Mixing Bass: How To Craft The Perfect Bottom End
By Mike Senior
This month Mike Senior, author of the best-selling book Mixing Secrets for the Small Studio, has a feature article in Sound on Sound magazine! You can read a preview of the article here:
Avoid all the low-frequency pitfalls and learn to achieve the perfect foundation for any mix, with our bass-mixing masterclass…
There is also a great companion website for the article full of audio examples and free multi-track practice projects!
On the website you will find:
– 21 audio examples demonstrating bass mix-processing techniques in action, complete with detailed explanatory captions.
– Links to 21 free, downloadable full-length multi-track recordings which present a wide range of bass-processing issues. Again, these links are captioned so that you know what to expect from each, and include sessions with string bass, electric bass, and synth bass parts of varying complexity.
Below is an excerpt from Mike’s best-selling book Mixing Secrets for the Small Studio.
When mixing there are some situations where you might want to add “oomph” at the low end of an instrument’s frequency range, or even below that. This is where a type of processor called a subharmonic synthesizer can help by artificially generating additional low-frequency energy that is still musically related to the unprocessed sound.
Although high-profile engineers such as Jack Douglas, Jon Gass, Jacquire King, Alan Moulder, and Thom Panunzio have all professed themselves users of such processors, I have to be honest and say that it’s rare to hear anyone applying them effectively in the small studio. This is partly because you need good low-end monitoring to gauge their true impact, but it also has to do with the fact that every manufacturer of a subharmonic synthesizer appears to use a slightly different algorithm, and you can never be quite sure how well each will respond to a given bass-instrument recording. One plug-in might work great on kick drums but churn out a load of woofy rubbish when presented with a bass line; another might handle only midregister bass parts; another might handle a good range of bass notes but throw a tantrum if there’s any drum spill on the bass mic.
Therefore, I personally rely on alternative strategies most of the time. For kick drums I insert an additional sample, whereas I supplement melodic bass instruments with a MIDI “subsynth.” Not only do both these techniques allow complete pitching and timing reliability, but they also offer much wider scope for tailoring the timbre of the enhancement to suit the production as a whole. Let’s deal with each in turn.
There are now lots of software plug-ins that will automatically detect drum hits in a track and play back a sample in time with them, but with kick drums you’ll only get good results if you refine the placement of each triggered sample by hand. “Software is very time-saving, but the drawback remains that it’s not as good as doing it manually,” says Cenzo Townshend. “You still have to go through each hit and move it in time to make sure it’s 100 percent correct and the phase is correct. You look at the waveforms, but you also need to use your ears.” Even once you’ve made sure that the phase relationship between the original and triggered kick tracks remains fairly constant, though, it’s as well to investigate whether additional overall timing/phase adjustments will further improve the combined sound.
Of course, sample triggering can also be used much more widely than this, allowing you to add new characteristics to any drum sound. It’s particularly useful with live drum recordings which, for whatever reason, need to rely heavily on the close-mic signals—for example, if the overhead mics are picking up mostly cymbals. Close mics positioned just a few inches from each drum will spotlight only a very small portion of the instrument’s complete sound, so the recordings from these mics will usually be rather unnatural and uninspiring to listen to. (Certainly, nine out of ten snare close-mic recordings I hear from small studios just go “donk”!) Triggering a sample alongside, or instead of, the close mic can help to provide a more pleasing overall tone in such cases. Andy Wallace uses an interesting variant on this technique to supplement his snare ambience: “I use the samples to drive reverbs…. The thing I like is that I can EQ them so that I can really tune the ambience and where it sits in the whole frequency response…. More so than I can with the overheads, because I normally EQ those so that the cymbals sound the way I want them to sound…. [I can] shade with a little more control using my ambient sample.”
But there’s another good reason for triggering samples within the context of a live drum kit recording: triggered samples have no phase relationship with the other microphones and no spill. This means that you can freely balance and process the sample without fear of destroying the rest of the kit sound—great if you only need the sample to supplement the sound in a specific way. For example you might apply slow-attack gating and assertive high-pass filtering to isolate just a snare sample’s high-frequency sustain components.
