Computer Games Sound Effects

Recording, Postproduction and Existing Database

Bartosz Zi´ołko, Martyna Gromotka and Mariusz Zi´ołko

Department of Electronics, AGH University of Science and Technology, al. Mickiewicza 30, Krak´ow, Poland

Keywords:

Video Games, Signal Processors, Audio Edition.

Abstract:

The paper describes the process of building a new database of sound effects recordings for computer games

and the ﬁrst version of such product. Ways of applying signal processors for postproduction is described, as

well as differences in audio edition for ﬁlms and games. Some aspects of using sounds in games are also

mentioned as well as the ﬁrst version of the list of possible tags of the audio ﬁles in the database. Both the

language of the tags and the datatabse will be substanially enlarged.

1 INTRODUCTION

An important factor at work in the audio creation

for games is dynamics of the signal (Marks, 2001;

Collins, 2008). It means the difference between the

worst and best possible level of the acoustic signal to

output or input of the device (Sztekmiler, 2003).

In real cases it is very difﬁcult to record sounds

with a high dynamic range. Playback and transmis-

sion of acoustic signals have their limitations as well.

Some very soft sounds will be inaudible at the play-

back, and those with a higher level, will be too loud

or distorted. Each recording or a reproducing device

has a certain level of noise and maximum output level

beyond which sound becomes deformed. Because of

the dynamics limitations, the acoustic signal devices

should be maintained above the noise level and below

the threshold value of voltage distortion.

Another important issue in case of games is that in

contradiction to audio edition for ﬁlms, sound effects

have to be ready for non-linearity and mixing during

the course of the game. The effects can be stopped in

a middle or overlaid on each other if a player makes

some actions. In case of overlaying, a simple correla-

tion can be not appropriate as typically sound related

to events in a game but can be be more important then

background music. Some sound effects have to be

played in a loop, but in a way that the end point is not

hearable.

2 SOUND EFFECTS

PROCESSING

The dynamics processors were helpful in building the

multimedia database. Depending on the level of the

input acoustic signal they inﬂuence or reinforce the

acoustic attenuation of the track in which they are

placed. Dynamic processors are used, not only be-

cause of the possibility of signal distortions, but also

to provide a listening comfort. If the dynamics of the

recorded material is reduced, manual changes of the

volume playback is not needed. In the opposite case,

the quieter parts of the volume could be not noted at

all, because the sound would be inaudible.

On the other hand, it could appear that the par-

ties, in which an acoustic signal reaches a high level,

are too loud. With these devices, one can manipulate

the value of the effective signal, which largely deter-

mines the subjective loudness by the recipient. For

the higher root mean square (RMS) value of the sig-

nal, the audio seems louder, even though the peak re-

mains the same. We used mainly following dynamics

processors: a compressor, a limiter, an expander and

a gate (Lyons, 2004) while building the database.

2.1 Compressor

The compressor reduces the signal dynamics. Typi-

cal target of its usage is to raise the RMS of a signal.

However, ﬁrst, the compressor attenuates the signal,

which exceeds a predetermined level. In this way, the

entire recording can be strengthened without exceed-

ing 0 dBFS peak (in the case of digital recording),

223

Ziółko B., Gromotka M. and Ziółko M..

Computer Games Sound Effects - Recording, Postproduction and Existing Database.

DOI: 10.5220/0003977702230226

In Proceedings of the International Conference on Signal Processing and Multimedia Applications and Wireless Information Networks and Systems

(SIGMAP-2012), pages 223-226

ISBN: 978-989-8565-25-9

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

which would override the sound track. Therefore, the

compressor reduces the difference between the loud-

est and quietest parts of the path. The signals are am-

pliﬁed in a proportion corresponding to the compres-

sion ratio. Parameters that can be adjusted in most

compressors are (Sztekmiler, 2003):

• Threshold is responsible for the moment at which

the processor is on or off. Threshold sets the level

of the input voltage, above which there is signal

loss. The signal below is unchanged.

• The size of gain reduction is determined by the

compression ratio

k =

∆U

out

(1)

where k is a coefﬁcient of compression and ∆U is

the size of input/output voltage above the thresh-

old in dB. This parameter indicates how many

times the input voltage level is greater than the

voltage at the output, e.g. 2:1, 10:1. This means

that a proper ampliﬁcation beyond the level will

be reduced by two or ten.

• The rate of response (attack) describes how

quickly after the crossing of the size of the in-

put threshold voltage level compressor will start

its function.

• Releasetime to the previous settings of earlier am-

pliﬁcation, after going back beyond crossing the

level set by the parameter threshold.

• Make-up gain enhances the output signal. It is

used because of the reduction strengthening of the

compressor.

• Knee is responsible for the part of the transient

characteristics of the processor in the activation

threshold. Soft knee is used to make compression

more natural and less audible, and sharp one for

strong compression.

