Wednesday, August 05, 2020

JVC DLA-Z1 4k projector; terrible calibration software!

I was recently asked to calibrate two JVC projectors for rec.709 and DCI-P3. These projectors have a modest amount of colour adjustment in their remote interface, but none of the factory presets are particularly accurate. For calibration JVC have their own software which is terrible! Why people don't integrate with LightSpace (particularly since Steve and his team are very keen to help manufacturers) I'll never know.
Anyway, before detailing two days of frustration in a couple of grading rooms it's worth reminding ourselves about the difference between Spectroradiometers (AKA "spectro) and Colourimeters (AKA "tri-stim probes")
  • Spectroradiometers measure wide band light energy - everything from 380nm (or lower) - very deep blue through to 740 (or higher) - very deep red. They are slow to make a reading (many seconds) and do not cope well with low light levels. 
  • Colourimeters measure just three wavelengths (just like your eyes) - which we'll typically refer to as Red, Green and Blue (but really are X, Y, Z colour matching functions) and so are vulnerable to metameristic failure (a mismatch between the primary colours generated by the display device and the filters used in the colourimeter) BUT they are fast (my Klein K10A can make a read in less than a second) and they are accurate all the way down to near-black.
So, best practise is to use your spectro to make measurements of primary colours (and peak white to be sure) and use that to calibrate the tri-stim. After that you have the speed and black performance you need with the accuracy of the spectro imposed. I tend to do this every time I encounter a new display even though the K10A comes with a lot of factory profiles and the trick the Klein uses is that their filters are very close to average human vision and so any metameristic mismatch between the probe and the display is close to perception which is all important.


Now, onto the JVC software, the first thing they neglect to tell you is to not run the network setting in DHCP mode if you want to do calibration; the projector tries to renew the DHCP lease every hour and so it's likely you'll loose connection and have to restart the process...


Next you have only two choices of low-end probe - the "DTP special" - the Spyder, and the only slightly better Xrite i1Pro2 spectro (I happen to have one of those) but bear in mind all the things we said about spectro earlier.
The Xrite needs to calibrate itself to it's supplied white reference tile every time you use it BUT the JVC software has not implemented that functionality - so, you have to load up some other software (I use Sony's monitor colour balance software), but LightSpace, ColourSpace or several others would do - connect to the probe, trigger a calibration and then disconnect.


Now you have to position the probe to collect enough light to make measurements - most projector calibrating gets done from the operator's position and probes like the K10A have aiming lights to show you where they are pointing at the screen. BUT, after two days of experimentation I found I had to have to i1Pro2 as close to the screen as possible whilst avoiding it's own shadow. It's marginally improved by offsetting it horizontally (so the long edge of the probe is parallel to the screen) as the shadow is not as significant;



These projectors have a setting for the LD power - you can drive the lasers at three different power levels. At the highest the image is too bright for grading work; around 120Cd/m2 at peak white which would be fine for a 31" grading monitor, but not a projector. At the mid-LD setting you around 60Cd/m2 at peak white which although still bright is OK. Again, what the documentation doesn't tell you is that it take around half an hour for the power to ramp up or down between LD levels. 


Finally, there is one other setting that can really kill you ability to get decent reads with the Xrite i1Pro2 probe and that's limited/full-range video on the input settings - yes! They have sited the internal patch generator before the video range decoder! So, with all this in mind if you don't;
  1. Have the probe as close to the screen as possible,
  2. Have the projector in High LD power mode for at least half an hour,
  3. Have the video input set for full-range video,
Then you will not be able to read a decent way up the 2.4 gamma curve for rec.709 (and the red channel is particularly affected). Have a look at the light levels as they are read;


This results in some terrible response in the resulting profile with the red channel in a terrible state, incorrect low end response and clipping close to black. 


However, if you get those three things right (above) then you get decent reads close to black and a proper response for the range;



How much easier this would have all been if you could use a tri-stim probe like the Klein but by limiting the software to using a Spectro you are bedevilled by low-light issues. Having to do your calibration at High LD and then switch the projector back to mid-LD when your done is silly. 
I suppose the reason it's like this is that these projectors are aimed at high-end domestic/board-room/lecture-theatre applications and not film & TV. The fact the software defaults all SDR gammas to 2.2 seems to indicate this and not having LightSpace support (when LightIllusion have offered to do all the API donkey-work) is unforgivable in the professional display device.

Sunday, May 10, 2020

Kickstarter projects; three out of four ain't bad...

