Podcast - Contemporary Display Standards

Hugh and Phil take a look at display standards starting with HD/SDi and working through analogue VGA through to DisplayPort.
Hugh talks about some of the work he's been doing with Skillset certifying University TV and Media courses.
Find it on iTunes, vanilla RSS, YouTube or the show notes website.

Broadcast Engineers of a certain age - enjoy!

I'm prep'ing a BVW-75P for training (yes - some people still want to know how to fix VTRs!); here are some pictures.

Secure DNS - what's a home-user to do?!

I find DNS a very interesting (how often do you hear that?!). When I was doing my degree in the mid-80s there was no such thing and you routinely updated you hosts file every few weeks from a master file stored at Sheffield University Computer Science dept. However - my faculty was very IP-aware (even then) and so we were running an early BIND server when I graduated and so I was at least aware of DNS before it became a big deal on the Internet.

DNS is an inherently insecure protocol for the following reasons;

• It runs over UDP/IP and so doesn't require the 3-way TCP handshake - it's easy to spoof IPs
• It's unencrypted
• It doesn't require any kind of authentication and so man-in-the-middle attacks are possible
• Problems with the protocol itself (i.e. independent of implementation) allow things like DNS cache poisoning (read up about the Kaminsky vulnerability from a couple of years ago).

I've used OpenDNS for several years and it's an excellent service that offers so much more than my ISP's DNS servers. Those guys have recently launched DNSCrypt which is a secure client for Mac or Windows that allow DNS look-up that avoids all the problems above.

HP xw6200 workstation and Windows 7

The HP xw6200 is a brilliant dual-3.6Ghz Xeon workstation that is the baby brother of the xw8200 which was Avid's workstation of choice for a couple of years until the Z800 came out in 2010. It's still a powerhouse and re-furb places like Tier-1 knocks them out for a bit more than £100. Given how pokey they are and how well build HP made them (you got quality when you paid >£2k for a PC in 2010!) I often recommend them to friends.

Anyhow - couple of gotchas;

• Make sure you re-set the BIOS to disable the onboard SATA RAID controller or when you install Windows 7 SP1 you re-boot and get a corrupt boot partition and have to start all over again!
• The graphics card is an nVidia Quadro4 400NVS - a quad-monitor CAD/NLE display adaptor that has no Windows 7 driver!

Still, an excellent deal if you're willing to put in the time to sort it out.

Temporal Dithering; good for colour depth, bad for extending!

I've become quite a fan of products based on Teradici - an on-the-fly compression system that allows dual-DVI w/peripherals to be extended over ethernet. It works very well and you can't tell you're not looking at something that's been packetised and extended over a network. Howver, a fly in this ointment is the current gen ATI graphics drivers on OS-X. They use a technique called Temporal Dithering;

Temporal dithering is a technique employed by some graphics cards to simulate colors that they cannot natively display by rapidly changing the colors of pixels, tricking the eye into seeing “in-between” colors. During PCoIP remote sessions, temporal dithering can cause extremely high bandwidth utilization because the rapidly changing pixels force the PCoIP protocol to constantly deliver large screen updates to the remote desktop.

The upshot of this is that when you have nothing going on screen - no mouse movement etc (where you'd expect to see no data traveling on the network) you get;

And the effect on screen is compression artifacts and a sluggish mouse pointer. The guys at Amulet Hotkey are looking into it for us, but it might be a deal-breaker.

Flailing around the web revealed someone at Disney who has produced tweaks to X's configuration file for use under Linux; unfortunately this doesn't work in OS-X as the dithering is done by the driver. However, just for reference (or the lulz!)

xorg.cong

Section "Screen"
    Identifier "Screen0"
    Device "Videocard0"

    Monitor        "Monitor0"
    DefaultDepth    24
    Option        "CIOverlay" "On"

    Option        "CursorShadow" "Off"
    Option        "NvAgp" "3"
    Option        "TwinView" "1"
    Option        "SecondMonitorHorizSync" "21.0-140.0"
    Option        "SecondMonitorVertRefresh" "47.0-72.0"
    Option        "TwinViewOrientation" "LeftOf"
    Option        "MetaModes" "1280x1024_72,1280x1024_72; 1280x1024_60,1280x1024_60; 1024x768_72,1024x768_72"
    Option        "TwinViewXineramaInfoOrder" "DFP"
#RandR    Option        "RandRRotation" "true"   # Requires xorg 6.8.1+
#NoEDID    Option        "UseEDIDFreqs" "FALSE"
#NoEDID    Option        "UseEDIDDpi" "FALSE"
#NoEDID    Option        "ModeValidation" "NoEdidMaxPClkCheck"
#ExactMODE    Option          "ExactModeTimingsDVI" "On"
    Option        "DPI" "85x85"
    Option        "AllowGLXWithComposite" "true"
    Option        "DisableGLXRootClipping" "true"
    Option        "AddARGBGLXVisuals" "true"
    Option        "AllowSHMPixmaps" "true"
#FALSE    Option        "Dac8Bit" "true" # forced spatial dithering instead of temporal for teradici performance
#FALSE        Option        "RegistryDwords" "DitherAlgo8=3;DitherAlgo6=3"


