One of the themes that I'm developing in the book is the notion that "a Long Tail without good filters is just noise." But what are good filters?

To begin, I'm using the catch-all term "filters" (which I'm not crazy about; anyone got a better word?) to describe the tools that help you find what's right for you in the massive variety of the Long Tail. The examples I use most often are search and recommendations from either people (be they influential bloggers or just friends) or software, such as Amazon-style collaborative filtering ("people like you bought...").

There are, of course, many other kinds of filters. Rankings (by anything from sales to reviews) tap the wisdom of the crowd to identify quality or value. Everyone loves best-of lists, and playlist sharing is a fast-growing way to discover new music, whether through the good taste of other fans or the questionable taste of Beyoncé. And then there's the role of the critic, tastemaker or editor, for which there is now demand in even the narrowest niches.

But when you think about it, the world is already full of a different kind of filter. In the scarcity-driven markets of limited shelves, screens and channels that we've lived with for most of the past century, entire industries are created around finding and promoting the good stuff. This is what the A&R talent scouts at the record labels do, along with the Hollywood studio executives and store purchasing managers ("Buyers"). In boardrooms around the world, market research teams pour over data that predicts what's likely to sell and thus deserves to win a valuable spot on the shelf, screen or page...and what doesn't.

The key word in the preceding paragraph is "predict". What's different about those kinds of filters and the ones I've been focusing on is that they filter before things get to market. Indeed, their job is to decide what will make it to market and what won't. I call them "pre-filters".

By contrast, the recommendations and search technologies that I'm writing about are "post-filters". They find the best of what's already out there in their area of interest, elevating the good (relevant, interesting, original, etc.) and ignoring or downplaying the bad. When I talk about throwing everything out there and letting the marketplace sort it out, these post-filters are the voice of the marketplace. They channel consumer behavior and amplify it, rather than trying to predict it.

This is an important distinction. In the existing Short Tail markets, where distribution is expensive and shelf space is at a premium, the supply side of the market has to be exceedingly discriminating in what it lets through. These producers, retailers and marketers have made a science of trying to guess what people will want, to improve their odds of picking winners. They don't always guess right--there are surely as many things that deserved to make it market but were overlooked as there are things that made it to market and then flopped--but the survivors get a reputation for some sort of mystical insight into the consumer psyche.

But in Long Tail markets, where distribution is cheap and shelf space is plentiful, the safe bet is to assume that everything is eventually going to be available. The role of filter then shifts from gatekeeper to advisor. Rather than predicting taste, post-filters such as Google measure it. Rather than lumping consumer into pre-determined demographic and psychographic categories, post-filters such as Amazon's custom recommendations treat them like individuals who reveal their likes and dislikes through their behavior. Rather than keeping things off the market, post-filters such as MP3 blogs create a markets for things that are already available by stimulating demand for them.

Here, in chart form, are some examples:

Interestingly, when I consider my own role I find that I do both. As the editor of a magazine with a finite number of pages, I'm a classic pre-filter. I indulge in all sorts of brutal discrimination and guesswork to decide which articles to run. But Wired also does lots of product reviews, and in that respect, we're a post-filter. We look at the universe of what's already out there and bring the best stuff to our readers' attention.

As long as there's a market for a pre-filtered package in the deliciously finite medium of bound glossy paper, I suspect there will continue to be demand for my old-fashioned discriminatory side. But the day when people like me decide what makes it to market and what doesn't is fading. Soon everything will make it to market and the real opportunity will be in sorting it all out.

(Note: If the image at the top of this page were mine, and not just randomly stolen from some site, I'd title it The Pre-Filters. Guys with shades manhandling someone in a limo is pretty much my mental image of the music industry.)