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  Cable Products > xStream™ Digital xStream™ Digital More Info Starting at just $179.00!  Bits ain’t bits. It’s a plain fact. While we’d all like to take some comfort in the notion that digital is simply ones and zeros and the cable that connects these ones and zeros from the CD transport or DVD player to your DAC has no bearing on sound quality, it simply isn’t true.The quality of the digital interconnect cable that ties the digital output of your CD or DVD player to an external DAC can make all the sonic difference in the world. The PS Audio xStream Digital interconnect series represents the current state of the art in digital interconnects. If you are interested in a no-compromise connection between two digitaly interconnected pieces of equipment, then the PS Digital series has no match. Critical links Digital performance can be affected in many ways and can be improved by lowering the jitter in the digital data stream by a number of methods, including: up-sampling through interpolation, the addition of dither, and by careful attention to how you deliver that signal (so the jitter doesn't get worse). Resultant improvements to the data stream can range from significant to “Oh My Goodness!!” The level of improvement an xStream Digital will bring to your entire audio and video system will be a refreshing change to the hundreds of teeny tiny, barely perceptible changes that you have worked so hard to achieve. What makes the xStream Digitals so much better? To understand why the xStream™ Digital coaxial and XLR balanced versions are so much better than the vast majority of digital interconnects, we’ll need to start from the beginning of our quest for the perfect digital interface. There is a lot of science and engineering that went into the xStream™ Digital cable.  Passing a signal that ranges from 5 MHz to beyond 300 MHz is not an easy thing if you want to maintain rise time and signal purity. We thought you might enjoy reading some of the particulars of the xStream's thought process and construction. What makes this cable so much better? To understand why the xStream™ Digital is so much better than the vast majority of digital interconnects, we’ll need to start from the beginning of our quest for the perfect digital interface. Basic requirements of a digital cable Digital cables are very different than audio cables. In a properly designed audio cable you want lots of solid conductor material, good shielding, a reasonable level of capacitance and low absorption dielectrics in the insulation material. Most high-end audio cables require bandwidths below 100 kHz. A digital interconnect requires minimum bandwidths of 5 MHz extending into the hundreds of megahertz to faithfully reproduce the digital signals. To achieve this level of performance there are a number of areas the cable designer must pay close attention to:
Shielding is simply a way to keep unwanted noise out of the signal path.  In digital cables this is a critical element for success as unwanted noises are typically more prevalent at higher frequencies, which happen to be quite close to the digital signals themselves. Keeping noise energy low is but one important factor in proper digital cable construction. Keeping what noise does get through uniformly dispersed is another critical element. Noise is injurious to a digital data stream because it can increase jitter. If the noise spectrum is not uniform in nature, the resultant spikes and peaks can exacerbate jitter levels. Jitter? Jitter in digital audio and video is one of the biggest contributors to poor performance. Jitter is time-base error. It is caused by varying time delays in the digital data stream. Cables can contribute to jitter even after being corrected with a device like a Genesis Digital Lens, by causing waveform distortions due to mismatched impedances and/or reflections in the signal path, or by allowing noise to enter the data stream. A revolutionary new way to shield from noise With our main goals for noise reduction defined as lowering the radiated noise and improving the uniformity of the noise, we required a unique solution that simply and effectively improved both parameters. We know from our experience that double shielding works wonders for lowering noise. Each shield and the space between the shields reduces the noise level dramatically.  We also know that if we use two different shielding techniques, a different spectrum of noise will be lowered by each shielding methodology and together we will have a high level of noise shielding.From the view of the noise on the outside of the xStream™ Digital, the first shield it encounters is a 90% OFC copper braid. This first woven braid reduces a majority of high amplitude noise. What the braid doesn’t stop, the next shield will. The second shield, which is located nearest the conductors, is a wound OFC copper foil shield. Use of a heavy density braided material first, followed by a thin copper foil is recognized in high frequency transmission circles as the best possible shielding there is. The uniform approach Our next task is to take advantage of the results of the two shields without actually connecting them together. In most cables, the two shields are isolated from each other with an insulation material laminated to the inner shield. To increase the level of noise reduction we would prefer to have a relatively large gap between the two shields. The xStreams™ are unusual in the way we separated the shields. We made the insulating medium between the two shields a separate and slightly conductive layer. By conductively damping the capacitive nature of the  insulating material