Wednesday, May 28, 2014

£3k for an Ethernet cable..!?

Just in case they take it down I had to do a screen grab! Yes, there are people selling "audiophile" grade network cables for three grand.

Buy yours here!

All sorts of dishonesty is written about high end audio cabling - directional conductors, "burned in" mains cables, even quantum effects are cited as important ways to "improve sound clarity" etc. You can believe that decent quality copper cable makes some difference at analogue baseband but by the time you get to AES and even network cables so long as the packets are getting through there is nothing the design of the cable can do to change the sound being re-produced. Even in the case of analogue audio (either line level or the speaker cable) good quality copper is all that's needed.
Still, a fool (make that an audiophile) and his money are soon parted and once you've spent thousands of pounds on cable you probably can "hear" a difference!

So, the lies peddled about this particular brand;
Perfect-Surface Technology applied to extreme-purity silver provides unprecedented clarity and dynamic contrast. Solid conductors prevent strand interaction, a major source of cable distortion. Extremely high-purity Perfect-Surface Silver minimizes distortion caused by the grain boundaries which exist within any metal conductor, nearly eliminating harshness and greatly increasing clarity compared to OFHC, OCC, 8N and other coppers.
Just nonsense!  Electrical signals travel down cables by the movement of electrons. Copper (Oxygen free or otherwise) is about the best conductor commonly available and the "grain" or "strand interaction" has nothing to do with the movement of electrons. BUT, let's not forget that this is a network cable and the transit of TCP/IP packets has NOTHING to do with the "harshness" or "clarity" of the sound.
Any solid material adjacent to a conductor is actually part of an imperfect circuit. Wire insulation and circuit board materials all absorb energy (loss). Some of this energy is stored and then later released as distortion. Solid High-Density Polyethylene Insulation ensures critical signal-pair geometry while minimizing insulation-induced phase distortion.
Are they hinting at capacitance here? "Energy stored and then later released as distortion" - where do you start. This is so misleading. Network cables are twisted pair construction (relying on common-mode rejection on each pair) - they aren't coaxial cables (if they are referring to capacitive effects?). "Insulation induced phase distortion" - have any electronic engineers ever measured that?!

All audio cables are directional. The correct direction is determined by listening to every batch of metal conductors used in every AudioQuest audio cable. Arrows are clearly marked on the connectors to ensure superior sound quality. For best results have the arrow pointing in the direction of the flow of music. For example, NAS to Router, Router to Network Player.
Please - audio cables are not directional! As many electrons flow in one direction as the other. This old chestnut was commonly trotted out for analogue cable, it was a lie then, and it's a lie now. With a network cable packets travel in both directions as the TCP/IP handshake brings up a connection, data is transferred and then the connection is closed. There is no directionality for the packets, the data they carry or the electrical signals that represent the bits. 

What this all comes down to is that these snake-oil salesmen NEVER subject this tat to a double-blind test. If they did you find out that there aren't a pair of ears in the world that can actually "hear" the difference between a £3k and £2 network cable.

Saturday, May 17, 2014

Sony PVM-A250 OLED - some colour measurements

I have a pair of new PVM-A250s in ahead of an install and wanted to test a couple of things out. My first one was to see if the monitor does the right things between it's studio swing-range HD/SDi 4:2:2 input and it's full-range HDMI 4:4:4 inputs. Aside from a slight shift in luma (big Y) the difference is minimal (and definitely not the usual 601/709 matrix-mismatch you see on other monitors).

Y, Cr, Cb 4:2:2 HD/SDi input, peak white field before calibration - out of the box these monitors are a tad blue and a bit too bright.

R, G, B 4:4:4 HMDI input, same source.

We're running these over many hours to see if they drift at all. Will add some more to this post next week with those results.

Friday, May 16, 2014

What's the best setting for Gamma with Rec.709 video?