# Other possible options. Enable at your own risk
#    Option        "RenderAccel" "On"
#    Option        "Overlay" "On"
#    Option        "SWCursor" "On"
#       Option          "TwinViewXineramaInfoOrder" "DFP-1,CRT-0"
#       Option        "ConnectedMonitor" "DFP-0,CRT-1"
# This can be used to clarify orientation
#    Option        "TwinViewOrientation" "DFP-1 LeftOf CRT-0"
#    Option        "IgnoreDisplayDevices" "CRT"

    Subsection "Display"
        Depth        24
        Modes        "1280x1024_72"
    EndSubsection
EndSection

Why IT practises are bad for broadcast installs

I'm in the middle of a big build where (in common with lots of film and TV facility builds) we're a subsidiary to the IT department and so have space in their comms room rather than have our own MCR. There are quite a few standard practices in building IT installs that don't map nicely onto the optimal configurations for TV builds;

1. Air conditioning - I go on about this endlessly but having done this many times I have a few observations about why under-floor hot-cold isle comms room cooling isn't suitable for TV equipment (and in fact it's not really suitable for IT builds!). Nobody in IT server-room construction has ever been able to answer me any of the objections below other than this is standard practice.

• Cold air is heavier than hot - why try and fight nature by pushing cold air upwards rather than dropping it down the front of the cabinets?
• Raised floors leak - cable entry holes into the room and once tiles have been lifted and dropped a lot of cold air is spilling out reducing the pressure in the cold isles.
• Lots of additional brush-covers for cable entry into the cabinets
• Dust is forced out of the floor void (and into the equipment!).

2. Patch panel layout - I shudder when I see structured cabling panels where the eight tie-lines to a room just present sequentially with no thought to how they'll be used. It's just lazy and means no attention has been paid until an engineer is patching up. It also means bays are very untidy from the start and you see super-wide bays with cable-management down each side. Things needn't be that messy from the start.  This is a real comms room;

3. "Flood wiring" of cabinets - This one relates to the previous point, but by avoiding thinking about the room and over-spending on 'flood wiring' you see 24-port panels at the top of EVERY CABINET going back to the haystack above.

4. Power specifications - Despite every bit of equipment having a switch mode supply (and hence being an inductive load) every MCB in most mains rooms are C-rated and double the required capacity (C32s for the 16A circuits etc.) - I'm sure using correctly rated D-breakers would be better from a safety and reliability point of view. Again - it's about not taking responsibility early on; keep our options open!

All of these are a function of the fact that the clever part of IT installs is in the switches and servers. The cabling is generic (one cat6 is much like any other) and so there is little compulsion to do it as nicely as it can be.  My heart sinks when I start a job and the first thing the customer's PM says is "...this is off the back of the comms room build"! 

This is the way I like to leave things;

HD/SDi over fibre and SMPTE 297M (2006)

I've recently installed an NVision 8144 router at a large facility and some of the output cards are for fibre - dual LCs on each SFP with 3G video conforming to SMPTE 297M (SDi over single mode fibre). Very nice. Over the last couple of years I've put in a load of the little Black Magic fibre transceivers and although they perform admirably (only had to replace one due to it being roughly handled by an OB rigger!) but I couldn't quite bring myself to believe that the mighty Blackmagic would conform to the same spec! They really are built to budget (and excellent for it). However, I had a situation where my choice was to buy the Miranda fibre receivers (at a grand a piece) OR use the half dozen BMs I already had. To my surprise the Blackmagics worked just fine. Maybe SMPTE compliance does mean something, in the case of fibre I assumed manufacturers would juts vary too much, but I suppose SDi over copper is universal, so why not over glass as well?

Audio podcast 2 - the engineering!

Hugh and I continue our discussion of audio and make particular mention of cabling for TV facilities.
Find it on iTunes, vanilla RSS, YouTube or the show notes website.

The next podcast - Audio 101

Hugh and I go over the fundementals of sound and recorded audio in the first of a two-parter Find it on iTunes, vanilla RSS, YouTube or the show notes website.

