HD-SDI video signal transmission

This is really just a few thoughts on running multiple HD-SDI signals along one cable- a number of production sound mixers have historically run multiple analogue sources over CAT5 cable (and even with a balanced audio return), however, the majority of video signals around set are increasingly HD-SDI, which are more fussy over the 75ohm BNC cable they’re distributed through.

My first thoughts were to up the spec of the cable, to CAT6 or CAT7, which have superior shielding, however I found that Muxlab make a passive HD-SDI balun which says it can transfer HD-SDI video over 120m of CAT5e cable.  As it only uses one pair of wires out of 8 in the CAT5e cable, I can’t see a reason why you couldn’t wire 2 (or even 4) of these baluns to run over 1 cable.  There also isn’t much to them, they’re a 75ohm to 100ohm balun transformer, however they need to work at 1.5GHz in order to transfer HD-SDI, and 3GHz for 3G SDI (and finding a suitable transformer is more difficult)

After looking at the 3G-SDI spec (SMPTE424M), I noticed there was a mode (B-DS), which allows 2 independent HD-SDI signals to be transferred in one channel.  So I had a look round for a box that could combine and split the two signals, and came across something even more powerful: Blackmagic’s SDI multiplex 4K mini converter* This allows 4 independent 1.5Gbit HD-SDI signals to be muliplexed into one 6G-SDI signal.  This will also allow for current monitors to work with fancy new 4K signals and it’ll also work as a distribution amplifier if things get a bit congested at video village (although this is not sound dept’s job).  I don’t know whether it’d be possible to run a 6G-SDI balun, CAT6 cable is capable of handling 10Mbit/s networks, however not over long distances (CAT7 would be more appropriate, if a suitable transformer could be found)

Another solution is running a quad split, where the converter box will put up to 4 different images on each quarter of the screen- a single, larger monitor could be a good solution to this, however an advantage could be to be able to get a cheaper HDMI monitor (as some have HDMI out), run the quad split close to that.  Decimator design make a number of suitable boxes for this, depending on your requirements.

*amendment- After contacting both Muxlab and Blackmagic about their 6G multiplexer boxes, they’ve both said they *should* support multiple streams, however they’ll all need to be in sync, however neither company has tested them.  So neither box has sample rate converters (or their video equivalent?) on the inputs.  I’d expect them to work if all the cameras have genlock sources on lockits

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Analogue audio over CAT5 cable

Cat5 cable can be cheap, it’s pretty light and thin but surprisingly well shielded with 4 twisted pairs in there which will all resist interference.  It also has 100 ohms impedance, which isn’t far off the AES/EBU standard of 110 ohms, so should be able to carry digital audio a fair distance.

So I’ve done a bit of a make and an experiment to make a lightweight 4 way multicore:

I got a couple of Neutrik NE8-FDY-C6-B connectors- these are fairly easy to assemble, there’s instructions on the site, and don’t even need a soldering iron- just some snips, really.  You could probably prep one with your teeth if in a desperate situation.
On the other end I attached 4 XLRs

As they’re not meant to be cable mounted (and there isn’t an appropriate connector) I had to improvise with sugru and heatshrink

Anyhow, they work and with shielded CAT5 cable (you have to look quite carefully at the specs, most isn’t) they’ll work with phantom power too.

There are also a few commercially available solutions for audio over cat5, the “balun” boxes don’t usually do any more than this.

I’ll hopefully have another make done next week (you wait ages for one…)

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What gear should I get?

Loads of people (mainly if they’re new), ask this question, and the answers are unfortunately more questions:

What do you want to do?
How often are you going to use it?
How will it work with other gear?

It’s quite easy to get sucked into the idea of buying things (ooh, nice shiny lovely things) but a lot of the time, unless you’re using whatever it is on a frequent basis, you’re probably going to lose money on it.

Have a look at a local rental company (for example, in London there’s Richmond Film Services, The Audio Dept and Better Sound to name a few) and see how much it costs to hire whatever you need.  Also it often costs only slightly more to hire professional level gear (Audio Ltd, Sound Devices etc), over consumer gear (zoom, sennheiser evolution) while the professional level gear will be more robust, sound better and be able to interface with other professional gear more easily.

Also look at the features in gear that work for you personally and get the gear that works best for the way you find you work more often.  There’s a few things that can catch you out around returns/routing on certain mixers which you sometimes expect to be there and sometimes aren’t (like where the return signal can be routed, is there a ‘bus in’?)

Also, always factor in the cost of cables when you buy something, you often need quite a few new ones with obscure connectors on

 

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Bag of f-stops

Just bought a new backpack for carrying most of my day-to-day gear around for doco type jobs after the old one was starting to get a bit small and won’t be able to fit my sound bag with the radio distribution system I’m putting together.

After having a look at lots of different bags, I found those designed for photographers seemed to fit my needs best, as they have quick access and you can see what’s inside them, so it’s harder to lose things in them.  Another criteria I had was to be as large as possible, yet still be able to take it as carry-on luggage on flights.

