
Both nodes have this property, which must be enabled manually:

.. image:: img/audio_stream_doppler.png

Enable it by setting it depending on how objects will be moved:
use **Idle** for objects moved using ``_process``, or **Physics**
for objects moved using ``_physics_process``. The tracking will
happen automatically.