Isolators and rotary mixers are sometimes spoken about in quasi-religious terms, but their defining qualities are actually quite simple. For instance, an isolator's sound can be explained by its ability to affect a wider range of frequencies than most EQs. The bass EQ on an average DJ mixer could cut between 10 and 100hz, while an isolator might go as high as 300hz (some isolators allow you to set this point yourself). Proponents of isolators and many engineers say that cutting or boosting wider frequency bands sounds more natural to the human ear than the relatively narrow cut of a traditional EQ, resulting in a more organic sound.Another sonic factor is the slope of the filter shaping the sound. Isolators have a gentle slope that lets more frequencies through, contributing to the smooth and open sound for which they're known. So while top-of-the-line components are an important part of the rotary sound signature, the inherent character of the isolator has a big impact, too.However, isolators can also be used recklessly. "Isolators are an advanced tool to EQ more dramatically," Rich Cufley from Sound Services told us. "Give Floating Points the E&S and it's an instrument. But many other people fundamentally misunderstand EQing—the golden rule is touse EQs, only use it to remove stuff. But boosting it is totally undesirable." A more subjective point is that too much fiddling with EQs can disrupt the flow of a set. Even the pros, such as Claussell or Theo Parrish, occasionally misjudge their isolator usage.The DJR400 won over fans, but it was a relatively niche product. "In 2003 in Europe, not many people wanted to hear about anything rotary in terms of mixers," said DJ Deep. "Except a few friends, mostly American, there was not much interest in Europe. I remember travelling to my gigs with the DJR100 prototype in a bag. Most of the time people were a bit sceptical about the whole thing. It took a very long time, about ten years, from 2003 till 2013, to take hold."In 2015 there was a tipping point. A flurry of new rotary mixers entered the market. Many replicated the main selling points of the DJR400. Rane, MasterSounds, Condesa, Bozak and ARS all released tabletop mixers complete with inbuilt isolators. Bigger rotaries were released, too, like Isone's FP mixer and the ARS 6700. Deluxe custom models made from solid brass gained attention . There was even a budget model, the Omnitronic TRM202MK3, which made owning a rotary more financially feasible. This has helped make the rotary mixer a more visible part of DJ culture than ever before.Some of a rotary mixer's most lauded features, such as producing great sound, are more nuanced than you might imagine. Any mixer won't produce great sound on its own. You need fantastic sounding records, well-configured turntables and a perfectly executed soundsystem. David Mancuso, a DJ that's probably done more than anyone else to further audio quality in DJ culture, didn't use any kind of mixer. As the late DJ said in an interview , "The less components you use, the better the transparency of the sounds. With each audio component, it may be very high grade, but eventually it will colorize what you're hearing.You use the minimum." If you want thesound, you might need to ditch the mixer altogether.A rotary mixer is not going to transform an average DJ into a great one. If you're looking for a tool to blend records together, there are more cost-effective options, ranging from fader mixers to digital controllers. But for retro-minded DJs they're hard to beat. Their converts remain evangelical. Why else would Louie Vega go to the effort of flying a sound engineer around the world with him so he can build a booth for a rotary isolator before each gig?"After listening over and over to DJs like Louie Vega and Joe Claussell, their control was perfect and the mixes were extremely smooth," said DJ Deep. "I couldn't figure it out on my straight fader mixer, until I got my hands on a UREI. I fell in love with it. Rotaries do not make you a good or bad DJ. They are simply a dope tool."

Isonoe 420 DJ mixer, Giant Steps, London