Crimp tool for all current video ends?

All the wiremen want me to buy them one of these! This tool can do SD01 standard def coax (Image 360), 1694 HD Coax and the newer Din1.0/2.3 mini-HD connectors.

UK electricity demand

After a major power-outage in North London this afternoon I went looking at the National Grid website; there is some fantastic realtime data there about the amount of power the UK is consuming and how much juice is transferred between regions.
I nicked these two applets but click the title link and have a truffle around - 41GWatts currently(!)

Here's an update - interesting article from The Independent on 13th April;

How the Supergrid could help keep the lights on about the electrical interconnects between the UK and other countries; apparently a 900-mile 0.8GWatt link is being proposed to Iceland!

Reliability of modern hard drives

A couple of things have got me thinking about the reliability of hard drives.

1. The eldest boy asked me about RAID levels and what extra reliability they bring.
2. I sold an old 500gig SATA drive from my media center to a guy on eBay and he's quibbling because he's found three bad sectors

Although RAID has bought tremendous increases in the speed and reliability of storage systems there are some basic engineering considerations around combining many unreliable parts into a whole. The Mean Time Between Failure for modern hard-drives (MTBF) is in the order of 30,000 hours. MTBF is a complicated field but if you look at the figures provided by manufacturers then they assume a Gaussian distribution with the 30,000 hours figure at the peak; a few drives will fail after a day, a few will last 100,000 hours, but the bulk will fail around 30,000 hours (around three and a half years). It's why I say to people "...it's not if this drive will fail, rather it's when!"
So - with this in mind I decided to find out the MTBF of a rack of ten drives, each with a MTBF of 30k hours.The formula is;

So, if you stick 30k hours in for D1 through D10 you find the MTBF for the entire system is only 3k hours - less than twenty weeks! In fact it's worse than this as the PSU in the enclosure and the RAID management card will have MTBFs to take into consideration as well. In fact if you ask any broadcast engineer "how often are you replacing drives in RAID arrays" and they'll tell you it's nearly a weekly occurrence for any decent sized facility, and this is why! Although it's been nearly a decade since I ran engineering in a good-sized facility I was often uneasy about how often RAID enclosures failed (loosing all of the media, which is what happens with a RAID-0 striped set). I had that 30k hours figure in my head but never calculated the system MTBF.

RAID-1 (mirrored drive sets), RAID-5 (distributed parity) and RAID-6 (double distributed parity) along with some of the advances that better file systems bring (Isilon's OneFS and Linux's ZFS) mean that failure of a single drive is no longer the disaster it once was, but if someone doesn't notice a drive has died OR (heaven forbid) a second drive dies whilst replacing the first you're stuck. Don't forget a lot of the chassis we're installing now have a couple of dozen drives (Isilon's NL36 nodes - done of a few of them recently) and so MTBF is even worse than the 3k hours above (however, server-grade SAS or Fibre Channel drives are considerably more reliable than domestic-grade SATA drives).

We also know that modern multi-terrabyte drives pack data so densely (similar sized platters to the first 10Mbyte drives of yesteryear, but hundreds of thousands more bits/mm-sq. of disk surface) that the disk's error correction/error recovery system is working flat-out all the time. The newer 2Tbyte drives have a Viterbi decoder to try and statistically extract correct data from the very noisy signal coming off the drive's heads. Additionally the drive's SMART system has to know about the number of bad sectors due to manufacturing imperfections (contained in an EPROM-based p-list table) as well as the number of grown bad sectors (which get swapped out as per the g-list). Spinrite is the best utility I've found for drive maintenance/recovery as it forces the SMART system to pay attention to bad sectors and swap them out. In a Hitachi Ultrastar 7k RPM, 500gig SATA drive there are 10,000 hidden spare sectors on the drive (each sector is only 4k bytes in size) to allow the drive to swap-out failed sectors. According to the data sheet Hitachi would replace a new drive if it had more than twenty bad sectors from the factory - any less and they regard it as being well inside manufacturing tolerances. If you Google "how many bad sectors is acceptable for a new drive" you'll find hundred of IT experts claiming that no bad sectors are acceptable. I don't know what planet they live on, presumably one where quantum mechanics operates in a different manner and electrons don't bump into each other leading to electrical noise!
Oh - the eBay guy; he ran a utility on the drive I sold him that reported three bad sectors. He asked me for a refund. Apparently a second-hand disk drive should carry a better guarantee than that provided by the factory when new!

