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

Definitions

Sound: compression waves transmitted through a medium

Wave: cycle of compression and rarefaction

Amplitude: measure of sound wave pressure

Coming soon: cool stuffComing soon: cool stuff

Definitions

Frequency: speed of wave oscillationMeasured 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 Sound

A “unit” of digital sound is called a sample

The sampling rate is the number of samples taken per second

Bit depth: size of sound sample data

See Figure 5.5.2, pg 598

Nyquist Limit

A 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, 24/192

The 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 Formats

Sample: 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 Envelope

Attack, 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 Parameters

Pan: 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 Filters

Low Pass Filter: only allow sounds below a certain frequency

High Pass Filter: only allow sounds above a certain frequency

Band Pass Filter: only allow sounds in a given frequency range

used for cutting “highs” and/or “lows”

3D Sound Methods

Head 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 Effects

Echo: 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 Effects

Two 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 Systems

MIDI: 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 Systems

MIDI:

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 Interaction

Phoneme: 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 process

Pre-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 End

Thanks for listening