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The Engineer's Bench podcast - "Top Tips; Audio"

Hugh and Phil talk about some tips and get-out-of-gaol-free cards with respect to broadcast audio.
Go to the website for a PDF of the notes.

https://youtu.be/QJO0Z4DuDFc


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

Shooting & editing HDR via Avid using CLog gamma

We've got BVE2016 coming up and one of the things Root6 will be showing is an HDR workflow via Media Composer using Canon monitors.

HDR is still a bit of a crap-shoot as far as standardisation is concerned with the BBC/NHK system, Dolby Vision, Sony's SLog3 and Canon's camera-native CLog. The principle of using an alternate gamma so that you concentrate the bit-depth where you want the extra range is well established;

The hope is that all of these manufacturers will coalesce around ST.2084 which (amongst other things) defines how you handle the specular highlights; those very bright parts of the picture which give a real addition to the look of the pictures. These are typically defined to be >500 Cd/m² which is MUCH brighter than broadcast white! The idea is that the last bit of dynamic range (10th bit - all values above 512) represent the highlights and everything up to 50% is akin to the usual video dynamic range. You calibrate the monitor such that 50% is set at 100Cd/m² and just hope that the colourimetry of the highlights tracks RGB-wise!

So - Root6's own Dave Skeggs and I set off around Soho and London Bridge to capture some night time and daytime footage. We were using a Canon C300 mk.2 set to UHD (3840 x 2160) at 25P (no interlaced fields at UHD and no high framerates at that resolution unfortunately). We set the colour space to an optimistic Rec.2020 and gamma to Clog. In that mode the camera shoots 410mBit/s XAVC codec MXF files.
We've been using Media Composer v 8.5 on an HP Z840 workstation & the new Avid/BlackMagic DNXio video hardware; we had to update the firmware to get it to generate quad-link SDi. Although HDMI works it is nobbled down to eight-bit and so would not be suitable for this test. I would put a link to the video but none of the video sharing sites support HDR and neither does the screen of your tablet/laptop/TV! I took all the monitor photos with my Fuji bridge-camera in a very bright office; you'll have to take my word for it!

Notice the headlights of the taxi - you can see details inside the light!

exactly the same frame; notice the dark details in the trees against the night-sky.

 Of course on Media Composer's GUI display you get the CLog gamma rendered as if it was Rec.709 and so it looks very washed out and lacking in detail

You can have Avid flatten the gamma of source clips so that it looks OK on the GUI - that doesn't affect sequences that the clip mas been used in.

 

Quite a large range of alternate gamma and colour spaces

 It shows up in the bin-view which is useful

 

So now clicking the source window and setting the monitor to regular HD gamma (BT. 1886 fact fans) shows you what the same material shot on a "regular" camera would look like; very little detail in the blacks and none in the whites.

 

 Root6's own DOP; Dave "is that in focus?" Skeggs

I'd forgotten how limited a normal video-camera's dynamic range was. The Canon monitors top out the specular highlights at 400Cd/m² which is somewhat less than a Sony BVM-X300 (1,000 Cd/m²!) but for €10k less than the Sony (and losing only a stop-and-a-half of specular highlights) the Canon 30" UHD/4k IPS panel represents superb value. I was a bit disappointed that the camera tops out at 29.97P at >2k resolution so I couldn't see how nice fluid video motion looked at high res; everything has a jerky film-look to it.
Steve Shaw at Light Illusion has a very good article exploring some of the fundamentals of HDR.

They broke multicast PING in El Capitan (well, kinda!)

I've written in the past about how much I rely on the multicast PING for getting the basic network settings out of a piece of equipment (that's has come back from a customer in some unknown state). Imagine my horror when I discovered they've broken it in OS-X v 10.11 El Capitan.

 So, here's the setup, piece of gear connected directly via an Ethernet interface to my laptop (with a hard-set IP address). Ordinarily using;

PING 224.0.0.1

would force the equipment to respond with it's IP address. Then it's easy to change your laptop's IP to be on the same subnet and you're in (like Flynn). No worries that the computer and equipment are on different subnets, multicast PING forces it to respond.

It appears I'm not the only one to notice this. See here on Apple's support site.

