Monday, March 13, 2017

Calibrating monitors for HLG-1.2 High Dynamic Range working

I've now done a couple of Sony BVM-X300 (4k/HDR OLED panel) monitors for HDR-TV deliverables to the BBC. The Beeb are behind the Hybrid Log Gamma standard, currently at 1.2 for broadcast. It's benefits over Dolby's 10-bit version of their Vision HDR system (also called DolbyPQ) are many and rather splendidly the DVB as well as most manufacturers are now behind HLG. I'll write further about why a scene-referred system is a better bet for domestic TV than a display-referred one (like DolbyPQ) but I just wanted to get down some notes on monitor calibration for HLG.

So first up you need to get the monitor into HDR mode (the correct one! As of v.2 firmware the X300 supports several; the camera gammas; CLog, CLog2, SLog & SLog3 as well as the deliverable standards; SMPTE-2084 (DolbyPQ) as well as SMPTE-2100 (HLG 1.2).

You'll notice the EOTF setting (lit. "Electronic - Optical Transfer Function") is NOT set for HLG 1.2; this available but in the current v. 2.0 firmware it is wrong. Select HLG (Variable), click the know again and dial in 1.2

Next up display a 50% grey field (100% can't be done as the monitor power-limits to stop 1,000Cd/m2 being displayed across a lot of the screen) and point your probe at the display. Remember that unlike DCI-P3 we are still at the 6504K white point of tele. However - at 50% grey we should be seeing low-50's Cd/m2 being emitted from the screen. 

You might have previously heard Sony's "best practise" (sic) advice of setting 50% grey to 100Cd/m2 but this is wrong. Look at the graph; this is the result of profiling an X300 (and they all seem to do it consistently) and notice what happens over the last couple of hundred Candelas at the top end. If you set 50% grey to 100Cd/m2 you get loss of detail in the specular highlights. For the correctly 1.2 HLG curve you need to set 50% to around 50Cd/m2 to 55Cd/m2- remember the Y-axis on this graph is logarithmic. 

The one display I had previously followed the Sony advice for was sufficiently out of it's linear range that the dark-greys drifted red minutes after I finished adjusting the monitor and (like all OLEDs) the noise in their blacks is sufficient to make the final tweak to 6504k hard work - the Klein probe was having to average over 32 reads to accommodate the OLED panel. Remember - the K10A is accurate to less than 0.001 Cd/m2 and not the 1.0 Cd/m2 it reads at 10% up the curve of HLG 1.2

So - once you have those under your belt you can PLUGE the display to set blacks correctly for the room (what did I say about scene/display referred?!) and then set about getting the deep greys and the 50% colour balance correct. I've done this now on two X300s with BBC R&D engineers in attendance and they have given this method their blessing!

For a probe I was using a Klein K10A with Klein's own ChromaSurf software. If I get the chance to profile an X300 for myself I will do it with LightSpaceCMS - still the choice of champions for display profiling and LUT-building. They also have an excellent article introducing HDR.

Friday, February 24, 2017

My favorite music podcasts

For me the last ten or twelve years has seen an almost 100% move to on-demand radio listening. The only live radio I listen to is the Today Programme on Radio 4 whilst having breakfast; I do put Six Music on at the workshop for the wiring guys, but for me (even shows produced for radio) are consumed as downloads.  Here are the things about music that I never miss.

