Stealth Audio Octava S/PDIF
Our customers and dealers often ask: what do you do differently compare to other cable companies? - I can easily talk for
hours about this. A lot of things that we currently do is done, or mentioned, or thought about by no-one else... A partial list of
these things, used in the Varidig Sextet:
The Varidig Sextet is, in fact, six-in-one: six Varidig cables, combined into one Sextet cable. The individual cables are
wrapped around a braided center core, and terminated with the absolute best available (custom, STEALTH designed and
made especially for DIGITAL audio transmission) connectors; each of the six Varidig cables has a solid core center (signal)
wire, and a quad-layer, variable pitch LITZ return.
The Sextet concept is similar to running several DAC chips in parallel in digital-to-analog converter (several well known and
highly advanced designers do that). Sometimes this configuration is called "stacked DACs".
The STEALTH Octava design is obviously based on the same concept, but takes it a bit further, running EIGHT full individual
Varidig cables in parallel.
Octava
To talk more about the Sextet and the Octava, I need to explain the “original” Varidig concept.
By the way, the name Varidig comes from Variable Digital. In my opinion, it's a good name. The only name that I like better doesn't belong to us – it is
"Bitmaster" digital cable by Empirical Audio. In my opinion, this Bitmaster cable is not as good as the Varidig (conceptually), but the name is great!
Our standard Varidig – approximately at 1⁄4 of the Sextet price - is a good cable, and usually it’s accepted by the listeners
well. The only questionable comment sometimes is that it sounds “dry” (this is probably the only complain I have ever had
reported back about the Varidig). The Varidig MAIN concept: OVERALL impedance correctness and impedance matching
between the cable itself and its terminations - is more "sound" from the pure technical point of view.
I didn’t create this concept, it's known to engineers working with microwave (very high frequency) electronics. The circuit board traces are often
made of variable thickness (for the impedance matching purposes) - so I just used the same idea and "transferred" the technology into digital
audio cabling.
Varidig is STEALTH exclusive technology
Varidig is different from any other digital cable on the market because its porous
Teflon® dielectric is thicker in the middle of the cable than it is at the ends. This specialized dielectric geometry eliminates
(greatly reduces) impedance mismatch at the critical points (where the connectors are attached to the cable, i.e. between the
inherently low-impedance RCA connectors, and the cable itself) which allows to achieve a true 75 Ohms impedance of the
ENTIRE cable (including RCA connectors) and therefore greatly reduces signal reflections in the cable.
The dielectric is porous (i.e. not solid, foam-like) and contains air bubbles. These air bubbles reduce the dielectric constant
from 2.0-2.2 typical for solid PTFE (Teflon) to approximately 1.4 in porous Teflon. In general, the lower the dielectric constant
of a dielectric used in cables, the lower the energy storage in cables. This transforms into perceived differences: "speed" in
analog cables, and “clarity” in digital cables).
In additional to impedance matching, the Varidig cable has considerably less pronounced internal cables resonance(s);
Less pronounced resonance (lower resonance “Q”) = more subjective clarity in sound;
When we place an audio system in a room, we prefer no parallel walls = no standing waves and less resonance; plus we
acoustically treat rooms for OPTIMUM damping (underdamped is bad (sounds too lively), and over damped is bad, too
(sounds dead, dull). What we need is optimum damping - not too much and not too little.
We apply this concept to our cables: in addition to its superior dielectric properties, porous Teflon is soft and can be
made more or less dense - i.e. various in mechanical damping. Fine tuning in this case is done by iterations (we vary density
of the dielectric and listen).
With Varidig, no length-dependent sound difference was noticed (or reported back to us), which confirms that the Varidig
cable sound the same in all reasonable lengths. This is based on the statistics we have accumulated (we carefully examine
the feedback we get from our customers);
S/PDIF and AES/EBU cables do sound differently despite their using the same design concept.
Why?
Because of several things, IMO:
1. Connectors considerably influence the sound quality in all cables, but in digital audio the quality of a connector is even
more important than in analog audio. S/PDIF and AES/EBU cables employ different connectors and this is partially
responsible for the sonic differences.
