Thoughts on Bass Sound Shaping

by bassbacke (started 2002-10-19). Constructive feedback is always welcome.

What's all this about?

These are my thoughts on bass sound shaping.

You may ask yourself what the heck is that supposed to be about and why is the guy so full of it that he creates this page on it? :)

It's supposed to be a kind of a brain dump. A summary of what I've learned about bass sound shaping over the years so I can share it and discuss it with others interested in bass sound shaping.

Bass sound shaping is an attempt to keep in mind as many factors that affect your bass sound as you can in order to control and shape the sound the way you want. Minimizing the number of variables where possible helps.

Since I am a rather technical guy, please bear with me. Statements like "it sounds killer", "kicks ass" or "is way better than..." without any explanation as to why or how make me smile at best.

Where does bass sound shaping start?

It may not be so apparent, but there are quite a few things shaping bass sound and only some of them have to do with electronics.

Factors affecting your bass sound before any amplifiers are involved:

Two basses from one vendor will often not sound the same since materials like wood come from mother nature and there is some inherent variation coming from that alone.

Two sets of strings from the same vendor also may not sound exactly the same and over time their sound changes dramatically. You can either replace them regularly or wait till they are completely dead and won't change their sound at all. Great soul bassists did that, but it may not be everybody's cup of tea. It's not mine. One reason not to do that is dead strings don't tune well.

Another factor is that we don't play exactly the same every moment in our lives. Some days are better than others, some are not. After all we're humans, not robots. At least at the time of this writing this is a valid assumption. ;)

Of course your bass pickups and electronics will also shape the sound of your bass. The "wars" on "passive vs. active" are not over and probably will never be. Permutations:

I've never seen active pickups combined with passive electronics before I purchased a Zerberus Red-Shark on 2002-09-09. :)

There are differences between single coil, double coil, humbucker and piezo pickups and what not but even within those categories sounds differ a lot. Since different people have very different tastes, we should consider us lucky that there is such a variety of basses, pickups, electronics, strings, etc. I certainly do.

Generally as soon as active components are built into your bass, you'll need at least a battery (some use two batteries or some alternative power supply). If you are too "challenged" to keep replacing them and removing the cable while you don't play, active basses are not for you. In this case I personally I think basses are not for you since it's folks like you who give us bass players a bad reputation. Just kidding. ;)

Why active electronics?

The only real drawback using active electronics in a bass I can think of is that your battery can go dead when you need it most, but many basses with active electronics allow some sort of a bypass in that event so you're not dead in the water even then. You can easily prevent this by always having a spare battery in your bass case or gig bag. We have to play by some rules... Here are some advantages using active electronics, which I'll explain below:

I don't really want to go into details as to why. Those people who are technically oriented already know those details and those who aren't most likely won't want to know or understand. Sorry, that's my experience. However both parties may be interested in knowing the effects rather than why that is so. After all you don't need to be able to construct and build a car to drive one. From time to time I may not be able to refrain from giving some technical background. I hope you won't mind.

Low output impedance means you can feed your bass signal into a broader variety of inputs. Passive basses will always need a high impedance input like those in bass amps. An active bass however can be directly plugged into a mixing board without any pre-amp still sounding OK. And that's just for starters. If your bass needs a very high impedance input and is fed into a rather low impedance input it will affect your sound. Also cables will have more effect on your sound. It's better to have as few variables (components that can modify your sound) as possible in order to make your sound reproducible. If such trivial things like a cable can have a great impact on your sound it is not  very likely you will ever have control over your sound.

A high output level helps to get high volumes and high signal/noise ratios. In other words less annoying noise.

Cables have some properties which you can more or less ignore when active electronics are involved, but when everything is passive the choice of your cable between your bass and your amp may have a real great impact on your sound. Cheap/bad cables will kill your treble among other possible problems. Invest in quality cables in any case, especially with passive basses. I personally prefer active basses since I don't want to have to worry about this.

