Computer based Hifi

[Idiocratease]

Well I will take a look. I have seen a lot of people raving about the quality etc. Cheers, Alan

[lazycatken]

Originally Posted by Idiocratease

Since the USB receiver only has to handle these 3 frequencies, the clocking to the separate DAC IC has almost no jitter.

I can't see any reason could result in this conclusion...
For instance, CD player only has to do 44.1KHz. Does this means CD player could be jitter free?
Check these
Asynchronicity: A USB Audio Primer | Computer Audiophile
Computer Audio Asylum - Steve read the post again - Gordon Rankin - November 02, 2009 at 07:03:40
No matter which circuit/solution, jitter must be taken care.

Originally Posted by Idiocratease

S/PDIF actually has to be sync'd to the exact frequency of the transport

That is so called PLL. Normally, it's done by S/PDIF receiver IC, e.g. CS8414.
And then, a clock is generated(according to S/PDIF) and send to DAC.
Problem is PLL can't generate low jitter clock...That's why a buffer and a separate precise clock is introduce in QDB76.

Originally Posted by Idiocratease

(i.e. if the transport is working at 44.0896K instead of 44.1K, the DAC has to sync to that frequency).
Therefore, the jitter problems of S/PDIF almost vanish using USB.

Using USB doesn't mean this...
Using Async mode USB and a precise clock could do this.

I guess, the statement of the article is just to give a simple explanation about the advantage of USB. But not precise.

Async USB is a good total solution, but only works for USB/PC. Buffer/async clock works for all. Although, the difference between signal source and the clock for DAC always results in buffer underrun/overflow. A longer buffer can simply make this problem happens once per couple minutes.

IMHO, I'll choose optical link + buffer/async clock to avoid electric noise from source. You know, such noise is hard to filtered out by circuits.

[Idiocratease]

Hi Lazycatken, It's complex for sure (to complex for me actually). The parts you picked up on were quotes I from articles rather than my opinion.

However, I can assure you that I am checking the optical route more carefully and awaiting a Wireworld Supernova 6, which a pretty decent cable. I will come back to you after I have listen properly. Cheers,

[lazycatken]

Originally Posted by Idiocratease

I can assure you that I am checking the optical route more carefully and awaiting a Wireworld Supernova 6, which a pretty decent cable. I will come back to you after I have listen properly. Cheers,

Check this. http://cplay.sourceforge.net/pmwiki.....04BitPerfect?
I made a test, got the same result.
My Toslink cable is cheap, made of plastic, 6 meters long!

Longer Toslink cable indeed results in poorer signal, but not error, just jitter. Such issue should not happen on your QDB76.

[phofman]

Originally Posted by lazycatken

Check this. http://cplay.sourceforge.net/pmwiki.....04BitPerfect?
I made a test, got the same result.
My Toslink cable is cheap, made of plastic, 6 meters long!

Longer Toslink cable indeed results in poorer signal, but not error, just jitter. Such issue should not happen on your QDB76.

The test results described on CMP are not that impressive, it is the only expectable result unless something is fundamentally wrong. IMO the upsampling should have been done to 24 bits only, eliminating thus the speculations about reasons of the LSB variations. In such case a single-bit identical result would be the only tolerable result for a proper digital loopback. There are no clock collisions, the whole chain is slaved to RME clock, no non-linearity issues in AD/DA conversions. Real-time upsampling is no major load for a resonably modern unloaded CPU, thus no underruns should happen.

OTOH, the 6 meters optical cable is a nice addition to the test conditions.

[lazycatken]

Originally Posted by phofman

IMO the upsampling should have been done to 24 bits only, eliminating thus the speculations about reasons of the LSB variations.

Ya...That's so strange... I can't realize why cMP guys did the 44.1K -> 96K upsampling... In my test, due to driver issue, I did 16bits -> 24bits. No upsampling.

To Idiocratease,
Check these graphs,
http://3.bp.blogspot.com/_QtIX994Ul0...l+phase+FR.png
It's impulse response of my system, EMU-0404 USB sound box as digital source, AK4380 as DAC. The two graphs show phase frequency response of Toslink & coaxial cable.

[Idiocratease]

Originally Posted by lazycatken

Y
To Idiocratease,
Check these graphs,
http://3.bp.blogspot.com/_QtIX994Ul0...l+phase+FR.png
It's impulse response of my system, EMU-0404 USB sound box as digital source, AK4380 as DAC. The two graphs show phase frequency response of Toslink & coaxial cable.

Hi There... I have not disappeared just listening to stuff, upgrading OS ect., and I'll come back you on the optical cable issue soon...

On your graphs.. I'm not an electronics whiz, have you analyzed the properties of the digital signal ?? ... I'm assuming these were not measured in the analogue domain (despite the fact that you have a freq x axis)... So I'm wondering exactly what you measured.... and I'm very interested in the difference you appear to have captured .... is the timing of the pulse slowing in the co-axial cable cf the optical... i.e. is the edge being more compressed at higher frequency, or being slowed down causing the phase to shift...?