Colourimetry 2 - Calibrating monitors for TV

After the intro to colourimetry Hugh and I talk about calibrating monitors for film and TV use. Find it on iTunes, vanilla RSS, YouTube or the show notes website.

TV Colour - the next podcast

Hugh and I lay the groundwork for the next podcast about monitor calibration. This episode concerns perception of colour in TV. Find it on iTunes, vanilla RSS, YouTube or the show notes website.

Speeding up HTTP

The big overhead with protocols that run on top of TCP/IP is the number of connections they open. A modern web page has many different kind of assets (HTML, scripts, Java, GIFs, JPEGs, etc etc) from many places (the primary domain, adservers, Google+ buttons etc etc) such that when you load the front page of facebook.com you may well have opened and closed a thousand TCP connections to a dozen servers. It's amazing that it works at all, but when you consider that each connection had to not only do the three-way TCP handshake, but it also had to run TCP flow-control starting slowly and ramping up packet rate until it started to drop packets and then dropping back. When Mr Burners-Lee wrote his original http server in the early nineties there is no way he could have anticipated how the web would grow.

It seems there are several approaches to optimising this - for the past ten years there have been various attempts to re-define TCP; MUX, SMUX, and SST protocols were valiant efforts that died on the vine because they essentially break how the infrastructure works. Whatever comes after http has to work over all the same IP v.4 routers, switches and proxies. In the last year I've become aware of two projects that work and don't require funky routers etc.

1. Amazon Silk - this is embodied in the browser that comes on the colour Kindle. Essentially it is a mega-proxy that not only collects all the assets for the page but re-renders pictures etc for the smaller screen and sends the whole lot in a stream. So one connection allows the whole pre-rendered page to arrive with the assets from Double-Click and Google (and any other third-party elements in the page) pre-collected for you by Amazon. It runs of their EC2 platform and does depend on them providing the service.
2. SPDY is a Google-sponsored project that doesn't replace http but optimises it. By employing pipelining (i.e. keeping a TCP connection open for all the assets from one domain), compressing headers and marking those headers that don't change so they don't need to be re-sent it speeds up the browser by around three-fold. Further speed increases come if the web-server is able to collect the third-party assets and deliver them over the same pipeline.

As ever Steve Gibson has covered these very comprehensively in Security Now! - SN320 for Silk and SN343 for SPDY.

What's in your rucksack?

Phil and High go over the basic set of tools and test kit that broadcast engineers on the hoof need! Find it on iTunes, vanilla RSS, YouTube or the show notes website.

Synchronous ain't always best!

Engineers have been trained since time immemorial that with multiple sources of video the best thing is that they are always locked together and timed to a common reference - ideally station black & burst (or TriSyncs nowadays). The reasons for this are numerous, but a couple;

1. Studios cameras into a vision mixer have to be locked to achieve clean cuts between the cameras - it would look rubbish if you had a frame roll every time you cut between sources. The same is true of sources into a continuity suite etc.
2. In the case of Avid for the longest time you had to make sure the VTR was locked to the same reference as the Media Composer (all the way from v.7 ABVB systems in the mid-90s to the last revision of Adrenaline in 2007!) otherwise the audio and video capture portions of the machine would free-run WRT each other and within minutes you'd be loosing frames of sync.

So - I had a coffee and chat with a pal this morning who works for a big facility that has won an archive digitising project and they are using the BlackMagic DeckLink 4K card to allow them to ingest 4 x DigiBeta tapes at once. The capture software is ToolsOnAir and they found that after the first clip was captured the second clip would be a frame out of sync, and progressively worse after that - unless you re-booted between captures! It turns out that if the four VTRs are allowed to free-run then you don't get the problem. Perhaps processing the vertical syncs places a burden on the card/software and if it happens simultaneously on all four inputs trouble ensues?!

It reminded me of a situation with a big broadcaster who was distributing their regional variations over Astra on a single multiplex. The stat-mux was very unhappy with material that was (for the most part) identical; only the ad-breaks differed. Most video cuts occurred at the same time across all six SDi feeds. The solution was to apply a two frame delay between all the sources (so o/p 6 was now 12 frames late WRT o/p 1).

Mains 101 - part 2 / Postscript

Hugh and Phil wrap up the previous mains safety podcast with some corrections and photos from Nigeria! Find it on iTunes, vanilla RSS, YouTube or the show notes website.

Phil & Hugh's next podcast - electrical safety.

Find it on iTunes, vanilla RSS, YouTube or the show notes website.

I'm representin' at BVE

Today I'm delivering a 'training taster' session at BVE 2012. Oh, the title link is my notes if you want to download them.