• Peak-RMS - compressor reacts to the RMS or

peak.

Short attacks of the compressor is usually used for

transient signals, such as explosions. In case of long

ones, the compressor would not manageto pass a fast-

changing signal, so its sound would change dramati-

cally. It could be heared as a signiﬁcant beginning of

the transient signal attenuation (the impact moment)

and will only sustain itself. However, sometimes it

can be done consciously to have this effect. Param-

eter Peak / RMS should be set also depending on the

type of a signal. Selecting peak is appropriatefor tran-

sient signals. Then the processor will respond to the

peak value, and not an effective signal. If the sound

is continuous and there are no signiﬁcant changes in

the level, RMS should be chosen. The processor then

takes into account the effective value, and its effect

will be less noticeable and more natural, which is of-

ten desirable for this type of signals.

Increasing the level of silent parts will increase the

noise level recorded track, so the compressor, as well

as other dynamics processors, should be used con-

sciously, knowing precisely the effect one wants to

achieve. All processes of denoising audio material

should be performed before using the compressor, be-

cause it will emphasise the unwanted sounds in the

recording. Dynamic processors are helpful tools for

editing audio, but it is not reasonable to use them too

much because they cause ﬂattening of the sound and

artiﬁcial sound recordings.

2.2 Limiter

The limiter is a dynamics processor, having similar

characteristics to the compressor. Its characteristic

feature is that the compression ratio tends to inﬁnity,

and the attack is as close to zero as possible. They are

the hardcoded parameters. Limiter is used primarily

to prevent the signal from clipping, reacting mainly

to the peak values of the signal. Thus, it does not al-

low to go beyond the level of 0 dBFS. This means that

after applying the limiter, output signal level will not

increase regardless of the level of input signal. The

processor allows to adjust the following parameters:

• Threshold - after crossing the threshold, limiter

starts to operate at time close to zero.

• Release time to the original gain.

The limiter should mainly protect from distortion

of audio, activating relatively rarely. Frequent cutting

of the signal by a limiter would have a signiﬁcant im-

pact on quality, because the nonlinear deformations

will appear. What is more, the dynamics will be sig-

niﬁcantly reduced and the sound recordingcan be per-

cepted as unnatural.

2.3 Expander

An expander works oppositely then the compressor.

It reduces the ampliﬁcation, but of the quietest parts,

with a level below the

threshold

. The same param-

eters can be adjusted, as with the compressor – the

attack is responsible for the delay of the expander,

and the release for the late inclusion of gain reduc-

tion when signal levels drop below the threshold. Too

high value of the response time can result in attenua-

tion of high, rapidly rising level, which will be heard

as “ragged”. The expander is used primarily to mute

SIGMAP2012-InternationalConferenceonSignalProcessingandMultimediaApplications

224

noise or unwanted sounds that occur between the use-

ful material.

Noise gate is a version of expander with ratio pa-

rameter set to 1: ∞. Then, no input signal, which falls

below the level set by parameter threshold, cannot be

passed to the output. Thus, the phonic circuit closes.

The main goal is to get rid of unwanted sounds, such

as glitches, breaks or noises which are heard in the

intervals between the wanted sound. In addition to

the gate parameters such as threshold, response time

(time from the moment of crossing the threshold to

gate opening), the recovery time (time from signal

drop below the threshold to closing the gate). One

can also adjust the hold time, which is responsible for

the opening of the signal processor after falling below

a preset threshold.

This processor is better than the standard denoiser

built-in the most of audio editing programs, because

it does not degrade the signal, and “cut” only the un-

necessary parts. If noise interferes with audio during

the useful sound, the gate is useless.

2.4 Summarisation

All of these dynamics processors not only attenuate,

suppress or do not pass the signal, but also signiﬁ-

cantly affect its sound. With their help, entirely new

sounds can be created, sounding very different from

those played back immediately after recording. This

is not always a desirable effect, but usually the cor-

rectly conﬁgured processor improves and enhances

the sounds from the recording material.

Dynamic processors can operate not only across

the whole band, but also in certain frequency sub-

bands. Band compressors divide the acoustic spec-

trum into areas in which all the parameters can be set

independently. Thus, each band is subjected to a dif-

ferent compression allowing more precise processing

of the dynamics.

Equalizer can be also useful to adjust the fre-

quency of acoustic signals. It can change the volume

for a speciﬁc frequency. It consists of band ﬁlters,

so that it is possible to amplify or to suppres of cer-

tain frequencies. Therefore, the timbre is changed.

Equalizer is used, among others in shaping the sound

recordings and correction of problematic frequencies.

Editing of the sound effectswas performed using a

digital audio workstation (DAW) developed by Stein-

berg - Cubase (Childs, 2007). It has a wide range of

tools for recording and editing, mixing and mastering.