  1. BBC Mastertapes - John Wilson presents artists talking about how they recorded a classic album. The show slips in two ("The A Side" and "The B Side") with Wilson doing the interview in the first half hour and then the assembled fans asking questions in the second. Wilson is clearly a music fanatic and never fails to engage with the artist. It comes from BBC Maida Vale and there are currently 74 hours for you to catch up on! Billy Bragg's "Talking with the Tax Man about Poetry" was the first episode back in 2012 and the glorious thing about it is I've discovered some records I never knew about and been really surprised by how much I enjoyed artists I thought were not my thing. Rufus Wainwright is a prime example. The artists always do a minimal arrangement of the well known numbers off the album their talking about and so of course the format tends to favour performers who can do it live.
  2. Between the Liner Notes - A podcast (not produced for radio) that takes some aspect of the music industry and devotes an hour to it. Really engaging and has a big radio rockumentary production feel. For me - a Gen X'er coming of age in the eighties the episode on MTV is required listening.
  3. Music City Roots - this is a "proper" radio show out of Nashville. I like it because Mike Farris has a show (which sometimes makes it into the podcast feed) but the main man is Jim Lauderdale who is a real champion of Alt-country and Americana.
  4. Sodajerker on Songwriting - Sodajerker is a songwriting team from Liverpool in the United Kingdom. Founded by co-writers Simon Barber and Brian O’Connor who, like most jobbing musos, have to suppliment their work with teaching and podcasting. They have had some great guests in their (so far 97) shows. In classic podcast fashion the length varies and the best one so far (for my money) has been Paul Simon although I've enjoyed all of them (check out ep.80 - Marcus Miller).
  5. The Bored-Again Christian podcast - a notable mention even though he stopped making shows five years ago. I discovered a few artists via this podcast; Sufjan Stevens and Danielson to name a couple.
Podcasting is the answer to the dumb mass-market HeartFM/TalkFM/LBC type radio. It's no coincidence that you don't get anything like this kind of treatment of musicians and who they do on commercial radio.

Friday, February 17, 2017

My GameboyZero - build no. 1

I've been building a little RaspberryPi-in-an-old-Gameboy project for running lots of old console and handheld games. RetroPie is a superb project that unifies all of this and makes it very easy.

See my first video here.

3.5" Analogue Composite LCD
3w Class D audio amp: 
Great Scott!

Monday, January 16, 2017

LUTs are sometimes not the answer.

As I often tell people; a LUT can only reduce the dynamic range of a display. For the most part that needn't matter, particularly if you have the whole of the DCI-P3 (or a decent chunk of Rec.2020) in your monitor. Applying a look-LUT to simulate a delivery style is one thing but increasingly people see LUTs as the first answer to monitor calibration rather than getting the display to as close-as-possible before profiling/creating a LUT. Hugh and I did a podcast on the subject.

A problem I've recently discovered with a monitor's internal Rec.709 LUT is that although the monitor has a huge gamut in it's native mode (which you can see from this recording of ChromaSurf's output) but the 709 presets have trouble.

Notice how it can reach a full green value of 0.1879, 0.7317 (Rec.2020 calls for 0.170,0.797); you'd think there would be absolutely no trouble getting Rec.709 right, and in fairness the primaries are fine. BUT, when I use both primary and secondary colour ramps;

I wind up with some distinctly funny looking banding in the secondary colours.

On this 'phone photo it is particularly noticeable in the yellows, but it's there in the cyan and magenta ramps as well. The fault isn't there when the monitor is in native mode (or indeed P3, NTSC or EBU), only Rec.709 (ironically the only colour space we really need for TV!).
So, I'll have to profile it in native mode and spin a 17-point 709 LUT as the one from the manufacturer is clearly got problems.

Another way of stress-testing a LUT is to use the TrueColor LUT stress test image.

Thursday, December 22, 2016

Power supply toroid in Mackie SRM450 PA loudspeakers

A friend brought one of these very common PA powered loudspeakers over to the workshop. An internal T4A mains fuse had blown and when I replaced it and re-powered there was a very loud 50hz hum for a few seconds and the fuse in the power cord blew. I assumed it was the audio path that was making the noise and I assumed that one one the probably faults was a short/open de-coupling capacitor that was letting 50hz through to the audio stage.

I found the schematic at Mackie-SRM450 (although this is for the rev.C of the board, but the PSU appears not to have changed).

So - I made sure both fuses were good and with Dave Jones's words "thou shall always check the rails" in my ears I disconnected the output of the large toroid from the two rectifiers/smoothing caps and tried again. I figured I'd make sure the o/p of the transformer was good (there is some de-coupling on the primary). However I got the same loud 50hz for a couple of seconds and one of the fuses failed. The toroid was also noticeably warmer than it had been! So - checking the DC resistance of the primary side showed it to be less than six ohms (so it was pulling an inrush of at least 40A!).

A quick flail around the web showed that the transformer is a known weak point of this design.