[lazycatken]

Originally Posted by Idiocratease

On your graphs.. I'm not an electronics whiz, have you analyzed the properties of the digital signal ?? ... I'm assuming these were not measured in the analogue domain (despite the fact that you have a freq x axis)... So I'm wondering exactly what you measured.... and I'm very interested in the difference you appear to have captured .... is the timing of the pulse slowing in the co-axial cable cf the optical... i.e. is the edge being more compressed at higher frequency, or being slowed down causing the phase to shift...?

Well, the test is not well controlled. Just to show some potential possibility...
Here's the configuration. EMU-0404 USB sound box as signal source, connects AK4380 DAC via Toslink or coaxial cable. The analog output signal of AK4380 is connected to EMU-0404 analog input via a Mogami cable, so called microphone cable, single end. The graphs are generated in process of impulse response measurement. A log sine sweep, 10Hz~22KHz, as test signal.

Since EMU-0404 analog input and Mogami cable are not perfect, we can see some phase shift in the lower end of the graphs.
Per higher end, as I mentioned, we can expect signal goes through digital cable without any error. Thus, the only issue left, per the difference between Toslink & coaxial, is jitter. AK4380 can not immune from jitter... BTW, any electric noise in the system could result in more or less phase shift. For example, disable a ground-lift of EMU-0404, resulted in more phase shift. Use MacBook Pro or Asus M4E got different result.

From the graphs, I can't say which one is better, since my equipments are not calibrated. But from the point of view of noise, I tend to use the cable introduced less noise. That should be Toslink.

[Charles Darwin]

A bit late to the thread but FWIW I use a quadcore MacPro, iTunes (whose folder resides in its own WD RAID edition HD), connected via FireWire to an Echo Audio AudioFire12 which is set to 24/88.2.
I rip my cds in iTunes to AIFF.
The result sounds better (read: cleaner) to me than any cd player I ever had in my house and it took almost 5 minutes to set up.

[Idiocratease]

Originally Posted by lazycatken

...

From the graphs, I can't say which one is better, since my equipments are not calibrated. But from the point of view of noise, I tend to use the cable introduced less noise. That should be Toslink.

Ok, so it's the analogue frequency response you're measuring from the DAC.
I'm surprised any difference between the two cables is visible at all on the graphs.

Anyway, going back the to Coax vs Toslink. I know it's been a couple of weeks of silence from me, but I have taken your comments seriously (thanks). And I promised to look into your suggestion more closely after my initial rejection of Toslink.

As I mentioned I got hold of a decent quality optical cables (Wireworld Supernova 6)

What's complicated matters, is I also set up a dual boot with XP and the new Window 7. And I didn't have a sound card for Win 7, so used the USB output into my DAC (Chord QDB76). Well I was amazed by how good it sounded!

It was immediately clear to me that despite what Marian say there is subtle corruption of the data with XP and the Marian Marc 2. Irritating things I heard on my music which I've always thought were 'problems' in the original mastering, turned out to be subtle high frequency grainy glitches introduced under XP.

So still trying to test what you say about benefits of galvanic isolation that Toslink brings (with a re-clocking DAC, to eliminate the higher jitter from the optical cable).....

... I checked the chip on the QDB76. It's a PCM2704. So I figured I needed a simple USB --> Toslink converter to insert an optical path into the system. I tried a U-Control UCA202 USB, but this did not sound so good (I opened it up and it actually contains a PCM2902; I'm not sure if that's the cause). So I then bought a Trends Audio UD-10.1 USB Audio Converter. This does actually contain a PCM2704 chip, exactly the same as my DAC. So 'in principle' should eliminate all variables except the Toslink circuit and optical path (anyone else reading this, please note my DAC is a re-clocker).

Well, it certainly sounded good. I'm not sure if any differences I hear are real or imagined.. However, the Trends Audio kit had problems, kept erroring with the USB system on the PC, sometime was not recognised on re-boot. And actually was not a brand new item when it was shipped to me... So it's gone back for a refund. Probably just a faulty unit.

Well this left me wondering about getting an good optical signal from Windows 7 (and the Realtek Toslink on the MB is not supported yet). I had taken against the Trends Audio unit by now.

I did a bit of digging, and bought a Creative X-Fi Titanium (I know creative have a bad name, and my past experience with them is bad too), but it was not so expensive and worth a punt I figured... Well, it turns out these cards have a 'bit-matched' option. It sound really great, works beautifully under Win 7, and I now have the DAC galvanically isolated from the PC.

Now don't have any issues with using the Toslink and more importantly I've almost by accident learned the Window 7 is a massive improvement to the audio quality (I have dabbled with Vista in the past but was glitchy, so I was not expecting much from 7). So if anyone is reading this rambling story here are the conclusions...

AUDIO CONCLUSIONS

Window 7 = Really very good
Toslink (supernova 6 anyway) into Reclocking DAC = Very good, probably better than co-ax
Creative X-Fi = double plus good

Hope this is of interest