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  1. #1
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    phase noise -- what is old is new again?

    first off, i am not an electrical engineer nor a computer scientist and would greatly welcome any corrections and/or further insights into this topic.
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    in the recent discussions here about audiophile networking equipment in general and ethernet switches in particular, their ability to reduce phase noise has been of particular interest. not having run across that term before in the audio world and wondering if it is something that i might need to address, i did some research into the subject...

    if my understanding of the subject is correct, it turns out that with respect to computer networking, phase noise results from an imperfect oscillator [clock] used to time the transmission of data over the network. imperfect clocks cause random fluctuations in the cycle of a waveform.

    these fluctuations can be measured as the difference in frequency (cycles/sec) of the imperfectly generated cycle from the theoretically perfect cycle. here, fluctuations are measured in the frequency-domain which quantify how much of the actual signal lies within the theoretically perfect frequency. this is the measure of clock phase noise.

    these fluctuations can also be measured as the difference in the time (sec/cycle) necessary to receive one full cycle from the imperfectly generated cycle from that of the theoretically perfect cycle. here, the fluctuations are measured in the time-domain which quantifies clock jitter.

    thus, phase noise and jitter are the exact same thing being measured in two different ways. in fact, phase noise and jitter are transformations of each other (via the fourier transformation which decomposes a function of time such as a signal into its constituent frequencies).

    ...so, returning to the discussion of audiophile networking devices several things stand out here:

    the purpose of clocks in networking devices such as routers, switches, FMCs, etc. is to time the transmission of data over the network and ensure that it travels at the appropriate speed such as 10/100/1000 mbps. so, as long as the clock in the device operates within networking standards, thereby, ensuring interoperability and efficient network data transmission, its job is done — period. whether the device is a $25 consumer grade switch or a $1,900 tricked-out audiophile switch is irrelevant to network data transmission — again, provided each operates within standards.

    in the paradigm of an asynchronous DAC receiving a usb or ethernet signal, the purpose of networking devices and their clocks is simply to transmit data over the network to the DAC. once the DAC has received the data it is then the clock within the DAC which is tasked with the timing the digital audio stream for analog conversion. the clock in a network switch has absolutely nothing to do with the timing of the audio stream received by the conversion chip within the DAC and, thus, nothing to do with system sound quality.

    to the extent audiophile networking devices have designs and/or parts which reduce electrical noise and any environmental noise such as RFI and EMI, these devices can then have a material impact on system sound quality. however, this is a completely different subject than clock noise.

    so… why all the recent buzz around network device generated phase noise?
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  2. #2
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    Re: phase noise -- what is old is new again?

    I cannot really answer that other than to think it is a way of selling more snake oil. I have read many times that people use Ethernet versus USB because of phase shift jitter bad USB port unthinkable noise. So if they are now doing the same thing with Ethernet???

    I would personally think keeping your music from traveling across a network (routers, switches, long runs of Ethernet cable, wall plates, more Ethernet cables, etc.) would be better... in other words straight from the music source to the DAC, but what do I know.

    For USB directly out of my server I use a Wyred 4 Sound Recovery reclocker which uses a Femto clock to assure that the entire signal arrives at the DAC correctly. It did make a small, but noticeable difference.
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  3. #3
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    Re: phase noise -- what is old is new again?

    Quote Originally Posted by Randy Myers View Post
    I cannot really answer that other than to think it is a way of selling more snake oil. I have read many times that people use Ethernet versus USB because of phase shift jitter bad USB port unthinkable noise. So if they are now doing the same thing with Ethernet???
    exactly... or at least that is the cynical explanation: use an unfamiliar and ominous term for an issue that has long ago been addressed so as to create demand for new products solving said issue.

    don't get me wrong -- i love to do tweaks and fondle gear as much as the next guy. however, i would like them to solve an actual problem, do so in a way consistent with the laws of physics, and have a (subjectively) positive impact on system SQ. i am not in the camp of plunking down $1k or $2k for a tweak / dongle, sticking it into my system, and seeing if happens to make a pleasing difference -- seems a rather random and inefficient process.

    with respect to the new audiophile switches, my theory is that those reporting SQ improvement are benefiting from a reduction in electrical noise. however, electrical noise is best addressed with optical isolation methods which i believe are dispositive on the issue.

    Quote Originally Posted by Randy Myers View Post
    I would personally think keeping your music from traveling across a network (routers, switches, long runs of Ethernet cable, wall plates, more Ethernet cables, etc.) would be better... in other words straight from the music source to the DAC, but what do I know.
    i agree 100% -- storage on board the server / transport directly feeing the DAC is ideal. unfortunately, files traveling over a LAN is a necessary evil for those that use any of the streaming services.
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  4. #4

    Re: phase noise -- what is old is new again?

