The Audio Ins and Outs in SAC
The most common question I am asked when people see that I am running a computer based live sound mixing system is "How do you get the signals in and out of the computer. The answer is that I have a professional sound card and AD/DA converters to handle the ins and outs to the computer.
All digital consoles are dedicated computers and have the AD/DA converters built into the system. The common CD and MP.3 formats for music are digital formats. Any music that you can download from the internet is in a digital format. Any music that you have stored on a computer or music player is in a digital format. The computers or players all have digital to analog converters built in to offer your music in a useable form. Our ears are rather amazing analog devices. The speakers, headphones or earbuds through which you listen to that music are also analog devices.
Computers process digital data. Stage microphones and DIs provide an analog signal. Most amplifiers require an analog signal to their inputs, although some of the digital amplifiers will accept a digital input signal. Since the computer needs to see digital data the analog input signals must be converted to digital data to be processed by the computer. Once the data is processed it needs to be converted from the digital data to an analog signal to be of value.
Computers running DAW (digital audio workstation) software are common in most recording studios. Because there is a market there are many options available in converter units and sound cards. There are separate units that just do the analog to digital conversion and units that do the digital to analog conversion, but the most common format used with SAC combines the AD and DA in an eight in/eight out single rack space unit. The low level signals from microphones and other sources require some pre-amplification to bring the signals to the proper level to be acted upon by the converters. Most units have built in pre-amps with a gain control for each input channel.
To be acted upon independently each input and output channel must remain discrete. The professional sound card allows for a high number of discrete input an output channels. Within the sound card these discrete channels are converted to a data stream on which the computer can act. Once the data stream has been processed the sound card provides discrete digital output channels to the converters. Because timing is important to keep everything in step the converters and sound card need a common clock. Most sound cards have a stable clock built in and provide the timing signal to the converters.
A SAC system consists of a good computer, a professional multi-channel sound card and converter units to convert the analog signals coming into the system to a digital format and the digital signals coming out of the computer back to an analog signal. The sound card and converter units are needed accessories for the computer. The SAC software runs on the computer and handles the digital processing of the data stream.