 The real bummer is that the transformer isn't stocked by Mackie (or indeed anyone else) and the folks at Save My Light only do a minimum order (ten pieces) from the Chinese factory that wind them when they have enough orders (and the chap there told me he sells an average of two a year).
So, do I just wait or pay him the thousand quid to have ten made?!

Time to keep my eye on eBay for a hopefully working second hand replacement?

UPDATE 16/01/2017: 

So after lots of flailing around the web and finding a few reclaimed ones for more than £150 I came across AJAudio on eBay (Alex Mathew was super-helpful) and he sold me one for £99.
Job done.

For info - the failed toroid had around 5 ohms DC impedance across the primary whereas the replacement has 8.5 ohms.

It's been shaking the workshop with loud music all afternoon!

Friday, November 25, 2016

My favorite rockumentaries of all time

  1. "Still Bill"
    The film follows the life of Bill Withers, from his roots in West Virginia to his career in the United States Navy, to his famed musical career and post-retirement family life.

  2. "Sound City"
    In 1991 Nirvana recorded the album Nevermind at Sound City Studios. The band's drummer Dave Grohl was inspired to create the documentary after he purchased several items from the studio, including the Neve 8028 analog mixing console, when the studio closed in 2011.

  3. "Muscle Shoals - the greatest recording studio in the world"
    Documentary film about FAME Studios and Muscle Shoals Sound Studio in Muscle Shoals, Alabama.

  4. "Oil City Confidential"

    A film by Julien Temple about the early days of Dr. Feelgood, Oil City Confidential, premiered at the London Film Festival on 22 October 2009, and received a standing ovation.

  5. "Pink Floyd; Wish you were here"

    The film gives an extensive insight of concept, recording the songs and designing the album cover. It includes exclusive interviews with almost every key person, who participated in producing the album. It is the second Pink Floyd documentary by Eagle Rock.

  6. "You've got a friend; the Carole King story"

    In her own words, the story of Carole King's upbringing in Brooklyn and the subsequent success that she had as half of husband-and-wife songwriting team Goffin and King for Aldon Music

  7. "Classic Albums; 'Damn the Torpedoes' by Tom Petty"

Thursday, November 24, 2016

HDR for Television; HLG, DolbyPQ etc - a primer

I have been such a poor blogger! It's been a month-and-a-half since I set finger-to-keyboard but I have been busy at work and home. Here is a presentation I gave at the Soho Screening Rooms for one of Root6's Tech Breakfasts.

You can download the notes from

Wednesday, October 05, 2016

HDMI, HDCP and SDi out from Bluray players

It's been a few years since the master HDCP key escaped into the wild and so it seems that particular content protection system is fundamentally wounded (if not dead!) but reputable manufacturers still respect the HDCP flag (even if no encryption is present) and the MPAA are still issuing device keys to manufacturers and volume keys to content producers.
So - I have been installing some Oppo Bluray players (nice, high end machines) and they support HDCP rather too aggressively; on a non-compliant display you don't even get the boot screen or any menus! So - an SDi converter is out of the question. 
The usual trick is to use one of these cheap'n'cheerful HDMI splitters which present a device key to terminate the signal but then send it to two outputs having done the decryption. 

Works perfectly with Backmagic HDMI->SDi converters with the exception of the audio; the Blackmagic knows nothings about DTS+ or DolbyDigital (or any of their variants) - it only understands the basic PCM stereo part of the bitstream and so that's what you get in the SDi stream.

However - in the case of these Oppo 103D players they have decoders on board and present the de-compressed audio out of the back as good old analogue feeds;

In these rooms I've fed them to the analogue inputs of the Tektronix WVR8200 test set and hence by selecting a different audio input you can toggle the TC Electronix ClarityX controller between 7.1 from the Avid and surround sound from the Oppo.

Tuesday, August 02, 2016

New grading room - a few notes.

