Files in this directory
=======================

All the files starting noise_x are test tones for the AutoEQ feature. They must be loaded onto the car player 
using emplode 2.10 (to ensure that the title tags are auto-generated correctly).

There is no need to put the files into any playlist, unless you wish to do so for your convenience.

pink_noise.mp3 is provided for your convenience. It is a type of noise in which each octave contains 
equal energy (up to half the sample rate). Note that future AutoEQ algorithms might use this file 
instead of the band-limited files.

The band-limited files were generated using CoolEdit using the following method:

1. Generate pink noise
2. Bandpass filter to the specified frequency range using very steep roll-offs
3. Normalise so that all files have the same RMS loudness

The files are named as noise_<lower cutoff>_<upper cutoff>.mp3

Note that the frequencies are more densely packed in the bass range. The files from 20 to 200Hz are 
each 2/3 octave width, and the files from 200Hz to 20KHz are each 4/3 octave. This reflects the fact that 
the natural frequency response of in-car systems tends to be smoother in the mid/high range than in
the bass.

Note also that the process of mp3 compression can perform very efficiently on band-limited content
since it is able to exploit the fact that most of the frequency spectrum is silent. Consequently,
the lossy psycho-acoustic algorithms will not have been engaged at all for most of these files (except
perhaps the very high-frequecy ones).

John Graley 

2 July 2004