Thomson has launched a Web site dedicated to the new formats, at All4MP3.com or MP3HD.com, and seeded it with an evaluation encoder that will allow users to create MP3HD files out of 16-bit, 44.1-KHz-encoded stereo .WAV files. Thomson also created an MP3HD WinAmp plug-in for Windows to play the files back as part of the same package.

The ubiquitous MP3 format is what’s known as a lossy format, tossing away what the algorithm considered to be unnecessary portions of the audio track in order to compress the file down to a more compact size.

In doing so, however, some of the audio content is lost, a problem for those who want to experience the full quality of the original source material.

The MP3HD format maintains backward compatibility with the basic MP3 format, a key advantage for the format, which enters the market with several already established lossless audio codecs already in place, including FLAC, HD-AAC, and Windows Media’s own lossless format. However, if not supported, the MP3HD file will likely play back as just a generic MP3 file.

“An mp3HD file is simply a “.mp3″ file including a standard mp3 file and additional information that is stored in the id3 tag (where other info on the track like artist name, song name, etc.. is also stored),” a spokeswoman for Thomson said in an email. “Therefore, an mp3 player that is not yet mp3HD capable will simply play the mp3 part of the file, as you said, as a generic mp3 file.”

According to Thomson, the format supports bitrates comparable to those formats, or about 500 Kbits/s to 900 Kbits/s.

A four-minute rock song encoded at 876 kbit/s will equate to 26 Mbytes, according to Thomson; other recordings could be ripped at 786 Kbits/s or 605 Kbits/s, for an average 4-minute file size of 23.5 Mbytes or 18 Mbytes.

One open question: royalty rates. Thomson charges 75 cents per PC software decoder, and between $2.50 and $5.00 for each codec; a hardware decoder is 75 cents, while Thomson charges $1.25 for a hardware codec. (The MP3 licensing page also contains rates for the MP3PRO format, an even more compressed version of MP3 that has since fallen out of favor.)

Interested parties should contact Thomson directly to negotiate royalty rates, the Thomson spokeswoman said.

Royalty rates will help decide if hardware manufacturers sign on to use the new format. At the Consumer Electronics Show in January, Fraunhofer IIS announced MPEG Surround, a surround-sound implementation of the MP3 format. Thomson did not announce that any companies had supported the codec.

“We are launching the format publicly today, and we expect to be in a position to make further announcements regarding its adoption in the coming weeks and months,” the Thomson spokeswoman said.

The problem, according to PCMag.com audio analyst Tim Gideon, is that a hardware manufacturer must support MP3HD to catch on. “It only matters when Apple, SanDisk, Samsung, Microsoft, etc. recognize the codec,” he said. “Until then, no matter how cool it is, it’s basically a theoretically cool thing that can’t actually be used.”