I have listened to both of the "Sierra Sounds " cds many times. And we're talking probably 100 times each. What's fascinating to me is, at least in my opinion, those sounds would be impossible to fake. First and foremost, the vocalizations run the gamut of speech patterns and inflections. In the various recordings, the vocalizations contain phonemes, laughter, elements of exasperation, and the fact that there are at least 4 different sources of the vocalizations as well. You can clearly discern a very large, deep voice. A very feminine high pitched voice, and occasionally a very small voice.
There is a part in the recordings where one of the hunters is mimicking one of the squatches. The squatch would whistle, or make some kind of vocalization, and the hunter would try to mimic it. At one point, clear as a bell, you can hear the squatch laughing at the hunter.
The sounds were studied in the late 70's. The results were: there were at least 4 different subjects making the vocalizations. According to their findings, the deepest voice had a vocal tract of someone/something that was extraordinarily tall. I want to say they put the subject at around 8 ft.
Also, they determined the whistles were made with the vocal chords, and not the pursing of lips (as humans do). The hunters believed the group consisted of "The Old Man", the deepest voice and probably the father. A female, the high pitched, feminine voice, and 2 younger ones. The first set of recordings were made in 1972. Those recordings were much more hostile sounding, and very rapid fire chimp like articulations. The second set of recording were made 2 years later in 1974, and the vocalizations were much slower, and had the sound of some sort of language. Also, the squatch in the first set of recordings was the "Old Man" in the second set of recordings. They believe the "Old Man" came back, with his family, and deliberately slowed down their vocalizations in an attempt to communicate in 1974.
Look for interviews with R. Scott Nelson on this subject. In the late 2000's, his son was doing a book report on Bigfoot for school. They did a web search and came across snippets of the Sierra Sounds. Mr. Nelson is a retired Naval crypto linguist. He was trained to find coded messages in any kind of audio correspondence. Language played backwards, foreign languages played backwards, etc. He immediately identified the vocalizations as "Language as we define it". He obtained the original recordings from Ron Morehead, and had the necessary equipment to eliminate all the background noise, clean up the audio, etc. etc.
Mr. Nelson said of the recordings, that again there were at least 4 different subjects, and in many instances they are talking over each other. They most definitely are speaking some kind of language as we define it. There were repeated phrases, and that they might even have names for one another.
He's actually studied other recordings from various parts of the U.S., and found similarities in them. In one interview i heard, Mr. Nelson sent the recordings to a colleague in Japan that specialized in ancient Japanese dialects. His colleague contacted him and thought it was a very elaborate joke.
When Mr. Nelson asked why, colleague responded with '" There are small bits of a Japanese dialect that no one has used in centuries in these recordings." Maybe the Samurai Chatter, as we call it, is just that.
If you have not heard these, they are very much worth listening to. There's actually lots of other interesting things about the vocalizations, but this kind of touches on the high points.