Managing the lower frequencies of the extra string
By Bob Ross
My father, in his admirable attempts to not just maintain an interest in what I do, but to actually converse about it, has gone to great lengths to learn about the tools of music-making. In doing so he may have embraced some generalizations and oversimplifications, but these mostly serve him well; for the longest time, for example, he was able to differentiate guitarists from bassists by simply reminding himself “4 strings = bass, 6 strings = guitar.”
Lately my dad has become very confused. And you’ve probably also noticed an abundance of 5-string and 6-string basses coming through the doors of your studio. Here in the tail end of the millennium it is absolutely de rigueur for every professional electric bassist to own at least one extended-range instrument.
With increasing competition for low frequency real estate from synthesizers, drop D tunings, and 7-string guitars (oh yeah, my dad is going to have a conniption trying to figure out a Korn concert), bassists have been forced to expand into a lower register just to be heard. The additional lowest string of these extended-range instruments gives bassists another half octave (roughly) to roam around in (as well as allowing registral leaps that would be otherwise nearly impossible on a 4-string bass).
For the sake of brevity, whenever I say “5-string bass” here I mean any greater-than-4-string bass with a low B string. (For instance, the 6-string bass has one extra string above and below the 4-string, so it has the same low-end range as the 5-string.) And when I say “B string” here I’m allowing for the inevitable variations in tuning, C and A being the most common. Having clarified that, allow me to opine:
The 5-string bass presents recording challenges not present with a 4-string bass.
To some that statement seems ridiculously obvious. To others it triggers a Fact Vs. Opinion argument that will last into the wee hours, long after all the beer is gone. I’m well aware that many bassists and engineers treat the 5-string exactly as they would a 4-string instrument, and come away with perfectly decent recordings. But, being both an audio engineer and a bassist, I’m not interested in decent recordings; I’m interested in excellent recordings!
Here’s the biggest challenge one faces when recording a 5-string bass: maintaining timbral consistency from string to string. As a fundamental aspect of string playing technique, violinists, cellists, guitarists, and yes, bassists strive to develop a uniform tone when playing passages that cross strings.
Good players do acknowledge that this is an ideal, a goal whose achievement is limited by the not entirely predictable nature of acoustic vibrations and mechanical resonances. And savvy players and composers will often take advantage of the individual timbral qualities exhibited by the different strings for coloristic purposes. But the aim is to maintain as consistent a sound possible as one plays from string to string, so that the instrument conveys a homogeneous timbre over its entire range.
And there ain’t a 5-string bass on the planet that can do that.
As soon as you move from the 4th (E) string to the 5th (B) string, the tone quality changes. For notes played on that lowest string the harmonic profile is different, the volume envelope is different, the transient response is different, the entire timbral fabric is different.
Listen to any bassist play passages that alternate between the B string and the other (adjacent or otherwise) strings. Those notes played on the lowest string have a much less developed fundamental. Their first and second harmonic are disproportionately out of balance, yielding a hollow, resonant timbre. Those notes generally seem louder, yet with a slower attack; they tend to “bloom” when plucked.
Consequently they don’t speak very quickly, so percussive articulations tend to emphasize the upper harmonics, as the fundamental doesn’t have time to develop. No amount of pristine playing technique nor high-tech instrument design can alleviate this (…yet, he says hopefully).
Now, to some listeners these differences may be subtle. It is probably safe to assume that the folks perfectly content to record 5-string basses exactly the same way they record 4-string basses fall into this camp.
Or perhaps they just never considered it, or never listened very closely. To my ears these differences are glaring. It’s evident on cheap mass-produced basses and esoteric handmade models alike. It’s evident when I’m playing my basses, when I’m recording someone else’s basses, when I’m listening to a bassist on a recording…. Even when barely listening to background music on a cheap car radio I’ll suddenly become aware that the bassist has moved to a note on his/her B string, it’s that obvious.
Okay, so maybe I’m cursed. But I don’t have perfect pitch, so it’s not the absolute note name that’s calling attention to itself—it is a set of spectral phenomena.
I attribute these phenomena to a number of factors. Perhaps most obviously, the notes below the 41 Hz open E of a 4-string bass are well below the usable low frequency cutoff point of much of our reproduction equipment. The fundamental frequency of an open B string is 31 Hz; if you’re only monitoring on NS-10s you probably don’t have a clue what I’m talking about when I describe the above sonic artifacts! Or at least you don’t have a reliable clue as to what’s happening with the fundamental frequencies of those lowest bass notes.
This alone accounts (at least in part) for the disproportionate first and second harmonics: with the fundamental severely attenuated by the limitations of the playback transducers, the lower overtones become more apparent. A number of synthesizers that use digital oscillators have taken advantage of the hollow, unstable timbre that results from filtering out the fundamental of a complex waveform…but I can’t think of any bassists who go out of their way to get a “hollow, unstable” tone from their instruments!
The slow articulation most likely is a result of mechanical inertia. For a string to vibrate soundly at 31 Hz a considerable amount of mass is required. These bass strings are typically 0.120″ to 0.140″ in diameter, often with more layers of metal windings than their less substantial neighbors.
