Topic: Live stream 4 ch audio

[Toyberg]

Hi all,
I´m diving in to a new project and before/alongside digging myself into weeks of google searches, I post here in hope of getting in touch with someone with a solution or productive hint. The technical side of this project involves live streaming of multichannel audio data (as part of a live documentary, so no post production can be involved). Does anyone of you have experience or tips to how on earth I would go about live streaming 4 channel output from a Tetramic - to a computer at the receiving end. I suppose summing the 4 output channels from the Tetramic- to an interleaved file is a start and a must before transmission to keep everything in sync on the receiving end. Since the transmission will be made over mobile connection (3G or 4G) the interleaved file must be rather light on data (maybe Ogg Vorbis or some kind of interleaved mp3 file?).
Bonus info: The documentary takes place at different spots in town so the transmission setup must be mobile. The receiving computer will be stationary and never be more than 2 km away from any transmission spot.
Any hints on where to start are welcome.
Tanks
//J

[rastasean]

what are you planning on connecting the microphone to, directly to a computer and then the computer uses mobile connection to connect to the server?

[Gutbucket]

I’m a Tetramic user. I know almost nothing about streaming, little about lossy codecs and enough to be dangerous with Ambisionics.

I assume you'll need to interleave any transmitted channels to one file to stream.
I think you are going to need a laptop to do some computation on the mobile side.

If you are forced to use a lossy file format to accommodate data transmission bandwith limitations, best bet is to convert to your final target output (ie: stereo, 4 channel speaker feed, 5.1) before transmission to avoid problems.  Lossy encoders do data reduction by leveraging human perceptual schemes, A/B-format is pure math based.  Perceputal lossy schemes which sound fine to humans toss data which may be critical for A or B format conversion to your final listenable output.  If you need to transmit A or B format, Look for a lossless file compression scheme which is not perceptual based.  FLAC would work but may not be enough compression.  Beyond that, B-format is more robust and somewhat less suseptible to odd asymetric errors than raw A-format mic output, so if your only choice is lossy transmission, you may look into doing the A-to-B format conversion prior to transmission.

Do you need height information? If not, convert from A to B format, then throw out the Z channel and you only need to transmit 3 channels (W,X,Y).

I think this is probably a good ranking order of preference-
1) Stream 4 channel A or B format losslessly compressed. If that's too data heavy, then-
2) Stream 3 channel B format without height, losslessly compressed. Still too data heavy?
3) Stream the lossy compressed, non-ambisionic final target audio output (stereo, 4 channel speaker feed, 5.1, whatever) as long as you don’t need to do additional manipulation later. Perceptual coding will not cause problems with those formats and will greatly minimize the transmitted data.
4) Stream 3 or 4 channel B-format compressed with something lossy, but it might not decode correctly.
6) Stream A-format compressed with somthing lossy but it's even more likey to have decoding problems, and strange ones.

Oh yeah, now that I think of it, there is also the old UHJ compression scheme which was used for channel reduction in the analog era. It reduces 4 B-format channels to 3, or 3 to 2 (it’s a lossy audio scheme vs. a lossy data scheme). Not sure if that is a viable option or not, or how it fits into in the digital realm.

I suggest subscribing to the sursound mailing list and querying the ambisonic heavy hitters and researchers.

[rastasean]

I'm not sure what services support streaming lossless so its likely mp4 will need to be used and the compression will depend on the available data transfer provided by the cell service.

please let us know what current equipment, other than the mac, that you have.

[Toyberg]

Hi rastasean and Gutbuckets,
First off, thanks for suggestion, reflexion and question..

On advice by you Gutbuckets I will definitely go for transmitting B-format. For choice between  FLAC, Vorbis or other format I might just have to figure it out depending on the gear I must use.


My plan on the transmitting side is to use: Tetramic (including Z hight axes) - Focusrite multi I/O soundcard - Macbook - Cockos Reaper (+If needed sunflower) - Shoutcast - Iphone G4 connection.
On the receiving side: Macbook connected to a fast home network - Cockos Reaper (VSTVisual Virtual Mic 4->8 + VSTVisual Virtual Tetramic) - multichannel soundcard 8 x mono out - 8.0 cube speaker setup.

Hick ups or missing steps in this equation(?), further thoughts on file size/transmission speed.

Cheers rastasean -and Gutbucket!



