mp3gain.exe version 1.5.1
copyright(c) 2001-2009 by Glen Sawyer
uses mpglib, which can be found at http://www.mpg123.de
Usage: mp3gain.exe [options] <infile> [<infile 2> ...]
options:
	/v - show version number
	/g <i>  - apply gain i without doing any analysis
	/l 0 <i> - apply gain i to channel 0 (left channel)
	          without doing any analysis (ONLY works for STEREO files,
	          not Joint Stereo)
	/l 1 <i> - apply gain i to channel 1 (right channel)
	/r - apply Track gain automatically (all files set to equal loudness)
	/k - automatically lower Track/Album gain to not clip audio
	/a - apply Album gain automatically (files are all from the same
	              album: a single gain change is applied to all files, so
	              their loudness relative to each other remains unchanged,
	              but the average album loudness is normalized)
	/m <i> - modify suggested MP3 gain by integer i
	/d <n> - modify suggested dB gain by floating-point n
	/c - ignore clipping warning when applying gain
	/o - output is a database-friendly tab-delimited list
	/t - writes modified data to temp file, then deletes original
	     instead of modifying bytes in original file
	/q - Quiet mode: no status messages
	/p - Preserve original file timestamp
	/x - Only find max. amplitude of file
	/f - Assume input file is an MPEG 2 Layer III file
	     (i.e. don't check for mis-named Layer I or Layer II files)
	/? or /h - show this message
	/s c - only check stored tag info (no other processing)
	/s d - delete stored tag info (no other processing)
	/s s - skip (ignore) stored tag info (do not read or write tags)
	/s r - force re-calculation (do not read tag info)
	/s i - use ID3v2 tag for MP3 gain info
	/s a - use APE tag for MP3 gain info (default)
	/u - undo changes made (based on stored tag info)
	/w - "wrap" gain change if gain+change > 255 or gain+change < 0
	      (use "/? wrap" switch for a complete explanation)
If you specify /r and /a, only the second one will work
If you do not specify /c, the program will stop and ask before
     applying gain change to a file that might clip



Additional info:
/w - "wrap" gain change if gain+change > 255 or gain+change < 0

Here's the problem:
The "global gain" field that mp3gain adjusts is an 8-bit unsigned integer, so
the possible values are 0 to 255.

MOST mp3 files (in fact, ALL the mp3 files I've examined so far) don't go
over 230. So there's plenty of headroom on top-- you can increase the gain
by 37dB (multiplying the amplitude by 76) without a problem.

The problem is at the bottom of the range. Some encoders create frames with
0 as the global gain for silent frames.
What happens when you _lower_ the global gain by 1?
Well, in the past, mp3gain always simply wrapped the result up to 255.
That way, if you lowered the gain by any amount and then raised it by the
same amount, the mp3 would always be _exactly_ the same.

There are a few encoders out there, unfortunately, that create 0-gain frames
with other audio data in the frame.
As long as the global gain is 0, you'll never hear the data.
But if you lower the gain on such a file, the global gain is suddenly _huge_.
If you play this modified file, there might be a brief, very loud blip.

So now the default behavior of mp3gain is to _not_ wrap gain changes.
In other words,
1) If the gain change would make a frame's global gain drop below 0,
   then the global gain is set to 0.
2) If the gain change would make a frame's global gain grow above 255,
   then the global gain is set to 255.
3) If a frame's global gain field is already 0, it is not changed, even if
   the gain change is a positive number

To use the original "wrapping" behavior, use the "/w" switch.

-.-