"This howl was recorded at the April public expedition in Iowa. If you look at a spectrogram there [appears to be] a double howl, one starting two seconds after the first at about 200 Hz higher register. The higher howl decays two seconds after the first one [...]. I verified as much as possible whether the howl was from our group or not. It was not from our group. The area that it came out of is undeveloped with deep woods lining the valley and swampy bogs in the valley bottom. The valley is a bit less than a half mile from side to side."
I gave Steve's audio a good review and post processing, then responded to him with the following thoughts:
"Steve, I have a somewhat different interpretation of the spectrogram than what you're reading. Allow me to elaborate.
It's not a double howl you're seeing, but multiple resonating harmonics from a single howl. The lowest "resonating harmonic" that you see is the loudest, most visible in your spectogram. It ascends to a peak of about 730Hz or so. The higher harmonic peaks at about 1100Hz. It's softer in volume but it adds "depth" to the vocal.
The way harmonics work is simple math. They should normally be seperated by a common multiple (e.g. 2x, 3x, etc.). Now when we subtract your lower harmonic from your upper harmonic (or 1100-730) we get 370Hz. If the lower harmonic (730Hz) were your true "fundamental" of this howl, the next higher harmonic would be at 1460 (2x730), and not at 1100.
What this tells us is there's a harmonic even lower than 730Hz. And if we divide 730Hz by 2 we get 365 Hz (which is pretty darn close to the 370 Hz difference we see in the two visible harmonics). This is just a round about way of telling you this howl is a single howl with an "attenuated fundamental" at ~370Hz.
The attenuated fundamental is ... a feature difficult for most normally sized humans to achieve (you can test it yourself with your own recorder). Only large bodied individuals like Bobo have been able to produce this reliably, in my experience (not saying someone smaller couldn't learn to do it though).
A couple other features I'd like to point out. First, obviously the duration of the howl. Nearly 15 seconds, is rather difficult for a human with no vocal training to achieve (or at least some amount of natural talent).
Also, notice as the howl trails off how the higher harmonic seems to end then restart at a slightly lower pitch. This is due to the voice changing from an /aa/ phoneme to an /oo/ phoneme."
There were a number of other points I shared with Steve about his clip. They're important clues that I look for when trying to authenticate possible sasquatch vocals, and his recording exhibits several of them. So in the end I feel Steve has hit the jackpot, and captured a reliably authentic sasquatch moan howl.