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Old 13th December 2007, 11:38 PM   #1
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Default spdif vs usb

Hi..!

I believe once this topic was written somewhere in this forum...just can't find it, haven't gone one by one thru 300 pages or so though.....

It seems to me that the usb connection proposes less jitter and more 'convinience' especially for the PC driver fans over the spdif. Probably there are other benefits but the reason above what I can think off now...

Since the last judge is our own perception regardless the tecnical specs, for this two kind of digital connection, can anybody share some experience about their sound quality reproduction...?

Thank you!!

Joshua
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Old 13th December 2007, 11:42 PM   #2
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Default dac spdif vs usb

ah....i'm sorry forget to mention that I'm talking about DAC!..

Joshua
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Old 14th December 2007, 04:42 PM   #3
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I really comes down to the implementation of each. Look at the recent Stereophile mag's review of the Bel Canto DAC. SPDIF was better than their USB implementation.

Most CD players have a much greater problem of bit accuracy than jitter. Remember a CD player has only one chance to grab the bits as the disc spins. If the disc is dirty, scratched, a finger print, etc. then there will probably be a slight loss of data. Most CD's are not truly "bit perfect".

I've invested more time getting my library bit perfect on a hard drive, then take steps to reduce jitter. I've been using a setup with a PC music library (a hard drive will keep reading until the data is bit perfect for fail) and stream the data to my DAC over Ethernet. Ethernet is also bit perfect and clocked completely different.

Sorry, probably got way off topic just to reinforce jitter causes errors and depending on the CD player you are probably not dealing with bit accurate data in the first place - thus compounding the issue.

Just a few thoughts.

-David
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Old 14th December 2007, 05:04 PM   #4
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I thought that most USB converters changed the signal to SPDIF which is less than ideal.
Some USB converters change the signal to 12IS, which some DAC chips can read direct. This cuts out a whole process and many say a lot of jitter too.
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Old 14th December 2007, 05:30 PM   #5
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Quote:
Originally posted by dublin78
I thought that most USB converters changed the signal to SPDIF which is less than ideal.
Some USB converters change the signal to 12IS, which some DAC chips can read direct. This cuts out a whole process and many say a lot of jitter too.

Agree! Specific reinforcing the implementation is critical. There are other factors as well. As usual it comes down to good design. Your point is a good one, if you are bypassing spdif, than spdif needs to stay completely out of the value chain.

Many times the biggest problem with spdif is an improper I/V design where the spdif cable's capacitance becomes part of the I/V circuit!

-David
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Old 14th December 2007, 05:47 PM   #6
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It is easy to dismiss the USB->SPDIF->I2S method as a mistake. But on closer examination you will see it is not. Going straight to I2S is great, in that it eliminates a bunch of circuitry and keeps added jitter to a minimum. However, one step forward and two back. You see, what you just did was to hard connect the computer system ground to the audio system ground. In the long run this becomes an issue. A lot of users of the direct connection method have had to resort to optical USB cables and other gadgets to fix the problems of noise and interference. Hello?

The beauty of SPDIF is that it is so easily coupled via a good transformer, thus providing all of the galvanic isolation you need between computer and audio. Of course, I2S could also be coupled via trannys (like DSL ones), but I don't believe anyone does it.

As far as SPDIF cable capacitance affecting I->V conversion, well you got me on that one.

jh
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Old 14th December 2007, 05:47 PM   #7
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Quote:
Originally posted by dw8083
I really comes down to the implementation of each. Look at the recent Stereophile mag's review of the Bel Canto DAC. SPDIF was better than their USB implementation.

Most CD players have a much greater problem of bit accuracy than jitter. Remember a CD player has only one chance to grab the bits as the disc spins. If the disc is dirty, scratched, a finger print, etc. then there will probably be a slight loss of data. Most CD's are not truly "bit perfect".

I've invested more time getting my library bit perfect on a hard drive, then take steps to reduce jitter. I've been using a setup with a PC music library (a hard drive will keep reading until the data is bit perfect for fail) and stream the data to my DAC over Ethernet. Ethernet is also bit perfect and clocked completely different.

Sorry, probably got way off topic just to reinforce jitter causes errors and depending on the CD player you are probably not dealing with bit accurate data in the first place - thus compounding the issue.

Just a few thoughts.

-David
Trying to understand from Bel Canto DAC technical paper, it uses asynchronous inside the system while maintaining the same SPDIF format from SPDIF digital source, so it actually has similar logic design with USB communication?

Joshua
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Old 14th December 2007, 06:03 PM   #8
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Quote:
Originally posted by hagtech
It is easy to dismiss the USB->SPDIF->I2S method as a mistake. But on closer examination you will see it is not. Going straight to I2S is great, in that it eliminates a bunch of circuitry and keeps added jitter to a minimum. However, one step forward and two back. You see, what you just did was to hard connect the computer system ground to the audio system ground. In the long run this becomes an issue. A lot of users of the direct connection method have had to resort to optical USB cables and other gadgets to fix the problems of noise and interference. Hello?

The beauty of SPDIF is that it is so easily coupled via a good transformer, thus providing all of the galvanic isolation you need between computer and audio. Of course, I2S could also be coupled via trannys (like DSL ones), but I don't believe anyone does it.

As far as SPDIF cable capacitance affecting I->V conversion, well you got me on that one.

jh
That's a good point - possible ground loop and noise injection from PC thru the ground path..

Joshua
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Old 14th December 2007, 07:45 PM   #9
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Default recommend a good dac

Not to get too far off topic but can anyone recommend a good external DAC for playing music from a pc? I was thinking spdif was the way to go because of the isolation and length of cable runs. I found plenty of usb projects but hardly any that use spdif for an input.
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Old 15th December 2007, 12:29 AM   #10
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Just go for it. Some are only a few dollars. See diyparadise.com.
Nothing ventured, nothing gained. Asuming you can afford a PC you can afford one of Yeo's. Best wishes
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