Thursday, 1 June 2006

Surround Sound

getting the rainforest into the dome...

We have a requirement for sound capture for field trips. One academic has suggested/requested capturing surround sound.

I have been fiddling with surround sound technologies for years. Mainly encoding to Dolby Pro Logic - which is a method of encoding 4 channels of audio into a stereo pair. This technology has been around for years, most films broadcast on public television still have their pro-logic encoding intact. Even some soaps and dramas (Eastenders, ER) are broadcast with Pro Logic.

I bought myself a Dolby Digital amplifier for my birthday. Dolby Digital is the next generation from Pro Logic. Dolby Digital encodes various numbers of channels, from 2 to 7.1 into discrete audio tracks, which are then multiplexed and sent down an S/PDIF connection to a decoder. Most modern Macs, and PC soundcards come with S/PDIF connectors nowadays. When playing DVDs or AC3 files, the encoded Dolby Digital information is sent direct to the decoder. There is no technology that exists as yet (other than high-end hardware built by Dolby Labs) which can encode to Dolby Digital in real-time. So to monitor and mix Dolby Digital soundtracks you need a multi-channel soundcard, and either discrete speakers, or discrete inputs on you decoder.

In my experiments, I have only ever played with synthesising surround sound, the challenge here is to find a microphone technique for capturing the surround information. The most interesting avenue for researching this is the world of classical music TV broadcast. Across Europe many broadcasting companies are readying themselves for the time when Cable and Satellite can deliver surround information digitally. The Austrian and Danish broadcasting companies in particular, have pioneered microphone techniques that have challenged the audiophile attitudes toward listening to classical music recorded in surround.

Current state (techniques)

Off the shelf (Schoeps)

Mid/Side - double stereo

Recording interfaces and 4 track machines

DPA Mic Techniques

Jerry Bruck on KFM 360
Claes' Mic Tests

Cheap Ambisonic setup