My name is Bill Bray. I am a physicist, as well as a musician. I am not an audio engineer, but I have about 30 years experience with audio engineering and professional recording. A large portion of audio engineering is troubleshooting recording artifacts in the studio. After 30 years of chasing recording artifacts, I believe I have substantial expertise on the subject.
Upon listening to your hum recordings in very high quality studio headphones, very, very carefully, as well as visualizing the waveform on screen, a few important points become obvious to me. One, the recording is extremely well done, and your choice of microphones is ideal for this phenomenon. Two, there is a notable resonance, an echo, or rather, multiple echoes coming from different distances, and changing medium (rock to water and back again). The echoes are most notable as the intensity at any given frequency changes. There are two primary echoes. These two primary echoes occur at an estimated 1 second, and about 1.5 seconds. At the speed of sound in air, this corresponds to about 100 and 1800 feet. However, at the speed of sound in rock, which ranges from 5 to 13 kilometer per second (depending on the density of the rock), with a gross average of about 8km/s, this corresponds to 8 and 12 kilometers. Upon looking at your map of hum sites, this 8 to 12 kilometer range covers the entire area of the map, or there about. Meaning, that the hum originating from any given source, i.e., Glenfield, can appear as an echo if recorded from another spot on the map. In your Glenfield recording, this means that the resonances (echoes) are coming from the sources surrounding Glenfield, where I see your pegs on the map. Three, there are multiple secondary echoes, much shorter, ranging from about 100 milliseconds (half a kilometer) to 500 milliseconds (4 kilometers). These appear to correspond to closer pegs on your map, as well as a lake due East of Glenfield. Four, very important, there is a distinct and obvious change in medium, associated with a change in velocity of the echoes. A change in medium can be the hum moving from one type of rock to another, but I don’t believe so. It sounds as though the resonance shifts to a much lower density medium, namely, I think, water (1500 meters per second). I believe this set of resonances is traveling out to the shore line or the lake, and echoing back from the water. This is the ‘garbled’ muddy edge in the recording, almost like a bubble or swell. Five, the base cycle of the sound, although it sounds random, is quite predictable and cyclic. If you load your Glenfield recording into a program called Audacity (freeware), and zoom in closely on the wave form, you can see that there are distinct peaks at 1.5 and 2 second intervals (both source and echo). The cycles in the high intensity region of the recording, at about 50 seconds, 1:50, and so on have about 1.3 second resonances following the signal of origin. The signal peak at 1:55.5 shows the 1/2 second echo very nicely, occurring at 1:56. This is a 4km echo. You would also notice that the minor peaks at 1:55.5 are sharp and close together, and that the peaks at 1:56 are soft and broad, corresponding to a change in medium to a lower density (water). On your map, this corresponds to the lake due East of Glenfield. At 1:57.5 you see the 2 second echo of the 1:55.5 signal of origin. The peaks at 1:57.5 are distanced at the same intervals from one another as the set of peaks at 1:55.5, meaning no change in medium. This means that the two second echo has a rock source of probably 16 kilometers. My map shows an island, East- South- East of Glenfield. I believe this echo originates from this island. Also, This would suggest the Island is quite dense. I believe this hum is seismic. It behaves as if it is traveling through rock and water, and has no origin in air or other medium. Radio, VLF, or other electromagnetic phenomenon can be ruled out as the source, since all of my listening skills tend to tell me this is the sound of huge portions of rock shifting and grinding together. A little research shows me that you have both seismic and volcanic hot spots in the region. If you load the waveform into Audacity, you have the ability to play it back at different speeds and different pitches. If you play the waveform back at 150% normal speed, the effect is amazingly revealing. Some of the source of the sound is actually the sound of automobiles accelerating on the highway. This is very, very clearly automobiles. It is not, however, the source of the hum. The automobiles are an artifact in the background of the base signal which causes the elusive rising and falling in pitch. The automobile sounds are passing through rock, not through air. The seismic hum is a base signal which remains much more steady, like a constant ‘growl.’ Sometimes listening to a noise source with the pitch altered, the speed, or even in reverse can be extremely revealing. If you play the Glenfield at 3 times normal speed in reverse, you can actually distinguish automobiles accelerating and decelerating – it sounds identical to a race track. This would be the highway East of the center of Glenfield. The Taos, New Mexico hum is infinitely more puzzling. There is no road noise. A map of Taos shows nothing but minor, rural highways. There is a function in Audacity called beat finder. It is an algorithm which detects peaks in the sample. If you run beat finder (under Analyze) at 35% it displays a series of peaks. There is a 170 millisecond series that appears at irregular intervals, probably an echo in rock. Otherwise, the sound is utterly random. A recording of the Chaco Canyon NM hum sounds like machinery. The State Park is about 60 miles north-west of the Los Alamos Hydroelectric Dam. A speeded up recording at 3x reveals a very regular periodic cycle to it. At regular speed the cycle is about 2Hz. In reverse, the cycle sounds identical to forward, meaning that the cycle is sinusoidal in origin. Sinusoidal means not-naturally round objects are the source. The most interesting feature is only audible if you raise the pitch two octaves. An underlying longer cycle appears underneath of the short cycle. The underlying long cycle is not sinusoidal. It is a square function – i.e., on-off-on- off-on-off; high-low-high-low-high-low. Nothing in nature behaves as a square function. The cycle is roughly 500 milliseconds at 3x, or 1.5 seconds at normal speed. Given the regularity and in particular the square wave function in the background, there is no possibility that the sound recorded in Chaco Canyon NM is of natural origin. Visual inspection of the Chaco recording reveals a very clear and distinct set of two signals that look to be (be eye) about 60 degree out of phase with one another. Sixty degree phasing and background square wave functions tell me this is a power station. Los Alamos is about 60 miles East. I believe it is noise carried through the water table. The Los Alamos Hydroelectric plant is there. The water table at Chaco Canyon is only 40 feet. The Taos water Table is about 100 feet. Unlike the Chaco and Glenfield recordings, there don’t appear to be any distinguishable resonances in the Taos recording, i.e., no echoes. A Google map shows me there’s truly nothing around Taos. Taos only distinguishing feature is being at 7000 feet above sea level. According to Wikipedia, Taos is famous for the Taos Plateau volcanic field. “The Taos Plateau volcanic field is an area of extensive volcanism in Taos County, New Mexico, United States.” New Mexico Tech (NMT.edu) regularly records seismic activity in the 2 to 4 range in the area. It seems clear to me the source of the Taos hum is seismic. Being elevated and nothing for the resonances to echo off of, the quality of the Taos hum lacks cyclic periods and sounds only like a low constant random growl. If anyone has other recordings of this hum, please email them to me at [email protected]. Please put in all caps HUM in the subject line so I know its not junk mail. Also, I need the details of where the hum recording was made. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Hum Sufferers" group. 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