I've been calibrating TV displays for around twenty-five years and have always leaned on the BBC practice of setting peak white at 80Cd/m2 and the white point at 6504k. For all the decades of standard definition work a gamma of 2.2 has been used. This is required because television cameras don't have a linear transfer characteristic and to make a black-white ramp match (i.e. it looks the same on the monitor as well as to the naked eye) you have to invert the gamma response of the camera at the display end. 
If you get this wrong you wind up with blacks and whites matching but all the shades in between don't - pictures either appear washed-out or all the detail is crushed out of the dark areas of the picture depending on which way you get it wrong.

When Rec.709 came along in the early nineties (for HD television) they changed a few things; new colour primaries, new luminance transfer function, wider gamut etc. They also made a subtle change to the definition of gamma. Like sRGB (the Adobe colour space for graphics working) and Rec.601 the "scene-referred" gamma of 2.2 is specified (in 1992 TV cameras were still tube'd devices) but the display gamma is governed by a complicated transfer law which many people have taken to be closer to a gamma of 2.4. However, a straight power curve of 2.4 is correct only if the display has a zero black level and an infinite contrast ratio, which no real-world display has. The new BT.1886 specification (from 2011) is complex and its precise recommendations vary depending upon the white level, and especially the black level, of the display.
However, if you don't want to bother with a precise BT.1886 calculation a 'best approximation' of this would be a gamma of 2.2 in the low end of the curve rising to a gamma of 2.4 at the high end. In fact it's worse than that - it's linear for the first 10% of the range.
So, what's a colour-calibration guy to do? Once again Charles Poynton comes to the rescue - he's forgotten more things about colour than most of us ever knew and I take his advise whenever possible.
Colors change appearance depending upon absolute luminance, and upon their surroundings. A very dark surround at mastering will “suck” color out of a presentation previously viewed in a light surround. A colorist will dial-in an increase in colorfulness (for example, by increasing chroma gain). The intended appearance for an HD master is obtained through a 2.4-power function, to a display having reference white at 100 Cd/m2 – but that appearance will not be faithfully presented in different conditions! The key point concerning the monitor's gamma is this: What we seek to maintain at presentation is the appearance of the colors at program approval, not necessarily the physical stimuli. If the display and viewing conditions differ from those at mastering, we may need to alter the image data to preserve appearance. In a grading environment, you might set the consumer's display to 100 Cd/m2, matching the approval luminance. However, ambient conditions in an editing environment are somewhat lighter than typically used for mastering today. The lighter conditions cause a modest increase in contrast and colorfulness, beyond that witnessed at content creation.

So, it seems the choice is this - 2.4 gamma in well-controlled grading/mastering conditions (particularly if your monitor has good dynamic range; OLED or Dolby reference monitor) and 2.2 in brighter editing rooms with lower-end LCDs.

Thursday, May 15, 2014

Top ten blog posts - views over the last year.

25 Feb 2009, 1 comment

23 May 2011, 12 comments

22 May 2009, 5 comments

13 Jun 2012, 1 comment


19 Mar 2013, 4 comments


11 Oct 2010, 3 comments



Wednesday, May 14, 2014

Three phase electrical supplies and technical earth

I had a customer ask a question yesterday about why single phase in a machine room is considered a good thing and why technical earths need to be unified. Here's what I wrote; it's not a complete chapter & verse but it's a good excuse to put in a link to the episode of the Engineer's Bench that Hugh & I did in 2012.

