Fin al conflicto entre la hacienda Sálamalag y Maca Grande 46

Stage A

Figure 3.4 displays the responses to Comparisons A1 and A2, where the test signal was distributed over either three or five loudspeakers arranged in an arc around the listening position, with the maximum extent of the arc covering a semi-circle in front of the listener. The fundamental harmonic remained in the centre loudspeaker. The most frequently reported differences for these tests were changes in horizontal or vertical position and spatial broadening.

The perceived changes in horizontal position were predominately to the right hand side. This was surprising as the author suspected any perceived changes in horizontal position may have corresponded to the positions of the lower harmonics. As can be seen in Figure 3.4, the positions of the third and fifth harmonics in Comparison A2 were both to the left of centre, yet the perceived location was predominately to the right.

The author cannot offer an explanation for the perceived differences in elevation, however, it is of interest to note that a number of subjects also reported that the reference signal was perceived as being at an elevation other than at head height.

As expected, the subjects tended to perceive the test signal as spatially broader than the reference signal, with the frequency of responses increasing with the angular spacing of the loudspeakers.

The ‘Brighter’ and ‘Annoying’ responses may be due to the higher harmonics ‘standing out’ more when presented as a spatially separated signal. This may suggest that due to spatial separation, the higher harmonics had not fused or had only partly fused with the perceived signal as a whole, thus forming a partially or wholly separate auditory event. The fundamental frequency of the signal used in Stage A was 440 Hz, which yielded higher harmonics in the region above 4 kHz. The author acknowledged that the presentations could be quite shrill (hence ‘annoying’) and for this reason the fundamental frequency of the test signals in Stage B was lowered to 150 Hz.

In Comparisons A3 to A6, the fundamental harmonic appeared in a loudspeaker other than the centre loudspeaker. From Figures 3.5 and 3.6, a clear correspondence between the position of the fundamental harmonic and the perceived horizontal position of the test signal can be seen. This occurred for both the three and five loudspeaker presentations. Again the frequency of spatially broader responses was greater for the five loudspeaker presentations than the three loudspeaker presentations.

In Comparison A7, a spatially separated square wave was compared to a combined square wave appearing in all loudspeakers. The main reported differences were ‘Brighter’, ‘Spatially Broader’ and ‘Horizontal left’. The differences in brightness may again be explained by the higher harmonics ‘standing out’. The ‘Spatially Broader’ differences demonstrate that the even though the mono signal presented in all loudspeakers is physically surrounding the listener, the spatializing techniques that are being presented in the same manner, contain extra auditory information (or conflicting cues) that results in a broader spatial perception.

Stage B

In Stage B, the spatially separated signals were presented through a circular, six-loudspeaker array, with the listening position being in the centre of the circle.

In Figure 3.7, which displays the combined results for Comparisons B1 to B16, the most frequently reported difference was ‘Multiple Sourced’. This suggests that with a signal that is spatially spread over a loudspeaker array that totally encircles the listener, the perceived signal is not fused into a single auditory event, thus implying a limit to the degree in spatial spread of harmonics for the spatializing techniques.

The predominance of the omitted fundamental signals in the ‘Brighter’ and ‘Higher in pitch’ differences suggest that due to fundamental tracking,

the timbre of the signal had changed so that the perception of the fundamental harmonic was not as strong, or that the second harmonic was being perceived as a separate auditory event, with the other harmonics forming a residue pitch that was not as dominant as the second harmonic.

‘Movement’ accounted for a number of differences, especially with the synthesized piano note. As the piano differed from the saw-tooth wave in that time varying (in amplitude) partials were employed in the synthesis, the author suggests that this may be a reason for the perception of movement. As the general perception was one of multiple sources, it is possible that as one partial or groups of partials decreased in amplitude and another (in a different location) increased, so in an attempt to group the partials, the auditory system may have ‘interpolated’ the positions of the samples, resulting in a perception of movement.

From Figure 3.9, the most frequently reported location of the test signal was ‘Left and Right Rear’, which describes the signal as having two sources, often described by the subjects as being similar to hearing a stereo pair of loudspeakers placed behind the head. The second most frequently reported location was ‘Left Rear’. Very few responses placed the signal to the front of the listening position. A possible explanation why the signal was predominately perceived as emanating from the rear of the listening position is that as the auditory system is confused by the conflicting cues, the ‘unknown’ sound perception could be thought of as

‘threatening’. For this reason, the perceived location of the sound is behind the listener so that a ‘fleeing’ response may be invoked in the listener to escape the potential ‘threat’.

From the results of Stage A, where the location of the signal corresponded well with the position of the fundamental, similar results were expected for Stage B. However, a relationship between the location of the fundamental harmonic and the perceived location of the test signal was not observed. A possible explanation is that again, the auditory system is receiving conflicting information about the signal and therefore cannot fuse or place the auditory event.