# Sound Synthesis of Objects Swinging through Air Using Physical Models +
## 6 Discussion  
The results from the listening test indicate that overall, our model performs well compared to other synthesis models. It has exceptional performance for the broom handle, baseball bat, golf club and wooden sword objects, where participants found sounds generated by our model to be as plausible as real recordings. The exception to this was the metal sword physical model sound effect, which actually performed worse in this test compared to our previously published test [1]. During the previous listening test [1], we did not have the physical dimensions of the sword samples. In this test, we had the dimensions, as well as the impulse response of the room in which the samples were recorded, thus enabling a fairer comparison. One possible reason for the poorer performance of the metal sword physical model was that all the other modelled objects were thicker than the metal sword. Thicker objects have higher Reynolds numbers, which results in lower \(Q\) values. Spectral modelling synthesis analyses a recording and extracts sinusoidal components. Thinner objects produce sounds closer to pure tones and hence are better synthesised using SMS than thicker objects. Figure 4: Magnitude spectrum of the physical model of the grooved sword. Table 8 shows that our physical model was significantly different from all other sounds, especially the real sounds and those synthesised by other methods. Since only one physical model sound was compared with a number of others, it is believed that a further listening test would be necessary to investigate if this result would be repeated over the range of sword dimensions and speeds. Results given in [1] indicated that the lower quality physical model sounds were rated as more plausible. These sounds had a fixed \(Q\) value that gave the impression of a thicker object. The diameter used to generate sounds in [6] was 0.01 m, substantially thicker than the sword we were modelling. It may be the case that listeners perceive a thicker sound as more plausible even if not physically accurate. This could be revealed in future perceptual evaluations. In the original paper [1], the value of \(\Gamma\) in Equation (6) was set to \(1\times 10^{-4}\). This was set perceptually as no exact relationship between dipole and wake noise had been identified. During the design of the listening test for this article, the value was again set perceptually, but this time, all objects were considered, including sounds generated using the Wii Controller. This resulted in the value of \(\Gamma\) being set to 0.2, increasing the wake gain. The broom handle, baseball bat and golf club objects were all cylindrical with thickness to width ratios of 1:1. For the wooden sword, this ratio decreases to approximately 0.37:1 and for a metal sword to approximately 0.14:1. The Aeolian tone model is designed around vortex shedding from cylindrical objects, and it is reasonable to assume that additional discrepancies may exist when there is a deviation from the thickness to width ratio of a cylinder. Another possible reason for the poor rating of the metal sword object compared to the other objects is that the number of participants who have swung a real sword and heard the sound may well be less than those who have perhaps swung a golf club and the other objects. Memory plays an important role in perception [31]. If participants have heard a Foley sound effect for a sword more often than an actual sword sound, this may influence their perception of the physical model. In contrast, it can be argued that participants will have more likely heard the actual sounds of a golf club at a live sporting event or within sporting broadcasts, and hence, their memory of these sounds would be closer to the physical model. Since all participants were from the U.K., the baseball bat would most likely not be as familiar to them as other objects, and hence, they might not have as strong a memory of the sound made by this object. This would make the difference between a memory of a Foley sound and an actual sound diminish.