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How is a Standalone CD Drive capable of playing WAV CDs?

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purifier

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I've been wondering about this a lot... I know that a CD ROM Drive has this ability but couldn't get an exact explanation of this fact... Can someone give me a detailed explanation please?

When you give all the necessary power supplies to a Computer CD-ROM Drive, it can be made to function as a Standalone CD Player that can play "only" Wav cds but not mp3s...

Why does it play Wav cds? What does it have inside? Please Help
 

pisoiu

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As long as it has an analog audio output on the front panel, it also has all the necessary hw. to play a wav cd, where all the data are kept raw. It won't be able to play mp3s because this require much more processing power. The only problem is how you will tell the unit to "play"? Few years ago, I used a cd unit as standalone cd (the only connection was power), but the unit had pushbuttons in the front, for play, stop...etc.

/pisoiu
 

purifier

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Thank you very much... Can you be kind enough to tell me about that hardware that is inside that is responsible for the Wav playback? I'm not quite getting as to how the "hardware" and the laser or whatever are interfaced so as to facilitate playback...
 

pisoiu

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I am not very familiar with what is inside, but I imagine the following: the interface with the laser block will pass the data to a processor which is responsible with interfacing with IDE. The same processor should take care about other functions which the unit must perform independently (check the presence of a cd, see what type is it, manage the motors inside the unit, etc.). All it has to do to play wav files is to make an digital to analog conversion with the datastream from the audio cd. No complex mathematical operations (such as decompressing an MP3 file) are required. Just my 2 cents opinion, I am not specialist in designing cd units, perhaps somebody with more experience in this will give you a complete overview.

/pisoiu
 

    purifier

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purifier

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Thank You very much... That was very useful atleast at this stage... That mathematical point of view is very interesting... So you mean to say that the audio data can be read directly from the CD and given to a Digital to Analog Converter and then to the output to get the sound? If thats the case, are there any extra add-ons you've come across in your project life that even add the mp3 capability to the CD-ROM drive without a computer being there all the time?
 

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If you grab a regular audio cd (ex. audiograbber), the output will be a wave file, and this is how the data is stored on the audio cd. This is an uncompressed digital format, so basically all you have to do if you want to listen it is to convert it to analog.
MP3 is a compressed lossy format, and the decompression takes some computing power (fast cpu and a some memory). Nowadays, there are a lot of dedicated ICs for this task. I did not used such ICs. There are a lot of car cd units and regular cd players which are capable to play mp3s. They have a hardware decoder, one example you will find here http://www.atmel.com/products/MP3/ .

/pisoiu
 

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Thank You very much... I guess that should be enough... Sorry for the trouble though :)
 

Sceadwian

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The effort of adding the external button controls that allow a CD player to play back audio CD's unattached to a computer is less than trivial. All but the most advanced CD player programs for computers only trigger those commands on the player. The drive itself handles the CD audio playback, because it's inherant to the CD standard and has been since it was first introduced. The data formats were added later. Newer programs like Winamp (when properly setup) will read the CD in a raw data format and then use the software to send that information to the sound card for digital to analog processing. (Allowing things like equalizer settings on CD audio data and much higher quality audio output) Most CD players only have a filtered 1bit dac, which is a far cry from the fidelity of some modern sound cards. Most CD/CDR/DVD/DVDR drives nowdays only have an eject button, because it's cheaper to make them without the play/pause stop/eject and fwd/bkwd buttons, and VERY few people every used a CDROM as a standalone audio player. Why bother when you can buy a diskman at Wallmart for 10 dollars?
 

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