I've been building a Baselight room recently - the monitor is a Sony X300 UHD/HDR display (expensive!) with an AKA custom grading desk. Here are some photos;

All courtesy of my colleague & pal Graham McGuinness

  1. The X300 is a heavy beast at 16Kg and if you want to hang it off a monitor arm - the only one I found suitable was from Novus; we've bought a few things from them recently and they are a very high quality manufacturer. The TSS-range is here but we tend to purchase from our friends at MW/ThinkingSpace as they hold stock and are super-helpful.
  2. The X300 out-of-the-box was a tad hot in 2k mode (they distinguish between rasters as 2k/4k - not HD/UHD; just to keep the DCI film snobs happy!). I was expecting the EBU recommended 100Cd/m2 but was 125 Cd/m2 and a bit blue-in-the-whites, but not enough to bother adjusting unless you were pointing a probe at it! So - this one is correct for rec.709 but the customer (hasn't yet) decided what their wide-colour-gamut and high-dynamic-range workflows will be.
  3. I had my friend and carpenter Tony Andrews (Andrews Construction - for all your carpentry and building requirements!) built the lightbox. In the past I've talked about Crown Plain Grey 5574 Matt Emulsion as being suitable for the backwall, but that's now a discontinued paint and so an excellent match is Delux's "CN8 Grey Steel 3".
  4. Display Port monitors and Baselight-1 - so running Baselight v.6 on an HP Z840 means you have a four display-port output nVidia card. Historically they would prefer you to use DVI monitors, but this is 2016 and a pair of HP Dreamcolor 27" monitors are being extended via Amulet (my favourite KVM extender). In this case you need to have Filmlight provide a new version of xorg.conf for X to see higher order monitors as primary and secondary GUI displays. 
  5. The Blackboard2 control panel is fed over a DVI adaptor hanging off port 2 of the nVidia. Be warned! It runs at a very funny raster (3460 pixels wide!?) at only 15 FPS. It doesn't respond to EDID requests and so consequently you have to use a very simple extender to run it to the suite - no KVM-over-IP, just a fibre balun (I used one of these).
  6. Similarity the USB for the Blackboard declares itself as an HID device but then ignores HID-probes, so again, only use a balun to extend the USB, no over-IP.

Tuesday, July 26, 2016

Fuji IS-Mini software for colour space conversion

For patch generation and LUT testing the Fuji IS-mini is hard to beat for sub-£1k. LightSpace will drive it for profiling monitors and since it has both HD/SDi and HDMI outputs it is very useful all the way to 1080 lines at 60P.

The software that comes with it is kinda utilitarian but can speak to multiple IS-minis over either USB or ethernet. So you can load LUTs to several units from a single computer and it will even listen to the commands from a Tangent Wave control panel and you have a very canny little grading system (all be with no memory!) - but for live colour correction it is used everywhere from HDR cameras feeding BT.1886 productions to folks who need to correct for unusual cameras in an otherwise standard OB environment.

Having said all that it isn't a patch (pardon!) on LightSpace but they have just released an unlocked beta that feature colour space conversion LUTs which might be of interest to general colour-tinkerers.

From Fuji's site;

The rapid adoption of 4K Rec2020 and the development of HDR has necessitated an increased need for colour space conversions, such as color gamut, various LOG curves and numerous other standards. As requests for products to handle this have increased, FUJIFILM has begun to develop a system for IS-mini users that will allow greater flexibility with colour spaces.

And the obligatory bullet points;
  • Convert the content of Rec709 to Rec2020. 
  • Convert the image data of SLog3 / SGamut shooting to HDR ST2084 / Rec2020. 
  • Convert Legal range to Full range 
  • Convert the image data of the various cameras to SLog3 / Rec2020. etc... 

Grab it here.

Saturday, July 09, 2016

Memories of 1999 at Resolution Soho

I'm working the weekend in a building that has been a TV facility for the last couple of decades. I had the privilege of being Chief Engineer here during 1998-2003 when it was the Soho branch of the Resolution Post Group. 
Having opened a few cable-risers it looks like this place is largely the same (aside from the decoration) and in many of the rooms there is still equipment I either purchased or had the pleasure of fixing or calibrating.

Custom talkback box; this is a little thing I home-brewed around 2000 - it's just a talkback box with a cue-light button on it. Still in use though!

This wooden-surround for the Wacom tablet for a Softimage DS workstation had an little audio switcher built into it (selects between DS, VTR return and CD). The grahics tablet was originally hidden inside the polycarbonate sheet so you couldn't see it.

