Game Audio

Mark PeskirNovember 14, 2005

ITCS 5010

Overview

• Terms/Fundamentals• Computers and Sound• Parameters, Filters, Effects• Types of Sound Production• Planning For Game Audio

DefinitionsSound: compression waves

transmitted through a mediumWave: cycle of compression and

rarefactionAmplitude: measure of sound wave

pressure

Coming soon: cool stuffComing soon: cool stuff

DefinitionsFrequency: speed of wave oscillation

Measured in Hertz (Hz)Pitch: a particular constant frequencyHertz (Hz): number of oscillations per

seconddecibels (dB): measure of the degree

of amplitudeNote: a predefined pitch used in music

Common Frequency Ranges

Human Hearing: 20Hz – 20kHzHuman Voice: 90 – 300 HzMiddle C: 261 Hz

Digital SoundA “unit” of digital sound is called a

sampleThe sampling rate is the number of

samples taken per secondBit depth: size of sound sample data

See Figure 5.5.2, pg 598

Nyquist LimitA sampling rate can only accurately

record sounds of frequencies at half its value

48 kHz sampling rate: can record a 24 kHz max frequency

That’s really high, so who cares?!That’s really high, so who cares?!

Common Sampling Rates“CD Audio” quality: 16 bit, 44.1 kIP Voice Chat (BattleCom, TeamSpeak):8 – 16 bit, 16k – 24k sample rateBurger King drive-thru: ???High-End sound cards support: 24/96, 24/192The Tradeoff: Performance vs. QualityThe Tradeoff: Performance vs. Quality

Flow of Tone Production• Tone is generated• Amplitude (volume)

set• Filters, effects, etc.

added• Sound is mixed with

other sounds• Sound signal sent to

speakers

Sound FormatsSample: short recording of live sound,

with frequency adjusted to produce other pitches/notes

Streaming Audio: a full soundtrack or complete sound effect, loaded into a buffer and played while the rest of sound loads

MechWarrior 2: used hybrid CD for MechWarrior 2: used hybrid CD for music!music!

Audio Compression• The Goal: reduce the amount of

data needed to produce quality sound (like JPEG images)

Two methods:• Bit reduction: reduce bit depth• Psychoacoustic Compression:

discard audio not generally heard (MP3)

ADSR EnvelopeAttack, Decay, Sustain, ReleaseCould define a variety of sound aspects(pitch, volume, rate of repetition)What would the envelopes look like for:What would the envelopes look like for:• Revving a car engineRevving a car engine• Cymbal crashCymbal crash• John Williams choirJohn Williams choir

Other Sound ParametersPan: the “left/right” location of the soundVolume: ratio of amplitude playedPitch/Frequency: can be assigned to

override a sound’s actual pitch3DGS:sound mySound = <gosh.wav>;snd_tune(mySound, 50, 100, -100);play mySound at 50% vol, 100% freq, leftplay mySound at 50% vol, 100% freq, left

Pass FiltersLow Pass Filter: only allow sounds

below a certain frequencyHigh Pass Filter: only allow sounds

above a certain frequencyBand Pass Filter: only allow sounds

in a given frequency rangeused for cutting “highs” and/or

“lows”

3D Sound MethodsHead Relative Transfer Function (HRTF)• used in stereo speaker config• dynamically changes balance for L/R• reduces high frequencies if behindToday: Dolby Surround Sound – 5.1, 6.1, 7.2!

Environmental EffectsEcho: early reflectionsReverberation (reverb): late reflectionsDiffusion: the “breaking up” of a sound

reflecting off of a rough surface (carpet)Obstruction: the blocking of a sound’s

direct path to the earOcclusion: high freqs being blocked by a

material, while low freqs pass through(car bass with windows up, underwater)

Environmental EffectsTwo current standards:• I3DL2: established by the Interactive

Audio Special Interest Group (IASIG)• EAX: created by Creative Labs for

SoundBlaster audio cards – multiple versions exist (1.0, 2.0, 3.0)

Difference in sound: ???Difference in sound: ???

Half Life 2: Soundscape DSP

Audio SystemsMIDI: Musical Instrument Digital Interface• file contains sound “instructions”• metaphor: sheet music for a computer• uses preloaded sound banksDigital Audio: actual recording• generally much better sound quality• more “real”• downside: much bigger file sizes

Audio SystemsMIDI:

Digital Audio:

Advanced Audio Programming

• Programmers should not have to Programmers should not have to deal with audio!deal with audio!

• Audio scripts handle production of sound (HL2 DSP presets)

• Common problems: sound variation, repetition, looping, ambience

Advanced Music Programming

• HALO 2: Quantum Audio – music has starts, ends, middles, transitions

• Interactive Music: “musical boxcars”

Voice InteractionPhoneme: individual voice soundLip Synching: matching phonemes to

mouth animationVoice Playback: generating words

using phonemesVoice Recognition: decoding voice

input to understood text of some kind

Dragon Naturally SpeakingDragon Naturally Speaking

Half Life 2: Phoneme Extractor

When you’re Project Lead:• Create an audio development

processPre-production: Production:audio engine SFX workflowgame style Music workflowfile system VO workflow

Foley workflow

When you’re Project Lead:• Create an audio asset list“How many sounds can this make?”“How often will we hear this?”“How much music can/should we

use?”• Excel spreadsheets are commonly

used

When you’re Project Lead:• Understand audio budget needs

•Audio Designer•Audio engineers•Composer•Voice actors•Recording equipment•Audio software•Audio hardware•Music gear

•Licenses (sounds, middleware)•Field Recording •Hired musicians•Music composition•Canned music, SFX, foley•SFX research•Sound processors•Sound file storage

When you’re Project Lead:• Integrate your audio team• Audio team works with art• Audio team works with animation• Audio team works with design• Audio team works with story writers

In short: COMMUNICATE!In short: COMMUNICATE!

The EndThanks for listening