2. In both DACs and transports, S/PDIF and AES/EBU chips are different, and these chips have different sound. In some
equipment pieces, chips are the same, but S/PDIF signal goes in and out directly, while the AES/EBU goes through a built-in
impedance matching transformer - which is also responsible for sonic differences.
3. There is no way to predict whether S/PDIF or AES/EBU would sound superior, the only way known to me is to get both
S/PDIF and AES/EBU cables and listen and decide which one sounds best (with the given transport and DAC pair).
The differences in digital cables – while still audible – are usually not as clearly “pronounced” as in the analog interconnects.
Mostly because a decent DAC can “lock” on a digital signal being transmitted via about any two wires, and still sound 1/2
decent... But with a good digital cable it will sound better!
Digital signal is transmitted via a digital “transmission line” – where the output impedance (of a transmitting device), the digital
interconnect cable impedance, and the receiver (DAC) impedance is the same: 75 Ohms (or 110 Ohms in AES/EBU, i.e.
balanced digital).
This is a CHARACTERISTIC impedance – which is NOT the same as electrical impedance.
The CHARACTERISTIC impedance is directly related to the geometrical dimensions of a cable and the properties of the
dielectric used. It can be calculated using several parameters of a cable, but all we need to know to understand the Varidig
concept is that for the given center conductor thickness (in a coaxial cable) and given dielectric, a thicker cable will have a
higher characteristic impedance than a thinner one.
The vest majority of digital audio cable used for S/PDIF are coaxial, and made from a bulk machine-made coaxial cable.
The funny thing about the characteristic impedance is that while it’s defined as the impedance of a cable of infinite length
(very very long), a short piece of this cable will have the same characteristic impedance - if this cable is constant in diameter
along its length.
The STEALTH Varidig digital cable is different: its thickness (diameter) is not constant and varies along its length; hence the
name Varidig – from Variable Digital.
Why is it done that way?
It will be clear very soon: right after we have taken a look at what’s going on in digital signal
transmission.
In the standard (usual) digital audio link, we have cables (usually 75 Ohms in characteristic impedance), terminated with
connectors at both ends.
These connectors are seldom BNC-type (bayonet), and often – the RCA-type.
BNCs DO exist in a true 75-Ohms form, but our common usual digital audio connector is the RCA.
Unlike the BNC, the RCA connectors are NOT 75 Ohms – usually 30 or 40 Ohms (the ONLY exception is the WBT Nextgen,
but the dielectric used in NOT Teflon, it's some molded plastic, plus they break way too easily - but still, they are excellent
connectors; the NextGen are not 75 Ohms either – they are about 90 or 100 Ohms...
So, our common RCAs are much lower in their characteristic impedance (usually somewhere in the 30 to 40 Ohms range).
Same about the RCA females.
When these 30 or 40 Ohms connectors are attached to a 75 Ohms cable, an impedance mismatch is created at the
termination points (at the both ends of the cable).
According to the digital signal transmission theory (and practice ☺) we have two things happening: our signal is either
PARTIALLY absorbed at these impedance mismatch points, or PARTIALLY reflected back (to where it’s coming from).
What portion of a signal is reflected back or absorbed is difficult to tell. SOME portion. More than nothing.
What does this mean? THE DATA IS PARTIALLY LOST.
However, some people even like it: they confuse this loss of information with an extra "warmth" of a signal) but the data lost
or reflected is easy to see as a picture degradation on a High definition TV screen.
For an audiophile with ears losing the data is not good. The reflected data is even worse.
When the signal is partially reflected back from the connector, it travels back along the cable, then it’s reflected back again
(off the other connector, and the other end of the cable) – i.e. it bounces back and forth IN THE CABLE until is dissolved into
smaller “PIECES” AND EVENTUALLY TRANSFORMS INTO HEAT. The artifacts of that “bouncing” portion of a signal
interfere with the main signal and distort the audio presentation.
This is an explanation why conventional digital cables of the same construction and material sound differently in
different lengths.
In the STEALTH Varidig cable there are no impedance mismatch points – because of its construction.
