Hi,
you all know that sound localisation relates mainly on interaural differences : level (ILD) and time (ITD).
Those localisation cues apply for real sources but also for phantom sources generated by two loudspeakers in stereo configuration.
To "improve" monophonic sound, some researchers proposed pseudostereophonic systems, mainly with assymetrical all-pass filters on left and right, widening the stereo image and increase of apparent source width.
On the opposite, better loudspeaker and room symmetry (phase, level and frequency matching, toe-in,....), should improve perceived localisation : better source accuracy and stability, less blur.
Here comes my question : how can we objectively measure subjective localisation ?
I'm not searching for a complete auditory model to estimate true source position but rather for an indicator to compare localisation from various loudspeakers in rooms.
In the huge litterature on auditory localisation, I found only a few showing objective measurement of a phantom source :
- Perceptual differences between wavefield synthesis and stereophony by Helmut Wittek, see page 42 : frequency dependant IACC measurement http://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CDcQFjAA&url=http%3A%2F%2Fhauptmikrofon.de%2FHW%2FWittek_thesis_201207.pdf&ei=RkBbUevHDsPYPZKngeAF&usg=AFQjCNEXr2ID8F7j0agoBUkIVtPaKJnHtA&bvm=bv.44697112,d.ZWU
- Moglichkeiten und Grenzen der elektronishen Raumkorrektur bei Lautsprecherwiedergabe, Sebastian Goossens und Christian Gutmann, see page 15 : measure of groupdelay in lower frequencies, level differences at higher frequencies http://www.tonmeister.de/vdt/webdownloads/Seminare/2011/Sebastian_Goossens_VDT_Abhoerraeume_elektronisch_korrigieren_Nuernberg_2011.pdf
From measured impulse responses, we can compute frequency related ILD and ITD and estimate perception of a "theoretically central" phantom source :
- azimuth angle : position, accuracy, stability
- source focus (no localization blur)
So I did a simple software to estimate localisation position computing ILD and ITD from IR measurements.
This soft will be free (but works on windows only) and is not yet finished (need just a few days more). So I'm happy if I can get some good suggestions here (and if some want to debug it, tell me)
This soft has a nice feature, the calculation is open : a GNU Octave script that everybody can modify and improve.
For now, the script does the following :
- frequency dependant windowing of the IR
- separate spectrum in 30 bands with a FIR filter
- calculate L/R IACC and level difference in each band
- compute localisation from both IACC and level (time intensity trading/adding)
First look of results :
A few remaining questions :
- can we really avoid measuring with an artificial head and simply work with L and R impulse responses ?
- should we use a frequency dependant time widow ? a longer window ?
- does the calculated IACC represent the real ITD over the whole spectrum ?
- is IACC + level enough or are there other parameters to add such as HF signal enveloppe, HRTF, binaural crosstalk,... ?
- what frequency filtering should be used : gammatone, 1/6 octave,...
- how should ITD be calculated ? IACC, direct phase, groupdelay, envelope of signal ?
- time/angle and level/angle are now linearly approximated : should this be changed ?
- should we measure over a whole listening area to check stability of localisation ?
- should we also measure with non central phantom sources ?
- and the most important, does this analysis correlate to perception ? how to precisely check it ?
you all know that sound localisation relates mainly on interaural differences : level (ILD) and time (ITD).
Those localisation cues apply for real sources but also for phantom sources generated by two loudspeakers in stereo configuration.
To "improve" monophonic sound, some researchers proposed pseudostereophonic systems, mainly with assymetrical all-pass filters on left and right, widening the stereo image and increase of apparent source width.
On the opposite, better loudspeaker and room symmetry (phase, level and frequency matching, toe-in,....), should improve perceived localisation : better source accuracy and stability, less blur.
Here comes my question : how can we objectively measure subjective localisation ?
I'm not searching for a complete auditory model to estimate true source position but rather for an indicator to compare localisation from various loudspeakers in rooms.
In the huge litterature on auditory localisation, I found only a few showing objective measurement of a phantom source :
- Perceptual differences between wavefield synthesis and stereophony by Helmut Wittek, see page 42 : frequency dependant IACC measurement http://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CDcQFjAA&url=http%3A%2F%2Fhauptmikrofon.de%2FHW%2FWittek_thesis_201207.pdf&ei=RkBbUevHDsPYPZKngeAF&usg=AFQjCNEXr2ID8F7j0agoBUkIVtPaKJnHtA&bvm=bv.44697112,d.ZWU
- Moglichkeiten und Grenzen der elektronishen Raumkorrektur bei Lautsprecherwiedergabe, Sebastian Goossens und Christian Gutmann, see page 15 : measure of groupdelay in lower frequencies, level differences at higher frequencies http://www.tonmeister.de/vdt/webdownloads/Seminare/2011/Sebastian_Goossens_VDT_Abhoerraeume_elektronisch_korrigieren_Nuernberg_2011.pdf


From measured impulse responses, we can compute frequency related ILD and ITD and estimate perception of a "theoretically central" phantom source :
- azimuth angle : position, accuracy, stability
- source focus (no localization blur)
So I did a simple software to estimate localisation position computing ILD and ITD from IR measurements.
This soft will be free (but works on windows only) and is not yet finished (need just a few days more). So I'm happy if I can get some good suggestions here (and if some want to debug it, tell me)
This soft has a nice feature, the calculation is open : a GNU Octave script that everybody can modify and improve.
For now, the script does the following :
- frequency dependant windowing of the IR
- separate spectrum in 30 bands with a FIR filter
- calculate L/R IACC and level difference in each band
- compute localisation from both IACC and level (time intensity trading/adding)
First look of results :

A few remaining questions :
- can we really avoid measuring with an artificial head and simply work with L and R impulse responses ?
- should we use a frequency dependant time widow ? a longer window ?
- does the calculated IACC represent the real ITD over the whole spectrum ?
- is IACC + level enough or are there other parameters to add such as HF signal enveloppe, HRTF, binaural crosstalk,... ?
- what frequency filtering should be used : gammatone, 1/6 octave,...
- how should ITD be calculated ? IACC, direct phase, groupdelay, envelope of signal ?
- time/angle and level/angle are now linearly approximated : should this be changed ?
- should we measure over a whole listening area to check stability of localisation ?
- should we also measure with non central phantom sources ?
- and the most important, does this analysis correlate to perception ? how to precisely check it ?