Broadcast Audio Goes Digital! Are You Ready?
COW Library : Broadcasting : Ryan Salazar : Broadcast Audio Goes Digital! Are You Ready?
The Merriam-Webster Online Dictionary defines the word "analog" as: "of, relating to, or being a mechanism in which data is represented by continuously variable physical quantities." An everyday sound, as what people hear, is referred to as "a natural analog signal." This analog signal is continuous, in that it happens without any interruptions or breaks. A digital signal is not continuous, because it uses a series of 1's and 0's to represent the sound as information or values which signify pitch and volume.
The only problem, and this isn't really a problem much anymore, is synchronizing an analog signal of infinite values of voltage at an infinite sequence of times (since an analog signal is "continuous") with a system that has a finite set of voltage values and may be updated only at a finite rate (which forms a "word" -- only so many 1's and 0's available to represent the otherwise continuous signal or a "word length"). This difference of technologies causes most of the problems when converting from the world of volts and time to the world of finite word lengths and clocks.
It's the ability to transcribe the analog sound into a digital code in order to be able to transmit it across the globe with no degradation that is your aim. However, it's the quantity of those 1's and 0's you can pack into a stream (aka "compression" -- not to be confused with the type compression that occurs during transcoding) that determines the degree of sound you achieve.
For example, the studio where I work has seven ISDN audio codecs made by Telos Systems. They are all analog, so they were connected with an SSL AlphaLink unit. That unit converts analog to digital and digital to analog. The analog signal from the codecs goes into the AlphaLink, is converted, and then the AlphaLink interfaces via MADI fiber cable with the SSL MADI-X8. MADI is indispensable. Used by small and large audio facilities across the studio industry, MADI technology, basically, allows the transmission of 56 or 64 channels of digital audio data at up to 48 kHz, or 28 or 32 channels of digital audio data at up to 96 kHz.
Don't be fooled, though; we had to coordinate pulling an existing ISDN line from each room... one at a time... and then re-terminate it at our new "centralized" rack, which I like to call our "hub." Once we were down to only a few live ISDN boxes in rooms (and temporary analog cable was everywhere), we then started rolling MADI out. It was a bit painful for our audio engineers, but in the end, magnificent!
The MADI-X8 then connects via fiber and digital BNC cables to the Avid MADI-HD hardware in each of our eight audio rooms. The MADI-HD is then connected via DigiLink cable to the Pro Tools HDX card. The 24-bit maximum resolution makes the MADI standard ideal for work with a large number of audio channels, such as when a digital audio workstation is used with a large format mixing console. At this point, signals can be received directly in Pro Tools, simply by selecting what audio feed you want!
In addition, I calibrated the output of all of our ISDN codecs to -12db going to our MADI system via the Avid DigiPre unit (which is in-line and in-between each audio codec) and the AlphaLink. So in effect, its ISDN audio codec out into the DigiPre and then into the AlphaLink; AlphaLink then sends fiber out to our MADI-X8 in digital fashion. Complex, but not as difficult as it seems!
The streamlining is incredible... if you want audio from ISDN codec #1, simply punch up MADI-1 on your Pro Tools recording track! ALL of our feeds can be heard in any room, simultaneously! As for "talkback" and sending audio back to the talent (in order for the remote studio and talent to hear the audio engineer's direction), it was set-up so that we can send four independent and simultaneous talkbacks! This means that we can record four remote talent feeds AND send them to each other so everyone can interact during sessions, without audio slap-back of each talent to him/herself. Amazing! The audio engineer utilizes SSL's audio routing software, which I programmed to interact with our Pro Tools rigs.
In this photo: Audio Engineer and great friend, Tim Brennan. Click image for larger view.
We are also in the process of setting-up mix-to-picture in our rooms. Utilizing our Facilis Terrablock storage, we reference HD-quality video for mixing and then feed it through Blackmagic Design's DeckLink Studio card and then off to a 47" flat panel. I am now also adding a smaller screen in our VO booth for ADR work!
As I've shown, making the move from analog audio to digital is nothing to fret over. There is enough technology that exists to make the transition one that is not only smoother than you could have thought but one you won't regret. We had to do it in phases, so it does take a little time and definitely some know-how. It might appear scary, at first, but once it comes together, it is well worth the effort! We now have far more capabilities than our facility ever had!
* "Analog." Merriam-Webster Online Dictionary. Jul 17, 2012.
* "Digital to Analogue Conversion." PHY 406F -- Microprocessor Interfacing Techniques. © James R. Drummond -- September 1997.