a term used to designate the as-yet unclearly defined feelings and sounds produced by the various different factors of rational musical intervals. Note that even among theorists who agree with the concept, there is disagreement over whether it is the prime series or the odd series which is the important set of factors.
Monzo's own theory is based on the following logic: we seem to perceive musical intervals categorically, that is, several different rational intervals, over quite a wide range in pitch, can all be perceived as the same musical gestalt (for example, a major 3rd), because of a myriad of various influences, including psychoacoustics and musical context; therefore, our perceptual apparatus is receiving pitch data that our cognitive apparatus quantizes - it is unclear how this quantization is effected.
In Monzo's opinion, this categorical interval quantization is based on the easy recognition of small prime-number factors, up to at least 13, possibly up to 19 or 23, possibly much higher. This prime-factoring seems to take place predominantly, or perhaps even exclusively, when the rational relationships perceived have the approximate proportions of the harmonic series.
There is also much disagreement on precisely how these prime- or odd-affects may be characterized, but there seems to be general agreement on the fact that there are different affects for different factors, at least for the lowest ones (2, 3, 5, 7, [9,] and 11).
According to Monzo's theory, the degree of affect diminishes in proportion to the increasing size of the prime-factor. Thus, the most easily perceived affect is that of prime-factor 2, which produces the effect known as octave-equivalence. Some of the words used to describe the affect of prime-factor 3 are "hollow", "powerful", "open". The affect of prime-factor 5 is usually described as "sweet", that of 7 as "bluesy". It has proven to be more difficult to characterize the affect of the higher primes verbally.