Archive for November, 2010
No, I haven’t gone mad. Yes, this is still a blog about hifi. Let me explain…
I was on the way to a dinner the other night in town, and I happened to walk past a restaurant with live music. I knew it was live music from the moment I heard it. Even though it was in the middle of the city, and there were cars and people and noise everywhere, and even though I could only hear it through reflected sound since the band was somewhere deep inside the restaurant and I was I was standing across the street and slightly down the road (and nowhere near line of sight), I knew at the first instance that it was a live band.
Fast foward to some time later. I’m in my living room. On my couch, listening to some similar music through my expensive speakers, tube amp and a Michell Gyrodec turntable that cost me a kidney. I close my eyes, and no matter what I do, I just know that it’s a hifi system. In fact, I realise that never in my life have I heard music through speakers that has fooled me into believing it was real.
Now, let me add at this point that while I’m no professional stereo reviewer, I’ve heard my fair share of high end gear. Aside from the gear of my own and that of my friends’, I’ve been at trade shows and various demo nights and listened to everything from $50k speakers to $60k amplifiers to cables that cost more than my entire system. A former client of mine had a $150k system which included some flagship Wilson Audio speakers and a turntable with a cartridge that had more exotic materials than the space shuttle.
Yet, never in my life have I walked past a room with music playing and mistaken it for live music. This made me realise something quite disturbing. High end audio sounds crap!
One would think that when audio gets even to the astronomical level, it would approach perfection. But this is simply not the case. The next time you get a chance to listen to a “good system”, take a note of what it sounds like. Listen to the sound that comes from it and ask yourself, “Does that sound real? Does that actually sound like a real piano coming from a wall? Does that guitar actually sound like it’s 10 feet from your chair?”. Chances are, it does not. It may sound similar, but it doesn’t even compare with live music.
High end followers go to extraordinary lengths to make their systems “more realistic”. They spend exhorbitant amounts of money on gear, they change their floors into carpet, they line their walls with curtains and they use rulers to ensure that their speakers are absolutely the same distance from the wall. Yet, I catch a small glimpse of music, partly amplified by cheap mobile PA equipment, reflected numerous times off walls, around corners, across a busy city road and barely finding its way into my ears…and the difference is so obvious.
Hi-fi stands for high fidelity. The purpose of hi-fi is to reproduce sound as accurately as possible. And naturally the best hi-fi would be something that is accurate. Something that sounds like the real thing. A high end system should be able to fool you into thinking that what you’re hearing isn’t actually recorded.
But this simply doesn’t happen yet.
Most men who walk into a hifi store ask for speakers with a lot of power and bass. Audiophiles may laugh at this, but essentially they are the same. Audiophiles want gear with low (amplitude) distortion, low noise, and low capacitance in cables. But they seem to forget that these things probably don’t matter all that much, since figures are hardly a sign of true quality. The sound I heard from that restaurant was distorted and noisy beyond any reasonable factor, yet it sounded real.
In the process of improving on test results and obtaining more bragging rights, we’ve forgotten the purpose of high fidelity.
These days I have a chuckle to myself everytime I hear of someone describing sounds as “warm”. In the process of trying to produce undistorted treble (IMHO the most difficult thing to achieve in a system), we’ve grown accustomed to manufacturers simply giving up and dulling the high end, inventing the term “warm” to cover for their inadequacies. I do believe that “harshness” exists: in the form of distorted treble. But “warmth” has simply become an excuse for the inability to produce accurate high range.
Next time you’re at a gig, take note of the snare drum and high hat. Close your eyes and ask yourself: “if that was a loudspeaker, would I say it was warm?”. The answer is almost certainly, “no”. Real life never sounds “warm”, because it is accurate. Some may even say that it’s “harsh” or “bright”. But if real life sounds like that, how is warmth a good thing?
High end audio is commercial, and business is based on delivering what we desire. If what we desire can be manipulated by the very people who fulfill them, then unfortunately, the results will be crap.
After Ed’s post on whether digital is perfect, we received an impressive response from readers who voiced their own opinions about the subject. As requested by many readers, I’ve decided to put this theory into practice and explore the technology behind HDMI and the quality of HDMI cables.
DISCLAIMER: As a real engineer could understand, I cannot possibly fit into a blog article the holistic theory behind digital data transmission. Some bits are over simplified to allow a layperson to understand technical concepts easily.
Can errors exist in HDMI?
