GIBBLED AUDIO IN THE DIGITAL DOMAIN!

First of all, the good news: the ubiquitous Compact Disc was developed before we knew enough about bit-reduction, digital compression, and general screwing around with data to come up with something really terrible. Sixteen bits per channel, 44.1 kHz sampling rate, and no compression. Life was simpler back then, but we didn't realize how lucky we were. Digital chaos was just around the corner.

Now the bad: even with the relatively pristine CD to work with, record companies have managed to come up with several ways to make our lives miserable, in both the analogue and digital domains. Today's CD's are often mastered with predistortion and clipping built-in, in (what to my ears is) a misguided effort to make CDs "louder." Given a dynamic range of 96 dB, there's far too much effort to keep the peak audio within a hair's breadth of the digital ceiling. As broadcasters, we should all be screaming out "Hey, that's our job!" (Tongue firmly in cheek).

I remember when CDs first appeared in radio stations: we were mostly concerned with that huge available dynamic range, and how to process the audio effectively for broadcast. Little did we know, the reality has turned out to be very different: more often, it's "how do we mask the clipping and distortion and generally crappy audio we're given to work with?" Highly compressed and clipped CDs are just the beginning… it is a very rare radio station that is able to resist the constant flow of MP3 files on to their local server, both for commercials and produced content, and sometimes even for music. Like all the new bit-reduction algorithms, MP3 isn't a single standard so much as it's a suite of standards, applied at various bit-rates in varying degrees by diverse operators with different goals and very different sets of ears. To say that the quality is variable is a dramatic understatement -- it's all over the map!

Compounding the problem, most stations still have bit-reduction techniques somewhere along their programme chain. These techniques are optimized and intended to work with what has become a very rare bird indeed, "unprocessed" audio. Whether the bit-reduction is MPEG for the storage system, or apt-X for the STL, it's not really meant to work on audio that has already been compressed and limited, let alone clipped or bit-reduced. The result, to a varying degree, is the creation of artifacts: new, unexpected alterations to the audio, whether it's a flanging effect, a distorted drumbeat, or even a weird spatial effect. Even without additional bit-reduction, however, our analogue and digital processors are also meant to work on "unprocessed" audio, and can react surprisingly when presented with bit-reduced waveforms.

The digital frontier has taken away our old headaches and, hydra-like, replaced them with a whole host of new ones. We no longer have to worry about tape head alignment, cleaning and wear, and turntable stylus damage. High frequency rolloff is no longer a worry. What we have to grapple with, is inconsistent quality between sources, and artifacts that come and go as programme files change. To make matters worse, the old problems were measurable with test instruments; the new ones are "psychoacoustic," and hard to measure in a meaningful way.

In the analogue era, part of the solution to the consistency problem was the multiband processor, which gave us controls that tended to draw diverse sources together for a more uniform sound. It is ironic that the same processor is now a big part of the problem.

What can be done? Distressingly, very little. The makers of Orban and Omnia processors have lately been aggressively meeting with the folks that master CD recordings, trying to educate them to the problems that heavily processed music will present to the broadcaster. Good luck with that!

In the same vein, you can try and talk your music department in to not accepting MP3 files as source material. I don't know that we can stem the tide of MP3s in commercial production, but maybe you can have a talk with your production department too, about vetting the files as they come in, and asking for better copies of the worst offenders.

Most of us thought that digital audio was going to take essential quality issues off of the table. Surprisingly, a set of critical listening ears has never been more important to the broadcast engineer.