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5 Auralisation
(Combined and Auditorium editions only)
Although much effort has been made to make it as easy as possible to use the auralisation
capabilities available in ODEON, its felt that a separate chapter is needed, as this is where all
the threads from room acoustics modelling, signal processing, wave signal files, transducers,
psycho acoustics, recording techniques etc. meet.
In the description of auralisation techniques special words are frequently used, please refer to
appendix B; Vocabulary for a short description. In this chapter it is assumed that you have
tried the short guided tour in chapter 2.1.
The basis for auralisation in ODEON is either Binaural Room Impulse Responses (BRIR's) or
surround sound impulse responses (BFormat is also available for the advanced user), which
can be calculated as part of the Single Point Response, in the Job List - if the Auralisation Setup|Create binaural
filters or Auralisation Setup|Create 2D Surround Impulse Response option is turned on. In this section, only the
binaural simulation is covered, but most of the points also go for surround Auralisation.
In short terms the BRIR is a two channel filter, through which a mono signal passes from the
sound source(s) to the left and the right ear entrance of the listener (receiver). Using
convolution techniques to convolve a mono signal with the BRIR, a binaural signal is obtained
which, when played back over headphones should give the same listening experience as would
be obtained in the real room. Mixing such binaural signals created with different source
positions and signals, but with the same receiver position and orientation, multi channel
simulations are possible (e.g. simulating a stereo setup, background noise versus loudspeaker
announcements or singer versus orchestra).
Listening to Binaural Room Impulse Responses
As mentioned above, the basis of binaural auralisation in ODEON is the BRIR's, which are
calculated as a part of the Single Point Response. Once a Single point response is calculated, it is possible
to play the BRIR, clicking the Play Single Point BRIR button. The BRIR may give a first clue as to how
the room sounds and it also allows some evaluation of the quality of the calculated point
response, e.g. whether to use a higher Number of late rays in the Room setup.
Although the BRIR may sound a little ‘rough’, it may work quite realistic when convolved with
a signal less transient than an ideal Dirac delta function (can be google’d). To get a more
realistic presentation of a BRIR as it would sound in the real world you might want to convolve
it with the Clapping signal file, an anechoic recording of hands being clapped, which is eventually
a less transient signal than an ideal impulse.
A note on directivity patterns for natural point sources
With natural sources we refer to sources such as human voice, an acoustical instrument or
similar, where a recorded signal for auralisation may be associated with the directivity pattern.
In order to select the right source for auralisation purpose please read chapter 10.
Head Related Transfer Functions and digital filtering
To create binaural simulations, a set of HRTF's (see Appendix B; Vocabulary) is needed. The
HRTF's are different from subject to subject and in principle you may measure your own ones
and import those into ODEON using the Tools|Create filtered HRTF menu entry in the ODEON
program. Measuring HRTF's is, however a complicated task so you will probably be using the
supplied ones. If you should be interested in creating own sets of HRTF’s for ODEON,
additional information can be found in the help available from within the ODEON program.
The imported HRTF's to use for auralisation are pre-filtered into octave bands in order to
reduce calculation time. The octave band filter parameters for the selected filter bank can be
seen on the filter bank name at the Auralisation Setup menu. The filter parameters are:
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