The trademarked LEDR test signal is the brainchild of acoustician Doug Jones. We'd like to thank Prof. Jones for granting us the permission to put this test online.
LEDR™ stands for Listening Environment Diagnostic Recording, a test to subjectively evaluate the accuracy of stereo image reproduction.
In the eighties, psychoacousticians began researching what are called pinna transforms, the way in which the shape of the outer ear filters the incoming sounds and permits our brain to infer their location. By embedding the filtering characteristics of the pinna into the audio signal, sound can be moved around the listener's head from a single pair of loudspeakers.
The LEDR test generates pinna-filtered audio that will literally float around your speakers, assuming your sound reproduction system is neutral enough to preserve the original signal characteristics.
These test signals are not designed for headphone use.
You will now be testing your stereo system and room acoustics for correct imaging. If you have any problem reproducing the LEDR test, look for interfering room surfaces in the direction of the distortion.
|UP Left||UP Right||OVER||LATERAL||BEHIND|
UP paths, Left and Right. The sound should begin at about eye level and then travel as straight as possible up to one or two meters above the loudspeaker. Use the Left and Right paths to check for symmetry. If the sound does not rise up from your loudspeakers, try using high quality headphones instead. If headphones work, your loudspeakers and/or listening environment are at fault. If not, the pinna transform embedded into the test signal is possibly too different from your own pinna transfer function; the LEDR test will then fail in this particular case.
OVER. The sound should begin at one speaker and travel in a smooth arc to the other speaker, from left to right and then return back to the left. The arc should be unbroken, smooth and symmetrical. The top of the rainbow should be as high as the Up signals.
LATERAL. This signal tests for conventional left-to-right stereo imaging. Since a speaker's acoustic center may not be its physical center, you should use the Lateral test to adjust your speakers until the sound traverses a 60 degrees angle from the listener's point of view.
BEHIND. This signal moves from behind the left to behind the right, then back behind the left again.