A Machine for Slicing Rooms

I am almost finished with a four-day workshop hosted by the Gray Area Foundation for the Arts (GAFFTA) in the Tenderloin district of San Francisco.  The title is "Spatial Sound with Supercollider".  In this workshop we have concerned ourselves with the manifold possibilities for taking sound and expanding it from the standard stereo listening environment.  This spatialization of sound is distinct from widely available standards such as Dolby Surround Sound in that we are digging into the components which reproduce spatial effects.  The program called Supercollider allows an incredible amount of control in how a recorded sound, even a mono-channel recording, can be reproduced for the listener with rich three-dimensionality.

In the workshop we have ooh'd and aah'd over the complexity involved in producing something like third-order ambisonics, where a sound source appears to cease emerging from the speakers and instead has a presence of its own in the room.

(red represents the  positive phase and green represents the negative phase of a sound)

In the above image, 16 different spherical dispersion models are used to reproduce a single 3-dimensional space.  The math to assemble these models and then disperse them into a multi-channel speaker array is heavy though not advanced, being entirely based upon sines and cosines.  These models for the dispersion of sound can be seen as the atomization of a space.  Each globe represents a directionality that, when combined with the other 'atoms' and decoded to a speaker array of your design, will produce a precise virtual environment.  Sound is not merely a temporal phenomenon; we are hearing space when we listen to a spatialized recording.

I find the analog versions of spatializing sound just as interesting as the digital models.  And for those sound engineers and musicians who are nostalgic for the sound that these analog reverb machines once produced, there are digital filters which simulate all the distortion and 'badness' that these setups are known for.

Plate reverb is particularly interesting because it is a two-dimensional machine that can produce the reverberation characteristics of a room, deceitfully producing a three-dimensional space.  It works simply like this: an electro-mechanical transducer produces vibration in a large metal plate which is held in tension.  A pickup (or two pickups for stereo sound) then records the new sound which has taken on the reverberation properties of the sheet of metal.  Check out this video which demonstrates some plate reverb effects.

The EMT 240 uses a 12" square gold foil sheet in tension to simulate the reverb in a room.

The plate is like an architectural slice of a room, where introduced sound produces wave-effects in the tensioned metal sheet just as it would in a real space.  Imagine then a whole building section represented inside a plate reverb machine.

Scientifically, we might be able to produce precise reverb filters of building sections, just as the physicist  Wallace Sabine did for the New Theatre, New York in 1913.  These plans and sections, modeled using the Schlieren method, describe the complex fluid dynamics of reverberant sound.

We are covering lots of fascinating techniques including HRTF (Head Related Transfer Function).  Each of these systems require the decoding of a mechanism which tells the brain where to find a sound in space.  It's a highly architectural exercise.