top 10 incredible sound part 1

I think sounds are always underrated. There are plenty of famous pictures, graphs, and movies out there, but for a sound itself to be famous (other than music), or to even really be that interesting, takes something special. So here’s some strange sounds – some may be familiar, hopefully others won’t be – but all are definitely incredible.


Slow Down

The “Slow Down” is a sound that was first recorded on 29 May 1997, on an autonomous hydrophone array in the Equatorial Pacific, coming from a southerly direction. It lasted about 7 minutes, and has been recorded several times every year since it was first detected. In 2002, it was suggested that the sounds could be caused by the friction of ice in Antarctica moving over the land, as the spectrogram of the sound is very similar to the sound of two objects rubbing together – if you rub your fingers along a table, record the sound, and slow it down (as the scientist who proposed it did) you end up with a strikingly similar sound. However, the matter has not been conclusively settled.

A similar sound is the “Upsweep“, a sound detected between 1991 and 1994, which consists of several consecutive rising sounds. Its cause is also unknown, but it is thought to be caused by some underground volcanic activity, such as the release of underwater gas or lava.



Singing Sand

Singing Sand dunes are a phenomenon found in about thirty places around the world. When different layers of sand rub against each other, pushed by the wind, or someone walking on it, it creates a deep booming sound. Ongoing investigations have found that the sound depends on the sand having particular characteristics, such as size and humidity, to make the sound. As a result of different types of sand, different sand dunes produce different notes – Sand Mountain in Nevada gives a low C, Mar de Dunas in Chile gives an F, and the sands of Ghord Lahmar in Morocco give a G sharp.



Magnetospheres

 An antenna on the spacecraft was picking up plasma waves, created by the unusually strong magnetosphere of Ganymede (about 3 times stronger Mercury). This was used to create an audio signal (above, the 45 minute signal is compressed into about 60 seconds), where the sound frequency corresponds to the frequency of the waves detected. At about 8 seconds in, Galileo enters the magnetosphere (there is a sudden increase in noise, sounding like a clap of thunder). As the spacecraft passed through the magnetosphere, the noise rose in pitch to peak, then decreased again. The irregularities in the recording, such as the sudden drop in volume at 15 seconds, are caused by irregularities in the magnetosphere of Ganymede as it passes through the influence of the immense magnetic field of Jupiter.



Pulsars

In 1967, Jocelyn Burnell discovered a source of pulsed emissions of radio waves which she described as sounding like an “idling truck” on the radio telescope, as it had a frequency of just over 1 Hz, about the same as a large idling diesel engine. A few theories were proposed as to the source of these emissions, including that they were coming from extra-terrestrials, because the pulses were so regular (they are more reliable than atomic clocks), leading to the first pulsar being called LGM-1 (standing for Little Green Men). However in 1968 they were shown to be coming from rotating neutron stars, which only emit radiation along one axis, so we only see the radiation when it points our way. In 1974, Antony Hewish, who had worked with Burnell as her doctoral advisor at the time, received a Nobel Prize for discovering pulsars, while Burnell did not – a decision that received much criticism from fellow scientists. Above is a recording of the Vela Pulsar, a pulsar with a period of 89ms, the shortest known at the time of discovery. The current fastest known pulsar spins once every 1.3ms, so fast that at the equator of the star travels at 24% the speed of light.



Lightning Pop

The lightning pop, or pip, or vip, or any number of words that have been used to describe it, is a sound that can be heard preceding the normal thunder associated with a lightning strike. It is heard if you are fairly close to the lightning, and is believed to be caused by an electrical discharge of nearby metal objects as the electric field immediately intensifies with the lightning strike. Above is the only recording I could find with a lightning “pop” – the cameraman was standing near a metal power line (he clearly knows his stuff about lightning), which was possibly where the sound of the discharge came from. It should be noted that the “pop” is not simply an artifact on the microphone, as people report hearing this sound with their own ears.