Creating auralisation in Odeon, binaural, surround sound etc.
A: Typically any hi-fi pair of headphones will perform well for the auralisation purposes. In the auralisation setup the user can specify the name of the headphone model from a default list so that the non-linearities of the frequency response will be compensated. If the model of the headphone used is not available then the generic setting Subject_021Res10deg_diffuse.hph can be used. When this diffuse field setting (equalization) is selected, the results are filtered in order to obtain an overall flat frequency response of the HRTF's; that is, the average frequency response of all the HRTF filters is calculated and the auralisation results are filtered with the inverse of that. If using headphones which are diffuse field equalized (most headphones attempt to be) and a matching headphone filter is not available, then the matching diffuse filter headphone filter can be used. You can read more about headphones in Chapter 5 in the ODEON manual.
Q: Why should I use the 32 bit IEEE float format, when it takes up twice as much space as the ordinary '16 bit PCM format' and it takes longer time to generate results?
A: The 32 bit IEEE float is a professional format. When using this format you avoid introducing quantization noise. When using a PCM format such as the 16 bit integer format, samples are rounded into 16 bit integer data. By rounding the sample data, a difference between the original data (floating point data) and the data saved in the PCM file may (or rather will) occur - it is the difference between these two signals which is the quantization noise. Quantization noise is exactly that: Noise! and as such it is undesired. Further this type of noise may sound quite nasty (include harmonics). When creating multi source auralisation, many auralisation files are mixed together and this will accumulate noise - including the quantization noise in PCM files. If mixing two files with an equal level of noise - then the level of noise is doubled (+3dB), if mixing 10 files then the noise level increases by 10 dB and if mixing 100 files then the noise level increases by 20 dB. By using the float format at least the quantization noise is avoided.
Q: Can't make wave files generated by ODEON in the '32 bit IEEE float' format play on my PC - what should I do?
A: Windows XP does by default not have a codec installed for this format, however there is a free codec package 'DC-DSP' available on the web. When this was written it could be found at
http://www.codecsdownload.com/DC_DSP_Filter_download.htm and had the version number 1.03. When this package is installed, all wave file formats that can be generated by ODEON are supported for playback (except the 32 bit PCM format). If you have installed programs such as 'Adobe Audition', then codex for these formats should already be installed.
Q: The difference in strength between left and right ear is very large, even though they are only 14 cm apart; is it a mistake in the Odeon calculation?
A: The difference in strength appears at high frequencies due to the head functioning as a sound barrier when the head is between one ear and the source. A HRTF-example of this is shown in the figure.
Q: Can I play auralisations in windows media player?
A: Odeon can produce loudspeaker mapped wave files in the WaveFormatExtensible format. This is fully compatible with Windows media player version /10/11 - thus you may use features in this application such as play lists - be aware the wave files can become quite large (3 times normal stereo waves for a 5.1 Surround Sound set files)
Q: How do I make a Surround Sound or Super Stereo setup?
A: You describe a loudspeaker configuration and its loudspeaker positions in the Auralisation setup (e.g. a 5.1 Surround Sound set). If this setup do not fully match the physical one, then windows will try its best to remap the signals to whatever speaker layout is available to Windows - best results are of course achieved if the layout entered in Odeon matches the one in windows (defined in the soundcards speaker setup for a sound blaster card) as well as the actual speaker connected to the soundcard.