Depending on the type of the edited signal, dif-

ferent signal processors were used and different fre-

quency corrections. It was possible to set the dynam-

ics in order to get rid of much of the reverb, which

is especially disturbing in impulse sounds. More

difﬁcult to edit were the continuous sounds, due to

less possibility of interference in the recorded sam-

ple. Both graphic equalizers and parametric ones

were used to obtain the desired effect.

Short duration paths were modiﬁed to allow to

loop the sounds for the continuous playback of one

track without noticeable discontinuity between the

end and the beginning. It was necessary to extract

additional fragments, where the sound was quite con-

stant. If there would have been too many changes or

pulses that stand out, the soundtrack would be some-

what rhythmic and predictable. Then the loop would

have a noticeable effect, which we wanted to avoid.

In the last stage normalisation has been made by

ﬁnding the samples with the highest peak and setting

the level of the track, so that the highest value reached

almost 0 dBFS. Thesignal should notcross it, because

then, there would be a digital clipping. This is why

a limiter was plugged at the output of the circuit to

protect from the distortion.

There is no clear existing standard, which would

inform what level of the effective value of the output

path should have a sound effect for a computer game.

The RMS value depends mainly on the scale of us-

ing dynamics procesors during mastering, in particu-

lar – the compressor. The smaller the difference in the

level of quiet and noisy signals, the greater becomes

the effective value of the signal. For music, these val-

ues permanently grow (Owsinski, 2006). After 2000,

they reached -10 dBFS, and for some songs even -5

dBFS, especially in popular music. For classical mu-

sic, where the dynamics of the song is a very impor-

tant element, the effective value is approximately -30

to -20 dBFS. In this case the dynamics is not as ﬂat

as in typical entertainment music. We decided that

the RMS for our sound effects will oscillate in similar

limits as is the case of classical music.

3 COLLECTION OF SOUND

EFFECTS FOR GAMES

The samples were stored in a collection of 305 sound

effects, which are 45 minutes from paths which to-

gether lasted 3 h 10 min. Overall, post-production

of sound effects for the collection lasted about 70

hours not including the process of recording samples,

which lasted several days. One of the major obsta-

cles was tiring of hearing, therefore, quite frequent

breaks were necessary. After a two-hour work of lis-

tening to the sound effects, the perception is worse,

so one can not properly perform the tasks assumed.

The collection is just the preeliminary one to establish

ComputerGamesSoundEffects-Recording,PostproductionandExistingDatabase

225

proper work routines, methods and to allow to work

on soundtracing algorithms for games. The collection

will be substantially increased in the following two

years to reach over 10 hours of sound effects.

The ﬁle format is an uncompressed PCM with a

sampling rate of 44.1 kHz and a resolution of 16 bits.

Files names of the particular sound effects give an ad-

ditional information about the sound: I - pulse sound,

C - continuous sound, L1 - possibility of looping, L2

- possibility of looping without impression of repeti-

tive sound, K - effect allowed for kids, A - effect for

adults only, F - effect good for funny games, P - effect

for positive games (Zynga type), H - effect for horrors

and mysterious games.

4 CONCLUSIONS

The process of preparing sound effects for games was

described. An existing and growing collection of such

audio ﬁles have been presented as well. The collec-

tion is a result of just started project. The most im-

portant aspect of preparing sound database for games

besides of quality is their usefulness in non-linearpro-

cessing, because sound effects have to be mixed a lot

and played in very changeable orderdepending on the

decisions of a player.

ACKNOWLEDGEMENTS

This work was supported by NCBiR grantfor RAYAV

project.

REFERENCES

Childs, G. W. (2007). Creating Music and Sound for

Games. Boston.

Collins, K. (2008). Game Sound. An Introduction to the

History, Theory, and Practice of Video Game Music

and Sound Design. London.

Lyons, R. G. (2004). Understanding Digital Signal Pro-

cessing. Prentice Hall PTR, Upper Saddle River, NJ.

Marks, A. (2001). The Complete Guide To Game Audio. For

Composers, Musicians, Sound Designers, and Game

Developers. Lawrence.

Owsinski, B. (2006). The Mixing Engineers Handbook.

Boston.

Sztekmiler, K. (2003). Podstawy nagło´snienia i realiza-

cji nagra´n. Podre¸cznik dla akustyk´ow (in Polish) Eng:

Fundamentals and implementation of sound record-

ings. Handbook for acoustic engineers. Wyd. Naro-

dowe Centrum Kultury, Warszawa.

Figure 1: Recordings of three sound effects: birds (in the

end intentionally fade out), a camera and someone walking

on leaves and their mixture for an event in game of a person

walking on leaves, taking photos of birds and going away

afterwards.

SIGMAP2012-InternationalConferenceonSignalProcessingandMultimediaApplications

226