Signal path: an Explanation of Moving Air with Mallet Instruments

This article first appeared in Percussive Notes, Vol. 56, No. 2, May 2018.

Jerry Gentry

When playing an acoustic instrument, the sound emerges and bounces off everything the waves encounter. If you apply reinforcement to project the sound into a larger space, you control the acoustic sound, which serves as stage volume, a personal monitor, and provides the signal for amplification. Then you, the sound engineer, or the person running the reinforcement controls the front of house. When you are playing a larger venue, you may be lucky enough to find a front-of-house engineer who has good mikes and an excellent EQ setup, has enough power to project your sound, and knows what a mallet keyboard is, as opposed to, Oh, you play a xylophone. In another scenario you might hear, I can make it fit the mix for the room, but it can't go to your monitor because of feedback.

In a perfect world, the crew loads in and does your sound check while you are having a glacier-cooled beverage in a posh green room, enjoying the adulation of your many fans, waiting for the stage manager to lead you to the stage where you get to show the audience how lucky they are to hear your playing. In a more realistic version, you are transporting an instrument, sound equipment, and everything else needed to make the show happen, and the venue is a third-floor walk-up! While the dream might be to embrace the former, there is far more of the latter. You do have choices:

Whatever choice you make, the signal path remains a constant: from your mallet to the stage to the audience.

Acoustic, Electric, or Electronic

The acoustic choice is a beautiful one, but it does limit the size of the room and audience. If you intend to get to bigger rooms and ultimately larger audiences, you will face the issue of volume. If you choose microphones (and there are a lot of choices, a wide range of prices, and numerous techniques of miking) you will need amplification, so you can rely on the venue to provide it or carry a small P.A. Either way, you'll need to know how much sound coverage to space is required of sound reinforcement and then how much can you afford and carry.

You can choose a full-on electronic keyboard. They are light and filled with possibilities, but they still need amplification to be heard by the audience and a monitor (or headphones) so you can hear the instrument. Another choice is a pickup system. You retain your acoustic instrument (and all its possibilities), but you gain the ability to light it up with your local rock/punk/avant-garde/DJ/computer-driven/graphic-improv unit, or any other creation you can hear in your head. If you play a full-on electronic keyboard, you have a virtual cornucopia of sounds at your fingertips. There is a learning curve, no acoustic sound for reference, and a different playing surface to adapt to, but you are dealing with a straight forward signal-to-amplification path and a world of processing at your fingertips.

In choosing to go with a pickup system, you also have the choice of reproducing the instrument's signal as analog or digital. An analog signal is produced in response to physical changes in producing a sound event; the harder you play, the stronger the signal, the louder the outcome. In the digital realm called MIDI,2 the parameters are more controlled but give you an interface with any collection of digital files, including sampled instruments. MIDI is a standalone subject and encompasses a different type of information technology than is required for just plugging in. So, our discussion will stick with analog.


Regardless of the system being used, you still have the treatment of the sound to deal with, so there is a lot of information to comprehend before you become the headliner -- or your neighbors tell you to turn down. Usually, the output from your keyboard's pick-up system travels via a wire with a connector,3 which is usually a quarter-inch male plug. Conveniently, most effects (stomp boxes) also use this type of connector. This output can go straight to the amp or mixer. This direct line might be perfect for your application or you might start with a pre-amp(lifier), which is a device to boost line-level sources and regulate the signal-to-noise ratio, more accurately reflecting the dynamics of the sound being produced. Luckily, the pickup systems in use now are of a high quality and accurately transmit an authentic sonic portrait of the sound waves. They also include a pre-amp designed for use with the system.

Sending a generated signal from an acoustic, electric, or electronic mallet keyboard to an amplifier with speakers is the first step to being heard. Choosing the sound reinforcement system is the next step. There are many considerations when choosing amplification. Some factors that come into play are wattage, speaker configuration, weight, mobility, cost, and coverage.4 Wattage required for mallet keyboards is flexible due to the wide range of systems available. An all-around starting wattage for clean sound and coverage is 100 watts, with two or more speakers for a medium-size venue or stage. If the rooms are smaller, then adjust the wattage and speaker configuration accordingly. Solid-state systems reproduce an accurate reflection of the sound wave and voice of the instrument. Tube amps are considered to be warmer, with the distinctive sound of the circuitry. Modeling amps give you a variety of classic amplifier sounds to choose from as well as on-board processing.

