Month: May 2013

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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