The Bridge is essentially like Rewire on steroids; its core is a proprietary sync spec that allows full transport between the two programs as well as functions like recording audio and the use of external plug-ins. As it's a communication protocol there's nothing to buy, assuming you're already a registered user of both Ableton and Serato, simply open up the latest version of each program at the same time and installation of The Bridge is free and almost automatic. Ableton has put a strong cap on usage of the interface, however it's strictly limited to Ableton Live and Suite 8.2 or higher, ruling out others like Live Lite or the Professional APC edition that comes bundled with Akai's family of Ableton APC controllers.
Like its municipal namesake, The Bridge allows for two-way traffic: Serato can now be played directly into Ableton and vice versa. In the first case, Serato DJs will find much to work with when using Ableton as a mixtape recorder. This set-up doesn't require Ableton to be open, actually: while working in Serato you simply need to choose .als as the output for your recording and the data recorded during your mixing session is converted into an Ableton Live Set. Afterwards, open up Ableton to find your mix laid out; here Ableton functions as a post-production platform, allowing you the chance to add effects or mastering plug-ins, adjust timing and generally fine-tune things.
It's a great way of alleviating the anxiety associated with mid-mix slip-ups. In this scenario, however, it's a bit ironic that both programs are called Live, as you're essentially using The Bridge as a means of interfering with the very "liveness" of a DJ mix. Exactly what data gets recorded, however, is entirely determined by what Rane hardware you're using. Those operating one of the more modest SL units won't be able to record any sort of fader or knob-twiddling data to the Ableton set; this possibility is reserved for those using one of the more formidable Rane mixers, like the TTM-57 or 68.
Now if you open both Ableton and Serato at the same time, you get the opposite flow of traffic across The Bridge: Ableton now becomes playable through Serato. This may not initially seem like that much of a breakthrough; after all, if you wanted to mix raw track material alongside the audio file of a different track you could just load the track into Ableton's Session view and rock out from there. Players who have already carved themselves out a solid set in Ableton may wish to do precisely that rather than adjust to incorporating Serato's interface into their performance. For anyone equally versed in the two programs, however, the Ableton-in-Serato setup offers enough smooth functionality and no-brainer ease-of-use that it pulls off exactly what innovative design is supposed to: make you forget what life was like without it.
Loading Ableton into one of Serato's decks allows access to Live's Session view. This is the part of Live geared toward performance rather than track composition, where clips, devices and FX can be deployed on the fly. A limited window below the decks shows Ableton's channels, track controls, effects controls and two sends. Anything you can do with Live normally you can do with Ableton opened in Serato: trigger MIDI, use internal Ableton instruments and run third-party plug-in instruments and effects.
This is a lot to play with alongside working the decks. Chances are that poking at all of these things with a laptop mouse will grow tiresome fairly quickly. At the moment there isn't a Serato controller that is equipped to trigger Ableton clips from within Serato, so your best bet is most likely a MIDI controller for Ableton like the Akai APC. I mention the APC here not only because it's an excellent Ableton controller in general but because its close adherence to Ableton's interface is extremely useful when operating Ableton as an element within Serato.
The main idea behind integrating Ableton within a Serato performance is the possibility of controlling Ableton's output on a Serato deck. Should you not feel swayed to sacrifice an entire deck, however, you do have the possibility of "syncing" Ableton with one of the decks, essentially allowing it to piggyback on a track you're already mixing. One standout advantage of loading Ableton on a deck is the use of on-the-fly looping while in Serato's Relative mode: you can loop Ableton's entire output and then, in a new twist for Ableton users, exit the loop right back on the downbeat.
One limitation with Ableton on a Serato deck is that you don't get a nice fat waveform to look at while you're beatmatching; instead you follow a much sparser bars and beats grid that still works fairly well. Furthermore, Serato gets the tempo information from the tempo listed for the Ableton set, so if your Ableton set contains material with varying tempos, make sure you've adjusted accordingly. Overall the deck control of Ableton is effective and reliable; you cannot, however, do anything like scratch or reverse Ableton's audio.
The primary concern that can arise in this "performance" mode of The Bridge is that deploying Ableton and Serato at the same time can hog a great deal of computer memory. I tested out The Bridge on a fairly sturdy Sony VAIO and yet some minor twitches and control issues were still detectable; most notably in the sensitivity of Ableton's response to extreme tempo changes via Serato's control vinyl. Controlling transport via the pitch fader worked fine, as did manual deck control (tapping, nudging, etc.) as long as it was gradual enough: whenever the decks were halted too abruptly, Ableton's audio would simply shut off rather than speed down accordingly. The additional usage of plug-ins or other VST instruments may be a further memory drain that can lead to crashes or freeze-ups. It's enough to serve as a reminder to test your gear thoroughly and make sure your computer is up to the challenge: electronic music is not the sort of endeavor best undertaken by charging untested into the field of battle.
In general you could argue that The Bridge is ultimately more of a boon to the Serato-centric, serving as a nuanced DJ-mix recorder and an expansion of live-mixing possibilities. And while this isn't stressed so much in the PR material for The Bridge, the Ableton-Serato performance possibility seems well-suited for a tag-team effort, with two hands on decks and two more on an Ableton MIDI controller. In any case, the success of The Bridge indicates that the more the two "Lives" can play together, the less it's clear any longer what "playing live" really means, as acts like mixing, looping and controlling continue to productively cross-pollinate.