Download ODEON Room Acoustics Program

Appendix B: Vocabulary
The techniques of auralisation make use of many of technologies and a lot of technical terms
and abbreviates are commonly used in the literature. Here is a short vocabulary to some of
the most used expressions - the vocabulary is not a complete description of the individual
words - the context under which the words are used are many and the subjects are rather
complex.
Anechoic recording
Anechoic recordings are recordings of sound sources made without any reflections from the
surroundings contributing to the recordings. A common problem with anechoic recordings are
that they may often include to many high frequency components, because they are usually
near field recordings and because they are recorded 'on axis' where these components usually
dominate. When using such recordings with auralisation systems this may often result in
unrealistic sharp 's'-sounds especially in case of long reverberation times. Anechoic recordings
are usually recorded in an anechoic room, but semi anechoic recordings may also be
acceptable for use with auralisation systems, this could be out door recordings of machinery,
trains etc. or studio recordings of music.
Auralisation, auralization
The term auralisation was invented by Mendel Kleiner who gives the following definition:
Auralisation is the process of rendering audible, by physical or mathematical modelling, the
sound field of a source in a space, in such a way as to simulate the binaural listening
experience at a given position in the modelled space.
When used in ODEON, one may think of auralisation as the art of creating digital simulations
of binaural recordings in rooms (which may not be build yet). The aim is to provide the same
three-dimensional listening experience to the listener as would be achieved in the real room at
the given receiver position with the simulated source position(s) and signals.
Binaural (recording)
Humans (usually) listens using two ears. This allows us to perceive sound as a 3D
phenomenon. To create a binaural recording, it is not enough to create a two-channel
recording (stereo), also the colouration created by diffraction from the human body has to be
included. This is usually done by using a dummy head with a microphone mounted at the
entrance of each ear canal - this recording may be recorded using an ordinary stereo recorder
- but is now refereed to as binaural. Binaural recordings are usually played back through
headphones to avoid colouration from the room in which it is played as well as avoiding
diffraction from the human body to be included twice (at the recording and at the playback). If
one has measured or indeed simulated the BRIR's (see below) in a room, it is possible to
'simulate' a binaural recording.
BRIR - Binaural Room Impulse Response
The BRIR is the key to binaural room acoustic auralisation. The BRIR is a set of impulse
responses detected at the left and right entrance of the ear canals of a dummy head (or
indeed at blocked entrenches of the ear channels of a (living) person residing in a room, when
a sound source (or some sound sources) has emitted an impulse. The BRIR should include all
the (necessary) information on receiver position and orientations, source(s) position(s) and
orientations, room geometry, surface materials and the listener’s geometry (described by the
HRTFs). Convolving the left channel of the BRIR and the right channel of the BRIR with a
mono signal, a binaural signal is created, which when presented to the listener over
headphones gives the impression of the three dimensional acoustics at a particular position in
the room. It is also possible to simulate the recording of the BRIR's, which is what ODEON
does.
12-131