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Computer Audio Asylum: My tests on the subject by John Swenson

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My tests on the subject

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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.



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Topic - WAV vs FLAC: the REALLY definitive test - truthseekerprime 17:52:58 06/14/07 ( 20)