So here's the answer; you can see the effect "No route to host", then I attach to a pocket-router with only the Amulet box on it and by attaching to it over WiFi (it's a router, no need to worry about "wrong" IP subnets) I can PING and determine the Amulet is on 192.168.6.102

I can only assume that by now having an ARP table in the way (the pocket-router) we have a source of H/W address to IP conversion. When there was just a cable between the devices and hard-set IP addresses multicast relies on the second device to answer the broadcast PING with it's H/W address in the return packet. I can only assume that OS-X 10.11 ignores that and instead does an ARP equiry of the router to match the H/W and IP addresses?

It's not a big deal as I do carry one of those little pocket routers in my rucksack as they are supper useful for lots of things;

• Isolating yourself from an (untrusted) client's network
• Isolating an untrusted machine from your network whilst working on it
• Making wired-only demo equipment wireless to aid in customer demos
• A source of IP addresses when lashing up an ad-hoc network.

Blackmagic iOS app works with Barnfind!

Super-impressed with how open Barnfind are over other manufacturers. I wrote before about how they work with Blackmagic control panels, but today for a demo I pointed the BM app at the BF chassis and it's all good.

Audio over cat6a cable?

My podcast-partner in crime, the mighty Hugh Waters asked me how often I run audio signals over twisted-pair data cable in media facility builds. Has has a customer who is eager to do it this way.

I’ve done it a few times and it’s fine with a few considerations.

1. Earthing is still important and since IT people have no idea about proper grounding it can be an issue. If it’s a cat6a install in a TV facility done by me I’d have no worries, but the average IT install might have issues. But as four twisted pairs with individual screens cat6a is ideal for audio. It’s the other parts of the facility I’d worry about,
2. RJ45s don’t have the same DC/LF performance as a good old B-gauge (or Bantam) connector; if the circuits are going to be patched often I’d be wary – mechanically they aren’t great next to traditional audio connectors, 
3. From a wiring perspective; how do you nicely terminate into XLRs from a piece of cat6a?
4. Track shuffling is hard,
5. AES – just fine. Cat6a has an impedance of ~100Ω per pair, ideal for twisted-pair AES. Same observations as 1, 2 & 3.

There you go. I did work at one facility where the engineer had got obsessed with structured cabling and did everything he could over cat6 – analogue video (via baluns), audio, RS422 etc. He liked the idea that you could patch an offline i/o with two RJ45s (stereo i/o on one and video i/o and remote on the other). It didn’t work well and I put in proper cabling and patching after a year.

Sometimes convenience blinds you to fitness for purpose.

Extending wireless networks; some gotchas

Visiting the family over Christmas and of course there are the tech-support duties. One of which was making a wireless network extend further through an old house with very thick walls. In the small amount of time I had there wasn't the option of running network cables to some strategic points where additional WiFi access points could be installed so I invested in a couple of Netgear wireless extenders. 

I've used these before and been impressed; fast throughput and lots of features. They are proper NAT routers and you can use them as firewalls between ethernet network segments or extend an existing wireless network. In that mode (and it's a small switch that sets that mode) the ethernet ports become wired outlets for the WiFi network; intended for set-top boxes that can't be connected via a cable. They can turn a USB drive into a NAS drive and all this for less than twenty quid!

The only downside is that they have a single radio and so can only repeat a network on the channel that it arrives as. In a relatively WiFi-free environment you'd think this wouldn't be a problem, but I didn't figure on how rubbish the provided BT HomeHub 3 is! 

Since they have a flip-out antenna I figured I'd place one downstairs and one upstairs as close as possible to the room with the aDSL router and see how I got on. 

• It is a cheap, plastic, single-board gadget
• It has no external antenna or even socket for one
• You have to use it as the BT mothership monitors for their own secret sauce

What I discovered after two days of frustration is that it is entirely intolerant of other devices sharing it's channel. The Netgears can only repeat on the channel they receive on and so I was off to a non-starter. I would work for a few hours an then both of the Netgears would drop off the network and a round of re-booting (and half an hour for them to all settle down again) told me that this was not a reliable configuration for non-technical users.

