A couple of weeks ago I wrote Our Favourite Audio Plug-ins To Give You Some Sweet Top End. In the writing of this round up of some favourite plugins for treating the top end, it quickly occurred to me that there was a natural counterpart to it covering the opposite end of the spectrum. So here is a round up of some favourite bottom end plugins and like the top end article, this isn’t a flat list, it illustrates a progression of processing from simple EQ through to more involved processing.

For most of us the first response to something feeling like it needs more energy at the bottom end is an equaliser. If the world were simple then all EQ’s would achieve the same results, but the world isn’t simple and some EQs are very different from others. Arguments might rage over which colour of SSL EQ is best but if there’s one EQ which deserves top billing for bottom end it has to be one which has its own ‘Bottom End Trick’ - the Pultec EQP-1A.

Universal Audio Pultec EQP-1A - Classic EQ With A Trick

Passive equalisers have been around longer than their more flexible active counterparts and while they can’t do lots of things, the things they do they do very well. The Pultec missed out of a place in the top end article partly because I like the Clariphonic so much but also because I had it pencilled in for this article. The gentle low end shelf is switchable to 20, 30, 60 and 100Hz and the curve and the valves in this design combine to give the richest bass you could ask for. Don’t pay any attention to the numbers. You might think that 30 Hz is too low for your vocal but if you try it you’ll probably find it does quite a lot.

But the party trick with which this design is associated involves using the separate boost and attenuate controls together. The non-identical curves combine to create a composite curve with a dip above the low shelf boost which clears muddiness making it ideal for anything from kick drums to whole mixes.

Rather than explain further check out the video from Puremix in which Fab Dupont uses real hardware. When it comes to plugins there are many options of this much modelled unit but my preference is the UAD version which is available without UAD hardware courtesy of their Spark platform.

McDSP F202 - Resonant High Pass Filter

Using filters there is a limit to what can be achieved. You can’t boost low end which isn’t present, a subject we’ll return to later. But for really winding up the bottom end, a resonant filter can be just the ticket.

McDSP’s F202 from their trio of Filterbank plugins is as old as the hills but it is super flexible and sounds great. If it ain’t broke etc… Particularly useful on drum sounds (pitched instruments aren’t the best candidates for this treatment) using a resonant filter, by which I mean one with a distinct bump just around the corner frequency, can be a powerful tool. This filter can be a low pass and for synth style effects this is great but I’m talking about a resonant high pass filter. If a kick drum, or any other kit piece, is lacking weight then dialling in a resonant high pass and using the resonant peak to accentuate the very lowest frequencies can be a quick and very effective way to bring in that little bit of 40Hz ‘woompf’ on your kick or 160Hz beef on your snare. You can achieve the same curve with a peaking band combined with a non-resonant HPF in you channel EQ but the convenience of having both the cutoff and the peak move together with the frequency control makes it so easy to set up by ear.

Sound Radix Surfer EQ - Tracking EQ

As I mentioned above, a resonant filter should be used with care on pitched instruments as, like with any static EQ, a resonant peak creates a hot spot which will respond differently to different pitches. If you want to beef up the bottom end but your bottom end is a moving target you might consider a tracking EQ. The original tracking EQ is Sound Radix’s Surfer EQ. It can function as a standard, static EQ but when a band is set to Surf it tracks the pitch of the audio and moves with it. You can fix the bands to specific harmonic overtones and by doing this avoid the timbre shifts introduced by static hot spots created by normal EQs.

This tracking is only suitable on monophonic sources so this EQ isn’t for use across mixes but for adding consistency to sources like vocals and particularly bass, there’s nothing else quite like it. The only place I find I use this regularly is on basses and if you’ve never tried it you really should. The lower the source the better I like it.

Leapwing RootOne - Subharmonic Generator

The accepted EQ wisdom that you can’t boost what isn’t there. This is true but there are plugins which will create sub bass content. Inferring what would have been there if the sound extended further down the frequency spectrum. We already have the converse of this in the form of exciters which create artificial top end and these themselves are based on good old-fashioned harmonic distortion. But this is harder to do for low frequency content.

The oldest example is the octave divider, an effect loved by bass guitarists for years. But creating new sub bass content on more complex audio is more difficult. Dialling in extra low end on drums is reasonably straightforward and pretty successful. Pitched instruments can work well if they are monophonic. More complex audio and particularly whole mixes have to be approached with care as the artefacts can soon become counterproductive.

I’ve used a few of these types of plugins. My favourite is Leapwing RootOne. It offers three bands of subharmonic generation with useful dynamic controls which can help introduce low end impact even on complex material. The inclusion of saturation in this plugin can help add a little texture but the main takeaway, whichever sub bass synthesising plugin you choose, is to be really careful about adding content your monitoring system can’t reproduce. Check on headphones and watch those meters!

Waves MaxBass - For Band Limited Systems

As well as manipulating the bass content already present with EQ and creating new sub content using sub bass plugins, there is a third approach which can help your bottom end. Using psychoacoustic trickery to get the listener’s brain to infer bass which isn’t there at all!

This approach relies on the structure of pitched sounds themselves. Without going in too deep, pitched sounds are based on a harmonic series of overtones which follow a specific pattern. If your plugin generates harmonics which would be present in a sound which had more bass content than it actually does, the brain infers that lower frequency. It’s a neat trick and can be used to create the impression of deep bass in band-limited playback systems.

The best known plugin which exploits this approach is Waves’ MaxBass. If you’ve never used it try it out. It’s not a magic bullet but it certainly works and, particularly if you know the specific system on which the audio will be used (something we rarely get in music production but for install-specific content this does happen) it can be very effective indeed.

Do you have any favourite plugins for helping the bottom end? Share your suggestions in the comments.