Along with KickStarter there are numerous crowd-funding sites and I've ploughed a bit of money into several. As well as electronics projects I have funded a few artists to record albums and have been very pleased. 
Here are four projects I backed, three of which came out really well and one which kinda got half-way there. The thing you have to remember is that backing things on KickStarter is not like buying something - you have to fully accept that some project just won't deliver.


  • PockEthernet is a tester for ethernet and IP networks. Serious network people use a Fluke DTX-1800 (I used to have access to one) - it's now discontinued, but like the replacement DSX-series all TDRs (Time Domain Reflectometers) are expensive (a few thousand pounds) but if you want to certify an install it is expected. At the other end of the spectrum you have the £50 DC testers that just make sure there is continuity on each of the eight legs and really just allow you to have some certainty in termination polarity etc. The PockEthernet is a half-way house with some TDR capability (not sure home accurate is it) but nice record keeping. Above a little DC-tester (like a ModTap or others) it can do some IP testing; POE, DHCP, VLAN tags etc. and so for me is ideal. 



You interact with it using a BlueTooth-attached app running on 'phone or tablet computer



The measurement reports can be over many circuits (so testing a whole patch-panel at once is do'able) and you can email/save as PDF from the app.


You can even brand the reports with your logo

  • BeeLine bike navigator - I often see folks with their smart 'phone in a waterproof wallet as a bike GPS. That's great, but when I'm cycling somewhere I'm not entirely familiar with I often like to find my way but certain in the knowledge that as I get closer I can make better navigation decisions. The BeeLine is a bluetooth attached smart compass that tells you what direction to go and how far your destination is. I've been using mine for maybe eighteen months and it works really well. It is stable and accurate with good battery life.

wiggly route; it was a Sunday afternoon!


  • Pebble Smart Watch - Although the Apple Watch is undoubtedly a miracle to technology I never felt it was for me; the biggest problem is the battery life; two days at best. It also seems to need a lot of curation. Friends who use them are constantly attending to them and I only really wanted a second screen for my 'phone with good notifications, health tracking and control of media players. The Pebble does just those things really well and nothing else. The battery on mine (Pebble Time Steel variant) lasts for more than a week and when they went bust at the end of 2016 I bought a second one just in case. They charge in about an hour.

The lockdown has been great for sleep but very bad for exercise...


I always return to the same watch-face "Graphite Too" as it has everything I use and is clear.

Thankfully after Pebble went bust and got bought by FitBit a group call Rebble acquired all the source-code etc and have been supporting the watches with new firmware and online services since.
  • Oscilloscope Watch - I know what you're thinking; what a daft idea! I've written a lot about this one in the past because I did get a very janky alpha-version (3D printed case, very early build of the software etc). Still, five years on and the project is still live on Kickstarter and so we live in hope!

Thursday, March 12, 2020

Modifying Blackmagic 6G routers for quiet(er) operation!

You can't deny the value in BMD SmartVideo Hubs - they are a fraction of the price of traditional broadcast video matrices. They have appalling return-loss on the BNC inputs and their control system is very simple (although in lots of cases that's a benefit). The temptation is to stick them in desks in edit, grading and audio suites, but they are noisy! The reasons are;

  1. Cheap, low air volume fans
  2. Tiny holes in the chassis through which to try and pull enough air
  3. No control of the fans even though the ones they supply have a tach output

'scope is showing the tach o/p of one of the fans, yes, I was routing video!

Even though the cheap/noisy fans BMD fit have a tach output it clearly isn't read by the hardware as the fans run at full tilt from power-on. This one had been on and routing video for a couple of hours (with the lid on) and it's like sitting next to a vacuum cleaner.
So, quick look at RS and filtering by size, volts and then listing by highest air volume & lowest noise I got these Papst fans - they also have a tach output (I had no plan to use that) and more importantly are induction-start motors (so they will run on much lower voltages; I had a feeling I could simply control them with a potentiometer with a similar impedance to the coils).

getting them ready to fit in the same JST 1.5mm pitch headers as the stock fans, 10K pots

fitted to replace the stock fans - I had to ream-out the screw holes in the fans for the screws to fit, double-sided tape for the pots.

The other issue is the tiny holes they have in those cases for airflow. With a bit of extruded aluminium and grill material you can get a good look.

Make sure you don't put another piece of equipment directly above it!

So, proof of the pudding and all that; I ran the stock unit for a couple of hours, pulled the lid off and took a photo with my thermal camera and then did exactly the same after the modifications. The results speak for themselves; the client has these in their audio suite and game me four more to modify.

before & after - running cooler and maybe 20dBs quieter

As an aside I found driving these fans at a constant 8v produced the best results.