Audio Interfaces as Location Mixers 2: Motu AVB Midi to OSC

Earlier this year I made a post about the theoretical use of audio interfaces as digital mixers.  Since then I’ve got some toys and the experiments have begun:

Motu 8D

I ended up getting a good deal on 2 of these interfaces.  They each have 8 channels of AES3 audio in and out with sample rate conversion, although some of the connections are 75ohm RCA for consumer SP/DIF.   They are also happy with a variable voltage range and are happy with reversed polarity on the DC input (even though the plug says 15V centre positive).  The AVB connection allows them to link together and address multiple channels from one interface, essentially making a modular interface with all sorts of connections.  Together they have 16 inputs and outputs.

Control Surface

I started off here running a Keith McMillen K-Mix, however it just runs standard midi control change and note outputs.  These are easy to deal with and re-route, however I came across some issues with resolution which were solved by using a control surface that runs the Mackie Control Universal protocol (MCU).  The cheapest one I could find was an iCon Platform M.

Lost in Translation

The problem with the MOTU interfaces in this instance was that they used a nice control protocol for computers to talk to each other, but not control surface hardware- they’re designed the interface with the view that it’s used on an ipad or similar.  They use Open Sound Control to communicate (documentation here), so there needs to be a way of converting midi commands to this.  It’s also one way- the interface doesn’t send any data back.  So, I needed a way of translating midi commands to OSC.

Pure Data

After looking at a few solutions, and realising I can’t program properly- it dawned on me that I could use Pure Data.  It’s an open source graphical programming language (similar to the proprietary Max/MSP) and I’d used it before on various music performance projects.  It would also run on a raspberry pi– so could have a low power dedicated computer to do the translation work.  I found it was actually pretty straightforward to get the midi in and the OSC out, however came across a few snags…

Linear faders

This is one of those terms where everything gets confusing.  Yes, linear faders can mean they’re in a straight line- rather than rotary faders, which you turn.  The potentiometers, however need to be logarithmic- every 3dB of attenuation is a halving of voltage.  In most midi applications this would normally be done at the software end, but here it’s just a number being fed in.  In order to do this a bit of mathematical transformation of the data was required and the higher resolution of the faders really helped in MCU (they’re used as pitch bend controls on each channel).


In order to run 16 channels from an 8 channel controller I decided (possibly foolishly) to create a second layer on the PD patch and send back data to the control surface.  It works, however the mute and solo buttons unexpectedly turned out to be a headache!


Wot, no Dante?

I had a look and I couldn’t find and DC powered interfaces with a Dante connection and a mix engine.  Best option I can think of is to use a MADI interface (such as a MOTU M64 or RME Madiface Pro) and a Directout or Ferrofish Verto series converter


I haven’t put a dedicated talkback control in yet, but should be a case of pressing a button to open a fader.  There is a dedicated talkback button on the newer Motu 828es, however- although it only has mains power

I Want This

If you want to have a go with it, please feel free to get in touch.  I can’t offer any kind of warranty or technical support at the moment- it’s just a thing I made.  It should hopefully work with any of the Motu AVB interfaces and midi controllers with MCU emulation.  It requires pd-extended 0.43-4 to run

Audio interfaces as location mixers

This is a bit of a ‘thought experiment’ as I haven’t actually got any of the kit to try out and found whether it actually works in a production environment or not.  I’m also not sure if this is currently a workable solution for me and will state the drawbacks, but this could all be useful to some people- at least as a bit of an experiment

Currently there aren’t really any digital mixers suitable for location work and I’ve been looking at potential solutions to this.   I’m aware that the Yamaha 01V96 is used quite a bit (in the US especially), but it’s big, power hungry and AC powered only.

A possible solution now is that a number of computer audio interfaces will work as standalone mixers (with a suitable control surface).  They have a considerable amount of DSP power available with the ability to run EQ and multiple submixes.  Another advantage is that audio can be sent to a computer, for playback of previously recorded tracks or even processing (auditioning noise reduction, for example).

Having done some research, here are some possible combinations of equipment:

Metric Halo ULN-8 / LIO-8

Metric Halo ULN-8

Effectively these are the same box, except the LIO-8 is a cut down version of the ULN-8, with no microphone preamplifiers or additional DSP plugin licenses.  They’ve been around for a while and use top quality components.  Metric Halo do continually support their products and are the only company I’m aware of who offer hardware upgrades to their audio interfaces.  At the moment there’s been mounting rumours of an upgrade to the DSP and interface with a 3D card (which would not involve buying a whole new unit), which would add a class compliant USB-C computer interface, improved DSP power and an additional card slot.

