When mixing bass in a two-channel (ie, stereo) mix, the topic of stereo content and mono compatibility in the low frequencies is hotly debated. Most recommend you keep all low-frequency elements in a mix – generally the kick drum, sub bass and other bass elements – completely mono.
This is generally pretty solid advice: keep everything bass-heavy in the middle of the stereo field, and those sounds will then retain low-end power when the overall mix is summed down to a single channel and played back over a mono system such as a club or mono Bluetooth speaker. Plus, bass that has an excess amount of stereo content is also known to make a lathe’s cutting head jump when transferring a track to vinyl.
However, check out current-day dance productions and you’ll see that producers aren’t always that cautious when it comes to panning and spatialising parts that live in the bottom end: dazzlingly wide subs pop out of the sides, synth basses jump around from left to right, and kick drums ring out with lashings of stereo reverb. So what gives?
Breaking the rules
1. When you’re working with stereo signals, a basic mono/stereo balancing plugin is essential. This will allow you to adjust the volume of a signal’s mono (mid) and stereo (side) components separately.
2. Want a particular bass sound to jump to the forefront of the mix and pop right out of the speakers? Then apply as much high-passed Haas widening or short stereo reverb as you can get away with before any negative phase side effects start to occur.
3. If you’re serious about your stereo widening, get to know iZotope Ozone’s Imager module, which lets you narrow or widen up to four independent frequency bands. For example, you can use it to mono a bassline’s frequencies below 100Hz, then widen the low-mids a bit, then heavily spread the upper frequencies – you get the idea.
4. Use bass spatialisation as a psychoacoustic feature in an arrangement. For example, keep a bass fairly mono for a chorus, then ramp up the sound’s stereo content when the chorus hits home.
Well, although you should (almost) always keep all frequencies below around 100Hz – approximately considered to be the ‘sub bass’ frequency range – in mono, there’s nothing stopping you from widening signals above 100-150Hz. By walking that stereo tightrope in controlled but creative ways, you can give your kicks and basses an extra few percent of perceived power, density and assertiveness when heard on stereo systems such as earphones, car stereos, home hi-fis and the like.
So as long as your track still sounds powerful and consistent in mono, and it’s not destined to be pressed to wax, there’s a fair bit of wiggle room when it comes to bass spatialisation. Like any advanced technique, though, it’s easy to go too far, so watch out – like with most mixing tricks, one perfect application will be better than throwing umpteen stereo plugins across everything in your mix!
Before we go any further, recognise how important it is to regularly check your stereo output’s mono compatibility using any capable utility or ‘monoising’ plugin. Summing your mix to mono will reveal any phase incoherence or cancellation, allowing you to judge the negative effects of any stereo processing you’re adding. In fact, we suggest you do this every time you make some sort of stereo manoeuvre anywhere – it’s a good habit to get into.
On the topic of phase inconsistency, watch out for synthetic bass sounds – sourced either from a synthesiser or sample collection – that feature unison detune or stereo effects of some description. Many synth presets are programmed to sound wide and impressive, but these may phase-cancel when summed to mono.
A typical mix often demands a simpler, narrower bass part, so it’s a good idea to use more basic synth bass patches from the get-go – but if you must use an overly widened bass, try reining in its stereo content with a mid/side utility plugin or M/S EQ.
Stereo bass layers
The concept of layering one or more sounds together in the search for one uber-powerful collective sound is a tried-and-tested technique for many producers, and when executed with a steady hand, this can be used for the purpose of bass widening, too.
If your track features a beefy synth bass containing plenty of frequencies across the entire spectrum, but lacks any stereo content, consider mirroring it with a near-similar synth patch. Keep this second layer fairly subtle, and you can afford to push it out to the sides of the mix – try panning oscillators within the synth, or processing it externally with wide chorus, reverb or delay.
As a rule, make sure this stereo layer doesn’t overpower the core central layer in frequency content terms – this signal won’t come through as strongly, if at all – in the mono mix, so you need to be able to afford to lose it!
Crafting custom bass widener auxes
Build super-stereo, mono-compatible basses with advanced parallel widening. Here’s how…
When working with stereo effects, your DAW’s auxiliary return channels are indispensable. By sending your solid, centred bass signal/s to a dedicated ‘stereoising’ aux return, you have complete control over the level, width and tone of the new stereo content you’re adding, independent to the mono stuff that’s already balanced in the mix.
This level of precision is even more important when stereoising sounds containing low frequencies, as you can meticulously filter/EQ to control the widening. You can also cue up multiple ‘stereoising’ auxes in a project. This lets you juggle alternative widening ‘flavours’ in the mix for different elements, or stack up two or more stereo treatments for the same sound.
Let’s learn how to structure and refine bespoke widening auxes, for later use as channel strips in your DAW…
Step 1: Load up a Haas delay, short reverb/delay or pseudo-stereoising plugin on an aux return in your DAW. Next in the aux’s plugin chain, call up a mid/side utility and isolate the side signal. This ensures that the 100% stereo signal will disappear when summed to mono.
Step 2: To curtail the aux signal’s bass content, go back and load an equaliser last in the aux’s plugin chain. A 100Hz high-pass filter is an obvious choice, or you can choose to ‘pocket’ a low-mid band for a more focused effect – but be sure to adjust your EQ in context, of course.
Step 3: Now head over to the mix channels you want to widen and send their signal to this aux. The amount you send will determine how much widening is applied. To tailor the tone and dynamics of the new stereo content, go back and EQ/compress the aux to taste.