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139.68.134.1
In Reply to: RE: You are getting close posted by Christine Tham on June 14, 2007 at 19:54:34
I would like to think all of us here had open minds...I mean we did embrace the PC route, and well I must think that most of Audiophilia are close minded about THAT choice.
ANyhow, I think I am close to being able to do the test you are discussing...sort of.
I have dedicated ac runs , and if that is OK, can power the computers and audio components seperately.
I do have a mic, but not sure if it is good enough. It is the behringer ECM 8000. I bought 2 for DRC, but haven't used them yet. I still need a mic pre.
Even if those components are correct, there are some things that are a concern. First, my 2nd pc is not that good as an output device and my dac is not as resolving as my Lynx card. It would be ideal if I had 2 of them. 2nd, I don't know if I can hear any differences since I never play Flac on the main rig, and the normal pc is not resolving enough to know, and I don't have any of the files I am familiar with there.
It would be best if someone who can hear the differences can do the test.
I also use an SB3, but synchronously reclocked in the DAC (low jitter clock in the DAC, SB3 synced to that clock). I CAN hear a difference between streaming flac or wav, I cannot hear difference between flac or wav on the server. The server is in a different room and power branch from the stereo system.This surprised my, the reclocking down in the DAC should prevent any jitter born difference from showing up. I did bit compares on the data actually going in to the DAC chip and its identical in all casses, so thats not the issue.
I have a pretty good spectrum analyzer that I use for looking at phase noise of clock signals, I can see very small changes in jitter with this, I can see changes that I cannot hear. Looking at the clock going into the DAC chips I see no difference in the spectrum when streaming flac or wav. This seems to indicate that the reclocking is working well.
So where is the difference coming from? The only two things I can think of are EMI radiated through space or noise on the power line. I haven't come up with some definitive tests on this so I don't have hard data, but I do have a hypothesis:
I've been finding out that most power supply transformers have resonances in the 100KHz to 500KHz range, some have very strong resonances and others pretty week. If you have a piece of gear with a transformer with a strong resonance its very susceptible to noise on the power line near that frequency. (intersetingly enough "high quality" transformers tend to have much stronger resonances, the core losses in cheap transformers tend to damp the resonances) The hypothesis is that the flac decoding process is generating some extra noise in this frequency range that gets coupled to the power line, exciting these resonances in some gear.
In order for you to hear the difference your gear has to have a resonance that matches that prodeced by the computer, its going to be very gear and computer dependant. Some will have it, some will not. Using a different computer might change the effect.
Ive used the spectrum analyzer to measure the the power line that a computer is plugged into and I CAN see significant changes in the noise on the line depending on what the computer is doing.I tried a laptop and a desktop and the laptop injected significantly less noise into the line. So there is at least some possibility that whats happening in the computer could be effecting your gear independantly of the "bits" comming out of the computer, or even the jitter on the signal.
One intersting aspect of this frequency range that the transformers are sensitive to is that it can sail right through our usual attemps at "power conditioning". The frequency is high enough that it sails right through most "line frequncy" transformers and chokes, but low enough that most RF filters don't touch it.
There ARE methods to damp the resonances in transformers, but they are almost never used. I have never seen it applied in any of the commercial gear I've looked at. Part of the problem is that its transformer dependant and not so easy to measure the proper electrical paramters to compute the right damping network. I'm in the process of doing this with my own equipment, I'm going to repeat the test after I've treated all the parts of the system and see if I can still hear a difference.
Thats pretty much where it stands right now. Sometime in the future I want to do some tests measuring the output of the power transformers of different parts of the system and see if I can see a difference when streaming flac or wav. And try it with or without the damping networks in place.
John S.
Hi,
Interesting observation. I'd like to look into this and would like to start by trying to duplicate your results. Would you mind describing in a bit more detail what was resonating and how you measured it? I presume these are "linear" supplies rather than switchers.
Thanks, Rick
Your post is interesting. On my system, the digital and analog boxes are powered separately by two ac regenerators, and my computer based transport, when powered, is suppled direct from the mains via a transistor follower regulated dc supply, in an attempt to isolate the PC from the Mains and from the regenerators.
However, poweering components on and off has an effect on the sound; and powering the computer (laptop based destop) has a greater effect.
The system has been set up with an emc meter to space components apart from each other abut the greatest offending item is the satellite receiver (about 2.3 GHz) which needs to be turned off for audio replay. Unfortunately, I have a Sky system which needes rebooting every time I disconnect the box from the mains.
So, even with great care and fanaticism, it is difficult to have a system which is immune to mains and emc effects.
The SB3 itself is probably a generator of emc itself. I have found it beneficial switching my broadband modem, home nertwork and computers off completing when listening crtical to the hifi system.
Thanks John for taking the time to post your results.
Your theory seems plausible, and does seem to account for why some hear it, and why some don't.
It sounds also like you are saying that in some cases, the better the gear, the more likely one is to hear such differences. Is this correct?
HOw does ones processor speed factor in to this?
DO dedicated lines help?
Dedicated and isolated lines do help, but they don't totally isolate. Listening to my VIA 1.3G with RME card whilst using my download computer is not ideal. The sound is a lot coarser than with PC and modem OFF. The VIA is powered by an isolating transformer, and the PC thru a filtered Belkin box.
The Behringer ECM800 is a good measurement mic (I have one myself) but doesn't have a high dynamic range, so the measurements may be limited by the noise floor of the mic (I suspect it uses internal equalization to achieve a flat frequency response).
I'm not really advocating doing a test - in fact the opposite. I would only recommend doing a test if you are pretty sure you hear a difference and wanted to confirm. If you don't hear a difference, just relax and enjoy the music.
Remember: a system that is working well should NOT exhibit a difference playing back WAV and FLAC. So if a difference is noticed, it actually indicates there is a problem that needs to be fixed - it's certainly not something to be desired.
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