114 lines
4.8 KiB
ReStructuredText
114 lines
4.8 KiB
ReStructuredText
.. _doc_importing_audio_samples:
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Importing audio samples
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=======================
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Why importing?
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--------------
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Importing Audio Samples into the game engine is a process that should be
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easier than it really is. Most readers are probably thinking "Why not
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just copying the .wav files to a folder inside the project and be over
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with it?".
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It's not usually that simple. Most game engines use uncompressed audio
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(in memory at least) for sound effects. The reason for this is because
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it's really cheap to play back and resample. Compressed streamed audio
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(such as .ogg files) takes a large amount of processor to decode so no
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more than one or two are streamed simultaneously. However, with sound
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effects, one expects a dozen of them to be playing at the same time in
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several situations.
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Because of this, sound effects are loaded uncompressed into memory, and
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here is where the problems begin.
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As is usual with graphics, the situation where programmers don't really
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know about audio and audio engineers don't know about programming is
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also common in the industry. This leads to a scenario where a project
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ends up wasting resources unnecessarily.
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To be more precise, sfx artists tend to work with audio formats that
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give them a lot of room for tweaking the audio with a low noise floor
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minimum aliasing, such as 96khz, 24 bits. In many cases, they work in
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stereo too. Added to that, many times they add effects with an infinite
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or really long fadeout, such as reverb, which take a long time to fade
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out. Finally, many DAWs also add silence at the beginning when
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normalizing to wav.
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This results in extremely large files to integrate more often than
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desired, with sound effects taking dozens of megabytes.
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How much does quality matter?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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First of all, it is important to know that Godot has an internal reverb
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generator. Sound effects can go to four different setups (small, medium
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and large room as well as hall), with different send amounts. This saves
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sfx artists the need to add reverb to the sound effects, reducing their
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size greatly and ensuring correct trimming. Say no to SFX with baked
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reverb!
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.. image:: /img/reverb.png
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Another common problem is that, while it's useful for working inside a
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DAW, high dynamic range (24 bits) and high sampling rate (96khz) is
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completely unnecessary for use in a game, as there is no `audible
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difference <http://www.youtube.com/watch?v=cIQ9IXSUzuM>`__. If
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positional sound is going to be used (for 2D and 3D), the panning and
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stereo reverb will be provided by the engine, so there is little need
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for stereo sound. How does this affect the resource usage? Look at the
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following comparison:
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+---------------------------+---------------------+--------------+
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| Format | 1 Second of Audio | Frame Size |
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+===========================+=====================+==============+
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| 24 bits, 96 khz, Stereo | 576kb | 12 |
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+---------------------------+---------------------+--------------+
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| 16 bits, 44 khz, Mono | 88kb | 2 |
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+---------------------------+---------------------+--------------+
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| 16 bits, IMA-ADPCM | 22kb | 1/2 |
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+---------------------------+---------------------+--------------+
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As seen, for being no audible difference, the 16 bits, 44khz takes *6
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times less memory* than the 24 bits, 96khz, Stereo version. The
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IMA-ADPCM version takes *24 times less memory* than what was exported
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from the DAW.
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Trimming
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~~~~~~~~
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One last issue that happens often is that the waveform files received
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have silences at the beginning and at the end. These are inserted by
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DAWs when saving to a waveform, increase their size unnecessarily and
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add latency to the moment they are played back. Trimming them solves
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this, but it takes effort for the sfx artist, as they have to do it in a
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separate application. In the worst case, they may not even know the
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silences are being added.
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.. image:: /img/trim.png
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Importing audio samples
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-----------------------
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Godot has a simple screen for importing audio samples to the engine. SFX
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artists only have to save the .wav files to a folder outside the
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project, and the import dialog will fix the files for inclusion, as well
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as doing it automatically every time they are modified and re-imported.
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.. image:: /img/importaudio.png
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In this screen, the quality of the audio can be limited to what is
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needed, and trimming is done automatically. As a plus, several samples
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can be loaded and batch-converted, just like textures.
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Looping
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~~~~~~~
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Godot supports looping in the samples (Tools such as Sound Forge or
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Audition can add loop points to .wav files). This is useful for sound
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effects such as engines, machine guns, etc. Ping-pong looping is also
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supported.
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As an alternative, the import screen has a "loop" option that enables
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looping for the entire sample when importing.
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