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It is now possible to make a piezo equipped fretless bass sound amazingly like an upright bass (URB). With some additional electronics and some parameter tweaking a very close approximation of the complex sound of the URB is now attainable. If fact John East, creator of the East bass preamps says the similarity is unbelievable.

The described device uses off the shelf components and is not a dedicated product, I call it a "URB Simulator" as the parameter settings of various functions are unique.

This is not a sales promotion, I have nothing to gain by distributing this information to the fretless bass community except goodwill.

A fretless bass is required, fretted basses do not have the necessary subtlety of control to be relevant in this discussion. Sorry fretted players, a significant contribution to the sound is the similarity of the two instruments, electric fretless and upright bass. Although it would be interesting to try a piezo equipped fretted bass to see how it sounds.

This information does not fully apply to magnetic P/U electric fretless basses. A piezo pickup is essential for the full effect. The device described is not a single circuit nor a difficult project, it is composed of readily available audio components.

After years of thinking about the characteristics of the Acoustic Upright Bass (URB) sound, I believe I have finally arrived at a fair understanding of this complex sound production instrument, and have translated this understanding into an electronic device that makes my piezo equipped fretless electric basses sound so much like a URB that it is truly uncanny.

Prior to the development of the URB Simulator I used low tension nylon strings because they seem to get a better "thump" and sound more acoustic. With the URB Sim I was surprised to find that regular flatwound strings actually sound closer to the tone I expect. This makes sense considering that most URB players use flatwound steel strings these days. Plus I prefer the higher tension of regular strings.

So far the URB Simulator works wonders with any piezo equipped fretless bass I have tried, from a home brew Fender style to a very nice Veillette MK-IV.

I intend to reveal all of the details here on this forum for you to create your own URB Simulator.

Here is the short version of what I have learned about the URB sound.

The URB is an acoustic violin that radiates sound in a complex manner, various frequencies are generated by different parts of the instrument. An electric bass is usually a solid wood structure and has an immediacy of electric note propagation that the URB does not have, and vice versa. This is the crux of understanding the problem of translating URB characteristics into electric fretless.

The sound that comes out of an acoustic upright bass relies on mechanical induction of string vibration, and vibration artifacts, into a highly reactive acoustically compliant resonant box, a bass violin.

First and most important, there is a propagation delay in the lower frequencies. It takes time to excite the air mass in the large URB body. The lower the frequency, the longer the delay.

In the mid bass, and high bass range the back and top directly radiate vibrations. There is a propagation delay here too but it is considerably shorter. In addition, there are nodes within the top and back representing zones of greater efficiencies contributing to the individual character of a particular instrument.

In the mid and higher frequencies sound directly emanates from the bridge and fingerboard as well as some from the top and bottom, and to a lesser extend, the sides. Much of this sound you might describe as noise such as the clack of string against the fingerboard, or the friction aspects of the string being pressed against the fingerboard as it vibrates.

Comparing all these interactions of various nodes and zones of resonance, and projection in the URB to the electric bass one sees that the electric bass is a much simpler instrument from a sound propagation standpoint. Since the electric bass has a pickup and usually almost no acoustic properties, the string vibrations are instantly translated into speaker motion with very little mechanical induction between the strings and body.

The URB body has multiple areas of sound generation and each has different attributes. In order to translate this into a device that approximates these attributes in fretless electric bass, a fairly sophisticated signal processing device is needed.

In the next post, I will list the signal processes needed to implement the URB simulator.

Now that you have a better understanding of the aspects of URB sound generation it is possible to simulate, or approximate them on a fretless electric bass.

First you need a piezo equipped fretless bass. I don't think a $3000 boutique instrument is necessary, most piezo pickups sound similar and we don't need an acoustic body so a slab will do fine. If you have a hi-class instrument, great, I think you will be amazed that even an expensive axe can sound more like a URB. It is my opinion that inexpensive instruments are not at a disadvantage, they can sound very much like a URB too.

One caveat, your ability to think like an Upright bass player is important. If you play in a style not possible on the URB then it will not sound realistic.

