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Audiophilleo 1 and 2 USB to S/PDIF transport - Page 5

post #61 of 1170

Agreed. I just meant the bios settings might not match for someone else, especially if they have an AMD processor or different bios etc.
 

Quote:
Originally Posted by DaveBSC View Post




This isn't a specific issue to your motherboard. When using any type of USB audio streaming, you do not want the CPU constantly shifting its clock speed and voltage.

 



 

post #62 of 1170

@pompom...

 

The most generalized and rigorous way  to express phase jitter in clocks is in terms of x ps RMS integrated from m Hz to Hz... for example, 15 ps from 10 Hz to 100 kHz. Specifying the bandwidth is critically important to make a valid comparison. These numbers are derived from measurements made in the frequency domain, using devices known as phase noise analyzers. The FFT is the key measurement technique. The $40K Symmetricom 5120a is an example; the $90K Agilent E5052. These prices give you a clue as to why not every company has these numbers readily at hand. But, these instruments are commonly available and the best manufacturers use them on a daily basis. Many designers do not understand the importance of phase noise and cannot be expected to bring out state-of-the-art products as a result.

 

Think of phase noise as the degree to which there are frequencies present at farther and farther offets from the intended frequency. For example, if 1000 kHz away from a 12.2896 MHz carrier there is -50 dB, in one product, but only -130 dB in another product, the second has much lower phase noise and other things being equal, will be a better clock.

 

Accurate clocks are as we all know critical for optimal A/D and D/A conversion. Furthermore, it is the opinion of some of the leading designers and recording engineers that the very low frequency offsets, meaning 0.1 Hz to, say, 100 Hz, are extremely critical with respect to realism, presence, air, and soundstaging.

 

My own experience is that with reference-grade gear, this is certainly true. Some DACs allow external word clocks, such as the Grimm CC-1, to be used, and with some, but not all, DACs, the increase in realism is extraordinary. The Grimm has very low phase noise in all parts of the spectrum. To get better phase noise, one has to go to very expensive but capable DACs such as the $20K TAD C-2000, which uses ovenized crystal-controlled oscillators.

 

Another type of jitter measurement relates to the clock period and is measured in the time domain. Think of this as determining when the edge of a clock signal actually takes place, compared to when it should take place. The overall jitter measured has various underlying subtypes (random, deterministic, data driven, etc.) which all, unfortunately, add up in the wrong way. A less measurement expensive device, such as a WaveCrest DTS (various models are available used for $1-2K), can make reasonably repeatable and sensitive measurements. The results are expressed as x ps RMS period jitter (y ps peak-peak). Devices under 50 ps RMS jitter should sound very well; the best devices, according to recording engineers and other folk with oversized ears and a lot of experience, are down around 2-3 ps jitter (the MSB DACs, for example).

 

The time domain jitter specs for S/PDIF are complicated by the fact that this signalling format mixes clock and data in the same serial bit stream. Thus, one must extract the clock, which in turn, requires a very high quality phase-locked-loop or PLL, and then measure the jitter. Building PLLs that are suitable for this is very difficult.

 

In either the phase noise or the period jitter technique, it's important that the measurements be taken at the S/PDIF output connector, because there's many a slip between the clocks and the outside world. Advertising copy that talks about "theoretical jitter" of such and such, well, draw your own conclusions.


Take a look at the phase noise plot... The Trimble (green) has integrated phase noise of only 16 femtoseconds, or 0.016 ps, from 10 Hz to 100 kHz. This clock is a special-purpose, single-frequency device that is designed for GPS applications, so, sorry, you can't put one in your DAC. The Grimm CC-1 is the blue trace, and it shows 260 femtoseconds over the same range; the Audiophilleo has 610 femtoseconds.

 

So, sure, one can measure jitter down to handsful of femtoseconds. What James was referring to in his excellent survey of jitter measurements on the Anedio Web site was more along the lines of eyeballing FFT spectra, measuring the jitter spurs, and then doing a simple calculation to get an idea about the jitter. The noise floor of the D/A process pretty much limits this approach to 1 ps; grosser values in practice. Some audio analyzers can do jitter measurements, but if you read the fine print, their accuracy is typically 1-2 nanoseconds (1000-2000 picoseconds).

 

And that, boys and girls, is that.

 

Trimble, Grimm, Audiophilleo phase noise.gif

post #63 of 1170
Thread Starter 

That's quite interesting.  Can't complain if the AP1 is better than advertised in this case.  It would be interesting to see a comparison of all the high-end clocks in this way.

 

Since I haven't (at least initially) noticed any difference using the jitter simulator in the AP1, I can only conclude that the result of the improvements it makes with my DAC have to do with some other aspect of the digital signal. Maybe it's simply that the output circuit is superior in some way.

post #64 of 1170

We'll be getting in several additional clocks this week and next. The products range from the $500 Black Lion Audio Micro Clock Mk 2 to high-end products such as those from Antelope and Esoteric.

 

The output stage of the Audiophilleo1 and 2 doesn't have any transformer; it drives the S/PDIF connector directly with ECL circuitry, which contributes to the fast rise times, and helps to keep jitter low.


