The original story: http://lange-flugzeugbau.com/htm/english/news/
noise_measurement.html
(Note our brand new homepage. Much more info in it
now)

At 17:36 04 August 2006, Greg Arnold wrote:
I wonder if it makes enough noise for engine operation
to be recorded by
the ENL function of a flight recorder.

Due to the RPM of the engine, the LE42 propulsion system
produses most of its noise on exactly the same frequence
which flight recorders pick up. There is no problem
recognizing powered flight.

cheers,

Andor