Bob Cain wrote:

You should at least hear signifigant increases in the noise
level when you get as far as -25 dB. Don't you? Or are you
working at greater than 16 bits for these trials?

16-bit's all I'm working with here.

Here are the readings for the 8 source WAVs I've used so far...

level peak
-18.7053dBFS -5.9999dBFS N01-05.wav
-23.7053dBFS -11.0000dBFS N02-10.wav
-28.7053dBFS -16.0004dBFS N03-15.wav
-33.7048dBFS -21.0011dBFS N04-20.wav
-38.7053dBFS -26.0013dBFS N05-25.wav
-43.7052dBFS -30.9956dBFS N06-30.wav
-48.7052dBFS -36.0054dBFS N07-35.wav
-53.7048dBFS -41.0011dBFS N08-40.wav

In all 8 cases so far, I've copied an original source WAV, adjusted each
copy via "Normalize -g -5dB", "Normalize -g -10dB", etc., on down to
-40dB. Then I've encoded each attenuated WAV to MP3 at 128kb/ps. Then
I've imported each of the resulting MP3s into Audacity where I've then
amplified them up to "-0.5". Audacity shows Full Scale as +/- 1.0 with
'0' in the middle, so -0.5 is just slightly below FS. I then save the
final decompressed MP3-WAV files back as WAVs to my hard drive.
Despite all of this processing, all 8 final WAVs sound "normal" to me.
By the time I got to -40dB, I'd have expected the final MP3-WAV to
sound pretty crappy but it doesn't - at least not by any degree which I
would expect it to sound.

level peak
-14.0943dBFS -0.9601dBFS N01-05.mp3.wav
-13.7098dBFS -0.7672dBFS N02-10.mp3.wav
-14.2900dBFS -1.0749dBFS N03-15.mp3.wav
-14.1163dBFS -0.9832dBFS N04-20.mp3.wav
-13.9006dBFS -0.9975dBFS N05-25.mp3.wav
-13.9302dBFS -1.0002dBFS N06-30.mp3.wav
-14.1153dBFS -0.9492dBFS N07-35.mp3.wav
-14.1134dBFS -1.0802dBFS N08-40.mp3.wav

Myke

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