With the JitterSim feature on, the phase noise is radically higher; you should notice a considerable degradation in sound quality. With this feature turned on, the jitter is something like 13 nanoseconds RMS integrated between 1 Hz and 100 kHz. These levels are possibly high enough to serve as rodent repellants. I just ran over to my reference system, and using the Bel Cantoo DAC 1.5, with Audiophilleo1 on its S/PDIF 1 input, turning the JitterSim on resulted in instant head pressure. There is a lot of vague distortion across the entire audio spectrum. Turning JitterSim off, instant improvement and relaxation. The extent to which your DAC can suppress jitter will determine how badly the sound is degraded, so that's a variable. In systems with limited resolving power, possibly the effects are not as noticeable.

 

The blue trace is the phase noise of the Audiophilleo1/2 using the 2.8 MHz clock; the magenta trace is the same clock but with lots of added jitter. In this case, higher dB is worse, meaning the phase noise is way higher. My limit to listening to it was about 15 seconds.

PN and JS.gif


Edited by DigitalDirect - 5/30/11 at 11:40pm
post #65 of 1170

and what happens when that superb SPDIF from the Audiophilleo gets turned into I2S by the SPDIF receiver in the DAC?

 

The best SPDIF receivers claim 50PS jitter dont they?

 

Let me know if Ive got the logic wrong here but it seems to me that its kind of absurd trying to get SPDIF great cause its bound to get all messed up again isnt it?

 

You can see Im technically incompetent in this but Im more interested in how it sounds. I think the Audiophilleo sounds great but I havent heard direct I2S devices as a valid comparison.

post #66 of 1170

To the extent that the conversion clock is extracted from the incoming S/PDIF (which it is in all but the most expensive $20K up DACs) the low phase noise is very helpful. Everybody else follows along from the extracted clock regardless of the internal pathways for the data.

post #67 of 1170

that response is like a politicians avoidance of a tough question to me

so if its OK i will ask the question again

why bother spending so much effort and money to get spdif really good when its going to be messed up with >50ps jitter on entering the dac?

SURELY ITS BETTER TO GET A DIRECT I2S DEVICE?

Personally I dont know the answer to that but I want to find out without wasting time and money

post #68 of 1170

Just paired the audiphilleo 2 with my assemblage 3.0 dac & audio-gd c-2 amp and I'm really impressed with the improvements so far.  Really brought out the potential of the assemblage. biggrin.gif

post #69 of 1170

Thank you for your most educative post even though I feel this is really getting too technical for me. redface.gif But at least it is nice to see my ears agree with your results, with noticeable improvements brought in my system by the AP2. 

 

I agree It would definitely be nice to see standardize jitter measurements among manufacturers.

 

May I ask you why do you use the range 10Hz to 100kHz for those frequency domain jitter measurements... Wouldn't be the 20Hz to 20kHz be more representative for the human audibel range... Is that related ? I though the SPDIF signal travelled at much higher frequencies (in the range of Mhz). Sorry for my dumb questions, just trying to make sense of what I read frown.gif

 

Quote:
Originally Posted by DigitalDirect View Post

 

Take a look at the phase noise plot... The Trimble (green) has integrated phase noise of only 16 femtoseconds, or 0.016 ps, from 10 Hz to 100 kHz. This clock is a special-purpose, single-frequency device that is designed for GPS applications, so, sorry, you can't put one in your DAC. The Grimm CC-1 is the blue trace, and it shows 260 femtoseconds over the same range; the Audiophilleo has 610 femtoseconds.



 

post #70 of 1170
Thread Starter 
Quote:
Originally Posted by tamahome77 View Post

Just paired the audiphilleo 2 with my assemblage 3.0 dac & audio-gd c-2 amp and I'm really impressed with the improvements so far.  Really brought out the potential of the assemblage. biggrin.gif


Good to hear. You might consider OPAMP-rolling that DAC too. It's possible you could still get a bit more with some of the newer OPAMPs available.
post #71 of 1170
Thread Starter 

I finally found the page about digital transports I was looking for and what I'd forgotten -- the shape of the S/PDIF square wave and its possible relationship to the differences we hear between transports.



Edit: I also had another go with the jitter simulation built in. I felt with the jitter simulator engaged that instruments lost a tiny bit of detail and were a bit smoother when they are more "sharp" and clear with it off. However, the difference wasn't enough that I'd call myself a reliable enough judge to be sure of what I was hearing.
post #72 of 1170

Hi Currawong

Interested in the Audiophilleo transports, do you (or anyone else) have any thoughts on the difference between running from USB power, running via a USB power adapter, how much power this unit takes from USB, what the rated DC input is etc.  Have reached a few dead ends after doing some legwork through this thread as well as audiophilleo site.

Thanks

post #73 of 1170

What wire/connector is recommended for using the Audiophilleo 2, spdif or BNC? 

 

 

post #74 of 1170
Thread Starter 

S/PDIF is a connection specification. I gather you meant "RCA".  

 

75 Ohm BNC is recommended, using the female-to-female adaptor included directly to the DAC.

post #75 of 1170

Quote:

Originally Posted by Currawong View Post

I think I'll have to stop by my local electronics store this weekend and get some parts.  I'm going to try the power supply for the Digital Interface and battery power. All my audio gear is still in boxes unfortunately. 


The Audiophileo should function best from battery power, as oscillators are very sensitive.  You could get comparable results from a really good power supply, but it would likely cost you more than it would to make a battery supply.

 

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