| Shine up your music to MP3: Peter Everett's fast encoder port |
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Published: 6th Apr 18:12:19GMT Source: Drobe News
By Chris Williams
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As part of drobe.co.uk's article series looking into digital music on RISC OS, we now look to Peter Everett's new application, Shine. Shine will take a WAV file or any music data file in the format of 44.1kHz signed linear 16 bit, and convert it into an MP3 file. Shine is in effect the opposite of David Chapman's MP32WAV application; an explanation of the difference between the WAV and MP3 formats is explained here. MP3 files can be played using AMPlayer as discussed by Justin Fletcher in a recent drobe.co.uk feature article.
MP3 is format where music is digitally encoded and compressed into file form using clever mathematical and audio processing techniques, ready for playing on a RiscPC. Shine has been optimised for speed as previous MP3 encoders for RISC OS take their time to convert music, a problem lying with that the ARM processors that RISC OS runs on aren't able to natively handle the complex maths involved. So considering a StrongARM processor isn't built for complex mathematics, according to Peter, a 3 minute stereo track can be converted into MP3 format in under 7 minutes on a StrongARM computer running Shine. An simple indepedant test of Shine on a StrongARM 233T took 6min 30sec to convert a 4min track to MP3 format at 128kbs. The exact speed of Shine's conversion powers is down to the sound quality required, (at least 128kbs is recommended), and the type of music been converted. When it comes to encoding music, there is a tradeoff between speed and output quality, however in his announcement Peter believes he has found a good balance.
On usenet, many people have being showing their appreciation of Shine's speed so we caught up with Peter and spoke to him about Shine.
"For some time now I have been interested in the methods used to squash up music", writes Peter. "How can you remove up to 80% of the musical content yet reconstruct it so it sounds unchanged? Amazing.
"I had looked at the standard source codes around and they are all so 'BIG' it is difficult to understand what is really going on. About the end of January, during an idle lunch hour, I stumbled on the Shine source. It is by Gabriel Bouvigne of www.mp3-tech.org and all credit should go to him and the people who wrote the original sources because I really have not done much.
"It is basically an imcomplete encoder, containing only the minimum parts to make it work. Gabriel states that it is a good starting point. The main thing is that it does not contain a psychoaacoustic model. This means that it encodes all sounds including those which you would not normally hear. As a result it will not make a good job of all types of music and will not work well at low bitrates. The advantage is that it has less to do which makes it faster and it is easier to understand.
"All I did was convert all the floating point operations to fixed point fractional arithmetic. There are a few floats left but they are not executed regulary and so don't make much difference.
"The speed increase by doing this was about 30 times. From taking an hour for every minute of sound track to taking about 2 minutes per minute. I was suprised to say the least. I have tried to maintain 32 bit accuracy throughout although this is a bit tricky in places. The ARM is good but it's not a DSP, so I suspect the quality has been compromised but I've not been that critical. Let's face it, this is not a serious application, just a bit of fun.
"It took about a month of odd hours here and there in the dark evenings through February, and for most of that time I was stone deaf in one ear due to a bad cold. So if it only works in one channel you'll know why."
Contacts
Shine for RISC OS: www.everett9981.freeserve.co.uk/pete.htm
Related articles
Thunderbird 'demo' port released
How to port RISC OS 5 to the RiscPC
Open source Quake 2 port emerges
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