Choosing the palette

One major aspect of the whiffer can benefit from the ideas presented here -the construction of the palette. The two key features of the palette are its size n and the particular palette odorants it contains. A palette designer should be concerned with determining both of these.

In a typical application of our scheme, we expect n to be given, being constrained by the limitations of the technology used, by the desired accuracy and by cost. Let us use the term tolerance, denoted to represent a measure of the extent to which the perception of the computed mixture P P .v deviates from that of the original odorant, dP (o; c). The exact formulation of the tolerance depends on the specific structure of the odor spaces involved.

In principle, a larger palette allows for a smaller tolerance. However, large palettes are more expensive and more difficult to build, hence a compromise between palette size and tolerance must be made. If there were no constraints on the palette, we could simply choose n to be large enough for the palette to contain all possible distinct aromas, which is at least in the order of 104, and very far from the ability of current whiffer technology. To be realistic, we must assume that for the near future n will be under 300.

As to choosing the palette odorants themselves, we envision an algorithm which, given the desired size n and a large collection of candidate odorants, computes the “best" n odorants for the palette. Such an algorithm can indeed be constructed, based on ideas similar to the ones reported upon here, and taking into account accumulated information about the psychophysical space (such as the density distribution of the various odorants). It is not out of the question that such an algorithm could also be used to tailor special palettes to specific application areas, to desired tolerance, to constraints on mixing ratios or quantities, etc.

Another interesting option in palette design is to adopt a multi-tier approach. There might be advantages in building the palette so that the palette odorants are arranged in tiers. In this way, mixtures can be prepared by taking larger quantities from the higher levels (catering for coarser descriptions), adding lower level odorants to fine-tune the output -as a kind of “salt-and-pepper" stage. Of course, the physical reservoirs for the palette odorants inside the whiffer can then be of different sizes, reflecting the differences in the typical use-rates of the various levels.