He's confusing the phase that his various supplies are on with the "best practise" requirement of a unified technical earth. Twenty years ago the 16th Edition of the IEE regs forbade powering bays next to each other with different phases. There is more than 400v of difference between the mains phases and so it was thought that having that much potential difference within reach of each other was more dangerous than should be allowed; hence the practise of powering the machine room off a single phase.
However, the other consideration is that the power company charges you 3 x your most heavily used phase. So, if you're averaging 100A on the red (your machine room maybe?) but only 10A on the blue & yellow phases you'll be paying for 300A of current whilst only using 120A - if you don't "balance the phases" your electricity can (worst case) cost you three time per KW/h than it should. So, what with the improvement in RCDs and the cost issue the 3rd revision of the 16th Edition (and it's carried into the 17th) allows for mixed phase supplies in machine rooms. Looking up section 514 all that is required is labelling;
"6.1 Labels to be Provided The following durable labels are to be securely fixed on or adjacent to equipment installed in final circuits. (i) Unexpected presence of nominal voltage (U or Uo) exceeding 230 V Where the nominal voltage (U or Uo) exceeds 230 V, e.g. 400 V phase-to-phase, and it would not normally be expected to be so high, a warning label stating the maximum voltage present shall be provided where it can be seen before gaining access to live parts. (ii) Nominal voltage exceeding 230 volts (U or Uo) between simultaneously accessible equipment For simultaneously accessible equipment with terminals or other fixed live parts having a nominal voltage (U or Uo) exceeding 230 volts between them, e.g. 400 V phase-to-phase, a warning label shall be provided where it can be seen before gaining access to live parts."
On the subject of a technical earth - it's an entirely different consideration to mains phases but best practice is that you run all your tech feeds - bays and edit desks etc, back to the same earth bus-bar in the MCR. This is then run to the incoming feed supply. It's not good to try and tie it to the domestic "cooking" earth somewhere upstream of the incoming supply. The attached PDF is what we spec to customers' electricians.  It’s worth pointing out that getting the earth’s wrong is not unsafe; you can have volts of difference between two earths and they still both work as effective safety earths, but a hundred mV of earth differential between and edit suite and MCR will be a problem – the HD/SDi signal is only a volt big after all and zero level analogue audio is 775mV.
I did a podcast on the subject;

Tuesday, May 06, 2014

Colour results from a Sony PVM-2541 TriMaster OLED monitor

Having spent a bit more time with the Klein K10-A probe I profiled the Sony monitor we hired to practice on.

Here you can see the colour gamut for the displayed compared to the Rec709 colour space for television.

It is an excellent match with the green extremity being a tiny bit mis-matched. I would not expect to see this from either a CRT or LCD monitor.
The white curved line is the "black body locus" and is where physicists define the colour of white.

1. Gamut measurements

White Field
Video  x    y    Y      
255  .313 .336   136.45 

Red Field
Video  x    y    Y      
255  .639 .332   28.35 

Green Field
Video  x    y    Y      
255  .296 .603   99.75 

Blue Field
Video  x    y    Y      
255  .149 .060   9.47 

EBU Overlap Gamut Value:  98.4%

2. Gamma measurements

White Field
Video  x    y    Y      
235  .313 .334   110.99 
207  .313 .334    83.10 
180  .314 .336    58.14 
153  .315 .337    37.74 
125  .317 .338    22.35 
 97  .319 .341    11.39 
 70  .324 .347     3.50 
 43  ---- ----     0.39 
 16  ---- ----     0.01 

Red Field
Video  x    y     Y  
235  .640 .332    24.30 
207  .641 .332    17.79 
180  .642 .332    12.87 
153  .645 .332     7.72 
125  .651 .333     4.20 
 97  .664 .332     1.88 
 70  .671 .325     0.65 
 43  ---- ----     0.09 
 16  ---- ----     0.01 

Green Field
Video  x    y     Y      
235  .296 .603    81.12 
207  .297 .603    57.73 
180  .297 .604    39.60 
153  .297 .604    25.74 
125  .297 .608    14.55 
 97  .297 .614     6.97 
 70  .296 .638     2.27 
 43  ---- ----     0.26 
 16  ---- ----     0.01 

Blue Field
Video  x    y      Y      
235  .149 .060     8.19 
207  .149 .059     5.73 
180  .149 .059     3.89 
153  .148 .058     2.39 
125  .147 .056     1.29 
 97  .143 .053     0.54 
 70  ---- ----     0.18 
 43  ---- ----     0.02 
 16  ---- ----     0.01 

You can see that the colour of white through grey tracks very well until you get to within 15% of black; you can generally accurately read the luminance level down to sub 1Cd/m2 but colour measurements become too noisy down there. The K10-A seems to perform better than our DK PM5639 in this respect.