The first question we need to answer in this quest for truth is this: can errors exist in HDMI data transmission? and if so, what is the likelihood of this occuring? To demonstrate this, we’ll need to take a step back and have a look at basic digital transmission theory. Much of this is explained in more detail in the digital lies post, but we’ll look over the essential ones again.
Digital Transmission Errors
This is how most people think digital transmission works:
1, 0, 1
Signal received is either:
1, 0, 1
A random set of numbers (or not at all).
In reality, this is not true.
Firstly, signals aren’t just transmitted as 1s and 0s. 1s and 0s are the symbols we’re transmitting. 1s and 0s don’t travel down copper wire. However, electrical current does, and hence we represent the 1s and 0s with, say, voltage.
This is what a transmitted signal (and the corresponding bit it represents) looks like:
Unfortunately, even the best cable in the world isn’t perfect. Chances are, there will be noise to some extent, and a good received signal may look like this:
The received signal is in red, as compared with the original in grey. Notice how noise will have an effect on the signal received. (Interesting fact: we also note at this point that fundamentally everything is transmitted and received in analogue, because in the real world there is no such thing as digital. Digital is just a syntax of communication. Analogue is the medium.)
In this case it’s fairly easy to decode the original signal. We can simply take a sample of the received signal in the middle of every bit and check if it’s higher or lower than the middle. We take a “peek” at what the signal level is at each of those vertical black lines. We compare this level with the middle, and make a decision as to whether it is above or below. As we can see above, there would be no errors in this case.
Unfortunately, cables are much less than perfect. As technology improves (HDTV, DVD, Blu-Ray, etc.), more data is required per time period. I.e. higher bandwidth. This means that we need to send bits faster.
Notice how there is an instant jump in the signal from 0 to 1, but there is a slight delay in jumping from 0 to 1 in the received signal. This is because cables don’t have infinite bandwidth. Now imagine the same bits being sent, but at 1/1000th of the speed of above, and with a cable that is slightly worse than above. What would the received bits look like?
This may be something similar to what’s received. The signal exhibits much noise and distortion. And normally (if this were analogue), it would be nearly unusable. But because of the digital scheme of transmission, we can still decipher the signal without error (using the above method of sampling/decision making).
But what happens if a stray bit of electromagnetic radiation hit the cable at the 3rd bit? Whoops, we just got an error.
The received bit would now be deciphered as 1, 0, 1, 1, 0, 1, 1.
EM radiation, power supplies, adjacent cables, even the earth’s magnetic field produces noise. And if a cable is poorly built, we can see even more errors being received.
So now we’ve established how errors can exist in digital transmission, let’s see what happens if it occurs in HDMI.
Digital Errors in HDMI
Fortunately, there are mechanisms outside of the transmission itself to reduce the impact of errors. In fact, when a bit error does occur, you will most likely not notice it happening. The effects of bit errors can be significantly reduced through digital coding mechanisms, as well as parity bits and error checking mechanisms. I won’t repeat on how this works in detail here (see digital lies post for details), however essentially the mechanism will detect when a bit error occurs, and when this happens, it will substitute a signal which it guesses (usually closely) to what it probably was. These processes are called channel coding and interpolation.
“It’s digital, it’s either perfect or nothing at all”
This is thus, a blatant lie from those who do not understand fundamentals of digital transmission.
Do HDMI cables exhibit errors?
So now that we’ve established that it could happen, let’s have a look at whether it really would in real life. Remember from the above, a few bit errors in the millions of bits transmitted per second would not be obvious to observer (by obvious, I mean “mosaic” style errors in pictures, clicks and pops in sound, etc.).
To achieve obvious errors in HDMI, the signal must be distorted to such an extent that multiple bits per bit words are received in error (to render parity bits useless). I.e., it will need to have a significant bit error rate for an extended period of time. Does this happen in real life?
Cable length restrictions is strong argument that HDMI can and probably exhibits bit errors in real life. Most 2m cables perform satisfactorily. However, extend these cables to 5m+, and things start to go pear shaped. Obvious errors start occuring. Yes, these are the multi-bit-per-word errors that can cause clicks and pops in sound, and little squares in the picture. Now I’m not suggesting this is proof, but from my experience in digital transmission, if an increase from 2m to 5m can introduce obvious errors in transmission, it’s a strong argument that smaller errors occur quite frequently.
Hell, even the HDMI parent organisation has a standard of 10^9 BER (bit error rate). I.e. one error per 1 billion bits. At HDMI’s frequency, that’s one bit error every 6 seconds.
HDMI is a one way protocol
“If HDMI cables can make a difference, why is there no high end ethernet cable?”
