NOTE: This is most definitely not a tutorial, I’m mostly making it up as I go along.
So, yeah – recently my radio station has acquired a rather lovely BSS Audio London Soundweb BLU-100. It’s a “sound management” device, which (on the main unit) has 12 inputs (6 stereo) and 8 outputs (4 stereo), as well as 12 logic inputs and 6 logic outputs. You can also add break-in and break-out boxes to get even more inputs and outputs. You can also hook two of them together with CAT5e and have 48 channels of audio going over it from one side to another. Oh and did I mention it also has an Ethernet and RS232 interface?
But what does it do? The question is rather what doesn’t it do. What we’re going to be using it for is mainly routing audio around the radio station, and doing on-air switching (i.e. feeding the transmitter with audio from the right studio at the right time), as well as doing the processing for the online stream.
It is programmed using a (free) program called London Architect. This program allows you to build up the configuration of the device by providing you with all the building blocks you need (source selectors, mixers, EQ, compressors, limiters to name but a few) and lets you join them up in any way you can imagine. It’s quite reminiscent of LabView, except for audio – to give you an idea. You can then send it the configuration over the network, and tweak the values using the same program. It’s pretty intuitive, and an extremely powerful tool.
Audio Processing
This thing has so many options for audio processing. For our purposes, our main use for this unit is to route audio from one place to another. For example, we want to route audio from Studio 1 to Studio 2, or vice versa. All that’s required to do this is to drop in a matrix router object, hook all the inputs and outputs up and then set where the signals get routed to. The particularly handy thing is you can define preset groups – for example a group of presets which alter what is sent to Studio 2. You can then set up a preset for every audio input (changing the source each time) – and then later you can recall the preset remotely (say, over IP) and the audio will instantly get routed to the right place.
But you can do more than that! There’s also EQs, and compressors, and levelers, limiters, crossovers, mixers, AGC mixers, and more. With these blocks it’s possible to build up pretty complex designs – right now I’m working on a broadcast processor which includes a multiband AGC, and a multiband limiter, along with a stereo field expander and bass enhancer (I think that project is probably a post in it’s own right).
The only thing that’s slightly annoying is not all of the objects are stereo. For example, limiters only have one input and one output. Not great for stereo signals. You can link the controls together, but they are still controlled by individual channels. Really, in that situation you need to be able to have a mix of both left and right which control the device so that it applies the same processing to both left and right (to avoid weirdness) – some of them have sidechain inputs, but not all of them unfortunately.
You also have to be a bit careful not to let the internal channels clip – which whilst there is a good bit of headroom, it distorts rather nastily. Also the compressors do suffer from distortion if you try to squash the waveform too much – but then at those extreme settings you’d expect that sort of thing of any compressor, especially a digital one.
The DSP power available is more than sufficient for our purposes. So far, even with the most complex design (in terms of DSP power, anyway) I’ve only just about managed to use 50% capacity. I may hit a barrier when I start putting everything together, but considering what can be done with it that’s pretty darn impressive.
Digital Logic
At the moment we’ve got a RB-OA3 which does that job through the use of offer and accept buttons in the studios. You can either “offer” control of the air chain (that is, what eventually feeds into the transmitter) and “accept” it. This is all run on standard 5V logic – you use push button switches and LEDs to operate it, which are in the studios. It’s essentially a finite state machine hooked up to some relays which switch the audio, not dissimilar to a hifi pre-amp.
With that in mind, we want to migrate away from this switcher to the Soundweb, as this offers the ability to do this switching over IP (and potentially in an automated fashion). However, it’d be nice to have an intermediate stage whilst we’re re-training our presenters how to use the new system (which will likely involve touchscreens in the studios instead of buttons) so that the switching works the way it always used to using the existing hardware.
Turns out London Architect also provides similarly powerful tools for building up logic, as well as audio processing. It has AND, OR, NAND, NOR, NOT gates, counters, truth tables, clock sources (logic pulses, as they’re called) amongst other things which can be arranged in such a way to develop pretty complicated things.
The most powerful is surely the truth table object, which maps a give set of binary inputs into another given set of binary outputs. For those digital electronics boffins out there, you might recognise this behaviour of that of a logic array. And, yes, you can build almost anything with these truth tables – the only limit is the number of inputs and outputs you can have (I think it’s limited to 12 inputs or outputs). So universial is this tool, a chap from Radio France decided to write what essentially is a truth-table compiler. You write code, in what suspiciously looks like VHDL, and it will compile that into the data to feed into a truth table. You then wire it into your logic circuit and import the values it generates into the lookup table. It’ll turn that truth table into a state machine (with some of the outputs feeding back into the inputs to indicate the current state), which can transition between states depending on what inputs you give it.
Aha! That sounds familiar! Once I drew out the bubble diagram for the RB-OA3 – I could then write down all the states and transitions into this language and compile it into a truth table. So that’s exactly what I did. All that I needed to do then was wire up the inputs and outputs to the appropriate I/O pins (a very straightforward task), have it fire off audio routing presets when certain states were reached and voila! Not only that, but we could also finally get the On Air light working in the studios (hurrah!).
So, to summarise: this thing is absolutely awesome. Every small radio station should have one. It’s a shame we’ve only got 2, both being installed – would like to have one to play with occasionally. I have a theory I could use one to control a fridge….