I ended up going with an F-Stop Loka in a nice loud blue colour so I can find it easily with a large “ICU” (removable bit with all the protective padding).  It’s really light and I think I’ve found all the pockets now.  I found the lowepro equivalents to be quite a bit heavier and found the protective compartment in the Vertex wasn’t deep enough to get my sound bag in.

Here’s the back that opens, so  can just lift my bag straight out, transmitters are in the side bit behind the big divider

 

 

 

 

 

 

 

 

Cables, adapters and memory cards are in the flap that opens:

Mics go in the top, with hypers/cardiods in the small peli underneath (you can see it on the back)

There’s also space for a laptop or ipad down the back of the ICU and a couple of spare XLR cables.

Boom pole and light stand (together they make a lightweight mic stand) go on the sides. Harness can also attach to the front

Batteries in the front pocket (might be able to squeeze a charger in too)

And last of all, in the top pocket, I’ve got a pocket recorder for quickly grabbing atmos or as an emergency backup.  Along with in-ear headphones and some tape and velcro

It’s looking like this will replace 2 bags at the moment and hopefully result in less strain on my back.  I also think it holds more than my wheely petrol bag

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Rocknroller mini trolley

It’s nice to be able to sit down in order to concentrate on mixing.  And on drama sets you’re often in a different room so need to be able to see what’s going on through a monitor in order to be able to queue fades and be able to put a script up and follow it.

As a bit of an experiment I’ve put together a ‘mini trolley’ .  You can spend *thousands* on putting together a decent one, but I’ve mainly thought of getting something I can pop my bag on and look at a monitor (or even two).  It’s a Rocknroller RMH with 2 laptop shelf attachments.  It’s designed as a sack truck really.

This is sort of a proof of concept, I’m wondering about maybe cutting back the top shelf so it doesn’t go as far forward (they’re made of wood).  In this setup it won’t actually stand up with the bottom lip extended (as a sack truck) and leans forward.  With the lip in it actually leans back a little but would fall over if something fell into it.  I’ll also be coming back to those antennas when the cables to test them have arrived…

However, this seems to fix the problem:

Now, if I could get some drawers in that petrol bag…

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Timecode / Logging networks (ACN and TCB)

Something which seems to have been gradually appearing is how all the data about what we’re shooting is now able to be logged and centralised much more easily. You can now run a computer network on set where script supervisor, camera and sound’s notes can be compiled together and matched to all the individual files.

Two different systems have started to emerge (very recently), Ambient’s Clockit Network (ACN) and Timecode Buddy (TCB) and related products. There’s also the Cameron-Pace metastrobe system, but I haven’t seen any documentation on it (and imagine it’s very expensive to hire).
ACN has been in development for some time and started appearing on Ambient’s newest series of lockit boxes (ACL204). They’ve had this video up since it began:
http://player.vimeo.com/video/42540614

Ambient have also teamed up with a company called Easyscott to deal with their logging and metadata distribution. It seems to be a powerful system, although it requires having a server on set which someone’s got to look after (they suggest the 2nd AC). Logging currently works on iOS devices but they’re planning compatibility with other tablets in future. The server’s also able to deal process a video feed, so playback can be done over the network, rather than the camera, which may save some time on set.

Something else Ambient have been talking about with ACN is actually being able to read/write metadata directly off machines via RS232/RS422. They had a demo of this working with a 3D camera rig at last year’s IBC (http://youtu.be/YNNUnBpo_NI?t=4m17s), where metadata was updated on a tablet but I’m yet to see it implemented in any audio recorders. I’d expect the manufacturers who have implemented ambient TC units in their products to be those working with this, however not all have an RS232/RS422 port on them (Sound Devices 7 series do, though). Ambient have also just announced new slate/TC display which works on ACN.

Timecode Buddy are the new kids on the block as far as timecode systems are concerned, their system works in a similar way to ACN (where timecode data is transmitted over wifi), but they also have a UHF range transmitter for transmitting TC between units.

They’ve teamed up with MovieSlate, who make a slate and logging app, which has developed into quite a powerful logging tool which will talk to TCB and receive timecode. I use it for sound reports, but with all the multicam plugins etc multiple iOS devices can share info across the network and receive matched timecode. Buying the app does add up though- it’s £17.50 for the app (on each device), but then another £35 each for the timecode, multicam and sound dept add-ons (making £122.50 per device). I don’t think there are any plans on moving movieslate to any other platforms and TCB have said they can only get the devices to display accurate timecode on devices where they know the hardware delays etc, so if making something for android they’d have to know every model of phone/tablet that would be compatible.

Denecke have also got onboard and are developing a slate which will receive TCB network information: http://www.youtube.com/watch?v=tl8jf_8gIOg

Finally, Movieslate are also working on adding a video feed from a Teredek Cube to the logging screen- so a live picture (or pictures) can be seen from the iOS device.  TCB are also working with Adobe in order to add timecode to their prelude live logger.
http://vimeopro.com/ipstv/ipstv-at-ibc-2013/video/74495522

Both systems look very capable, ACN/EasyScott looks like it’ll be able to do a bit more in future- but involves a more complex setup, while TCB/MovieSlate seems to be a bit more portable, as you don’t need to move a server around with you (and find power for it).

