Like most everything else, professional audio production happens almost entirely in the digital domain these days. The digital transition has enabled amazing production capabilities on PCs using digital audio workstation (DAW) software. But with the digital transition came the need for a digital interconnect that had the bandwidth needed to move audio streams in real time along with the need for timing and synchronization capabilities that allow mixing of multiple audio channels. The 1394 or FireWire interconnect has proven to be the only interconnect that can support pro audio applications.
The range of professional audio applications spans live performances to the studio. Only a few years ago, the production task was limited to studios with the huge budgets needed to buy racks of tape decks and the special analog mixing equipment. The digital transition allows professional quality on much lower budgets and indeed musicians and bands can now buy their own equipment and produce material for CDs and Internet distribution.
Let's examine the type of products and the topology of a system used in professional audio. And first we should differentiate the professional space from the consumer or prosumer market.
Any desktop or notebook PC today comes equipped with baseline audio capabilities and there is low-cost DAW software on the market. But the baseline capability usually means a single stereo channel in and out. In desktop PCs, soundcards may add support for a few additional channels. Moreover there are external audio I/O interfaces with configurations such as 2 input and two output channels.
The professional market starts in the 8-channel input and output range. Even an individual musician needs such capability, as many non-professionals are now discovering. A larger band might need 16, 32 or even more input and output channels. The professional market is built around three basic components - the PC, I/O boxes or interfaces, and a mixer. Some manufacturers integrate both I/O and mixing in a single product.
The I/O box typically includes a microphone preamp for each input channel. The devices also include A/D converters to digitize the input, D/A converters to output analog channels, and sometimes DSPs to perform other audio processing. The I/O box links with a PC via 1394. The analog outputs from an I/O box might connect to a mixer or potentially to speakers. And the mixer would generally connect to the 1394 bus also, to receive the digitized audio channels.
Live session and post production
A typical usage scenario illustrates the channel demand and how the 1394 interconnect is utilized. Here it is:
A band might choose to record a live performance for subsequent distribution via CD or the Internet. Independent of the microphones used by the performers, the recording requires a number of dedicated microphones. You would typically use at least four or more microphones for the drum kit.
You need a microphone for the amplifier/speaker used for each guitarist. In some cases -- such as with an electric guitar - you can use a direct connection between the guitar and I/O box. But the robust sound produced by a guitarist is a compilation of the sounds made by the guitar, the effects added via the amplifier or a dedicated device such as a reverb or delay box, and the audio qualities of the amplifier and speaker.
You also need microphones for any other amplified instruments. And you need inputs for the singers. Even a small band can require 15 or more channels.
During the live performance, the production equipment must support both the concert and the recording that will be put through a separate production process later. During the concert, the I/O box would stream the channels over 1394 to a mixer used by a band member or support personnel to optimize the concert sound. The same stream would also go to a notebook PC for recording. Typically the band would want to record the raw audio as opposed to the output of the mixer used at the concert. That affords the musicians freedom to optimize the mixing process once back in a studio.
Figure: The basic layout of a combined peer-to-peer cascading/linking of two mixers with simultaneous recording and playback of 32 channels to/from a computer.