Review: Can VirtualDJ really create acapellas, instrumentals and isolate stems in real-time?
The latest version of the popular DJ software makes bold claims around stem separation. But does it actually work?
Virtual DJ is the most popular DJ software in the world. That might come as a surprise to some, but with 121,470,946 downloads, and counting, the versatile entry-level and competent professional DJing solution is the go-to option for many hobbyist, mobile and bar DJs in hundreds of countries. What makes Virtual DJ so appealing, apart from the fact that it’s free for basic use, is its flexible nature. Complete newbies can be presented with a stripped- back, simple GUI, with friendly artwork, only the core controls and an easy-to-use, two-deck interface.
As your DJ skills progress and you want to explore more features, there are endless built-in tutorials, customisation options, third-party extensions and an extensive list of compatible hardware, from the cheapest sub-£50 portable unit to the industry-standard Pioneer DJ 2000nxs2 CDJs. While many other DJ software continues down the road of closed systems designed for specific hardware, VDJ’s one-size-fits-all approach continues to make it hugely popular for all skill levels and budgets.
You’d be forgiven then for thinking VirtualDJ would shy away from innovation in favour of appealing to the masses, and would only add more experimental or advanced features when they’d been adopted by the wider industry. But with VirtualDJ 2021, the French company has added something genuinely innovative that has the potential to shake up how we approach DJing for good. Real-time stem separation is here.
Stem separation is basically a fancy way of saying you can isolate the vocals, drums, bassline or any other element of the track, without the need for an official acapella or instrumental. It’s been something of a holy grail for many DJs and producers over the years, so much so that Native Instruments even introduced a whole new format called STEMS back in 2015. It came with accompanying hardware and new software that let producers create their own stems to use in Traktor, while Beatport also jumped on board to sell tracks in STEMS format. Problem was, it was restricted to Traktor, it took a lot of prep in advance and your whole back catalogue had to either be re-bought or transferred into stems format from the parts you already owned. So while the idea was solid, the implementation meant it never made its way into the shared DJing consciousness.
VirtualDJ 2021 makes the bold claim that not only can it separate stems and parts from existing stereo tracks that are fully mixed down, it can do it in real-time right there in your DJ software. You can even fade these different parts in and out, like controlling a mixing desk in a studio, lowering the vocal only, or bringing down the kick, muting the bassline or isolating just the instruments. Being able to isolate any major part not only of all your own music library but the millions of tracks opened up by streaming from SoundCloud, Deezer and Beatport LINK has huge implications for how DJ’s perform and what’s creatively possible. But does it actually work?
The exact technology behind the stem separation in VDJ 2021 is largely a trade secret, with VirtualDJ owner Stephane Clavel only giving us some sparse details. Traditionally, if you use a three-band EQ to DJ — Low, Mid and Hi — and you reduce the frequency of Low, for example, the kick’s frequencies might largely disappear but so will anything else that occupies those frequencies, like a bass line, the low end of a snare etc. A technology called FFT allows you to create a visual representation of a track, and then remove only the frequencies that are related to a sound — its harmonics — kind of like when you identify and remove one colour from an image in Photoshop. How effective it is, depends on the algorithm — VirtualDJ say they used a ‘black box’ that was fed thousands of tracks, to better learn how frequencies interact and how to isolate them based on a sound, rather than a frequency range, like an older three-band EQ would.
The real challenge though, was the CPU. Doing this in real-time, on multiple stems, on up to four different tracks, takes a lot out of even the most powerful computer. Add in the other functionality and the required stability of DJ software, and the fact that VirtualDJ appeals to entry-level users so is more likely to run on cheaper, less powerful computers, VDJ had to write their own code to get it to work. And it does.
Isolating stems in VDJ can be done in three ways. Clicking the arrow beside the usual Low, Mid and Hi three-band EQ knobs gives you a drop-down menu with the options Frequency (the traditional three-band option), EZRemix (which changes the knobs to control Vocal, Instrument and Beat) and ModernEQ which changes the knobs to Hi-Hat, Melody/Vocals and Kick. Tweaking each of these knobs, adjusts the volume level of that stem. Increase it all the way to the right and it solos the Kick, for example. All the way to the left and it mutes it.
Alternatively, you can also use the performance pads to mute and solo five different stems: Kick, Inst, Vocal, Hi-Hat and Bass. Clicking on a pad mutes that stem, or ctrl-clicking will solo it. Using the default GUI, the waveforms are in different hues of blue and red so it’s easy to see what stems are active and which are muted without requiring multiple waveforms.
The separation of the stems is very impressive. So new is the technology that during the process of this review, VDJ and the algorithm was given four different updates, improving it marginally with each one. They also added a new ‘bleed’ function that can be set between 0 and 100% that dictates how much of the muted stem you want to allow to come through. More on that later.
The technology behind the concept means that it can never achieve perfect isolation but it’s some of the best we’ve heard and on certain tracks, you can barely hear any artefacts or any ghosting as the stems are removed. On others though, it’s more obvious when a vocal has been removed. How obvious depends on the track being mixed — older music tends to work better, disco and pop music from the ’70s and ’80s tended to be mastered quieter which means fewer harmonics in the stereo file, therefore it’s easier to isolate certain parts. More modern music definitely has more artefacts, as would be expected given modern mastering traits but still is very impressively handled by VirtualDJ and you could get away with it anywhere that doesn't have a luxury sound system that would highlight those sounds. Besides, more modern club music tends to have a DJ-friendly arrangement anyway, with intros, outros and breakdowns of just the drums and bassline, or stripped back parts throughout the track, so the technology is less relevant for straight-up dance music, unless you wanted to remove the vocal for a quick mix out.
