|December 21st, 2012|
|sound, vsl1818, music, tech|
The AudioBox VSL1818 mixer officially only supports an ipad as a remote control, but now you can use anything with a web browser. Demo video:
The code is on github.
Below are more details than you probably want on the protocol that the VSL speaks with its remote and that I've co-opted for my own sinister purposes.
There's a udp protocol where the remote can find out about potential VSLs to connect to (and apparently vice-versa). It involves ports 7070 and 7071 and message-categories 1 and 10 (see below). I didn't do anything with this protocol because in my setup the VSL is always open and is running on the same computer.
The container format for a message looks like
signature: 4 bytes message_len: 4 bytes message: message_len bytesIt's all little endian and the signature is always 0xaa550011 (or '11 00 55 aa' in the order it comes over the network).
Each message begins with a header that gives some version information and says what kind of message it is:
unknown1: 4 bytes unknown2: 4 bytes category: 2 bytes unknown3: 2 bytesThe three unknowns are 0x01020103, 1234, and 10 respectively. They're probably something to do with versioning, but I don't know what they are. I leave them alone. The category indicates what the rest of the message is.
Category 5 messages have information on levels. They are:
channel1: 1 byte channel2: 1 byte ... channel128: 1 byteThe first eight bytes are channels 1-8 and give prefader input levels. I didn't look farther than this because I don't intend to use these. They're sent really often, maybe 20 times a second.
Category 4 mesages have information on the names of channels. Their format is:
unknown1: 2 bytes channel_id: 2 bytes channel_name: 48 bytesI don't know what unknown1 is, but it's always 0. The channel_id is an integer and the channel_name is a null-terminated string giving a human-readable name for that channel.
I tried sending one of these messages back to VSL to name the channels (because you can't change their names in the app) but it didn't do anything. Which is too bad; I'd really like to be able to name input channels.
Category 3 messages are what you send to VSL when you connect. They look like:
mac: 32 bytes device: 32 bytesBoth are null terminated strings. The mac is just the computer's mac adress, in ascii, like C8:BC:C8:1B:9F:0A. The device is what you think you're connecting to. So in this case, AB1818-VSL.
Category 2 messages have information on how a control is set. These are used both initially to transfer the state of the board and then to send updates as they come in. Format:
control_id: 2 bytes value: 8 bytes channel_id_str: 32 bytesFiguring out what control_id was what I needed to do experimentally, but what I know now is:
3000 master 1 master pan 3005 aux 3-4 16 pan 3-4 3007 aux 5-6 17 pan 5-6 3009 aux 7-8 18 pan 7-8 3013 A 3014 B 3052 mute 62 phase reverse 3021 high pass 3063 postThere are more controls, including ones for all the complex effects (eq, compression) but for now I only care about these.
The value is a double precision floating point number, always between 0 and 1. Some channels are binary settings (mute, phare reverse, post) and for those it's always exactly 0 or 1. The channel_id_str is a null-terminated string, and it looks like in3,0,2. The first number, 3 in this case, matches up with the channel_id we saw in the category 4 messages. I don't know what the other numbers are.
If you want to update a setting, all you have to do is send the appropriate category 2 message back to VSL.
It seems like a reasonably nice and well designed protocol.
- Is Pandora Really Exploiting Artists?
- Cheap College via Marrying
- Contra Dance Unplugged
- Belief Listing Project: Giving
- Giving Up On Privacy