Friday, May 02, 2014

Klein K10A photometer for TV colour cablibration

Had a splendid day today getting to grips with the new Klein K10A photometer and testing it out on a couple of Sony broadcast monitors; an LMD-series LCD and a PVM-series OLED.

For many years we've been relying on the PM5639 colour probe - originally made by Phillips and now badged by DK. It's the right hand probe in this picture and they have served us well through hundreds of calibration sessions. However - they are photometers and as such are tied to the display technology that they are intended to be used with. The CRT one is only to be used on old-school tube'd monitors and the LCD head is for newer style broadcast monitors. The reason for this is down to a phenomenon called metamerism (sometimes metameristic failure)  where you attempt to faithfully capture all colours from a wide-band source (sunlight etc) with only a tri-stimulus detector (TV camera, colour probe, human eye) you run into the inadequacies of the source-detector response. Here is the spectrum for a typical phosphor-based colour CRT;

You can see that the blue and green emissions are kinda what you'd like but the red is all over the place! Red was always a challenge with CRTs but the folks who manufactured the calibration probes knew this and they arranged the bias and gain of the photo-diodes in the detector to match the characteristic of the phosphors; this allowed them make good measurements off the front of a CRT but since LCDs and other display types have quite different spectral graphs the CRT probe would struggle to accurately read the colour off the front of a newer style monitor. Metameristic failure.

This image shows the Klein and the DK probes pointing at the same OLED monitor. If you can't read the values;

DK - x:0.314, y:0.312, Y:102.2 Cd/m2
Klein - x:0.329, y:0.313, Y: 98.9 Cd/m2

With the attendant colour temperature difference.

So which is correct? Why the difference? Well, the DK probe is, as mentioned, an LCD probe and so can't be trusted on display types that have a different spectral distribution. How can you then trust the Klein with multiple display types? It's a photometer after all; isn't it built to match the spectral distribution of a certain monitor type? Is it only good for OLEDs? No - they took a different approach. Rather than matching to the spectrum of a certain monitor type they have tweaked/weighted their photo-receptors to match the human eye; so the probe suffers metameristic failure for all display type but it's the same metamers as your eye fails to see; and that's what counts. If I'm matching two monitors it's only important that they look the same.
We all know that CRTs, LCDs, Plasmas have different spectral distributions but so long as to the eye you've got two displays matched they are matched. The Klein allows you to load profiles into the probe head to provide for better matching but it really is sub the last 1%. I followed their instructions for making a new OLED profile and it allowed me to get the white point a few kelvins closer to 6504k but it wasn't that much of a difference. Apparently the 2nd gen. Sony OLED TriMaster monitors have a new formulation in the blue pixels.
Anyway - we're very pleased with the K10A; it's very easy to use, the ChromaSurf software is clear and makes calibrating a breeze.
Anyway - I wrote some notes - colour for TV 101 kind of thing. Grab them here.

Thursday, May 01, 2014

Nick McKeown talking Software Defined Networks at the IET this week

I went to the Appleton Lecture at the IET (my institute) this week; here it is as a webcast and well worth watching. The first half is all about the history of packet-switched networks but the meat of it is the second half were he talks about software defined networks.

From Wikipedia;
Software-defined networking (SDN) is an approach to computer networking which evolved from work done at UC Berkeley and Stanford University around 2008. SDN allows network administrators to manage network services through abstraction of lower level functionality. This is done by decoupling the system that makes decisions about where traffic is sent (the control plane) from the underlying systems that forward traffic to the selected destination (the data plane). The inventors and vendors of these systems claim that this simplifies networking. SDN requires some method for the control plane to communicate with the data plane. One such mechanism, OpenFlow, is often misunderstood to be equivalent to SDN, but other mechanisms could also fit into the concept. The Open Networking Foundation was founded to promote SDN and OpenFlow, marketing the use of the term cloud computing before it became popular.

Appleton Lecture 2014 - Software Defined Networks and the Maturing of the Internet
Nick McKeown
From: IET Appleton Lecture 2014, 30 April 2014, London

2014-04-30 00:00:00.0 News Channel