HELP US SOLVE A MYSTERY!

(last modified 10.1.2002)

Background

We have been making sensitive outdoor acoustical measurements. Our primary goal is to study Auroral Sounds (sounds and other acoustical effects related to the Northern Lights). One night (27.03.2001 20:41:10 UTC) our measuring system picked up some arabic music! The music was audible only 6-7 seconds in a recording of totally four hours. Up to now we have not found any clear indication of possible malfunctions in our measuring system. However, it is possible that one (or even two) SW or AM radio stations have somehow broken the shieldings and caused these interferences. We continue to analyze and test the system and its possible weak points. Up to now we know that the signal route of these radio sounds is the coaxial from the microphone preamplifier to the DAT recorder. DAT has not picked up these signals directly "from the air".

The following three explanations are the most probable ones:

1. Bad connection at the mic preamplifier output. Coaxial works as an RF antenna. RF signals are detected by some nonlinearity (e.g., the first active stage in DAT).
2. Bad connection at the mic preamplifier output. Coaxial works as a VLF antenna. Radio signals have been modulated down to the VLF range and picked up.
3. No system malfunction. The radio sounds are true acoustical waves and have been created by some nonlinear processes in the atmosphere (or environment).

Meanwhile we work on with these technical problems we hope help from the audience to find out which radio stations are in question.

Up to now we do not even know the possible wavelengths, probably the SW range is in question, the AM range is possible, too.

We would like to emphasize that these examples are the most mysterious ones up to now. Thus they may be caused by some technical problem.

However, from the spring 2000 we have collected other interesting audio material during tens of nights under different geomagnetic conditions in different places in Finland. This material contains more clear and more easy to analyze acoustical details we still work on. (Read more in our News).

Two audio examples

We release here two short equalized audio examples:

1. Monophonic signal taken directly from the original recording (down sampled and equalized in order to remove infrasounds and to emphasize the musical components).
2. Stereophonic signal, where the left channel equals to the signal in example 1 and the right channel is modulated down (carriage at 9091 Hz) and equalized (see closer technical details on other page).

The recordings are quite noisy - barking dogs can also be heard.

DO YOU RECOGNIZE THE MUSIC?

What is this music? Who are playing, what is the name of the piece?

Which radio station did this come from?

(it should be a SW or AM station perhaps in Algeria, Libya , Tunisia...?)

LISTEN and SEND your comments to: repo-raportti@acoustics.hut.fi

IF SOMEONE HAS AN AUDIO TAPE OF THE RADIO PROGRAM IN QUESTION - PLEASE TELL US!!

Date of recording: 27.03.2001 20:41:10 UTC

Audio Example 1.

WAV-sample (10s, 16-bit, 22050 Hz, 442 kbyte)

AIFF-sample (10s, 16-bit, 22050 Hz, 442 kbyte)

Waveform and spectrogram of the music found in the noisy signal. Duration 10 seconds, frequency band: 0-11025 Hz.

Audio Example 2.