This is necessitated by the fact that an electric bass has the same vibrating length for all of its strings, unlike a piano whose lower strings increase in both diameter and length. To vibrate at a lower pitch in the same length, you must add mass. (Companies like Novax and Dingwall do make basses with different string lengths, but that requires necks with frets that aren’t parallel. Think about that for a second and forgive me for not treating them in depth here.)
For the same reason that large transducers have a slower transient response (think big undamped woofers, or large-diaphragm dynamic mics), these massive strings have a certain “rise time” before they are vibrating at full excursion.
Finally, some of the timbral differences are a result of structural differences in the 5-string bass’ construction. A wider neck to accommodate the extra string(s) is by definition going to have more mass, which means its resonant frequency and dead spots (extremely non-resonant frequencies) will be different from an otherwise identical 4-string bass. Likewise, the headstock needs to be larger to accommodate the extra tuning machine(s), and this will significantly alter the location of the neck’s resonant frequency and dead spots.
Several bass builders have addressed these issues by using composites in place of or in combination with wood. While carbon fiber, phenolic, and epoxy materials can eliminate many of the above-mentioned resonance issues, they are not without their shortcomings in the subjective aesthetics department; suffice to say I love my graphite basses, but I could never do entirely without the sound of a conventional wooden instrument.
Anyhow, maybe you agree with me that these sonic artifacts are prevalent in extended range basses, maybe you never thought about it, and maybe you think I’m just being a wanker, but in any case by now you’re probably saying, “Okay Bob, so what do you do about it?”
1. Subsonic monitors—if you can’t hear it, you can’t fix it. No, I’m not suggesting you all run out and hire Tom Hidley to retrofit your project studio for 20 Hz Infrasonic® mains. But you do need some reference that will allow you to meticulously examine the lowest octaves of music.
Perhaps it means adding a subwoofer to your existing monitors or getting a sub/sat system as an alternative speaker system. Perhaps, given the typical inability of a small minimally treated control room to actually develop an uncolored 30 Hz wave, it means getting some headphones that are flat to 20 Hz or below.
What it definitely means is having some listening tool that can provide accurate information about deep bass. This should be your “bass microscope” that you use for isolating and identifying low frequency aberrations and anomalies. Only when you can reliably hear what’s going on in the nether octaves can you make confident decisions about bass parts.
2. Multi-band compression. Unlike eq alone, a multi-band compressor can simultaneously shape the spectral balance and the attack profile of those rampant low B strings.
While it might seem like overkill to dedicate your tc Finalizer to salvaging bass tracks, they do work wonderfully for this application; just remember to turn off the look-ahead delay. I’ve also used the very affordable yet flexible Rane DC24, the MasterWorks multi-band compressor plug-in that ships with MOTU’s Digital Performer, the BSS DPR-901 Dynamic Equalizer…and most often I’ve just cobbled together a makeshift multi-band compressor out of an active crossover and two separate wideband (i.e. conventional) compressors.
The objective is to isolate the very lowest notes on the 5-string bass and give them independent compression ratios and attack/release times from the rest of the instrument. Depending on the instrument and the musical context I’ll cross over anywhere from 40 Hz to 65 Hz… I’ve even gone as high as 100 Hz (though not by choice; that’s as low as the variable crossover would go!).
The highpass output feeds a compressor set up for whatever the desired “normal” bass sound is. The lowpass output feeds a compressor set up with a slower attack time and a higher compression ratio. You don’t want gain reduction to occur on the beginning of those notes on the low string, the attack is already quiet and slow enough as is. Delaying the onset of gain reduction allows the natural attack to speak through; adjusting the makeup gain allows you to bring this up into proportion with the faster/louder attack of the other strings. The higher compression ratio then lets you tame the ramping up in volume that normally plagues the uncompressed B string.
Also, be careful that the release time on the lowpass compressor isn’t set too fast, or the gain reduction might track the actual rise and fall of these extremely slow waveforms on sustained notes.
3. A 4-string bass. That’s right, dump the 5-string and go back to a conventional instrument. If you’re not the bass player this can be the most difficult solution to implement… but often it winds up being the simplest way to overcome problems.
If the tune you’re recording doesn’t make use of any of those notes on the B string, that lowest string is nothing but a liability. Or a status symbol. Or a thumb rest. Especially with inexperienced players, the unused B string can be left vibrating sympathetically with the other strings that are being played, infusing a quiet subsonic thrumming all over your bass tracks. (Which, unless you did #1 above, you wouldn’t know about until the mastering engineer pointed it out.) And if the bassist is using the B string as a thumb rest, there can be sonic artifacts in your track as a result of the pick or plucking fingers striking the muted B string.
Obviously this approach doesn’t apply if those ultra-low notes are mandatory for the tune you’re recording, or if the part isn’t entirely scripted and the bassist needs the option of accessing those notes… but it’s an important alternative to consider. As an engineer/producer this has come in handy more times than I can remember.
As a bassist I’m still initially resistant to it, but professional responsibility usually wins out over pride in the end.
Bob Ross (email@example.com) is a producer, engineer, and (yes) bassist in the Boston area.