So - after a bit of chin-scratching I came to this configuration;

• Netgear no.1 is wired to the BT hub and set for Access Point mode; it's re-serving the connection with a new IP range and (crucially) a new WiFi channel some distance from the BT hub.
• Netgear no.2 is set for wireless extender mode and is located at a mid-point in the house repeating the signal from no.1

This has been stable for more than a day now (I've insisted that my boys use the furthest repeated network) with only minimal speed loss (typ. 8 mbits^-1 against 10mbits^-1 at the BT) so I'm going to run away and hope!

Colourists are the last people who should have a say on monitors!

I was recently in a decent grading room - Dolby PRM 4220 monitor and I was demo'ing a Boland BVB25 OLED display. The demo unit had come back from a try-out at another customer's and I hadn't had a chance to check it's calibration (Rec.709, illuminant-D yada yada...) and so I grabbed the colour probe kit and calibrated it whilst chatting to the engineer and colourist. Once done I looped it off the Dolby to see how they compared and they were quite different! The Dolby was sat-up, over-saturated and a bit red-in-the-whites. The conversation went;

Colourist:"It doesn't match my Dolby",
Me:"…you just watched me calibrate the monitor for Rec.709",
Colourist:"It's wrong",
Me: "Is the Dolby set for Rec.709?",
Colourist: "No, I feel that when I export Quicktimes for customer approval how I have the monitor set now matches what they see better"

 I also have the same convesation about black levels endlessly. An online editor had a go at me because I'd left his monitor "too crushed in the blacks" - here is a frame from his timeline;

It is a continuous battle to persuade people that monitor calibration is NEVER a matter of opinion, rather it is defined by measurable technical standards and when I calibrate a display it is correct. Your material may well not look how you want it, but don't corrupt your monitoring pathway to make your project look good.
Often I'll ask the colourist what standard they want the monitor calibrated for; it's rare that they know what I'm talking about, but they'll often venture an opinion that their display is currently "too cool" or something (quite how they know without a reference I'm not sure?).

I suppose a lot of this is down to the fact that colourists are people who have to be very confident in their ability and are paid handsomely for what they do. However, they have to realise that their mojo doen't extend to how their monitors are set up. When I demo a monitor my heart sinks when someone says "we'd better let the colourist have their say" - monitoring is not about creative magic, it's about compliance.
This December I've calibrated over thirty customer broadcast displays; I've been there/seen that more than you!

Gotchas with updating firmware over RS232

I've recently been upgrading Boland BVB25 OLED monitors over their RS232 serial ports; aside from needing a USB/serial adaptor (I use the Keyspan which mimics an old PC serial UART) you also need a null-modem cable (i.e. where Tx and Rx are swapped over). You can tell if a null-modem cable is required by the sex of the connector on the back of the equipment. A 25-way or 9-way D(male) indicates a DTE ("Data Terminal Equipment" - a PC or terminal) and a female connector a DCE ("Data Communication Equipment") - a modem in RS232 speak. So, if the gear is a DTE then you need a F-F cable and by definition is has to be a cross-over (AKA "null modem" cable. I've banged on about this in the past, and there is also the consideration of handshaking; does you gear/app need the hardware pins (DSR, DTR, DCD etc) or does it use software flow-control (XModem etc). Hugh and I did a podcast on the subject if you need to brush up on your serial comms.

Anyway, because RS232 is such a low level way of doing things it's often the case that the receiving UART in the equipment can get direct memory access before the OS has loaded and you may need to jump through some hoops to get the thing into "serial update mode". In the case of the Boland monitors we sell it's necessary to have the updater software running and looking for comms before you do a power-down reset of the monitor; and not just power-down - tug the power cord, and then within a second or so of re-applying the power the monitor will start talking and appear dead from it's front panel but stuff is going on.

This kind of three-finger tomfoolery really reaches a zenith when you're upgrading the Linux SOC kernal on Amulet DXiP cards!

4k and UHD cabling and signal standards

I've had to dig into signal transport for 4k/UHD over the last week or so. Essentially I have a test-signal generator (SRI Visualizer TG100) running at a maximum raster of 4096x2160 at a maximum of 25 progressive frames/sec (and only 4:2:2 colour sampling; Y, Cr, Cb) with a 6G single-link output (so really 4 x 1.5G links) and HDMI 1.4 (so the same raster as the SDi). The monitors are the 24" and 30" Canon IPS 4k native monitors.