This monitor shelf was a bit of a mission; galvanised scaffolding poles are held in a triangle shape by chandler's wire & connectors. The tear-shape glass shelf sits on top of that (the ends of the poles have rubber caps) and the monitor's weight stresses the structure to keep it solid. I thought it would collapse in a week but here it is a decade-and-a-half later!
Also notice the PMC TB1 loudspeakers; most of the rooms here still have them. They were all purchased between 1999 and 2001 and are all still sounding good.

Back in 1999 there were no WiFi walkabout 'phones or office-grade DECT handsets. So - I bought the best domestic ones I could find and then spent a few days seeing where the best place was for the base-stations for maximise coverage for the runners, engineers and tape-ops (we still had those!). It turned out to be an external wall at the rear of the building. They're still there! (Although no longer used).


My good pal Malcolm Baldwin reminded me that he'd made the talkback box - he commented that he'd never really liked it but I thought it was splendid. Just shows that some engineers have higher standards than other...!

Friday, July 08, 2016

HPA Tech Retreat, 2016 - I'm speaking about CWDM & signal transport for 4k/UHD/HDR

Next week I'll be representing at the HPA Tech Retreat; I even made it to the "featured" list!

From the Root6 blog;

In a session titled ‘Fibre/CWDM Infrastructure for Live and Remote Rec. 2020 and HDR Applications,’ Phil will argue that we now have enabling and affordable technology with CWDM to deliver high quality images without resorting to IP. “With the (some would say unseemly) rush to IP and Rec.2022, are we in danger of losing the very things that make broadcast video production so good – namely low-latency and uncompressed pictures? With a four-fold increase in data rates brought by UHD/4K and the last five years having seen commoditisation of CWDM, – we now have an enabling technology for quality in the face of the IT department!”

Wednesday, June 22, 2016

USB current draw by HID devices and Amulet Zero Clients

One of the complaints I often get from Amulet users is that they get strange results when using power-hungry USB devices. The prime culprits are Wacom tablets (particularly the Intuos and Bambo series) but today I went to a facility where they were getting intermitent behaviour from the left hand control and shift keys which in Media Composer is a real pain. 
The most common third-party Avid coloured-keycap keyboards are from Logic
They come with a USB hub built in and so you'd expect them to draw a bit more than an HID device, but it's worth looking up what the spec is for USB power draw. This is stolen from Wikipedia;

There are limits on the power a device may draw, stated in terms of a unit load, which is 100 mA, or 150 mA for SuperSpeed devices. There are low-power and high-power devices. Low-power devices may draw at most 1 unit load, and all devices must act as low-power devices when, starting out as, unconfigured. High-power devices draw at least 1 unit load and at most 5 unit loads (500 mA), or 6 unit loads (900 mA) for SuperSpeed devices. A high-powered device must be configured, and may only draw as much power as specified in its configuration.
Or, in summary;

However, flipping the keyboard over gives a different story;

Wow, 1.1A - more than twice what the spec says. However - these keyboards are used the world over and it seems that motherboard USB ports are more than able to power them. I thought I'd get my own reading to see what the current draw was so I stuck one of those USB volts/current monitors in line. The keyboard continued to work but the USB-meter gave me a 0mA reading; it was working the day before, but today, no dice. When I got it back to the workshop I opened it up and discovered the current-shunt resistors was blown away!

 see bottom left on the +Vcc rail - where's the resistor?!

So I conclude that the keyboard is actually pulling a lot more than 1.1A (at least at in-rush).

So, Amulet can supply 2.0A across the USB hub on it's Zero Client with a maximum of an amp on any one port. All much better than the spec but somewhat less than the Logic keyboard is pulling. In the case of power-hungry, non-compliant keyboards and tablets I stick in a powered hub and that normally fixes the problem.

Thursday, June 09, 2016

Stuck pixels on LCD & OLED monitors

Because they're semiconductors (and pretty tiny ones at that!) the pixels on modern HD monitors can become "stuck" such that you get a dot that is either black or white (in the case of all three sub-pixels; R, G, and B being stuck on or off) OR a primary (or secondary) colour where less than three of the sub-pixels have stuck. It usuall looks something like this;

see how the blemish aligns perfectly with the pixel raster

You have to get your face about an inch away from the screen to see a single stuck pixel on a 1920x1080 25" display, not exactly edit/grading viewing distance!
A piece of software that has helped me in the past is JScreenFix which is a little Java app that allows you to hook up your laptop to the monitor - thankfully all current model broadcast displays have HDMI but you might have to make arrangements (DVI to SDi converter, for example). 