Because HDMI is a one way protocol. That means the data travels in one direction, and there is no response from the receiver. Therefore, the source has no way of resending data if it is corrupted. TCP/IP works by breaking data into packets, and resending packets if received corrupted. However to resend data, the sender must know that the original was received corrupted, and for this to occur, the receiver must be able to talk back to the sender. This can’t happen in HDMI.
Manufacturing standards & material efficiency
The art of engineering is not to achieve perfection. It is, rather to achieve efficiency. To approach perfection requires an exponential increase in resources. However a good engineer would simply approach it as close as possible with what’s available.
A cable manufacturer’s goal is to sell as many cables as possible. To do this, they must have the lowest price possible. To get the lowest price, they will save on as much material as they can. How much material can they save? What controls are in place to ensure that this happens? Well, nothing, actually. There is no enforced worldwide standard of HDMI cable making. Although HDMI is licensed, there is no real control mechanism for the standard of manufacture. Cable makers are fairly free to do whatever they like.
As a result it’s possible that there may be cables out there that don’t even meet the standard. There can be cables which introduce hundreds of errors every second, but the consumer is none the wiser. (This is partly an advantage of HDMI). However, by no means is HDMI perfect.
The point of this article isn’t to say that a $40 cable is better than a $10 cable. It’s not even to say that people would care or notice the difference, or that when small errors occur whether the difference is noticeable. It might very well be impossible to notice them in a side by side comparison.
The point I’m simply trying to make is that it is not impossible for there to be a difference, and that people shouldn’t believe whatever rubbish that gets posted all over forums. Everyday, people all over the internet talk about digital signals as though they’re experienced cable designers. I’m not a cable designer. I’m not even a real expert in HDMI technology. Hell, what I’ve just said might be complete rubbish as well. But why take it as gospel without at least doing some research? Google a few terms that I’ve mentioned. Look it up on wikipedia for 5 minutes.
Digital is far from perfect. Errors happen all the time, in every cable, in almost every instance. Should you spend $200 on a high end HDMI cable? Probably not. Once a digital cable reaches a certain quality (negligible error rates), it is nearly impossible to improve on it. However, I wouldn’t be at all surprised if a $5 cable made in China isn’t made to specification. And although it “works”, it doesn’t mean it’s error free.
There are people who may be happy with the cheapest cable on the net, much like there are people who are happy to listen to mp3. For me, personally, I’d fork out the extra $20 to buy a reasonably good set of cables to hook up my TV, knowing that my $4000 TV is getting its full use. Sure, the $5 version might be just as good. But for the extra $20, I’ll think of it as insurance.
The following is taken from the FAQ section of HDMI.org:
“… It is not only the cable that factors into how long a cable can successfully carry an HDMI signal, the receiver chip inside the TV or projector also plays a major factor. Receiver chips that include a feature called “cable equalization” are able to compensate for weaker signals thereby extending the potential length of any cable that is used with that device.
With any long run of an HDMI cable, quality manufactured cables can play a significant role in successfully running HDMI over such longer distances.”
As you can see, the performance of HDMI cables goes far beyond the simple “if it works, it works” statement.
“… there may be instances where cables bearing the HDMI logo are available but have not been properly tested. … We recommend that consumers buy their cables from a reputable source and a company that is trusted.”
I wouldn’t be surprised if the majority of the cheapies on ebay aren’t certified, or have dodgy certification. Hey, 99% of them might work great. But there’s also a chance that a large majority of them don’t.
We are by no means holding an opinion on whether any of these actually work. Some definitely do, some definitely don’t, some are untested and we don’t actually have an opinion. However their root “technology” theory is explained.
This is certainly not an exhaustive list. It’s not even an extensive list. We’ll be continuing to add to this post as we think of more.
Please feel free to contact us if you can think of more to add to the list!
Bi-Wiring speakers is the practice of using two sets of cables for each of the speaker drivers (tweeter and woofer). As explained in the diagrams below.
As demonstrated above, conventional wiring uses a single run of speaker cable to both drivers. Most speakers come with multiple wiring posts to allow for bi-wiring/bi-amping, however they are usually shipped with a bridging bracket which connects them together for conventional wiring. This is removed for bi-wiring purposes.
The argument for bi-wiring is that firstly, the cables are effectively doubled up. Additionally, that the bass signal will interfere less with the treble signal as the cable runs are separate (cables can also be made differently to “suit” different frequency ranges).
Argument against bi-wiring is that it actually creates problems as the reactive properties of the two channels will be further differentiated, causing increased misalignment in phase.
