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Old 24th January 2005, 06:48 AM   #1
Leolabs is offline Leolabs  Malaysia
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Question Digital audio from IDE

Anyone has a schematic of a circuit that is able to extract digital audio signal(at least PCM type)from the IDE port of a normal CDROM??Hardware base??
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Old 24th January 2005, 02:34 PM   #2
gmarsh is offline gmarsh  Canada
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I can't provide a schematic just yet, but here's what would be involved in such a project:

- decently fast microcontroller (ATMega, single-clycle 8051, etc) which connects to CDROM's IDE bus and performs audio read commands.
- clock generation hardware.
- I2S generation hardware, probably a XC9572 or similar CPLD, which accepts parallel audio data from the microcontroller and an audio clock and shoots out serial I2S.
- digital audio transmitter which converts I2S to SPDIF/AES/toslink/whatever.

Actually. a Microchip dsPIC chip has internal I2S generation hardware and likely has enough GPIO to handle an IDE CDROM.
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Old 24th January 2005, 02:50 PM   #3
Jennice is offline Jennice  Denmark
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If I recall correctly, a lot of the CD-ROM drives I have had in my hands, have a digital audio out connector (located next to the analog out). I do not know the format, but it must be easier than using the IDE channel.

Is there any particular reason for not using this digital audio port?


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Old 24th January 2005, 03:03 PM   #4
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Is there any particular reason for not using this digital audio port?

The ttl level spdif cannot be of very high quality. There are all sorts of compromises involved not the least of which is a dubious ceramic oscillator. Of course some cdrom chipsets allow non-oversampled I2S which is much better. Getting audio out of the IDE channel is certainly not trivial.
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Old 24th January 2005, 06:13 PM   #5
ghetto is offline ghetto  United States
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Does anyone believe there would be any benefit to getting the audio data via IDE if there are already I2S signals available on your particular CDROM?
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Old 24th January 2005, 06:38 PM   #6
gmarsh is offline gmarsh  Canada
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Quote:
Originally posted by ghetto
Does anyone believe there would be any benefit to getting the audio data via IDE if there are already I2S signals available on your particular CDROM?
You can use your own clock - an "IDE-to-I2S" jig can generate its own high quality clock, or use one from an external DAC. The drive will spit out data on demand, it doesn't necessarily have to be at an "audio speed" established by the drive.

It may be possible to hack a CDROM to operate in I2S slave mode... it'd be a fun adventure to open up a drive, look up the datasheets for the chip used, and see if you can get that to work.

But if this works and then your drive dies or wears out, then you're repeating the datasheet hunt once again unless you get the exact same drive to replace it... There's another advantage of a jig - it should work with any cdrom/cd-rw/dvd drive you plug into it.

I'm contemplating doing a design of this now.
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Old 24th January 2005, 09:33 PM   #7
ghetto is offline ghetto  United States
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Personally I think an IDE based controller would be awesome. If people are serious about designing such a beast, I'm pretty handy with VHDL, PIC and AVR and could write and test code. Further I think a PCB that included whatever controller is settled on, plus high quality power supplies, user interface (buttons, LCD, RC5), and maybe even a popular DAC would make a great basis for a group buy.
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Old 24th January 2005, 10:55 PM   #8
jleaman is offline jleaman  Belgium
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ok i am going to follow this thread now too. BUt to say i have 2 cd players right now. one being a cd rom drive from a computer and the other one kinda the same but a manufactured dvd player in side there is a SMPS psu and a DVD rom and a screen ect ect then a dac board. Now when compairing the 2 the cd rom based one with NO IDE conversion sounds way better but useing the other one i can hear the difrence for sure. it spins the cd at hi rpm and converts the digital audio to non digital.. humm is it really worth it to use a cdrom and convert that to digital then to non digital ?
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Old 24th January 2005, 11:22 PM   #9
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old thread on this topic I was reading earlier:

DIY Computer CD Drive
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Old 25th January 2005, 12:51 AM   #10
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Originally posted by jleaman
ok i am going to follow this thread now too. BUt to say i have 2 cd players right now. one being a cd rom drive from a computer and the other one kinda the same but a manufactured dvd player in side there is a SMPS psu and a DVD rom and a screen ect ect then a dac board. Now when compairing the 2 the cd rom based one with NO IDE conversion sounds way better but useing the other one i can hear the difrence for sure. it spins the cd at hi rpm and converts the digital audio to non digital.. humm is it really worth it to use a cdrom and convert that to digital then to non digital ?

Errrr, the data on the disc IS digital. There is no conversion.
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