Here are the general categories of gear needed.

1. A very capable parametric EQ.
2. A crossover capable of dividing the signal into five zones.
3. Multiple digital delays with short 25 - 8 ms delay.
4. Dynamic processing Compressor/Limiter
5. A simple mixer
6. Optional, a Reverb to simulate acoustic induction of string crosstalk and external sound waves exciting the URB body.

I had one of those Ahah moments when I knew I could do this simulation, I hurriedly put together a rack of the required components as a prototype and to test that it worked. I was very excited when it did work even though I did not have enough crossovers.

Houston, we have a problem. The test rack is six spaces large and is too heavy. Now the hunt is on to find a piece of equipment that incorporates all, or most, of the list above.

An all night internet search led me in the direction of a device known as a Speaker Management Controller as used in large PA systems with multiple speaker arrays that need time compensation, EQ, dynamic processing, crossovers, phase alignment, and more.

Lexicon makes a nice unit but I can't afford their gear so looked for a lower cost alternative, I found the Behringer DCX 2496 Loudspeaker Management System, perfect! This 1U device does everything required, is affordable, and works well. It is made in China but that's another issue.

This unit has six processing sections and six outputs so I needed a mixer to get it all back into mono. This time it was simple, just about any line mixer will do. I'm using a Behringer RX 1602 1U line mixer. It is possible to hard wire the balanced outputs of the DCX 2496 back to mono but resistors need to be added to each leg of the signal or damage may occur. Also, I wanted to fold back some reverb so thus needed a mixer. Since the outputs of the DCX 2496 are balanced XLR I needed to build six XLR to 1/4 TS (unbalanced) cables.

That's all I needed, a speaker management system, a mixer, and a reverb. I'm using an Alesis Quadraverb I had lying around. That's three rack spaces and is a reasonable load considering that I usually play jazz and like to travel light.

It is possible to reduce it to one rack space if the mixer and reverb are eliminated. I have not done this yet but it is an attractive idea providing your sound image does not require reverb.

Now that we know about the speaker management system we need to determine what we want to do with it.

Next post will describe using and programming the DCX 2496.

The next post will involve many parameters and will get quite involved.

Will wait for interest from the Fretless community before creating this lengthy post.

Please leave a reply here if you are interested in the next installment.

Dec 19/2006 - Original Post
Jan 20/2007 - No Interest
Feb 26/2007 - No Interest
Feb 20/2010 - No Interest

It appears that there is little interest in actual parameter data so have decided to not post that here. Please PM me if you need the data.

This is very interesting! I guess that studios would have use for this concept as well. I´ve been playing fretless since the 70:s but has just bought my first bass with a piezo. Now I´m looking for a fretless neck to suit it!

You seems to have made a great job here and even if I really don´t understand it all it´s a great resorce!

/Jocke

I have now reduced the device to a single 1U rack. To implement this I created a 6 into 1 fan-out with a 1K resistor in line for each output channel on the DCX 2496.

Many thanks to John East for his technical advice.

With the addition of a half rack space preamp to add a front end and reverb, the entire thing fits in a 2U effects rack case.

Additional details provided on request.

Thanks for all the informations,man! My fretless is piezo equipped, so I will look gladly at everything that's been written here...
Honestly I don't have all that knowledge, so I just try different settings and go for what sounds good...I found that cutting a bit of middle and high frequencies directly from the bass and adding a little bit of low frequencies on the amp I can obtain a sound that's fairly similar to the classic URB sound (Ray Brown/Ron Carter type), while adding a little bit of treble the sound is more Eddie Gomez (maybe my favorite upright player)...of course I play nearby the neck and I emphasize the vibrato to get that "URB feel".
I know that some players like Jimmy Haslip or John Patitucci used the Roland DEP 5 processor to get more room (check "Politics" or "the Spin" by Yellowjackets), it would be intersting to try it...if I had the cash!

