ST-Computer Leser-CD 2000 January

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Text File | 1999-12-10 | 8.2 KB | 195 lines

********************* * FalcAMP v0.80ß * ********************* Audio MPEG Layer 3 player for Atari Falcon 030 computers By Denis "STGhost" HUGUET and David "Splash" CARRERE ----------- ╜Sector One 1998-1999 Sector One is proud to present the first beta release of an MP3 player for Falcon 030 computers. I/ What is MP3 ? ---------------- The MP3 fileformat has become one of the most used audio format in the world. This format is in fact the "layer 3" of the MPEG audio streams. Unlike most people think, the MP3 isn't a better compression system: for a given bitrate, it will give the same filesize as a "layer 2" file. The "layer 3" has been developed for low bitrate streams so that it provides a good way to transfer audio data across Internet. But at com- mon bitrates (those used for good sound quality) it doesn't differ in quality compared to "layer 2" files (except if a bad encoder has been used, of course). The "layer 2" is recommended for very high quality encodings (high bitrates). II/ The player -------------- Well, it took us a lot of time but here is the first release. This program is spread as a TTP executable file as we're still working on it. It will allow you to play MP3 files under these conditions: -only layer 3 is supported -MPEG 1, MPEG 2 and MPEG 2.5 fileformats are supported -Mono, Stereo and Dual-channel files are accepted, not Joint-Stereo. (in fact, there is a trick to listen to Join-Stereo files, see below) -the file is not severly damaged (simple error-recovery built-in) If the file is recognized, it will be played until its end unless you press the 'space' key before. It is pure monotasking...it will run under a multitasking OS but it will freeze alot the system ! That means that the player will slow down other programs but it can also be slowed by other programs (CAB for example). Also, avoid to play files from a slow harddisk or from a slow CD, because it would probably entails cuts into the sound (disk buffering). Next versions, we'll have some GEM interface and an interrupt based decoder that will reduce the CPU time usage and speed up the disk buffering. So don't cry about that for now please ! Please keep in mind that both processors, even though they're working in parallel, need to synchronize so if you get a rate higher than 100% it means that one of the processor is too slow...either you're doing too much things in parallel on the 030 side or the dsp is simply too slow (should only happen if you don't use an audio clock on a standard Falcon for playing an MPEG 1 stream). The only condition to run this player is to have 1.6Mo of free RAM on your Falcon 030. This amount of memory is required mainly to speed up the player. However, if you want to play MP3 files on a standard Falcon without an external audio clock, you should avoid big screen resolution because this may cause some slowdown of the replay, this should be very important if you have a VGA screen on your Falcon. You can either keep a large screen by shrinking the number of colours or use a small screen with a lot of colours... III/ Features ------------- The player supports some extra features: -External audio clocks automatically detected and used (dual clocks and FDI recognized too) -Linear sample interpolation to convert MPEG replay frequency to Falcon audio frequency. Useful only if you have not an external clock. -ID3 tags v1 and v2 recognized: they will be displayed at the beginning of the replay (v1, v2.2.0 and v2.3.0 recognized) -Displays details about the fileformat at the beginning of the replay (after ID3 if any). These infos are based on the first frame, but it supports format-changes on the fly (except for frequency) -Variable bitrate supported -CPU speed boards accepted and recommended (especially if you don't have any external audio clock and you want to play 44.1kHz or 48kHz files). It's not very important for this version, but it will be for the next release (if you want to use it as a desk accessory for example). IV/ Known bugs and limits of this version ----------------------------------------- - The accuracy of Layer 3 final resolving has to be improved. The DSP's 24 bits fixed-point representation is not convenient for the Layer 3 decoding algorithm we used. When the sound is weak, the signal/noise ratio could decrease, lowering the sound quality. We will add new DSP routines later. - The Joint-Stereo encoding scheme isn't supported yet but will be decoded as a normal Stereo-encoded file. This will result in more or less noisy clicks on the left channel and probably weird sound on the right channel...This filetype will be supported in the next release. - We did our best to make this player works with 16Mhz 030/32Mhz DSP. Most of the time, the file will be replayed correctly, even if it could use most of the available time of your Falcon. But problems are possible sometimes with 44kHz and 48Khz stereo MP3 files, resulting in a kind of echo effect or adding noisy clicks. If you have a 50Mhz 030/50Mhz DSP, you should never have this kind of problem ! Anyway, to let standard Falcons users listen to all MP3, we added a special "Standard Falcon" mode, wich will output Join stereo and Stereo files as if they were mono. A 32Mhz DSP has then enough time to process the file at correct rate. To use this special mode, keep the SHIFT key held when starting FalcAMP. We did our best to make this software system friendly, and to prevent any unexpected freezing of your computer. But, please, keep in mind that we cannot guarantee a complete reliability, all the more this is a betaversion. You have been warned ! For bug reports, please send an email to STGHOST or SPLASH, using more or less the following model. Try to fill it with maximum accuracy. FAMP's standard bug report: ~~~~~~~~~~~~~~~~~~~~~~~~~~~ a- Executable file and my configuration My FAMP version is the: ___, FAMP.TTP filesize is ______ bytes. Hardware configuration of your Falcon: model, memory, and additional hardware (clocks, faster CPU/FPU/DSP, enhanced sound system, ...). Software configuration of your Falcon (when you found FAMP's bug, else the most frequently used): TOS version, additonal OS. b- Layer 3 file (Please, always keep the file wich is not played correctly until we answered.) A bug occured with: ________.MP3 file (available at: ...). Filesize is: ... Displayed infos are: ... Kind of error: -> Famp give me the following error message: -> Famp is locked -> The sound is not correct. Here is a short description of what occured: -> ... V/ Authors ---------- Who did what in this player: (I know what you did since last summer :-) STGHOST (030 part) deunstg@free.fr File parsing, disk caching, scalefactor decoding, fast Huffman decoding, clock detection, error recovery and many weeks of debugging SPLASH (DSP part) dcarrere@worldnet.fr Sound system init, DMA-DSP transfer, requantisation, antialiasing butterflies, IMDCT, polyphase filerbank, linear interpolation, and many more weeks of debugging FAMP is a 100% assembler product, based on AMP 0.71, AMP 0.76, MPEGA and ISO MPEG sourcecode, that we completely changed, improved, and optimized for Falcon. We'd like to thank: -Tomislav Uzelac for spreading his sources of AMP -Stephane Tavenard for giving us his sources of MPEGA -All people who believed in us... We decided to spread this software as a freeware. We did FAMP for the fun, and also because we were dying to listen MP3 files on our Falcon ! Also, maybe we did it because people used to say that it would be probably impossible to do, and we were convinced that it was possible. Anyway, because of the huge work we put into this player, we wait -at least- for support and aknowledgements, and -at most- for money if you think it's worth the price. If you use FAMP often, please, do not forget us... It may speed-up the release of next version ! :-) Have fun !