The song of the veery is a haunting, ethereal song. Males sing at dusk, a time when not many other birds sing and daytime winds have calmed. It's also a time when the air turns damp; dense, moist air transfers sound waves better than dry air.
If you listen to the song carefully, you can hear an echo or tremolo effect (more on this below), because songbirds have, essentially, a double voice box that can produce two notes at the same time. (The left voice box is lower pitched than the right one.) In a sense, a singing veery harmonizes with itself.
Songbirds hear "faster" than we do, so slowing down the veery’s complex song gives us a sense of the subtleties birds hear, as well as the singer's vocal skills. Vocalizations communicate a lot, including predator alerts, and keen hearing is just as important as vocal dexterity.
There are fewer veeries today than when I was young. NH breeding bird surveys began in the 1960s and have tracked a 50% decline in their numbers over the years. That reality, like the veery's song, is haunting, and all the more reason to savor it again.
The tremolo mentioned above is a classic auditory illusion, known as “binaural beats”. When two tones with similar, but not identical, frequencies are played at the same time, your brain processes them as a singular, fluttering tone. Here’s a simple way to hear it for yourself (this works best through headphones).
First play one tone by itself.
Now play the other by itself.
Now here they are together. (Unfortunately our CMS won't let you play two files at the same time, so I've mixed the two together. I promise I haven't applied any processing to these, this is just one tone layered on top of the other.)
There are hypotheses that playing the beats at different places on the frequency spectrum can reduce certain brainwave activities, or even stimulate the production of hormones in certain glands.