This device involves a nine filter parametric EQ at the input, then separating the signal into 5 frequency zones, then delaying the three lower ones by a small amount (not usually audible to the human ear), some dymanic processing, some additional parametric EQ.

The frequency bands overlap a bit to simulate the nodes on a violin top where it may be more efficient, also the crossovers use various crossover filter types (Butterworth vs, Bessimer etc., at 12dB, 18dB, or even 48dB)

And some other neat stuf to get a fair approximation of a URB.

Full parameter list coming soon, thanks for asking!

If you decide to implement this concept, a Behringer DCX-2496 is needed. I suppose that some other speaker management system would also work if you just happen to have one lying around, but you would have to adapt the parameters.

It's very interesting

I don't own a bass now. If I buy the Tune WB6 it will be helpfull

Thank you very much

Update Feb 2010

I have eliminated the preamp used as a front end (with added reverb) so now driving the URB Simulator directly from the bass. Impedance mismatch is not an issue.

It seems to sound a bit clearer without the added gain stages, the reverb was just muddying it up for live use.

Now it is just a single 1U device, very lightweight and an easy addition to my live rig.

I would like to have a bit of reverb but only on the upper two or three frequency divisions, leaving the bass and mid bass regions un-effected. This would require re-installing a line mixer and reverb so then back up to three rack spaces, a rack case and the weight that goes with it.

I spent more time tweaking parameters by A/B-ing with a recording of Ray Brown solo bass. It is fairly easy using this method zeroing in on the sound of recorded URB to get very close to the tone of whomever it is you wish to emulate.

My jazz buddies are fairly impressed with the sound I'm getting but would still prefer an actual URB not because of any difference in tone, rather the look of the big ol' dog house bass. So it does come down to show biz as far as impressing the natives go when playing a true upright bass. But then one has to deal with the various difficulties of playing URB such as arthritis of the little finger, delicate easily damaged acoustic instrument, size, weight, Cost, COST, COST, feedback, back strain, etc.

something i'm gonna try is getting an acostic bass guitar and playing it with guitarron strings...big nylon's that are kind of gut sounding. not sure if i'm gonna take the frets out but i've wanted an acoustic for some time and found a real player i just can't pass up on. $250 Hohner (the harmonic company not Hofner) 32" scale.

of course the guitarron is a kind of fretless bass used in Mexican music. real great sound.

WOW !!!! Impressive Thanks FretLessSince68 for the post.

Do you have any sound clips (solo, live band or studio track)?
Any preferred flatwound string for the best tone (TI, Pyramids, La Bella)?
Any difference in sound with Lighter vs Heavier gauge string?
How close does it sound if I don't have a piezo pickup on my bass (Ibanez musician fretless)? Can you recommend a good piezo to retrofit my bass?

I will buy one of these if (Behringer DCX-2496) or similar if I can make it work for me.

Do you have any sound clips (solo, live band or studio track)?

Yes, PM me and I will send via email attachment.

Any preferred flatwound string for the best tone (TI, Pyramids, La Bella)?

No, I like standard tension, have only used D'Addario Chromes and LaBella black teflon tape on the Piezo bass. As I mentioned above, the Chromes sound very realistic. Without the URB simulator black tape strings sound more realistic.

Any difference in sound with Lighter vs Heavier gauge string?

Don't know, I prefer standard tension strings.

How close does it sound if I don't have a piezo pickup on my bass (Ibanez musician fretless)?

Does not work with magnetic P/Us.

Can you recommend a good piezo to retrofit my bass?

In my experiece most piezo P/Us sound similar, so no brand preferences. The preamp is more important.

I would not reccomend modifying your favorite bass by adding a piezo bridge.
Better to experiment on a less important axe.

Hey this work you're doing looks really great. I'm a luthier and I'm in the process of building a hollowbody fretless bass and I'm trying to give it the ability to sound very close to an upright. Id line to know in more detail your crossover points and delays. Ideally I would love to include these electronics into the bass itself but that may not be realistic (if you know anybody that can help me design the circuit.). Love to hear some clips too.

PM me and we can discuss it.