Last but not least it's of great help if you can effectively control your bass sound on your bass and not only on your amp. You don't really want to step back to your amp in a live environment to add or lower some bass or treble. On passive basses usually all you can do is to attenuate treble. Often that's just not enough. That's my opinion. Play your passive basses if you like. I won't talk you out of it. They can also sound just great. It's just more variables with those making it harder to keep the same sound. Then again this may not be your goal, anyway. ;)

However, some active electronics are better than others. Some make a lot of noise, some change the sound in undesirable ways. Make sure that you get proper active electronics in order to really enjoy them.

Once you're settled on a type of bass and pickups, setup, type of strings and playing techniques, you got some level of control over your basic sound - hopefully.

What other factors are there?

Bass amplification systems in general are comprised of:

Note: there can be more than one power amp and more than one speaker cabinet.

Most pre-amps do more than impedance matching and boosting such as sound controls, compressor/limiter and probably other sound processing.

The components mentioned above can be combined in one box. Most so called "heads" or "tops" are pre-amps combined with power amps, e. g. Hartke 3500. Sometimes these tops are built into speaker cabinets which most people will call a combo such as SWR Super Redhead. While they are rather compact, they tend to be very heavy. Having components in separate boxes allows for the greatest flexibility but you have to move around more boxes. Sometimes they are also more expensive. I personally think it's worth it.

We're plugged in. What next?

In order to describe my ideas about bass sound shaping I use a setup I used for quite a while as a reference starting with my pre-amp. My setup did the trick for me. It may not work for you. In any case it can help deliver my ideas which in turn hopefully inspires you. I'd love to hear from you if it does.

The idea behind my approach to bass sound shaping is that I try to keep the parts "power amp" and "speaker cabinet" as transparent/neutral/HiFi as possible. If I have to factor in amp and speaker sound coloration my experience is I will never get a reliable bass sound. My idea is to feed the PA through my DI a sound that could be recorded without having to process it much. Again I'm trying to keep the number of variables as low as possible. You may not like my sound but I don't get my sound by chance and if I wanted a different sound I have a good chance to "dial it in". Choose a different sound if you will, but believe me it's good to be able to reproduce it.

Very low frequencies

Let's hope you're plugged into a high impedance input, especially if your bass has passive electronics. Now there are some amps that are supposed to go really, really low, such as 5 Hz. This sounds great at first but it's not really. How comes? The problem with that is, that's way below what humans can hear, what a bass should produce and bass speaker cabinets can reproduce. You will end up wasting a lot of amplifier power trying to reproduce something nobody can hear which leaves less headroom for your bass sound. We're talking live instrument amplification. Every bit of power counts.

Generally all frequencies below your lowest note on your bass should be cut off since it will not help your sound and will only lower the maximum volume and sound quality you can achieve. How low are we talking about, then? Well, it depends on how your bass is tuned. Let's check out a number of rather popular tunings and see the lowest note they can produce:

Tuning and lowest notes

# of strings tuning lowest frequency
4 E-A-D-G 41.2 Hz
5 (6) B-E-A-D-G(-C) 30.9 Hz

Some people even go down to the A below that be which results in 27.5 Hz. Let's assume standard 5-String tuning. In that case all frequencies below 30.9 Hz will only eat up your amp's power and headroom, produce nothing but heat in your amps, speaker cables and speaker coils, not adding anything to your sound and lowering your maximum sound pressure. That is assuming you don't use octavers and such which can make your bass signal go even lower. In any case humans don't usually hear anything below 20 Hz. We hear that barely, some people notice frequencies down to 16 Hz. Most bass speaker cabs won't go much lower than 35 Hz (if your lucky). Many 4x10" will not get even near that. Check out my bass speaker cabs overview to learn more about that (and cry?).