The Canon monitors will take quad-link HD/SDi and (in the case of the 24") HDMI. So, feeding the SRI single-link into a Blackmagic 4k multiplex (to produce quad-link) and then into the Canon produces four quads in the wrong colour-space!

 For an insight into what the multiplex is doing it's worth looking at the two standards for quad-link SDi. Put aside if it's 4 x 1.5G or 4 x 3G (that allows an increase to 50 or 60P OR 4:4:4 colour). But, in this case we're de-mux'ing a 6G to 4 x 1.5G signals. 

The original 4k-over-four-BNCs standard

The more recent standard; each link looks like an HD version

Clearly the converter is producing 2SI but the Canon expects SD quad-link. In fact the guys at Canon tell me they have a firmware update early in 2016 to address this. The other error is that the Canon has mistaken the 4:2:2 video as RGB - but it has at least got the raster correct.

So, what to do? Well, by throwing in another converter and taking the HDMI out of the SRI means the BM mux will get an older SD quad-link input;

This produced what we need; clearly HDMI has not concept of mutliplexed pixels and so we're now fully in SD quad-link;

tugging BNC no.4 shows the monitor is now in quad mode

The monitor gets it all right

The other thing that you have to pay attention to in "True 4k" displays (for the film snobs!) is that feeding 3840x2160 signal into a 4096x2160 monitor and letting the monitor scale-up to fill the line risks killing your resolution;

The aliasing should only the present in the top-most block, the other alias frequencies you can see here are due to my iPhone's camera!

Some very strange aliasing when a 3840-pixel line is mapped to 4096 pixels

As ever with display devices, pixel-pixel (native resolution) is always preferred

Barnfind integration with third party control panels

Barnfind are one of the products I'm responsible for at Root6 and I love them for their forward looking attitude and the fact they embrace open standards; if you see an SFP hole or a BNC connector you know that it will work with any other manufacturers (unlike Evertz who re-define the standard and put an X at the start of the product name!).

So - the BarnOne BTF1-07 is the chassis I have in my demo kit and at IBC this year Wiggo and the guys were showing a much wider set of third party control panels they have integrated to work with their cross-point router. So, to make our demo more compelling I bought a BlackMagic VideoHub Smart control panel and set about making it talk to the BarnOne.

Since I have to rock-up at customers' facilities to show this gear I figured it's daft to rely on their networks and so I've included a TP-Link travel router to dish out IP addresses to the panel and the BarnFind; it also allows you to use a wireless laptop to then run the demo. These little gadgets have single WAN and LAN facing ports but rather splendidly the BlackMagic panel has a little ethernet hub inside so you can loop the network connection to the Barnfind. 

This screen-grab is from BarnStudio - the config/control software for Barnfind products. It has a discovery protocol so it can find any chassis on the same LAN segment. However - I discovered a couple of gotchas;

• When upgrading the chassis you can either attach a USB stick to the front and the embedded Linux machine will grab the image OR you can use BarnStudio. Initially I couldn't get either to work! 

• Barnstudio just instructs the Linux machine to do an apt-get (or similar) and so it has to be able to see out to the internet; connect the WAN-side of the little router to the workshop network!
• If you do the USB route then the installer checks the signature on the package; again, it needs to get out to the web to verify the cryptographic signature.

• The Blackmagic panel does not have any host-discovery protocol built in and so it seemed only sensible to set the router to always dish out the same MAC/IP address combinations by using the DCHP reserved assignment page in the router. Then assign those number in the BlackMagic config software.

After that it really is very simple - you set the virtual buttons to be whatever sources and destinations you want. You can even reserve some to be macros (which are then just a list of route assignments) - in fact that is how you would do duplex signals; Ethernet etc. You have to assign both the in and out of each SFP (Tx and Rx). You don't have to have sequential sources or destinations and I can't honestly see how they could have made it any better!

So - with BNCs 17 & 18 on the front of the Barnfind defined as 3G HD/SDi video in and out and these button assignments on the BM panel I've got proper router control. These forty-button panels will be very useful for controlling all the synchronous broadcast signals (HD/SDi, HDMI, MADI etc.) and asynchronous data signals (Ethernet, fibre-channel etc) running through a Barnfind router (and then out and over CWDM fibre?).