This is the only computer audio interface I’m aware of with a locking DC connector (4 pin XLR)!  There’s also a second barrel plug, which could be used for redundant power.  It has another unique property in that it’s the only DC powered interface with sample rate converters on the AES3 inputs.  This means I could run my radio mic receivers directly into it using their digital outs.  It’s got 8 analogue audio I/O and 8 digital AES3 I/O

Now for the drawbacks: it’s a big box- a deep 19″ rack unit 432 x 330 x 44 mm but it weights 2.6kg which isn’t too bad.  It currently only has a firewire interface and OSX drivers so requires a good bit of fiddling to get current computers to work with it.  They really need to update this and talk of the 3D card being ‘coming soon’ has been going on for about 2 years now.

Also, with the current architecture, the midi input will accept controllers using the mackie control protocol but needs to have a computer running in order to be able to control the mixer



These are effectively a load of different interfaces with different I/O which can be combined using the AVB protocol.  For a while there was just the Ultralite AVB which could be DC powered, but at the end of last year a couple more, the 624 and 8A were released. Furthermore a whole bunch of digital boxes were announced last month with AES3, ADAT and MADI interfaces.  All of these are in a compact ‘half rack’ format

I’m particularly interested in the 8D, however only half the inputs are AES3, the other 2 are SP/DIF and may require adaptors and/or sample rate conversion

The DC inputs aren’t locking, but will take 12-18V, only draw 10W on the current half rack interfaces and they don’t care about polarity either

The main drawback is controller integration- they won’t accept midi control, only OSC over a network.  Their suggested method is using a tablet computer using a web interface. It should be possible to hook up a tablet to a midi controller and use an application such as TouchOSC or Lemur to control the interface as a mixer.  Another future possibility is programming a BomeBox, although that doesn’t have OSC compatibility yet

RME UCX / Babyface Pro


RME Fireface UCX

These RME interfaces will all work with their totalmix FX mixer out of the box, and accept Mackie control midi commands.  A few features such as some of the talkback functionality won’t work without a computer, however.

The drawback, however is with some of the digital interfaces used.  They all us ADAT optical format, which isn’t common in broadcast equipment, so a converter box is required.  RME do one, the ADI-4DD, however it doesn’t have any sample rate converters, so 2 AJA ADA4 boxes would be required to provide use with mutiple digital sources which cannot be connected to word clock.  Again, power is with a barrel plug (and it’s not too fussy about voltage or polarity), although the babyface can also be powered over the USB bus, so could be a redundant power connection.

Waves / Digigrid LV1


Waves LV1

This is a system designed to work as a powerful digital mixer with a dedicated computer running all the mix software and also plugins at low latency.  It’s not cheap, but is built for purpose.  Working it on DC power may be a challenge (and I expect it may be greedy), however and would require a bit of hardware hacking- looking at the motherboards on some of the host computers (the smallest Impact model, for example will run from 12V but would involve fitting a 12V PSU and invalidating the warranty).  Interface wise, only the MADI ones will run from 12V, so a MADI converter with the I/O you require would be required.  DirectOut make the Exbox.AES which converts 16 channels of AES3 to and from MADI but without sample rate converters (but is has redundant locking DC inputs!)

Keith McMillan K-Mix

Keith McMillen K-Mix

This is actually a real hardware digital mixer- 8 analogue in and 10 out (including the headphone out, which can be freely assigned).  I’ve bought one of these and it’s a really compact and useful machine.  However, it doesn’t quite cut it for me I/O wise- I could do with some digital ins and outs.  It’s powered over USB, but can accept 2 USB connections, so redundant power can be supplied.  The touch control surface is surprisingly useable, there are ‘tracks’ along the faders and indents at 0dB.  The only disadvantage with the touch control is you can have ‘jumps’ if you take your finger off and it’s not in exactly the same place as where the fader is.  The K-Mix works with the Keith McMillan MIDI expander so can use 5 pin DIN cables

Icon Platform M

Icon Platform M

This is just a control surface- but a small DC powered one.  I owned its predecessor, the iControls Pro which wasn’t bad, although from picture it looks like they may have improved the build quality since.  The motorised faders are 100mm but did require a press downwards before moving them, so weren’t super smooth.  In fact I quite like the idea of having smoother, non-motorised faders on a control surface).  Icon have also recently showed off an expander, the Platform Z which adds blocks of 8 faders to the ‘M’.  This is designed to work with a computer so only sends class compliant MIDI over USB.  Various boxes are available which will work as MIDI hosts, however

Asparion D400

Asparion D400F and D400T

This is another control surface, again with motorised faders, a modular system except the build here looks more rugged than the Icon at first glance and has more buttons (but less knobs).  Also USB out only so may need a host device if not being used with a computer

25 pin modular system

This is a bit of an ongoing project, but started having thoughts about it after working with an Audio Ltd 2040 system while assisting a production sound mixer on a drama job.  We were having serious range issues throughout the job, the cause of which was possibly something attached to the camera.  The only way we could get round this was to move the receivers closer in ‘remote boxes’.