between the two shields, we were able to increase the gap, maintain even noise distribution, and lower the total noise on the conductor.A unique material known as conductive PVC is wound around the copper foil before the cable is braided. This lowers the capacitance and evenly distributes the noise currents, providing an almost uniform and noise free environment for the precious digital data stream. Skin effect Once we had solved the problem of shielding the xStream from outside noise we next turned to the transmission of the signal itself. At the frequencies used by digital audio and video signals, every factor of the cable becomes a critical element, including the way the electrons themselves travel down the cable. The higher the frequency of the signal, the more this signal is pushed to the surface of the cable, and that means the skin of the conductor itself carries a considerable portion of that signal. This phenomena is known as skin effect. Skin effect is a tendency for alternating current (AC) to flow mostly near the outer surface of a solid electrical conductor, such as metal wire, at frequencies above the audio range. The effect becomes more and more apparent as the frequency increases. The main problem with skin effect is that it increases the effective resistance of a wire for AC at moderate to high frequencies, compared with the resistance of the same  wire at direct current (DC) and low AC frequencies. In fact, at the frequencies we deal with, over 50% of the signal rides on the surface of the conductor as opposed to the inside of the wire. The effect is most pronounced in radio-frequency (RF) systems or digital. But it can also affect the performance of high-fidelity sound equipment by causing attenuation in the treble range (the highest-pitched components of the audio). Skin effect can be reduced by using stranded rather than solid wire. This increases the effective surface area of the wire for a given wire gauge. So, to make best use of our conductor, we need to concentrate on two areas: the amount of surface area and the material of the surface area. Smaller is better How would you increase the surface area of a wire? The wrong approach would be to use a single strand of wire (as many cable manufacturers do). For a given diameter of wire, there can only be a minimal surface area. The correct approach is to minimize the diameter of the wire and increase the number of strands. In fact, by going small enough in diameter and large enough in the number of conductors, we can increase surface area by more than 10 fold over a single strand of wire. In a nutshell, increasing the surface area of the conductors while maintaining a large wire gauge (with the increased number of strands) means that we get great signal flow with low resistivity.  Electrical resistivity (or its inverse, conductivity) depends on how difficult it is for electrons to move in a medium (in this case a metal core of OFC and an outer layer of silver). The electrons in a metal are distributed on different energy levels, which form bands. In discrete molecules the energy levels are widely spaced, and in metals there are many levels closely together, hence the expression 'bands'. Different metals have different molecular level spacings, which allows us to take advantage of the copper/silver amalgam. There are valence bands, which are like bonds and conduction bands, which in metals are usually empty or only partly filled with outer electrons only loosely bound by the atomic cores. The lower energy levels of the conduction band are below the highest levels of the valence band, making it easy for electrons to move into the valence band where they can move freely across the metal crystal. The highest energy level filled at absolute zero temperature is called the Fermi-level. At higher temperatures some electrons can have slightly higher energies and hence can populate the conduction band. Of course, we presnt this merely for information as running our cables at absolute zero temperatures might void the warranty-:) These bands also have shapes, called Brillouin-zones, representing some area with a high probability to find electrons. The exact nature of the energy levels in valence and conduction bands and the shapes of them – which depend on the crystal structure of the metal – determine its conductivity and resistivity. It  is for these reasons that we rely on pure copper (known as OFC or Oxygen Free Copper) and pure silver plated onto the copper.As a small engineering based company we do not have the means to measure the results of all this, but we can certainly theorize and, at the end of the day, we use our ears to 'prove' what we think works. Bottom line, the info we present here represents our thinking process and knowledge on the subject. The xStreams represent the final product, and since they are (by far) the best sounding and measuring cable we can find, we'd like to believe there's some validity to our thinking processes as explained. Silver is a great conductor While we are not fans of using silver in audio cables, we are proponents of using it in digital interconnects. Silver is slightly more conductive than copper, while copper has other qualities prized by cable designers. Therefore, an amalgam of these two materials nets us a superior conductor. At audio frequencies this approach can lead to an exaggerated treble region. In digital audio signals, silver plating provides improved signal transfer at the frequencies we are concerned with, while the copper core provides proper current density. xStream Digitals, both XLR and RCA, use the highest purity silver plating over OFC copper on all conducting surfaces to improve signal flow. Waveform Purity A little know fact about digital audio is that the rise time of the digital data (the time it takes to move from one state to another) is critical to low jitter. Digital data is made up of a series of on/off transitions, better known as 1’s and 0’s. The 1’s are the on-state and the 0’s are the off-state.  