Mapping a Space Through Sound

Question

Hi there,

I'm working on a sound experience project in which visitors to a space can quickly scan the sound of its rooms. People would interact with a gestural interface at the doorway, which would have a map of the floor plan. Hovering over a room on the map would trigger a live audio stream of that room.

Each room will have a microphone connected to a MacMini, via a mic pre, an audio interface and a wired LAN connection. The mini will stream the audio to an IP or URL via software. The destination, or the device that uses these streams, is another Mini, running a MaxMSP patch which reads input from the gestural interface and uses these as a large switch to decide which audio stream to play through its speaker system. (The stream corresponding to the room selected)

Privacy of the audio streams is very important. I cannot use a streaming system that broadcasts publicly, like ShoutCast. (It may have a private option, not sure). In addition, for privacy and to avoid identification of any individuals and the contents of their conversations, I will transform the audio so conversations are unintelligible. Ideally, this would be a visible, hardware device which also signals its purpose (to mask the audio) so that people in the space are not freaked out that they are being recorded.

My goal is to give people a sense for what each room/zone sounds like, and so what is important is relativity, and not necessarily accurate representation. I'd like to capture a rich frequency range and people moving through the space, so I may bump up to stereo mic's.

All the gestural stuff is not relevant here, though a couple of questions on mic'ing and streaming:

• What is the best way to stream live audio? I did some research on IceCast, Jack OSX, MuSE, Quicktime Broadcaster. Any recommendations? Latency is not super important.

• If I have stereo mic setup for each room (whether it's from 2 separate mics in an X pattern, or through one stereo mic) is there a way I can record 2 channels with the built in connections on a Mac Mini, without a dedicated audio interface? If not, what is a good solution that is cheap ($40-70?) but has good quality?

• What would be good placement for a diverse range of zones/rooms. As of now, the equipment I have to test with is one shotgun mic, one Rode NT4A Stereo, a Yeti, and possibly a tabletop setup with a 57. How much are my mic pre's going to affect the sound quality? I have one Tube Amp (crap?) and a MOTU Ultralight, but will need a couple more.

• Lastly, can you think of good leads for abstracting the audio so it's unintelligible? I was thinking maybe stutter edit to reorder snippets of sound.

Also, if you know any other similar projects like this, please let me know!

Thoughts much appreciated, Steven

Answer 1

Instead of streaming audio, I would simply recorded it and have it delivered to the other minis as an audiofile using applescript. You could also use an PHP database to ease the process.

You will not be able to use the audio inputs on your minis without preamps. Considering that you will be toying with the voice, I'd say the quality of the mics and preamps are not that important. The preamps' noise and mics' self noise will definitely have an impact though.

I don't know if you really need to use stereo micing though. One omni, hanging in the center of the room might be enough. And you will definitaly have to use condeser mics.

As for abstracting the audio, spectral smearing and granular playback might do the trick. Then again, delay with hi fedback fed into a long reverb might do it too… Depends on what you're after.

hth

Answer 2

I have seen some cases of Jack being used successfully so it seems like a good shot to me.

You really need a pre to bump up the gain. I don't see the need for stereo miking unless you really need the stereo information. I would go with an omni-directional mic in the center of the room. Depending on the acoustics of the room, you might end up with too much room sound and not enough clear speech. This would affect the output of the processed audio. Test with different placements of different mics to find the best solution before getting more gear.

For processing the audio, I usually use a granulator like KTGranulator or the Michael Norris Spectral Plugins. These two will make all speech unintelligible. For more extremely sounding ones, you can add a Destroy FX or two. A combination of these plugins will give you a wide selection of sounds.

Answer 3

How many rooms are there, and how far away are they? It seems unnecessary to send audio over LAN when you could just lay XLR cables and have it going to an audio interface on the main computer. Not to mention sound quality. Interfaces with lots of inputs are also cheaper than many computers.