The only criticism is that the software matrix takes a second or so to update after panel changes are made; but I can't honestly see when that would be an issue - this software matrix is  tool for the engineer, not the operator.

As an aside they have recently published a very complete integration guide with lots of examples and advice.

http://media.barnfind.no/marketing/BarnGuide%202.0.pdf

Colour of the wall and lights in grading rooms

In the last year or so a lot of my time seems to have been taken up with getting monitors and other display devices to show the correct colours for film and TV. However, as with all other areas, context is everything and the colour of the wall behind the monitor (and the colour of the light illuminating the wall) are as important as the calibration of the monitor.

Picture from Robin at Wire Broadcast - Grading Suite at Envy

Nobody has perfect colour memory (remind any colourists you know!) and if the rear wall of your grading room is slightly yellow your eyes will adjust to that and you'll tend to grade pictures as if yellow is white and in truth your pictures will be missing blue. So - what's the standard? ISO 3664:2009 specifies "N8" as the neutral grey for accurate colour environments. Essentially you want a paint that favours no reflected colours. You can spend big bucks buying the approved paint from eCinema or RPimaging but you'll wind up spending many hundreds of pounds for a few cans of paint and it isn't really necessary.  I've had splendid results with Crown Plain Grey 5574 Matt Emulsion. In fact ColorTechnics specify that paint for use with their VeriVide D65 “Artificial Daylight” CIE daytime illuminants fluorescent tubes.

Having said that I've never bought the approved tubes, preferring to go to the electrical wholesaler and pick up normal shop-type ones. It turns out that the pet-store industry favours D6500 colour tubes as the light output stretches down into the UV end of the spectrum (sub 300nm wavelength) which animals respond well to. One thing that I have been told is that there is small variance between batches and so it's best to overbuy so that once you've got the holders and baffles fitted you should visually (or using a photometer) make sure the colours are matched. It takes only around 100k of difference for you to be able to spot it immediately and so it's not surprising the manufacturing tolerances are not good enough for TV.

So - wall painted, florescent tubes fitted; what next - well, since you're looking for around 15-20% of the light output of the monitor as a surround (so around 20Cd/m² from the wall) you need a way to control the brightness of the tubes. You could dim them but there is always the risk of the switching waveform breaking through onto your audio system AND tubes change colour as they are dim'ed (particularly as they age) and so the best thing is to fit mechanical baffles to them; Bryant do some excellent ones - but throw away the tubes as the ones supplied at 6000k colour temperature; a tad too red for grading suites.

There are a few other things people obsess about when setting up grading rooms;

1. The Tek WFM601 used to come with an option for a white display (quite a lot more money IIRC) so that the colourists eye wouldn't be drawn by the green phosphors!
2. Computer monitors - you should run them dimmer than the 200Cd/m² peak that most people have.

I'd agree with the second point, but the first one seems unnecessarily picky.

Of course, the biggest offense to anyone who cares about colour fidelity in the film and TV world are these things, Philips Ambilight TVs!

 

UHD-TV test material; how I'm going to demo monitors

After all the monkeying around with the Canon monitors last week I decided I need a decent variety of clips to show off UHD displays to the best of their ability. For some reason customers are not satisfied with just seeing test signals?!

So - although I have the TG-100 for uncompressed 4k test signals (the Visualiser really shows all you need to know!) and I can show:

• Resolution
• Colour Space
• Temporal performance
• Dynamic Range

So, I went looking for some well shot UHD footage at the TV 4k raster of 3840x2160 (I know, all you DCI-snobs, "true" (sic) 4k is 4096x2160). The Harmonics site has some nice short uncompressed YUV-planar format videos; http://www.harmonicinc.com/resources/videos/4k-video-clip-center#4k-clip-center - But don't expect your laptop to be able to play these guys! At 12GBits^-1 they are monsters and so for ease of use you may want to compress them down to a more manageable 500MBits^-1 (or so) using GLYUVPlay which can be found at Henryk Richter's site. In video coding research, standalone implementation and testing of video codecs often involves the use of raw YUV streams. Since these streams can be parsed and generated by very simple means, raw YUV files are very common in video codec standardization and development. 

