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

Thursday, March 10, 2016

Crypto - March 2016 Root6 Tech Breakfast notes & Ross Anderson

You can grab my notes here, event details

Also - good watching on YouTube:

Tuesday, March 08, 2016

A review of Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography by Michael S. Tooms

All of my colourimetry comes from doing it; my theoretical knowledge isn't that great as I didn't study it at university and the colour training at the Beeb, although entirely appropriate to what a TV engineer needs was just that; TV-centric.
Over the last ten years I would credit the following industry colleagues for widening my understanding and appreciation of colour reproduction;
  1. Martin Euredjian of eCinema Systems was a colourist and telecine engineer before he started making reference-grade LCD monitors - Root6 sold them for a while (around a decade ago) and Martin was very generous in his product training. He opened my eyes to the problems of metameristic failure between different display technologies.
  2. Martin Parsons of Image Eyes who used to be the head of colour at MPC; like me he's now a colour-gun-for-hire but I always enjoy getting his take on things and since he 's done an awful lot of calibration he knows when it's appropriate to maybe go slightly off standard to match two displays and keep the colourist happy.
  3. Steve Shaw is the proprietor of LightIllusion where I have bought probes, LUT boxes and of course LightSpaceCMS which really is the best calibration package out there. In terms of speed and accuracy nothing comes close.  Steve is very gracious with his knowledge and runs a good forum on his website as well as being a prolific presence on Lift, Gamma, Gain.
I recently was recommended Michael S. Toon's book Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography.  I picked this up at Amazon to read on the iPad Kindle app and like most academic volumes it comes in around sixty quid.

So - as mentioned, my background is the CIE1931 chromaticity chart and how that then relates to Rec.601, 709, the DCI-P3 colour space and Rec.2020 (the proposed colour space for UHD TV which is as yet no available on any current-model monitor).

Any practical skills I have with colour come from;
  1. Calibrating and matching TV cameras ("racking" or "shading" in the USA) for studio shoots.
  2. Calibrating and matching TV monitors - firstly in tape edit suites (it was always common practise to have two grade-1 monitors; the record monitor and the preview monitor).
So I think I have a good eye for quickly spotting how two displays differ - I can match two monitors or cameras pretty quickly but like most people I don't have perfect colour memory (and don't let any colourists tell you that they do!).

The first things the book set me straight on was the history of colour research before the CIE1931 diagram. Before cinematography and early colour TV experiments the concerns of industrial colour science was mixing of paints and pigments. An important consideration in colour mixing is being able to predict new colours from the volumetric mix of two pigments and the early colour models (Munsell and Guild & Wright) tried to reflect this with a choice of primaries at 460, 530 and 650nm giving rise to constant lines of "just noticeable difference" - JND - on their chromaticity charts.

However - the negative lobes associated with the gamma (green) and rho (red) responses mean that an all-encompassing colour chart should place the primaries outside the spectral-locus which gives rise to non-consistent lines of JND and a grey-scale definition in video colour spaces that seems to be at odds with the equal-energy point in the centre of the CIE1931 chart that gives us our white mix.

one of the worksheets that are available for download with all the empirical data used in the book tabulated and plotted

So I have no hesitation about recommending this book; it is readable and has enough maths so that you never think there is an slight-of-hand going on. For me it has filled in the holes that bothered me in my knowledge of colourimetry. If all the changes that are going on currently in the industry (principally Rec.2020 and the XYZ colour space) are something you have to deal with then this provides and excellent bedrock of colour knowledge.

Friday, February 19, 2016

Free Tektronix UHD/4k info posters

Get 'em here & here!

Sunday, February 14, 2016

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.

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

Thursday, February 11, 2016

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.

Tuesday, February 09, 2016

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;


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

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.

Monday, February 08, 2016

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.

Tuesday, January 19, 2016

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.