A popular misconception is that the quality of the 1’s and 0’s doesn’t matter. Nothing could be further from the truth when performance is the issue. Yes, digital equipment will operate and produce excellent results even with the lowest quality transmission of the data stream. But, if a high end performance is desired, waveform purity is a “must have” parameter. xStream™ Digitals maintain waveform purity better than any digital cable we have measured to date. Why purity matters Maintaining the generated rise time of the data stream in a uniform manner is critical to the success of a low  jitter approach.The rise time of the data determines at what point in time the DAC or receiving unit recognizes the transitional state between the 1 and the 0. The quicker the rise time the sooner the circuit will recognize that a transition has occurred. If this transition point varies with pulse width or frequency, then the data will trigger the DAC slightly out of time, increasing jitter. Therefore, maintaining a uniform rise time is a critical element in a digital cable design. How we maintain rise time Keeping the data rise time constant with frequency requires, in addition to increased conductor surface area and proper materials, a low capacitance and a low and constant dielectric absorption rate in the materials nearest the signal conductor. These materials are the insulating layer between the center conductor and the outer shield group. The best insulating dielectric known to man is nothing. That’s right, nothing. A hard vacuum. An air insulating dielectric would be next on our list. Unfortunately neither of these insulators is very practical in a cable. The center conductor needs to be supported, and until the day we figure out a non-physical contact Star Trek style levitating force field, to suspend the center conductor between the shields, claims of pure air dielectrics and vacuum dielectrics need to be viewed with some level of skepticism – at least in a consumer cable.  But there is an alternative, one that has many of the properties we are striving for. It is known as LDPE Foam, or PE Foam for short.LDPE (low density) foam is produced from a polymer assemblage based on low-density polyethylene with the addition of a foaming agent. It’s pretty tricky stuff this PE Foam and if constructed properly, is made up mostly of air. Picture soap suds for an example of this technology. Soap suds are, for the most part air, held together with a thin film of soap. PE Foam is identical, but instead of the soap used in our example we replace it with a thin “film” of polyethylene is that holds the air “bubbles” together. LDPE Foam has very low capacitance and a reasonably consistent dielectric absorption factor (dielectric constant). These characteristics, coupled with the 10-fold surface area of our silver plated conductors, helps to maintain waveform purity and constant rise time in the digital data stream. Insulation using PE foam has what we would refer to as a low dielectric constant (aka permittivity, DK, Er, etc.). A dielectric constant is the property of a material that determines the relative speed that an electrical signal will travel in that material. Signal speed is roughly inversely proportional to the square root of the dielectric constant. A low dielectric constant will result in a high signal propagation speed and a high dielectric constant will result in a much slower signal propagation speed.  A good analogy is to imagine yourself running along the beach with your feet six inches deep in the water. The dielectric constant is analogous to the viscosity of the water. If the tide goes out you are running in air (dielectric constant lower) and you can run faster. If the water suddenly turns to molasses, you are running in slow motion (dielectric constant higher). Construction geometry (a recap) In any complex delivery system, the net results of all parameters in the cable contribute to its performance. Great care and a lot of work has gone into the design and development of the xStream™ Digital cables. The xStream™ Digital’s basic philosophy of design relies on superior high frequency signal transmission coupled with excellent shielding from outside noise and attention to the connections and connectors themselves to avoid reflections in the cable. The xStream™ Digital starts with many fine strands of OFC copper and each strand is individually silver plated with a high purity silver in an effort to maximize skin effect. These strands are then bundled together to form the center single conductor, in the case of the RCA xStream, or in pairs to build the XLR balanced version of the xStream Digital.  