I have made the H.264 variants and you can find them on my Google Drive folder.

So it's time to change ISP (again!)

So it looks like TalkTalk have had their customers' database exfiltrated and it seems they have done everything wrong! It's a shame as I've found them to be a fine ISP (MUCH better than Virgin) with good speeds and impressive uptime. They haven't bugged me endlessly with the TV and mobile up-sell and the bill has remains consistently ~£15 month^-1 less than Virgin ever was.

So, having watched with a mixture of annoyance and amusement here are a few thoughts; 

1. Don't claim that "we take customer account security extremely seriously" after a breach; behave like you believed it before the hack,
2. Don't hide behind the claim that "...we have been suffering a sustained attack" - all ISPs (or any big internet-property) is under constant DDoS and other assault; it's no excuse today.
3. Don't tell customers to go and update their user passwords and then have a broken website for twelve (and counting!) hours afterwards,
4. Hash your customer database with a reliable method (even MD5!) and salt the hash - in 2015 this is now considered standard practice for people who "take security extremely seriously" (sic),
5. Don't tell customers to "keep an eye on their bank accounts and credit card statements" - this is your fault, don't load the responsibility for the mess onto customers,
6. Put data security and best practice ahead of sponsoring TV talent shows,
7. Have a chief executive (who had the nerve to go on Newsnight) who actually knows how your customer database works - they're the CEO of an ISP for goodness sake!

So that's it; perhaps now ISPs will use results of proper pen-testing as marketing rather than the guff that passes for customer information currently in service provider adverts. If one company includes the word "bcrypt" on their website they'll get my business.

Canon's 4k Native IPS television monitors

I had an excellent half day with Canon's UK imaging display guys to look at their DP-V series 4k native displays. To my shame I had assumed that they would be like the HP Dreamcolor or Eizo ColorEdge series monitors which are advertised as being suitable for film and TV work but as I've often said; "..an SDi BNC and a preset called Rec.709 does not a broadcast monitor make"!

In the case of those two manufacturers they assume that taking their print-prep graphics display and making it SDi capable is all that's needed; forget proper RGB linearity and a controlled white-point. In the case of the HP they still advertise it at 250Cd/m² for white (four times what it should be - you can't grade with that) and every time I've had an Eizo to play with I've found the same. Even employing a LUT to tame something like that is a bad idea as having to take 250Cd/m² down to a more sensible 80Cd/m² means you've lost two stops (12dBs, two significant bits) of dynamic range; not what anyone wants.

So - native 4k displays using LED-backlit IPS-LCD and not OLED. Every display technology suffers issues and although I think the poor inherent RGB tracking of OLEDs is entirely addressable in a LUT (which is why I love the Boland BVB25 for colour-accurate TV work) OLEDs are noisy once you get very close to black thus limiting their dynamic range (fine for 10-bit TV work; but for 16-bit HDR film imagery, not so much - yet!). Canon has consequently chosen IPS-style LCDs (with a level-modulated LED backlight). The LED backlight is the same technology as that used in the Dolby PRM-4220 grading monitor which is how they achieve the high dynamic range with a possibility of >1000Cd/m² for specular highlights in HDR 16-bit video. I got to see the originators of this technology, Brightside, back in 2005. 

So, proof of the pudding etc - I profiled the 24" edit suite variant and it was very close to the Rec.709 spec (the fact that I left LightSpace set for a 2.2 gamma whilst the monitor has a true BT.1886 gamma for HD rasters may be to blame). With 4k source material the results look great.

 I started at 2k to see how it did

 At 4k I can only manage 25 FPS at best!

Zooming in on the frequency grating shows aliasing, but only on the camera pics, I couldn't photograph it with my 10Mpix camera without catching aliases in the camera's OTF.

Getting closer gets a bit better, but to the eye the resolution is astounding

 

The Sarnoff ladies at true-4K

 

I profiled the display at 17-points so 5,000 measurements take around two hours with the Klein

 

Looks pretty good for greyscale performance, and I suspect if I set LightSpace's gamma correctly it would be better

The coloured dots are rec.709 and the big cube is the gamut of the display; it covers the colour space nicely.