These were an RK3 rack in a box with a battery and antenna inputs and outputs, and we rolled out either individual XLR cables or a multicore to connect to the main trolley.  As the receivers themselves are very expensive, it’s not really practical having duplicates doing the same thing, so it was a case they could quickly be pulled out of the RK6 and slotted straight into the remote boxes.

However it’s a case that it’s not possible to do this with other receivers, such as the Wisycom MCR42, which I use.  There is, however quite a common standard for camera receivers.  Pretty much all slot in receivers have an option for a universal ‘Panasonic’ standard 25 pin connector on the base, which will output 2 channels of balanced audio.

So, I’ve now got 25 pin bases for all my receivers.  There are a number of options for antenna, audio and power distribution, which have 25 pin options.  I already owned the Audio Ltd EN2  distribution rack (which still isn’t up on their website, it’s about £550 +VAT) but got an additional 25pin base.  I was scatching my head and looking at getting something made up so the receivers slotted in, but realised the camera mount brackets had holes in the same place as the mounting points on the audio CX2 receivers.  Audio do a base for the receivers with a bar with mounting points on. So just screwed on the brackets and  now have slots.  A disadvantage with the 25 pin section on the audio ltd distributor is that it adds a bit too much weight, there’s a steel plate along the back and I’m not sure it really needs to be there.  When I get some time, I may drill out sections from that

The second mounting solution I have is a Lectrosonics Octopack.  Here it’s a case that the screw holes are in different places to those on the wisycom receivers, however Richard Meredith’s Audio Dept made a run of very purple mounting flanges, so the receivers sit in the slots properly and can also be screwed in so won’t come loose:

It’s not just wisycom which will work, almost any ‘slot in’ camera receiver should have a 25pin option (except Sony, who don’t like to play with others).  Other examples are Lectrosonics SRb, Audio Ltd CX2.  There’s also another distribution system, the PSC Six Pack.  There’s another mod to the wisycom camera plates (see the picture further up on the Audio Ltd distributor) where grooves have been drilled in the camera bracket so the cables can fit.

You can also ‘mix and match’ different brands of receiver, however they don’t always orient the connector the same way round. Here’s a Sennheiser EK3041 (it’s actually on, but the display’s nowhere near as bright as the wisycom):

They also work on their own without antennas, here’s a quick and light cable for the back with power and audio connections:

Sound Devices 552 (internal view)

I’ve just bought a Sound Devices 552 for quite a reasonable price, due to a fault where the power input’s shorted (it’s fully functional using AA batteries).  I opened it up to see if it was something I’d be able to fix, but it looks like it’s something on the big surface mount board (possibly just a protection diode), so I won’t be touching that- it’ll be visiting Shure.

Anyway, I took some photos while it was open. Note the in-jokes on the PCBs, the sheer amount of electronics they’ve crammed in there and all those transformers:

Multiple Recorders

I’ve been asked to provide 6 individual isolated tracks for a job next week, and the most either of my recorders do is 4.  I gave production the option of hiring a lovely Sound Devices 788T but they weren’t too keen on the cost.

So, here’s what I’ve made:


I’ve also found that the Edirol R-44 does have Word Clock over the CTRL Sync jack- if you plug it in to the Tascam HD-P2 they’ll sync.

If we’ve also got all the correct cables these also will be synched up to a Nagra VI run by a second recordist- 12 channels, voila!

The mixer’s mainly there so I can monitor both recorders at once

I ran them for 30mins with a mic attached to the mixer (going into both recorders) and didn’t see any deviation of file lengths (although the start/stop times were slightly different)

Last Christmas Variations

Here’s something I made the other day after getting a bit distracted while fixing up a slightly faulty Yamaha SHS10 keytar.  It’s all done with by playing the demo (Last Christmas by Wham!) and making different connections on the circuit board

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I’ve been told that Stewart Walden’s (now Keith) Cucumber Sandwich is played on a Casio SA10, and features ‘Wake Me Up, Before you Go-Go’

If anyone else knows of any other keyboards featuring George Michael’s work, please enlighten me