Each conductor bundle then has an outer jacket of mostly air trapped in Polyethylene (LDPE Foam) extruded over it to form a low capacitance low dielectric absorbing bundle.This copper, silver, LDPE Foam bundle is then encased in an exotic shielding package made of an OFC outer braid, coupled to an inner OFC copper foil through conductive PVC, reducing noise and distributing that noise evenly through the entire cable. The connectors Aside from the obvious benefits good connectors provide: a firm low impedance connection over a long period of time, there is another phenomena to worry about: reflections. Reflections back towards the input end of the cable are caused by variations in impedance along the length of the cable assembly. This includes differences in impedance between the cable and the devices to which it is attached. Typically the connectors and the interface between the connectors will be major contributors to the reflection. To lower reflections, every solder joint and connection junction must be optimized. Even the small cups inside the connectors, that are used to solder the wires to the jack, must to be the correct size relative to the wire’s gauge if we want to minimize reflections in the cables. To make sure that we have the lowest level of reflections possible, we designed our own RCA connector and carefully selected the XLR version with these requirements in mind.  Each RCA and XLR connector on the xStream is precision machined, gold plated, and then soldered with a high silver content solder to make sure as little signal as possible is lost. The outer jacket Well, we said everything matters in a digital cable. Fortunately we don’t have to be too exotic when it comes to both the outer jacket and the protective braid. What is important here is flexibility without the propensity to kink. If the cable kinks, there will be impedance differences in the cable itself causing reflection problems and performance degradation. If the outer jacket and protective braid are so stiff that they promote sharp bends and kinks, the performance of the cable will suffer proportionally to the number and magnitude of the bends and kinks. On the xStream™ Digital nothing was left to chance. We built the outer jacket of a soft and pliable mix of both PVC and a high durometer softening material to keep the cable flexible. Finally, on the outside of the cable, we place a sturdy nylon single weave braid to finish the cable off. Available configurations xStream digital cables are available in many different lengths as standard: 0.5 meters, 1 meter and 2 meter lengths are the standard sizes. xStreams can be purchased in both single ended (RCA) versions (SPDIF) as well as balanced XLR (AESEBU). The xStream™ Digital Transmission Cable It is indeed, by far, the most exciting cable ever created for the transmission of a broadband digital signal. And most exciting of all is that the finest digital cable on earth sells for a mere $199!!! Yes, it is true. There are only a handful of things you can do to a cable before you have to start labeling your features as “pixie-dust”. But as you know, PS Audio prides itself on being the audiophiles' company and continues to be the performance/value leader in the market today. And now, xStream Glass! For those of you without a coaxial (RCA) digital output on your source equipment, you probably have an optical output called a TOSLINK. Long considered an inferior transmission method relative to coaxial, most Audiophiles have shied away from TOSLINK because of its limited bandwidth. One of restricting factors in a TOSLINK cable's performance has been the materials they use. Plastic. A much better optical transmission medium is glass used in the very expensive ATT glass cables found on a very few machines. The xStream TOSLINK cable is uniquely constructed from hundreds of fine glass optical fibers, rather than plastic, and the results are nearly at par with a coaxial xStream. If you are limited to an optical output, now there's help! xStream Glass is the answer for improved performance. All this from a $199 cable? You bet! All this and more! We were way beyond pleased at the results of this research and we were truly surprised at how far away from “correct” the vast majority of digital interconnect cables are and how much of a difference the xStream™ Digital interconnect made to our systems and is sure to make to yours. • Tremendous increase in image space, and realism “you are there” sonics. • Reductions in bright, hard digital artifacts! • Benefit’s are truly universal, regardless of price of connected equipment Applications xStreams will work with any high frequency data transmission system, including AC3, SPDIF and video to name a few. xStreams are the perfect medium of transmission between your DVD player and surround processor or video processor or DAC. xStreams work wonders between a standard CD transport and your DAC. Multiple xStreams can maintain near perfect signal purity even though they are cascaded in series. For example, xStreams have replaced literally thousands of dollars in digital interconnects in systems that are more complex than most and are providing jaw dropping results.  One example is a state of the art high-end audio system utilizing xStreams connecting the Sony SACD transport, to a Digital Lens, to a Purcell upsampler, and finally to the 30.6 Mark Levinson DAC itself. The system has never sounded better and all that has changed were the digital interconnects.Why you should try one The NEW xStream™ Digital Transmission Cable from PS Audio; optimized for AC-3, DTS, SPDIF and high speed digital signals of any kind, is now shipping. This just might be one of the more sensible things you can do to update your system. Sure, you can go to a lot of expensive add-on equipment like jitter reducers and upsamplers, and while we certainly wouldn't discourage you from trying those, we believe that improving your transmission line for the data stream is the first step in a succesful digital audio system. It can improve things dramatically. In fact, try one at home and see! This might be the best $199 you've ever invested in your system. Give us a call, click here to purchase on line, or visit your dealer. But, whatever you do, get it right. Get an xStream™ Digital today and your system will thank you for it.
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