    Quote Originally Posted by aKnyght View Post

    ....
    so… why all the recent buzz around network device generated phase noise?
    ....
    A. Because snake oil is still being sold in the industry.
    B. Because folks who bought the oil feel that they have to praise its benefit to justify what they claim they "hear".
    C. All of the above.

  5. #5
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    Re: phase noise -- what is old is new again?

    The USB audio protocol is error-detecting non-retransmit. Ethernet is error-detecting retransmit, and another application layer protocol will be used on top. There are differences in how they work and how they're used, and it can be a mistake to consider them equivalent.

    All digital transmission protocols are designed with certain operating specifications in mind, which the hardware must satisfy. In other words, generally speaking any potential jitter is already accounted for when using the correct hardware and software in the intended environment. The only time it becomes a significant problem is when things are outside of your control, like transmission over the public Internet which is a general purpose system.
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  6. #6
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    phase noise -- what is old is new again?

    Quote Originally Posted by aKnyght View Post
    exactly... or at least that is the cynical explanation: use an unfamiliar and ominous term for an issue that has long ago been addressed so as to create demand for new products solving said issue.

    don't get me wrong -- i love to do tweaks and fondle gear as much as the next guy. however, i would like them to solve an actual problem, do so in a way consistent with the laws of physics, and have a (subjectively) positive impact on system SQ. i am not in the camp of plunking down $1k or $2k for a tweak / dongle, sticking it into my system, and seeing if happens to make a pleasing difference -- seems a rather random and inefficient process.

    with respect to the new audiophile switches, my theory is that those reporting SQ improvement are benefiting from a reduction in electrical noise. however, electrical noise is best addressed with optical isolation methods which i believe are dispositive on the issue.



    i agree 100% -- storage on board the server / transport directly feeing the DAC is ideal. unfortunately, files traveling over a LAN is a necessary evil for those that use any of the streaming services.

    On board server storage is a simple connection to DAC with Ethernet cable, USB or AES, (I use the latter does not need to be enhanced, simply a straight and balanced connection.)

    Audio switches play an important part and benefit enhanced with; Optical isolation Passive grounding and Power.

    I have done a fair amount of front end support to make streaming extremely close to server playback.

    I stream (Qobuz, way less Tidal) more during listening sessions as I don’t have all that much on the server, maybe 30-40 albums?).

    And now with my long awaited turntable in place, my money is going towards building my album collection, IMO can’t beat holding the physical media.




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  7. #7
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    Re: phase noise -- what is old is new again?

    In Isochronous Asynchronous USB the amount of phase noise and jitter are wholly dependent on the clock oscillator and other circuitry in the DAC itself. Nothing else matters upstream. There are mechanisms where electrical noise from upstream components can be injected into the ground or power supply of the DAC by capacitive and inductive coupling. This is alleviated at least in part by galvanic isolation which is common in most higher end DACs. All galvanic isolation circuits are not created equal. Some pigs are smarter than other pigs. As mentioned previously, an optical interface would completely eliminate any coupling.
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  8. #8
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    Re: phase noise -- what is old is new again?

    Quote Originally Posted by W9TR View Post
    In Isochronous Asynchronous USB the amount of phase noise and jitter are wholly dependent on the clock oscillator and other circuitry in the DAC itself. Nothing else matters upstream. There are mechanisms where electrical noise from upstream components can be injected into the ground or power supply of the DAC by capacitive and inductive coupling. This is alleviated at least in part by galvanic isolation which is common in most higher end DACs. All galvanic isolation circuits are not created equal. Some pigs are smarter than other pigs. As mentioned previously, an optical interface would completely eliminate any coupling.
    +1 -- pretty much says it all on the subject
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  9. #9
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    Re: phase noise -- what is old is new again?

    The technical side of all this is beyond my time. I coud study it and become an Objectivist . Instead I listen to others and if I hear enough to support trying it, i buy and give it my subjective evaluation. For whatever reasons I found linear PS to routers and modem and audio grade switches make digital more enjoyable on my setup. Others seem happy with a laptop to a dac. Others are never happy with all the bells and whistles.

  10. #10
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    Re: phase noise -- what is old is new again?

    Quote Originally Posted by Kingrex View Post
    The technical side of all this is beyond my time. I coud study it and become an Objectivist . Instead I listen to others and if I hear enough to support trying it, i buy and give it my subjective evaluation...
    on the flip side, i could ignore all the research and fact gathering i [and others] have done and become a subjectivist...

    subjectivism - noun, philosophy: the doctrine that knowledge is merely subjective and that there is no external or objective truth.



    seriously though, in the end we all go with our ears and what is pleasing -- that is how it should be.
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phase noise -- what is old is new again?

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