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Hi everyone!!! I am planning on making my own mp3 player and I have some basic questions about sound in general if anyone can help. 1) frequency. I know frequency is the of complete cycles something happens. How exactly does this relate to mp3’s and sound in general? 2) Bitrates. Is this the number of kbps the codec decopresses per second? 3) Channel: What does channel mean when it comes to mp3? What’s the difference between Stereo, Joint stereo, Dual channel and Single channel? Does it sound different in some type of way? Now how does all this fit together to make a mp3 player? I know these questions are really basic but maybe someone here can help me understand how all this relates to a mp3 player? So say you have a mp3 file that is Joint Stero,128 kbps bitrate, and a frequency of 44100 Hz…what exactly does all this mean? The last question i have is this…Every mp3 file I look at is MPEG 1. Does all codecs decode everything into MPEG 1 rather than MPEG 2 or MPEG 2.5? If anyone knows any good links or better understanding of sound please let me know so I can also read up on it. Thank you if anyone can help me out!!! Edited by - bravescharm on February 22, 2002 6:10:23 PM

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you want to make a player(using existing decoders) or your own decoder?
if you are just making the player then you can use directshow, bass, fmod, or openal for the decoding and you don''t have to worry about anything that you''ve mentioned.
if you''re making a decoder then the only thing i know is that mp3''s are mpeg1''s (layer3). mpegs2''s are totally different and i have no idea what mjpeg2.5 is.

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thuned,
I want to make my own codec. as in doing my own compressor/decompressor routines. The thing is, to really do a good player, I need to understand the complete meanings of stuff like frequency, Bitrates and Channel and how they all relate to music, mp3's and sound in general. So if anyone can help, please do...Thanks



Edited by - bravescharm on February 22, 2002 12:08:47 AM

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Well, if you know next to nothing about the meaning of frequency, bitrates, channels, etc etc... you''re going to have one hell of a time trying to write your own player/codec for any sound format, let alone something compressed as well as mp3 is... but anyway I suggest you start learning the basics from by looking up information on Linear Systems and Signals (z, fourier, and laplace transforms... time and frequency domain.. analog/digital conversion, Shannon''s sampling theorem, Nyquist Rate, quantization... all good buzzwords to search for if you''re looking for theory)

Once you understand that you can move on to searching for pages on Audio Compression and more specific things about MP3, and you might actually understand some of it =)

This is of course, assuming you really want to learn the fundamental theory behind signals and compression... it''s a pretty big field, driven a lot lately by cell phones (they''re all about real time signal processing and compression) and other things that use digital signal processors (DSPs)

This is all really complicated stuff, especially without any previous experience... I''ve had a semester and a half of this, and I can''t say I fully understand all of it either... (and I have a test this Wednesday over it too ;P)

and just so I actually answer a question... mp3 files are MPEG 1... mp3 stands for MPEG 1 Layer 3... There''s three different layers to MPEG1 audio... Layer 1 has a 4 to 1 compression, layer 2 (.mp2 files) has 6:1 compression, and layer 3 has 12:1 compression... MPEG 2 you may have heard of as AAC (Advanced Audio Compression) which is what''s used for high quality audio in MPEG 2... AAC hasn''t seemed to catch on despite higher quality and better compression, though it''s nothing earth shattering .. not enough to convince people to replace their 30 gigs of mp3s at least heh.. there''s also MPEG4 and MPEG7 audios... though they''re probably not what you''re looking for.. MPEG 2.5 is MPEG 2 with lower sampling rates (8, 11.025, and 12Khz, shudder)... made up by the Fraunhofer people as best I know

anyway, best of luck to ya... it''s kinda interesting once you muck through the mucky-muck (theory)

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