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Old 10th November 2003, 03:59 AM   #1
dqswim is offline dqswim  United States
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Default Computer coax digital spdif output.. USB?... Sampling rate??

Can someone reference or suggest a way to get a CLEAN and SIMPLE digital coax spdif signal out of my computer, Nothing special just 16bit 44.1khz cd sound..(Please no resampling... I currently have an SBLIVE.. resamples to 48khz)...

For reference I plan on sending the signal to a msb link for dac...through active crossover eq. BB opa2134 to diy pass zen variation 4 amp highs.. to open baffle dipole speakers

I figured that usb would provide the least noise and jitter by seperation from the computer case. So I looked at the offerings from M-audio; sonica theater and audiophile usb cards looked promising. The xitel pro link was also checked out.

The PCM2902 and uda1321 "diyaudio" references and associated datasheets were also checked out, I can solder somewhat but a simple prebuilt solution would be cheaper and easier.. not nearly half the fun though

I contacted Xitel about The Xitel Pro link, (uda1321 ??) and this is the reply i got

"it adheres to the AC97 specification for audio that sets the
sample rate for digital outputs at 48kHz. So the coaxial and optical
outputs are set to 48kHz instead of 44.1kHz."

someone must listen to digital sound from their computer without paying the resampling price??

maybe usb is not the way to go??
thnks..
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Old 10th November 2003, 05:28 AM   #2
JoeBob is offline JoeBob  Canada
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PCM290X can be very easy to work with and with a DIP adapter they should be easy to solder to. I'm currently working on a PCM2702 USB DAC (like the 290X but without SP/DIF out) and if you go the DIY route I'm sure you'll achieve much higher quality than a boughten solution for a low price.

No need to go fancy, but quality components and a good layout will do well in this amplication.
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Old 10th November 2003, 10:10 AM   #3
dhaen is offline dhaen  Europe
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diyAudio member Ukram has posted his PCM2902 project links in this thread:
USB DAC project
Although it is exacty per TI application sheet, it's reassuring to see that a diy'er has made it work

TI are accepting requests for samples....
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Old 10th November 2003, 05:09 PM   #4
dqswim is offline dqswim  United States
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appreciate the suggestions

looks like the pcm route is the way the go around here, so I'm strongly considering the pcm2902 route as the best option, simplest and highest quality

Simply usb in, digital spdif out... hopefully I can hack the ti circuit down even more

soldering a class a amp is one thing.... soldering this small chip should get interesting
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Old 10th November 2003, 08:47 PM   #5
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Default Re: Computer coax digital spdif output.. USB?... Sampling rate??

Quote:
Originally posted by dqswim

... someone must listen to digital sound from their computer without paying the resampling price??
Yes, through a M-Audio Audiophile 2496 PCI card. It supports all sample rates up to 96 kHz without resampling. Also over its S/PDIF out.

Cheers
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Old 10th November 2003, 11:38 PM   #6
dhaen is offline dhaen  Europe
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Quote:
Originally posted by dqswim
..snip...soldering this small chip should get interesting
Got my samples today 0.65mm lead pitch
Are there any SOOP28 to "something sensible" adapters available at a reasonable price? Or must I PCB?
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Old 11th November 2003, 10:42 PM   #7
dqswim is offline dqswim  United States
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check out these proto boards that look like they could do the trick.. will cost about $10 or so w/ shipping vs $22 at digikey for ssop/dip

http://protoboards.theshoppe.com/
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Old 12th November 2003, 07:27 AM   #8
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Hi dqswim,

The simple solution is a sound card with a CMI8738 or Envy24HT chip, neither of which resample for digital output.

CMI8738 cards - Zoltrix Nightingale Pro 6, Chaintech AV-515M, Aopen Cobra AW850D Deluxe (not the AW850 or regular AW850D).

Envy24HT & Envy24HT-S cards - M-audio Revolution, Mad Dog Entertainer 7.1, Chaintech AV-710

The pricing on these cards can vary based on the onboard DACs, etc - for straightforward digital I/O, they should all work well. The M-Audio Revolution is a favorite ($90 or so). New Egg carries the Chaintech cards at $21 shipped for the CMI8738 card and $27 shipped for the Envy24HT-S card.

Good hunting,
Nikhil
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Old 12th November 2003, 10:32 AM   #9
deandob is offline deandob  Australia
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Default USB

I looked into USB a little while ago with the uda1321 as it exposed I2S and did not force you to use an internal DAC or SPDIF as output (like the IT PCM2902 does). However without some serious buffering the nature of the USB protocol will mean that you will loose the occassional sample which is not acceptable for a high end solution. It may be possible to hack a Xitel link pro as the circuit board uses a custom logic chip between the uda1321 and the DAC. I have even worked out how to setup the uda1321 so that at startup it goes into I2S mode (email me if you need the details).

I came to the conclusion that to get high quality sound out of a computer you need to use a pro soundcard that is external to the PC (eg. the m-audio firewire 410) and expose its I2S connections to a better quality DAC than used onboard.

Regards,
Dean
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Old 12th November 2003, 11:45 AM   #10
deandob is offline deandob  Australia
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Default resampling

Dont forget that Windows resamples as well as some of the cheaper soundcards. To avoid Windows resampling, keep the software volume control at maximum (so no digital attenuation) and use either ASIO or kernel streaming. Winamp and foobar are the two most popular players that allow you to avoid software resampling.

Regards,
Dean
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