The Bi-Amped configuration uses two amplifiers per speaker, as demonstrated below and following on from above.
This means that the power available to the speaker is increased, and hence there is less work to be done for each amplifier than if a single amplifier was to be used. The benefit here is not in the cables, but in the additional amplification power.
Single Crystal Copper (SCC)
As copper cools, it does not form into one continous block. It will usually form into a block of conjoined crystals on a microscopic level. These crystals have varying properties and thus may conduct current differently. Additionally any gaps between the crystals may exhibit unwanted electrical properties.
Single crystal copper is made in such a way that a piece of copper may only have a few crystals per meter. This means that they’re more homogeneous and thus are a purer conductor.
SCC is not manufactured widely and hence they tend to be rather expensive.
Smooth Surface Copper (SSC)
The smooth surface copper design argues that although a strand of copper wire may have reasonably similar diameter across a long length, since the surface of standard drawn copper cores may be quite rough, the diameter of the cable effectively changes across a length at the microscopic level. Changing diameter means changing properties and hence will add unwanted characteristics to the cable. Additionally, since the majority of the current travels on the surface of the conductor, the detrimental affects to conductivity is amplified.
Smooth surface copper is made in a way that ensures that the surface is smooth throughout the length, reducing differences in behavior in each part of the cable.
Ultra High Purity Copper (UHPC or variant)
This one comes in a number of different names, essentially meaning that it’s purer than regular oxygen free copper (OFC) which tends to be around 99.5% pure.
Teflon is not just slippery, it is an excellent insulator. Teflon can be used as insulation in a cable. The increased di-electric strength (see below) improves conductivity and reduces cable reactance.
A dielectric is something that does NOT conduct electricity, but is a good conductor of magnetic flux (magnetism). Dielectrics are necessary not only to keep wires from shorting (as insulation), but also as conductors of magnetism. As any good physics student would know, as a current is applied through any conductor, it will exhibit a magnetic flux around the conducting material. Depending on the insulation layer, the flux may be generated in different levels. Flux affects how conductive the conducting material is, and thus a better dielectric improves conductivity and reduces reactance.
Battery Power (Cables)
Some cable companies argue that dielectrics (or sometimes conductors as well) have a memory and requires “burn in”. Some cables come with a battery which permanently runs a current through an auxillary conductor built into the cable to keep the “burn in” from disappearing when not used.
Battery Power (Equipment)
Mains power is AC and needs rectification before use in almost all hi-fi applications. Rectification turns AC into DC, however this conversion can be difficult in achieving optimum noise performance. Noise in the DC rails will usually cause additional noise in the system.
Batteries have very little noise. Mains conversion is usually the most practical method for high power devices such as amps, however battery powered units can be used for less power hungry units like pre-amps.
Cryogenic treatment involves cooling a subject (usually a steel) to extremely low temperatures. This improves many properties including strength and durability of the metal. Its use on copper is not proven and there is poor theory on how it works, however audiophiles believe it improves the sound.
Some audiophiles believe that as signals are passed through a conductor, the conductor gets “magnetised” and will exhibit detrimental effects as a result. Demagnetisation CDs are used to pass a certain signal which “demagnetises” the conductors.
Gold / Silver / Rhodium Plating
Gold plating is commonly used in conductor contacts due to its ability to resist corrosion. This means that there are few artifacts on the surface of the conductor, leading to improved contact.
Silver is more conductive than copper or gold, and the argument is that a silver plated contact will also conduct better. However silver also tends to tarnish rather easily. When used to plate a copper strand, it enhances conductivity since much of the current in a cable tends to travel close to the surface.
Rhodium is a very rare metal, very hard and inert. This improves conductivity while resisting wear and tear on the conductor surface through its life.
Skin effect is a phenomenon seen in conductors when a very high frequency signal is passed through. When this occurs, the majority of the current tends to travel through the surface of the conductor, rather than uniformly. There are many different designs proported to alleviate this problem, including ribbon conductors, conductors of varing diameters, etc.
EMI (Electromagnetic Interference)
Interference occurs when electromagnetic radiation is passed through a cable. Electromagnetic radiation causes variations in current, and hence interference. Interference in cables is reduced by designs which involve shielding or crossed/twisted conductors.
RFI (Radio Frequency Interference)
EMI in the spectrum of radio frequencies is called RFI. RFI is common due to the amount of radio frequencies in our airwaves.
This is an active list. We’ve started with mostly cable terms (mostly due to their wide availability) but we will continue to update this page as we think of more. If you can think of some, forward them to us!