|The Twelfth Annual Interactive
PROJECT BAR-B-Q 2007
Group Report: Game Producer’s Guide to Audio
|Participants: A.K.A "Audio Four Dummies (+1)"|
Scott Snyder, Edge of Reality
|Chris Grigg, Beatnik|
|Simon Ashby, AudioKinetic||Jim Rippie Invisible, Industries|
|Facilitator: Linda Law, The Fat Man|
There is a serious problem today with game audio and it is NOT production quality.
Most designers and producers do not understand the extent to which audio can be used to enhance their product quality, partially because they do not have a game audio language or style book that they can use when designing their games. This results in games that do not have audio integrated into their game design, engine design, budget, or production plan/milestones. Because such audio is only an overlay and not an integral aspect of gameplay, overall game quality suffers.
This workgroup wanted to articulate game audio concepts and guidelines for the development process that game designers should use in early stages of product development in order to fully integrate music and sound into the creative design and project plan for the game.
Game Development Process Audio Guidelines:
Get the audio team on board as early as possible and keep them on board. This section looks at each phase of game development, starting with conception all the way through graduation from college, and recommends appropriate audio action items for each stage.
These are the building blocks of game audio. Your game will use some or all of the following as determined by the nature of the design, the resources available, and the audio team’s plan.
audio engine: A software layer that manages audio playback via inputs such as audio files, playback parameters/variables and playback scripts.
channel: Typically refers to the available number of simultaneous sound or instrument tracks. For example, old 8-bit games often had 3-channel sound, which meant three simultaneous tonal sounds or voices could be used (they also often had a fourth noise channel). Today hundreds of simultaneous channels are available in most game consoles, although many portable game players remain very limited in the number of channels.
compression: 1. Also known as dynamic range compression or DRC, is a process whereby the dynamic range of an audio signal is reduced. Limiting is a type of compression with a higher ratio of reduction. 2. File size reduction, as in MP3. A loss of audio fidelity usually results.
DSP: Digital Signal Processing/Processor: refers to the processing of a signal (sound) digitally, including using filters and effects.
environmental reverb (I3DL2): Audio processing that conveys a sense of the space where the listener is located. I3DL2 is a guidelines document published by the Interactive Audio Special Interest Group that defines requirements for minimum system features and functions needed for an audio renderer providing, among other things, environmental reverb capability.
sound event: A sound event is not an audio file. A sound event contains all the information needed to appropriately play back an audio file or combination of audio files. See cue.
falloff: In the real world, a given sound from a given sound source is perceived as louder when it's closer to the listener, and quieter when it's farther away. Eventually it's too far away to be heard at all. In game audio, 'falloff' is the manner in which loudness decreases with distance, usually described as a distance vs. attenuation curve. See also min/max distance.
format: A sound file format. Examples are .WAV, .MP3, .OGG, and .MID.
hook: A call in code (a stub) that initiates a cue/sound event.
listener: The point in the world where the sound is heard.
loop: The playback of an audio file, or series of audio files, repetitively such that when the end point is reached, playback continues immediately from the beginning until a command is issued to stop the loop. An audio file that is intended to be used in this manner is sometimes referred to as a loop. Often a looped sound will sound unnatural when it stops unless the stopping event also triggers a release sound or fades before it stops.
MIDI: MIDI is a technology that represents music in digital form, but it is not like other digital music technologies such as MP3 and CDs. A MIDI file is not a digitized sound file, it is a message file. The messages contain individual instructions for playing each individual note of each individual instrument. MIDI encodes musical functions, which includes the start of a note, its pitch, length, volume and musical attributes, such as vibrato.
min/max distance (as it applies to falloff): When a listener is within the minimum distance of a sound source, it is heard at full volume and the volume is not automatically adjusted for distance. Between the min distance and the max distance, the falloff curve is used to automatically adjust the volume for distance. When the distance between a listener and a sound source is greater than the maximum distance, it is not heard at all (fully attenuated).
mix: verb To combine individual sound elements in an appropriate way by controlling their volume, panning, reverb, EQ, and other effects. noun The resulting audio playback experience.
Nyquist Frequency: The highest frequency that can be represented in a digital signal of a specified sampling frequency. It is equal to one-half of the sampling rate. For example, audio CDs have a sampling frequency of 44100 Hz. The Nyquist frequency is therefore 22050 Hz, which is an upper bound on the highest frequency the data can unambiguously represent. To avoid aliasing, the Nyquist frequency must be strictly greater than the maximum frequency component within the signal.
occlusion: Muffling a sound because an object comes between the sound source and the listener. Amount and character of the muffling can depend on the material properties of the blocking object, and on how completely the sound is blocked (i.e. less blocked when the source is behind an edge of the blocking object, vs. more blocked when behind its center).
Redbook audio: The standard audio for CD’s. It is a 16-bit, 44.1k stereo uncompressed format.
release sound: A transition sound to provide a graceful exit from a loop. Examples: A bell and a ricochet have long releases. A short piano note has a short mechanical sounding release as the hammer comes back in contact with the strings.
sample: 1. A measurement of amplitude. A sample contains the information of the amplitude value of a waveform measured over a period of time. 2. A collection of sound files and definitions that are used to make up a single virtual instrument (i.e. violin).
sample rate (also known as sample frequency): The number of times the original sound is sampled (measured) per second. A CD quality sample rate of 44.1 KHz means that 44100 samples per second were recorded. If the sample rate is too low, a distortion known as aliasing will occur, and will be audible when the sample is converted back to analogue by a digital to analogue converter. Analogue to digital converters will typically have an anti-aliasing filter which removes harmonics above the highest frequency that the sample rate can accommodate.
script: A simple text file created by the audio artist, for the purpose of controlling the behavior (including adaptive response) of a cue/sound event.
stem: A mix that does not contain a complete set of the audio elements but does have appropriate volume, reverb, pan, etc. applied to the elements that it does have. For example, a .WAV file that contains only mixed drums.
streaming: A technique for transferring data such that it can be processed as a steady and continuous stream. For example, in online applications with streaming, the client browser or plug-in can start playing the data before the entire file has been transmitted. For streaming to work, the client side receiving the data must be able to collect the data and send it as a steady stream to the application that is processing the data and converting it to sound or pictures. This means that if the streaming client receives the data more quickly than required, it needs to save the excess data in a buffer. If the data doesn't come quickly enough, however, the presentation of the data will not be smooth.
track: Depending on the media type, an audio file may have multiple, individually selectable or controllable tracks intended to play in parallel. For example, an audio file or file image may have multiple channels, each of which may be individually muted, faded, or processed with DSP.
trigger: An event that signals the beginning of a sound or series of sounds
voice: In referring to digital audio, voice is used to describe an instrument or other type of sound, rather than specifically a vocal part. A music keyboard, for instance, may be pre-programmed with 64 voices, or instrument sounds, which will include (typically) piano, strings, guitar voices, and so on. Someone speaking is called VO (voice over) not voice.
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