It’s much more comfortable with pop, modern or vintage, and older classic disco and dancefloor records and hip-hop. It’s a lot of fun creating real-time mash-ups, and VirtualDJ’s automatic key matching means you can throw in pretty much any track and have a good go at making them work together. There is an element of trial and error, and vocal, kick and bass stems operate much better than instrument and hi-hat, depending on the track, so don't expect the same result for everything.
Throw in VirtualDJ’s support for Beatport LINK — Beatport’s streaming platform that lets you stream their entire catalogue into software — Deezer, SoundCloud and Beatsource streaming, you can basically type in any track you can think of into VirtualDJ, load it within 20 seconds and have a fairly usable acapella or instrumental right there and then. For those who’ve spent their record hunting days searching for acapellas of classic tracks, or for those who love to do mashups of modern radio hits, it’s an absolute dream come true. While other stem separation software exists — iZotope’s RX7 being the main example that many people use to remove certain elements of a track — they’re not real-time and they’re not integrated within other performance aspects like FX and EQ.
If you do use the performance pads instead of the EQ modes, you can switch the EQ back to classic low, mid and high and then use that to tweak the sound further. For example, when you remove Vocals, sometimes there’s a filtering effect as the higher-frequencies are removed across the board. You can dial them back in slightly with EQ, but don’t expect miracles. However adding a bit of reverb and delay to a vocal that has some artefacts goes a long way to masking them and making the vocal sound more natural. Or, as the filtering and artefacts sound a bit like flanging and phasing effects, simply dial them in intentionally as part of the mix to make it seem intentional. Also, if you are using the Performance pads instead of the EQ settings, there’s a bleed function that sets how much you want to hear elements of the muted stem. That might sound counterintuitive but for things like vocals, you might want to re-introduce a bit of the sibilance to avoid an over-filtered sound. Sometimes removing vocals can sound like a LPF is being activated across all stems, so it stops that from happening. It’s default is 50% which works well for most sounds.
As we mentioned already, using three-band EQ coupled with FX can help a lot to mask or obscure any obvious digital artefacts created by the AI, or dial back in any frequencies that are obviously filtered. But another way to do it is to use the second, or third and fourth decks to play drum loops or samples to beef up or even replace the kicks or drums you removed from the original with a more modern one for example. It sounds better sonically and is essentially the same as live remixing where you take the drums of the original out but add your own. It’s also better for older disco records where the kick is live and isn’t quantised — you can simply take that kick out and replace with another without it flaming or clashing with the original. Again, it’s not the same as muting the kick on a multi-track, but in the middle of a DJ mix with all the other elements going on, it’s more than usable.
We could give many more examples of how you could implement the technology but it’s best to just download it and play around with it yourself. After all, the basic version is free. If you want to add hardware control though, it’ll either cost you $19.99 a month or $299 for a one-time purchase. We tried it with the Pioneer DDJ-400 and were quickly able to map the stems buttons to our performance pads and start muting and performing, and then use the three-band EQ and filter to tweak further. One of the most impressive things about VDJ2021 is the immediacy — we handed the computer to non-DJs and they quickly got the concept and were happily muting, soloing and trying out FX on stems. Loading your favourite track and hearing the vocal in isolation for the first time has yet to get boring.
Other things that would be useful are stem-specific cue points for when a vocal drops or when a beat comes in etc, but we appreciate it’s early days for the technology so we expect a lot more stem-specific features will come in future updates.
So now we know it works to an acceptable degree, and is being updated regularly, as well as Algoriddim launching a similar stem-separating tool on their Djay iPad app (although it requires the latest A7 chips) it’s fair to say the tech is here to stay. And given how easy it is to record on VirtualDJ, you could now simply isolate a vocal and record the acapella as a WAV file and use it in your tracks as a producer, or sample it and tweak it. It’s never been easier to instantly grab a stem from a full track for use in your music. Of course, the same legal issues as using any sample in your track prevail — you need to get permission from the rights holder. There, we’ve said it. The rest is in your hands.
Stem separation might be the biggest addition to VDJ 2021, but it would be remiss not to discuss the other features in the software. Like we said before, it is one of the most flexible DJ software out there, and supports hundreds of controllers and loads of custom settings — everything can be tweaked and mapped to an almost overwhelming level. Streaming from Deezer, Beatport LINK, Beatsource, iDJ Pool and Digitrax Karaoke (although, not sure how useful that is now you can create instant instrumentals) means millions of tracks to access (for a fee depending on the service), as well as playlists from Apple’s Music app, Traktor playlists, Serato crates and any other files stored locally.
You can tweak everything about the layout, including downloading free third-party skins from within the software. There’s built-in tutorials and tips, radio and live stream capabilities, podcasts recording functionality, a remote app for your mobile device and even a karaoke mode. And it’s all completely free. Our earlier stat about VDJ being the world’s most popular DJ software might not be so surprising after all.
VirtualDJ 2021’s stem separation — and the way it’s implemented — is very impressive. They’ve managed to create an interface for something fairly complex, simple to use and considering how many controls and buttons are on a standard DJ software’s GUI, it slots in naturally. The sound isn’t perfect but it’s good enough for trying out ideas, create quick mash-ups, or just satisfy your curiosity and hear your favourite tracks in a whole new way.
There are some tricks to make it sound better with the aforementioned ‘bleed’ control, EQ tweaks and running other drum loops under tracks. We haven’t been able to test how interfering the artefacts are on a club system for obvious reasons, but we think, for now, it’s best used at home, house parties and other mobile DJ situations rather than on a clean and crisp £100k club install. Though we’d love to be proved wrong.
For what is undoubtedly the first step of many for this new tech, it’s a very impressive start. How far you go creatively with it, is up to you.
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