download the audio file 3.wav.gz

hints :

• Setup baudline to be a Netscape helper application as described in the FAQ.
• Turn on the 60 Hz notch filter in the play deck.
• Use the Digital Gain Boost in the play deck to increase the volume of this quiet signal.  Up to +0 dB of gain can be added before clipping occurs.
• Try playing the mystery signal at different speeds, slow it down or drop it an octave.
• Loop on the transitional points, play it again and again until you start to hear things.

What is it?

It is the squeaky air brakes of a garbage truck. The pulsed 400 Hz tone is the standard brake pad squeal sound that most likely mimics the pressure the driver is applying to the brake pedal.  The blips and traces in the 4000 to 9000 Hz zone appear to be a pseudo random walk which consists of some occasional harmonic content.  It is possible they are metal-on-metal resonance caused by a loose or vibrating brake pad.  The wide band noise burst at the 4500 millisecond mark is the air being released from the air brakes as the garbage truck comes to a complete stop.