Specific outcomes from the project
Frequency dependent properties
Relationship between width and IACC at low frequencies dependent on frequency
It has been found that at low frequencies the relationship between width and IACC is dependent on frequency. To model this, an equation has been derived from the expected range of IACC values in natural sound fields at low frequencies.
Previous research has indicated that the perceived width of narrow-band stimuli with identical IACC values is dependent on the centre frequency of the stimuli. Also, previous research has shown that there is rarely siginificant decorrelation at low frequencies due to the long wavelength compared with the size of the head at these frequencies. In other words, below approximately 200 Hz, the IACC is rarely below approximately 0.9. This lack of variation in the IACC at low frequencies has caused some of the existing techniques to avoid making measurements at these frequencies. However, it is known that low frequencies are important in the perception of spatial impression.
An experiment was undertaken to investigate the perception of IACC at low frequencies, and to derive a method to compensate for any varitions in the relationship between the IACC and perceived auditory source width at these frequencies. It was found that the IACC is inversely correlated with the perceived auditory source width of low frequency stimuli, as for stimuli at higher frequencies. It was also found that the increase in the width at low frequencies caused by a specific decorrelation was greater than at higher frequencies. This frequency-dependent variation in the relationship between the IACC and the perceived width appeared to be approximately the inverse of the expected frequency-dependent IACC values for a head in a diffuse field. It is therefore possible that human perception makes up for the limited variation in IACC at low frequencies by increasing the sensitivity to this effect in this frequency range.
A method to compensate for the variation in the relationship between the IACC and perceived width was derived based on the expected frequency-dependent IACC in a diffuse field.
[Mason et al 2005a