Monday, April 19, 2010

Blackmagic Videohub & RS422

I've talked about BlackMagic's router range - the VideoHub before but never installed one of the larger 72x144 models.
They are very thin! Where you'd expect the cables to terminate at the back of the bay these have to be long enough to terminate at the front of the cabinet.

Here are a few notes relating to it - it's amazing that you can buy a 3G-capable HD-SDi router (with RS422) for around ten grand. To do the same with Probel et al would be north of £50k. However - there are a few things you lose with your budget router.

  • Remotes control - although in the past I've mentioned how the VideoHub can't do the TX/RX crossover that all 'proper' matrices do (i.e. they know how to handle controlled/controlling devices) they have introduced this in v.4.3 of the control software (that runs on a USB-attached Mac or PC - can can even re-share control over a network so you can run the same control applet on your Avid/FCP workstation). In v.4.2 you had to declare what a device was - either a 'deck' (a controlled device) or a 'workstation' (a controller). This falls down when you think about doing two-machine front panel editing between two VTs - the recorder becomes the controller and so you have to go into the labels menu and temporarily declare that VT a 'workstation'. The reverse is true if you want to run your Avid in VTR-emulate mode (when the timeline can be controller like a piece of video tape). We thought 4.3 was the answer to all our RS422-payers but it doesn't work that well - and when it gets it wrong you have to keep making and breaking the route in the hope that it gets it right. So - we're sticking with v.4.2 (BlackMagic s/ware archive in the title link).
  • Touchscreen - our customer wanted a touchscreen to control the software which works quite well - I'd recommend at least a 19" 1280x1024 res screen as a 17" is fiddly.
Of course - in a non-TX environment these things may not matter. It really is a very good deal!

Thursday, April 15, 2010

Why did late 60's/early 70's rock singers have two mics taped together?

I've been enjoying "Guitar Heroes at the BBC" on BBC4 where they compile clips from Whistle Test, Rock goes to College, TOTP etc. I've always wondered why rock singers from a period of only a few years would have two mics taped together. By the time I was paying attention in the late 70's the practice seemed to have stopped so I suppose it was a technical development that made the change.
I asked the question on Twitter and Facebook and got great rock'n'roll answers; " they could take it to 11", "early form of stereo recording" etc. In fact when I went back over my old BBC notes I had been told why they did it but only a few weeks out of university I don't think I understood common mode rejection!

Ronnie Van Zant of Lynyrd Skynyrd c.1973 - two mics!

So - having re-read my notes and had a trawl around the web (my word, there is some awful rot spoken by people who know very little!) here are the two reasons (and I'll list them based on the technology that fixed the problem), they both rely on the fact that the two mics are wired anti-phase to each other and the assumption is the singer sings predominately into only one of them (doesn't matter which).

1. pre-compressor/limiters you needed a way of loosing some of the induced stage and line noise - this does it.
2. pre-parametric eq - you needed a way to reject howl-round and this does it.

So - you mix the anti-phase feeds in two channels on the desk and all noise/feedback etc gets canceled and the voice (predominantly coming down one feed) remains. Interestingly another technique to gate a mic is to have either an optical detector on the mic stand or a pressure mat in front of the mic which mutes the channel when nobody is near the microphone.

Monday, April 12, 2010

My blog is blocked in UAE!

Fantastic - China as well - I'm kinda glad they don't want my kind of radical engineering ideas been seen there! Thanks to my good pal Tim Taylor (who's working out there at the moment).

Tuesday, April 06, 2010

I'm going to leave Virgin Media (and so should you)

I've been with Virgin Media since they were Blue Yonder and then NTL and have consistently upgraded as faster cable connections arrive. I like lots of bandwidth because sometimes I need to download large files quickly but I find that for Skype, iPlayer and the plethora of other bandwidth hungry apps you can never have a big enough pipe.
Several times over the last couple of weeks my connection has slowed to a crawl. This screengrab from my 'phone is typical - unusable for anything other than email or IM. Eventually I called tech support (which is often a painful affair!) to be told that I'd fallen foul of the traffic management cap. All the details are in the title link. Bear in mind I never signed up for this - they introduced it without fanfare last summer and the details are show in the table below;

So let's take the slot between 16:00 and 21:00 - if you pull more than 3.5gigs across your connection you trigger the cap and they slow you for five hours. "Hang on, who downloads three and a half gigs of an evening?" you ask - but it's not the downloads that get you. We're talking about an 18,000 second slot which (do the calculation yourself) means that if you run your connection at two megabits per sec (it's actually a tad less) you fall foul of the cap - ten percent of what you pay for (on my twenty-meg connection) will give them the excuse to slow you down.
So - in a household of teenagers it is by no means unusual for more than one person to be watching the iPlayer (Sarah and I on the TV using the Wii, the boys of their computers) - so that's 2 or 3 x 800kBits per sec, maybe a bit of Skype (around 400 kBits per sec) and add to that a download or two and you've fallen foul - and over recent nights I have every evening!
Part of the problem has been the dodgy DVB-T tuner in my PVR - I've been downloading BBC shows in HD rather than recording them!

Virgin's response is one of fairness - why should some people hog all the bandwidth? The implication is that their network (the only one that is 100% fibre-to-the-cabinets as their adverts remind us) isn't up to delivering the bandwidth we have been sold. This is bogus because when I raised this with them their response was to try and up-sell me to the fifty-meg package which has no restrictions! It's a marketing strategy. I bet when they launch their 100meg connection the fifty meg one will suddenly have limits introduced to 'maintain a fair usage model'.