 

[rastasean]

sounds like you have some good hardware that will work out!
I haven't found any documentation that streaming flac is possible with shoutcast, wowza, adode FMLE, however streaming ogg in icecast is possible.

mp4/aac should do quite well, it just depends on what the total stream size is. What's the max you have been able to stream before?

[Gutbucket]

My plan on the transmitting side is to use: Tetramic (including Z hight axes) - Focusrite multi I/O soundcard - Macbook - Cockos Reaper (+If needed sunflower) - Shoutcast - Iphone G4 connection.
On the receiving side: Macbook connected to a fast home network - Cockos Reaper (VSTVisual Virtual Mic 4->8 + VSTVisual Virtual Tetramic) - multichannel soundcard 8 x mono out - 8.0 cube speaker setup.

You'll need to run the VST version of VVTetramic on the transmitting side machine to do realtime A>B-format conversion.  Once it's standard B-format you needn't use the Tetramic specific versions on the recieving side to derive speaker signals or decode to other formats.

I want to hear that cube setup!

Having only decoded my Tetramic recordings to stereo or mono feeds, not even 4 or 5 channel horizontal only, I find myself scheming on attaching 8 identical small speakers to the corner verticies of one of the ubiquitous pop-up canopies. Like this one-


woah, 12 channel-

[Toyberg]

mp4/aac should do quite well, it just depends on what the total stream size is. What's the max you have been able to stream before?

rastasean, I have not tried what the max stream is on a 4G net in praxis, but the mobile phone company Telia write that the theoretical upload speed for their mobile net is 50Mbit/s, and that the expected speed in urban areas will average at 5-20Mbit/s. 5Mbit/s should more than cover the needed upload speed for streaming a compressed filetype.

You'll need to run the VST version of VVTetramic on the transmitting side machine to do realtime A>B-format conversion.  Once it's standard B-format you needn't use the Tetramic specific versions on the recieving side to derive speaker signals or decode to other formats.

Gutbucket, thanks- You are quite right about this!

Those tents look like they where built for the speaker setup you are planning, and the size seems quite right as well:) I have put up cubes at different locations with 8xYamaha HS50M and it creates an impressive and realistic soundsphere:) My best experience with 8.0 have been setting a 2x2x2 cube up in a cramped basement space. Ignoring the limiting room size the cube makes a soundsphere image that reaches far beyond then the walls of the room. Small apartment owners should really incorporate cube setups to create a larger aural image of their actual living space:)

Will update as the objects fall in to/or not in to place.

[Gutbucket]

Do the HS50M work well for you?  Appropriately sized & powered?

Looking forward to hearing more about the project as you move ahead.

[Toyberg]

To be honest I do not like the HS50M´s very well, too cold and harsh in their sound for my taste, but if on a budget, or being able to borrow them as I did, they work ok. But I always use the HS50´s with a sub since the speakers do not deliver very well on bass or low ends. I´d much rather keep the size of the cube at a minimum in size and spend money on small but good speakers, than make a large cube and have to use big but less good speakers. With the HS50´s I found up to 2.7m x 2.7m x 2.7m to work well. In a larger size cube then that, audio gaps between speakers started to be obvious.
If you are planning to put the "tent-cube" up outside in public, then a passive speakers setup would be a good way to go. To much power cords to worry about with active speakers...

[Gutbucket]

Thanks Toyberg, those are exactly the things I've been wondering about.  And agreed about the advantage of passive speakers for this potential setup.

[Toyberg]

Ok, I have figured out how to setup things on the transmitting side now. I can use Jack and ac3Jack to LIVE downmix the 4-channel B-format output created and sent from the Reaper Daw. AC3Jack create a single 4 channel interleaved file in ac3 format, that I can streame to the receiving end. Everything LIVE and in sync:)
Now I´ve to figure out how to set things up automatically to split the ac3 back to 4 mono channels, so they individually are sent into Reaper and treated by VVMic vst to 8.0 out on the receiving side. 

If anyone knows, please drop a comment!

[live2496]

This software AC3Filter sounds like it might do what you require.
http://ac3filter.net/wiki/AC3Filter

Also Bruce Wiggins plugins (Wigware) has a decoder that you could use for windows. He has tutorials for Reaper.
http://uod-true-multi-channel-mixing.wikispaces.com/Reaper

Gordon

[Gutbucket]

Toyberg,

You still around?
How did this work out for you?

Inquiring minds would like to know.