First job for my pre-amp

The first thing a bass pre-amp should do is match the impedance from high to low. My pre-amp boosts the signal by factor 11 and cuts lows by 6 dB/octave using a 6.8 nF capacitor and a 1 M Ohm resistor. Usual RC rules apply which make this cut off frequency ca. 24 Hz (-6 dB). Since RF can be a problem, I've added some high frequency roll off as well using a 1 kOhm resistor and a 100 pF capacitor (not in the scheamtics, yet). So I have four functions in one little circuit: very high impedance input, low cut, RF protection and factor 11 boost with low output impedance. The output of this pre-amp is directly connected to a Behringer Ultra-Q PEQ 2200 mentioned below for sound control using 6.3 mm plugs. I might replace that with a simple sound control (three or four band) some time in the future.

If you don't want to mess with electronics yourself you can use ready to use devices such as BOSS CS-3, equalizers etc. Plain simple anything "active" that allows for direct connection to your bass and tolerates a low output impedance.

Isn't treble good?

The instrument is called bass, not treble. :)

Of course this depends on the style you play and the sound you want, but the more treble is in your bass sound the less you will hear real lows. It's basically because we can hear higher frequencies better than lower ones.

If you listen carefully to great recordings of basses, treble often is not the most dominant part. It may sound great alone but together with a band you may want to have rather little treble.

Sound Control

Behringer-PEQ2200.jpg

The Behringer Ultra-Q Pro PEQ2200 can cut off highs with a low pass filter at 12 dB/octave if you want to. Which frequency? Well, it can be tuned from ca. 2.5 kHz to 30 kHz (off). In addition to that it has a high pass filter which can be tuned from 10 Hz to 400 Hz which I have dialed into 25 Hz. Last but not least it offers a five band parametric EQ. Not just frequency and amount but also bandwidth can be tuned. Using this I can get many different sounds out of my basses. The output of the PEQ 2200 goes directly to a Behringer MDX 2200 Gate/Compressor/Limiter shown below using an XLR cable. The Behringer PEQ 2200 fits nicely into 19" racks and is rather affordable. If you don't like parametric EQs you can substitute it by a graphic EQ. Try to get one that has a low pass/high pass filter as well.  

Why not build my own sound control? Well, I can't build this as cheap as the Chinese. Too much work (for me that is - you can try your luck). Then again I did some research. I might end up experimenting with a three or four band sound control. If it is any good, I'll let you know. :)

Compression

Behringer-MDX2200.jpg

The Behringer Composer Pro MDX2200 offers a gate/expander, compressor and limiter function (two channels - I use only one). This device is great sounding and very flexible considering the price. It also fits nicely into 19" racks. So far I have not found usable schematics for compressors, so bear with me.

Output signal levels at this stage are at +4 dB. One has to set threshold levels on the compressor accordingly. The XLR output of the Behringer MDX 2200 is directly connected to my Samson S1000 power amp using an XLR cable. Of course any good power amp can be used, you're not limited to any brand.

Pre-Amp OK, but when will I hear anything?

After the compressor output levels are setup to be between +4 dB and +10 dB (using a limiter) which is great to feed into a power amp as long as I run the amp's volume below -10 dB. Since the Behringer MDX 2200 also has a 6.3 mm output I can use that to go directly into another OP amp with 1:1 amplification driving a 10:1 transformer which I use for my DI. The signal is low enough again since it's divided by factor 10 to avoid sound people from going crazy because of input overload and unwanted distortion. Also the signal is galvanically separated from the rest of your electronics (no hum and such). This is not a must, it just saves you from dragging around some DI box. However, I've never heared of a PA company not having a spare DI to connect you, so you may be very OK without that little gadget.

I just can't imagine it. Draw a picture?

Yeah, OK. Some people will prefer a picture, so why not:

bass-setup.jpg

In case you're interested, here are the schematics of my pre-amp. Please note the schematics are out of date.

Credits

I will try to keep a list of people who give me feedback on this web page in alphabetical order of their first names. I will refrain from listing their email addresses here to save them from SPAM coming from web email address crawlers. Interestingly so far only one of them is a Bassist. Where are you, bass players? You must have some opinion on the matter, right? :)