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rOOm sImulaTIOn fOr mulTICHannel musIC and fIlm

1.1 Music Production
In many studios, one good reverb is used to render the

basic environment of a particular mix. One aux send, set at

different levels on the different channels, is used to obtain

depth and some complexity in the sound image.

To obtain a sound image of a higher complexity and depth,

several aux’s and reverbs have normally been used.

Tuning of the levels, pans and reverb parameters in such a

setup may be very time-consuming.

For effect purposes, anything goes, but if the goal is a

representation of a natural room or a consistent rendering

of a virtual room, it may be hard to achieve using

conventional reverbs.

1.2 Film and Post Production
For applications where picture is added to the sound,

several psychological studies have proven audio to be

better at generating entertainment pleasure and emotions

than visual inputs. When it comes to counting neurological

synapses to the brain, vision has long been known to

be our dominant input source. However, a study by Karl

Küpfmüller [4] has suggested, that stimulation of even our

conscious mind is almost equally well achieved from visual

compared to auditive inputs.

Sense

No of Synapses

Conscious Input, bps

Eye

10.000.000

Ear

100.000

Skin 1.000.000

Smell 100.000

Taste 1.000

Stimulation of conscious mind [4]

Realism in audio is just as important when it is

accompanied by picture.

In multichannel work for film, several reverbs configured as

mono in - mono out are often used on discrete sources. By

doing so, the direct sound and the diffused field are easy

to position in the surround environment. The technique

is therefore especially effective for point source distance

simulation.

As an alternative, several stereo reverbs are used on

the same sources to achieve a number of de-correlated

outputs routed to different reproduction channels.

With both approaches, adjustments can be very

time-consuming, and a truly engaging listening experience

is difficult to achieve.

2. MULTIPLE SOURCE ROOM SIMULATION
To obtain the most natural sounding and precise room

simulation, an artificial reverb system should be based

upon positioning of multiple sources in a virtual room. Each

source should have individual early reflection properties

with regards to timing, direction, filtering and level.

We have found this to be true for both stereo and

multichannel presentations.

If the target format is 5.1, at least two directional

configurations should exist in the room simulator, namely

for home (110 degree surround speakers) and theatre (side

array surround speakers) reproduction.

The room simulator should also be flexible enough to easily

adopt to new multichannel formats, e.g. the Dolby EX

scheme.

By changing the production technique slightly, multiple

sends from e.g. the aux’s, Group busses or Direct outs of

the mixing console can be used to define several discreet

positions as inputs to the room simulation system.

From a production point of view, multiple source room

simulation can be configured two ways, as described

below. Any large scale console build for stereo production

can adapt to both routing schemes.

2.1 The Additive Approach
The conventional approach to reverb is additive. Dry

signals are fed to the reverb system, and wet-only signals

are returned and added at the mixer.

With a multiple input room simulator, this configuration

works much better than with an single source reverb,

because at least each source can be approximated to fit

the nearest position rendered. However, normal power

panning still needs to be applied in the mixer.

An even more precise rendering can be achieved using the

integrated approach described below.

2.2 The Integrated Positioning Approach
The sources in a mix needing the most precise positioning

and room simulation, should be treated this way:

The source is completely positioned and rendered into

a precise position by passing the dry signal through the

simulation system, from which a composite output from a

number of source positions are available.

XY positioning to any target format, stereo or multichannel,

will be rendered as a best fit. The positioning parameters

(replacing conventional power panning) can be controlled

from a screen, a joystick or discrete X and Y controls.

With all positioning done in the room simulator, consoles

made for stereo production may thereby overcome some of

their limitations.

3. ALGORITHM STRUCTURE
This part of our paper describes a generic algorithm

currently in use for Multichannel Room Simulator

development. It is not a description of any particular

present or future product, but rather a presentation of the

framework and way-of-thinking that has produced our latest

Room Simulation products and is expected to produce