Here's the interface as I used it today to mark three dead pixels on a broadcast OLED;

This is the random pattern (video noise) that it fires at the hundred or so pixels around the area of interest. The idea is that you leave it running for a while and hopefully it will provoke the thin-film-transistor (in the case of an LCD) and the diode (in the case of an OLED) to recover it's ability to start switching again.

In the case of the monitor I had a go at today I was able to clear down two of the three stuck pixels, but the final one that remained resistant to repair was interesting; a photo shows it to be probably some contaminant in the panel rather than dead pixels or sub-pixels;

the blemish seems to be in the inter-pixel space?

Tuesday, June 07, 2016

Colourimetry, Rec.709 and HDR video; a presentation.

A couple of weeks ago I was up in Glasgow doing a presentation at Root6 Scotland's PlatformOne event. Gerry shot some video so here it is (in case it's useful). 

The PDF of the notes is here, the URL of the YouTube clips is

Wednesday, June 01, 2016

The damage 100m of good-quality coax does to a 1080i signal.

I've posted measurements of the degredation that cables does to video signals before; see here, but I was grabbing a couple of screen caps for an industry colleague and here they are.

Friday, May 27, 2016

Boland's new hi-brite 7" camera/on-set monitor

It seems to be a thing for small on-set/camera monitors that they should have a hi-bright mode when being used in non-edit environments. The Boland BVB7a is an excellent little monitor and can be powered from the camera's 12v battery feed as well as coming with a DC PSU. It can take SDi (single or dual-link) as well as HDMI and composite (yes!). I shot a little video of me profiling it's colour capabilities.

Wednesday, May 04, 2016

BM UHD/4k converters - some gotchas

I've used a few of these guys recently - Blackmagic's quad HD/SDi input to HDMI 2.0 output for taking the UHD / 4k (either tile or 2SI standard) and making something that will display on a 4k domestic TV.

They seem to work quite well, but here are a few things that I had to get around;

  1. Firmware - I had two identical ones and I initially tested both with Quad-SDi out of Avids at UHD (3840x2160 at 25 & 30P) - all good. But when I started a 4k project (4096x2160 at 24P) only one worked - the other showed nothing on it's HDMI output. Eventually discovered only one of them had current (v.7 as of May 2016) firmware!
  2. Power cycle if colour space wrong - both have periodically decided they are going to mistranslate Y, Cb, Cr -> R, G, B - power cycling fixing it; hopefully the next firmware update will stop this?
  3. Four signals are always interpreted as UHD; if the Avid is running an HD project the four SDi feeds out of the back are all identical and the converter has no way of knowing it's not quad-link. The Tektronix 8200-series and the Canon VP3010 monitor both have to be told (and I set presets for just this) but the BM converter needs to see three or fewer signals to realise it's only a 1920x1080 raster. In the case of this job setting up two macros on the video router (one to route all four, one to send a non-used input to i/p's B, C, & D of the BM).
  4. Glad I'm rocking a MacBook Pro! I would not have been able to update the firmware otherwise as I've yet to move on from Windows 7 - and the workshop PC is still 32-bit Windows 7!

Saturday, April 02, 2016

The Engineer's Bench Podcast - tops tips for video

Next in our tips series - broadcast video.
Go to the website for a PDF of the notes.

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

Wednesday, March 23, 2016

Tech Breakfast – “Encryption”, Soho Screening rooms, London

A presentation I gave; starting with the fundamentals of cryptography (difference between symmetric and public-key etc), I talked about encryption techniques used in the Enigma machine (with a genuine, working example) through to HDCP and the other forms of content protection used in our industry: 
  • Symmetric vs Public-key crypto 
  • Examples – DES, AES/Rijndael etc 
  • HDCP, Blueray and the MPAA etc 
  • PCoIP – security of KVM extenders 
Notes are here