The Internet being what it is, it’s child’s play to find a selection of decent samples for most drums. However, on the off chance that typing “free drum samples” into Google doesn’t provide more choice than you could ever want, there are lots of commercial outlets that can provide you with tons of material. Check out www.timespace.com or www.soundsonline.com, to mention but two large-scale international distributors.
Incorporating a MIDI Subsynth
Propping up a lightweight bass line with a low-frequency synth part is a stalwart of many urban styles in particular. “The bass is very important,” explains DJ Premier. “If the low end of a [loop] sample isn’t really heavy, I’ll always follow the exact bass line of the song and put that underneath. A lot of people ask me what EQ I use to get the bottom end of my samples to come through so strongly, but I’m like ‘Man, it’s not EQ! I’m playing the same notes verbatim.’” This is often pretty straightforward to do if the bass is repetitive and tightly locked with a regular song tempo, but if not then there may be some initial donkeywork involved in sorting this out. Even if it takes half an hour, though, that time investment is usually worth the peace of mind that comes from knowing that the low-end frequency balance will be totally dependable. Usually only the freakiest of extended jazz-funk free-for-alls have me waving the white flag and scurrying back to traditional subharmonic processing. Once the MIDI part is in place, you need to consider what kind of sound the subsynth should use. One common option is to double the bass line at the octave below using a simple sine-wave patch. In this case, there’s nothing much to do other than set the sine wave’s level and listen to it in solo just to check that the synth’s envelope settings aren’t so fast that they create unwanted clicks.
Things get more complicated if you’re using a subsynth to try to beef up the existing fundamental frequency of a bass part, because the subsynth will overlap the main bass part’s frequency range. If the subsynth’s waveform isn’t in phase, then phase cancellation might actually cause the combined sound to become even skinnier! Moreover, because this phase relationship will usually change from note to note, you could end up with an uneven low end that’s all but impossible to balance with the rest of your mix. If the existing bass sound’s fundamental frequency is strong enough to cause difficulties such as this, then try to get rid of it to make space for the subsynth at the low end. A steep highpass filter on the main bass part is one solution here, but at times you may need to use the more surgical approach of notching out individual frequencies, preferably with the assistance of a high-resolution spectrum analyzer.
In the event that you want to do more than just add a suboctave or emphasize the existing bass fundamental, a sine-wave synth oscillator may not be the best bet; other waveforms will fill out the overall tone better. I like using a triangle wave most of the time, because it doesn’t have such dense harmonic spacing as a sawtooth and it’s duller-sounding and less characterful than a square wave—both of these properties seem to make it better at blending with (rather than overwhelming) the sound it’s layered with. Whatever waveform you use, though, you should also take the same precautions against phase cancellation of the bass part’s fundamental frequency. I’d also steer clear of detuned multioscillator patches, because the “beating” between the two detuned layers may cause the subsynth’s fundamental frequency to fluctuate unacceptably in level. It probably makes sense to stick with mono patches as well so you don’t get mono-compatibility problems. These restrictions mean that you only really need a simple instrument to generate subsynth parts. Whether you engage the subsynth’s own filter or sculpt its output with EQ is purely a question of what kind of low-end tonal enhancement you’re looking for. With a triangle wave in particular, you might not feel the need to filter it at all, although I do personally employ some kind of gentle low-pass filter most of the time to restrict its contribution to the lower octaves.
One final point to make is that subsynth parts usually need to be controlled tightly in terms of dynamic range or else they can really eat into your track’s overall headroom. This is where the MIDI-triggered method really pays dividends, because it’s simple both to restrict the dynamics of the MIDI part and to compress the subsynth’s output. So even if your low-frequency monitoring facilities aren’t up too much, you can still rely on a subsynth to give consistent low end if you pay attention to your DAW’s meters.
Mike Senior is a professional engineer who has worked with Wet Wet Wet, The Charlatans, Reef, Therapy, and Nigel Kennedy. He has transformed dozens of amateur mixes for Sound On Sound magazine’s popular Mix Rescue column. As part of Cambridge Music Technology, he also provides in-depth training courses and workshops specialising in the documented techniques of the world’s top producers.