Time will tell whether one will be VHS and the other Betamax…
Zaxcom’s zaxnet system already sends audio and timecode around set, maybe metadata will be added to this?

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Timecode accuracy

Most pieces of professional audio and video gear designed for sync sound recording workflows run timecode, so that editors can easily match up picture and video which have been recorded separately.  However not all of them can be trusted to run on their own without drifting out of sync.  In order for equipment to avoid slipping out of sync, very accurate clock circuits must be used, which require specialised circuitry (temperature controlled crystal oscillators or TCXO).  They’re also expensive, so manufacturers often don’t implement them in their products.

I’ve gone through a load of manufacturers specifications to try and find timecode accuracy in equipment and here’s what I found.  I couldn’t find any specs for timecode accuracy in a number of products, in fact no cameras meaning they need to be attached to an external source.

Also, timecode alone will not stop picture and sound files being different lengths.  High accuracy clocks are also required to feed wordclock on audio devices and genlock on video in order to slave other devices to these rates, otherwise you’ll experience a difference in file length in accordance to how much your clocks are drifting.  This can be especially bad on long takes or syncing up live broadcasts
Also each of these figures goes for the accuracy of one source at maximum (specified) drift.  if using two of the same source, these figures should be doubled.

TC Source TC accuracy (parts per million) Time to drift 1 frame (mins) @30fps
Sonosax 1 555.55 9hrs 15mins
Zaxcom 1.54 360.7468 6hrs 1min
Tascam (specs from HS-P82) 100 5.5555 5mins 33s External Sync necessary
Ambient* 0.2 2777.75 46hrs 18 mins (requires tuning for this accuracy)
Ambient ACN 0.1 5555.5 92hrs 46mins
Timecode Buddy 0.16 3472.188 57hrs 52mins
Fostex (specs from PD606) 100 5.5555 5mins 30s External Sync necessary
Roland (specs from R88) 15  37.3737 37mins External Sync necessary
Denecke 1 555.55 9hrs 15mins
Betso 0.2 2777.75 46hrs 18mins

 

*in Sound Devices 7 series and 664, AETA 4minx, ARRI Alexa and Pre- ACN Lockit boxes

Updated to include Roland R88

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4 channel mini line mixer – nearly there

I’ve been working on a design for a small line mixer since January, on and off. I’m getting pretty close now- I’ve got a working circuit and managed to get the enclosure design working. I need to make a few tweaks to the board design, as some components need to be moved in order for it to fit in the box

This particular one is an unbalanced design, with 4 inputs over 2 mini XLR inputs, outputting to a single mini xlr output. The reason for this is to work with my Sonosax recorder and mixer, in order to be able to be able to add the recorder’s 4 XLR inputs to a mix (on the bus in for the mixer) and still record pre-fade ISO tracks.

The holes at the top are for L-C-R panning switches, which will need to be glued into place (one’s actually on the table in the photo above to the left).

I’ve made sure to use high quality components in the circuit- resistors on the inputs are matched within 0.1% tolerance and high quality op-amps have been used. The most expensive parts were the sfernice conductive plastic potentiometers, though.

There’s no internal batteries, but it will run on sources from around 9-16V, with the internal regulator providing +15 and-15V for the op-amps

Here’s how it fits in the bag.

It shouldn’t be too different making a balanced design using 5 pin mini XLRs- I went through one in the design process. There’s also a headphone amp on the board, I’m wondering where I can squeeze a 3.5mm jack and a small level pot in there.

As the boards are being fabricated I may be able to sell some of these as kits, if it’s useful to anyone else

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Won something!

I found out last week that a little short film I did, Best directed by William Oldroyd won the Sundance London short film competition. Unfortunately (thanks to the masses of Pink fans at the Millenium Dome) I managed to miss the screening, but got to see some of the other shorts and have a chat with some of the other directors and crew involved.

It was shot really quickly in an afternoon on DSLR with a very small crew, with the actors getting changed in a nearby cafe and, although the church knew we were shooting a film there, they didn’t know what the content was.

http://www.sundance-london.com/blog/short-film-competition-winner

Here it is; some people may find it offensive, it might not be safe for viewing at work

BEST from William Oldroyd on Vimeo.

Since then I’ve done another short with William- Wanted: Murderer, where I also did the post mix.

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Travel NP1 charger

I’ve been looking for a small NP1 charger for a while- something which came to mind after I’ve had a few jobs where I’ve been away for a few days and didn’t want to take my big 4 bay one.

I think I’ve found quite a neat solution after finding some 14.4V Li-Ion chargers on ebay being sold by Audioroot (French company which makes high-end power distribution systems and portable microphone preamplifiers).

I bought a couple of these (one’s going spare if anyone’s interested) and soldered on a female hirose socket (HR10-7J-4S) so I can just attach an NP1 shoe with a hirose plug.

It also *may* work with the unregulated flying lead on the Hawk Woods battery distributors, but I’ve emailed them to confirm- so I don’t blow something up

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