As part of some ongoing audio analysis, I looked at the frequency ranges of the calls in these audio recordings and noted four interesting things:
1 - The calls are squarely within the range of frequencies most humans are capable of, but also in the range of other purported BF howls.
2 - The calls exhibit significantly more power than any of the human vocalizations on the recordings, either the hellos, or the casual conversation. Whatever makes those calls has a powerful vocal capability.
3 - The couple instances of muttering sounds are very low in the frequency range, mostly below 300 hertz, which is quite deep.
4 - In one of the recordings from 2008 there is one call that is immediately preceded by two rapid hoots, very similar to the type heard from other apes. These are particularly interesting because they happen very quickly and transition into a howl so rapidly that I believe a human would be extremely challenged to produce these sounds (not impossible with significant training, maybe, but certainly not easy).
After some more off and on listening to these recordings I've found three unusual calls that I thought were worth mentioning. I don't have permission to share snippets of their audio, but I can share some spectrograms that I've generated from these recordings.
The first call came from the August 30, 2008 recording and caught my attention because it is very reminiscent of the unique four tone howl that was recorded during the 2009 BFRO expedition to Minnesota (see: http://s2.excoboard.com/exco/thread...hreadid=2118821 ).
The Michigan four tone howl is visible in this spectrogram:
And you can compare it to the Minnesota four tone howl in this spectrogram:
The differences are; tone's 3 and 4 are reversed from one recording to the other, and in the Michigan example the 4th tone is carried out as a long howl, where in Minnesota it cuts off abruptly.
What I find compelling about the Michigan four tone howl (and the Minnesota as well) is the lingual dexterity required to produce such a rapid change in frequencies, while simultaneously generating so much power. I don't feel that this is within the normal human's ability to accomplish (if you know someone who can do this I'd love to have a recording of it).
The next MRP spectrogram worth highlighting is this one from August 30, 2008:
I mentioned this one in the December 1 notes above as containing a couple hoots, but after looking at it more closely I can report even more. In this call, it starts out with a high keening howl. But, AT THE SAME TIME, the vocalizer generates a grunt and two ape-like hoots.
The grunt-hoot-hoot is simultaneous to the keening howl, and both sequences are only about a half second long (very fast). They start at the same time, and end at the same time, and transition into a long whooping howl (similar to the many other calls in the recordings).
This is a very complex lingual accomplishment, and I'm hard pressed to believe a human has the ability to generate it (but again, if you can prove that assumption wrong, please do). And I'll admit I was still wondering if this could be a "manufactured" sound, but on a second pass through the recording I realized a similar "grunt-hoot-howl" call was issued about five minutes earlier in the same recording (only not so clearly or noticeably). I'll develop a spectrogram of that call later for comparison.
The third unique call which I spectrogrammed is not outside of the human vocal range, but its a very unique call and its "human-ness" was part of what makes it stand out. Here's the spectrogram of this call captured in the August 2, 2008 recording:
This call starts with a voice warble that sounds just like the old "George of the jungle" cartoon where George yells "AH ah AH ah AH ahhh". Then the howl changes into the normal form for these recordings and ends with a unique "oooowWAAAAH"! Again, this is within the range of a human, assuming that human had some really powerful lungs, but it's a very interesting sounding call.
***As mentioned above, I noted a second howl in the MRP recordings that came earlier than, and appeared similar to, the complex grunt-hoot-howl previously described. While this second howl is not quite as clear, it is very similar in form, including the complex beginning with a high pitched howl in sync with two low frequency grunts (not quite hoots). Kind of interesting to see the two spectrograms side by side. They're very similar.
Here's the one from 1:32 in the August 30, 2008 recording:
And here's the one from 3:52 in the same recording:
So far I haven't had any luck isolating the lowest frequency sounds in the August 30, 2008 recording (where I'm focusing most of my attention at the moment). There's a lot of noise at the low end of these recordings, and it may cover up any sounds that were emitted that low.
I have had some luck with a low-pass filter though that attenuated a lot of the high frequencies and allowed me to bring out the low end mumbles and grumbles a little more clearly. For me, the big question is "what's that warble sound" at 7:05. It sounds somewhat mechanical, yet biological at the same time. The nearest thing I've heard to it is an unbalanced tire at long distance on a roadway, or maybe a horse exhaling through its mouth, flapping its lips.
I started from the beginning and paid attention to the grumbles and mumbles. They all sound like they're being emitted by the same speaker throughout the recording. Early on, they sound louder, more energetic. Toward the end they become quieter and more relaxed. It could be a reflection of tension easing in the speaker over time. The first "mumble" is at 0:56 and if I loop it I hear it's composed of 5 syllables. They're not intelligible words, but they are distinctly uttered pulses of sound.
The second mumble is more like a growl, at 2:50, just after the dogs and coyotes go quiet. It's two parts. The first part of the growl rises in frequency, then the second part drops in frequency. Next at 2:54 theres a single moaning mumble and at 2:56 another moaning mumble, just a little stronger. At 3:02 a very soft moaning mumble and one more at 3:10.
At 3:33 there's another low mumble and this one has the first hint of repetition, somewhat similar to the warble heard at 7:05. There are at least 4 rhythmic sound pulses in this mumble. Another moaning mumble at 3:37 seems time synchronized with four breaths right after that, first time I've noted them synced up so cleanly (indicating they could be coming from the same source).
Another moaning mumble at 3:50, just before the complex grunt-hoot-howl call. And at 4:02 a more aggressive growling mumble in the midst of several wood knocks. At 4:36, a faint breathy mumble and at 4:48 two more moaning mumbles, but this time with a hint of warble creeping in.
At 6:03 there's a very deep breathy exhale, that sounds like it comes from a large chested animal. I just mention it because it's worthy of attention. It's the third in a series of breaths, each progressively deeper than the one before.
Then at 6:14 theres a mumble that sounds like a series of muttered, but unintelligible syllables. Altogether I hear nine syllables, but what I find more striking is the wavering pattern of the last seven. They too seem to suggest a warble.
Another growling mumble at 6:25.
At 6:54 there's a very faint warble. It sounds different from the earlier moaning mumbles with warbling characteristics. Less vocal, more mechanical or airy sounding, and very faint.
Finally, starting at about 7:03, there's an extended warble sound. Still faint in relationship to other sounds on the recording, but clearly among the loudest of these low frequency sounds. It sounds like a louder and longer version of the warble at 6:54, slightly mechanical, but still seemingly biological in tone.
GUT MODE KICKING IN: I will venture to postulate that this sound too is coming from the source of all the earlier moaning mumbles. But in this case it has somehow lots it's mumbling quality. Maybe its an example of exhaled air, as people commonly do when releasing tension. I don't know, but that's just where my gut takes me on that one. Unfortunately there's not enough information to nail it down any better, but I will point out that a similar warble exists on an earlier recording. Which in my mind does a lot to correlate this warble with the source of all the other mumbles and howls. GUT MODE OFF.