A number of patterns and metrics (for music)

Spearman's rank correlation coefficients
for all possible year pairs.

Spanish attempt  to `measure the evolution of contemporary western popular music´ got good visibility by science journal Nature.
They say, popular music is a key cultural expression that has captured listeners' attention for ages.
So?

Many of the structural regularities underlying musical discourse are yet to be discovered and, accordingly, their historical evolution remains formally unknown.

Formally unknown partly partly for example, because Spain is a marginal province on the map of the rock.

They say, here we unveil a number of patterns and metrics characterizing the generic usage of primary musical facets such as pitch, timbre, and loudness in contemporary western popular music.

Many of these patterns and metrics have been consistently stable for a period of more than fifty years.

but it is not actually the straight line, but as Z, rock-music complexed was sitting in the late 1960s, and especially in the early 1970s.
Since then, true, began a straight line.

However, we prove important changes or trends related to the restriction of pitch transitions, the homogenization of the timbral palette, and the growing loudness levels.
This suggests that our perception of the new would be rooted on these changing characteristics.

Hence, an old tune could perfectly sound novel and fashionable, provided that it consisted of common harmonic progressions, 

What does this mean? I have been abducted by a chord structures from Chopin.

... changed the instrumentation, and increased the average loudness.
One of the platitudes is caused by a 16 bit-resolution is a format of music.