Speakers are the projection of your voice on the instrument to the audience. If you are playing venues such as intimate jazz places, you can go with lower wattage and fewer speakers. The selection of amplifier and speaker is crucial to reflect the range of timbres generated by the electric vibe, marimba, bells, or chimes. Your sound is coming from the speaker; let it be a good one (or two or three or more). More wattage with multiple speakers means a consistent sound at variable decibel levels and the benefit of moving the necessary amount of air, regardless of venue size.

If you are playing arenas and your sound requires 300 watts with eight 10-inch speakers, the Ampeg Bass Rig is a good benchmark. It features a beautiful sound but does require roadies. A workhorse keyboard amp for normal size clubs is the Roland Jazz Chorus. It has power (120 watts), multiple speakers (two 12s), and wheels. If budget is not a concern you should try the Bose L1 Compact System. It's a unique amplification model utilizing small speakers in a single cylindrical tower, which gives the player great coverage and excellent dynamics. Using multiple-speaker enclosures spreads the sound to any part of the stage and venue depending on where you place them.5 Take the process you use to pick your mallets and instrument and transfer that to selecting what system will project your sound to the audience.6

You've chosen what you need to get you to the next level; hopefully at your disposal is transportation required to carry your instrument, mallet bag, pickup system (with pre-amp, mounting, and repair kit), amplifier, hand truck or dolly, merchandise and table, wardrobe, mailing lists, extra cables, and extensions. The picture is expansive and always expanding, but that's another part of the job description.7

Effects and Signal Routing

Now that you can be heard, regardless of the format utilized, there is the question of sound treatment. This is where you color your amplified acoustic sound color it, just as you do when playing in any acoustic setting. In the amplified setting, you have the additional coloring options provided by processing. If your goal is simply to be heard with your keyboard sound, congratulations -- you are well on the way. Your acoustic technique will translate to an electric landscape. As you explore the parameters of electric playing, your touch will adapt as will your sonic horizon.

At this point, you may decide to treat your sound, intuitively sculpting it. For this you will need effects. The evolution of technology has produced an incredible selection of such treatments available to the artist. All effects take the envelope of the sounds produced and alter the wave forms of the original signal into the desired musical event. My rule of thumb is, think electric, play electric.

The example of signal path presented here is a pickup system installed on a three-octave, graduated-bar vibraphone going through a variety of analog sound processors. It is a blend of effects, arranged and ordered to fit a very specific aural concept that is constantly evolving. If you choose an electric keyboard, the processor or outboard effects will offer these same alterations of sound waves. There is no limit.

The first in-line effect is the wah-wah pedal. The wah is the modulation of tone from bass to treble, treble to bass, or any position within that range. The pedal affects equalization by using the position of the pedal to emphasize the spectrum of bass, midrange, or treble.8 This effect pedal requires physical manipulation, like the pedaling of the vibraphone and with just as many layers. The easiest way to learn technique is to use it on every beat. This will allow you to hear the equalization effect in time to the music. From this framework, you can make the wah a part of your line just as the hi-hat can be utilized in a drum set.

When using multiple effects, there's the question of placement, or order placed in the signal path. There are many opinions on this topic and personal experimentation is recommended. Most experts put distortion first, followed by the wah, followed by phasers, reverbs, delays, and all the rest. Any effect in the signal path begins with the gain stage. Some units are passive, while some have built-in gain (or compression: -10db/-20db). So, you should always be aware of the output line level of the signal. The obvious symptom of too weak a signal is the inability to trigger the effects or sound strong in the reinforcement, but too strong a signal will generate feedback.9 While feedback is generally avoided because it implies out-of-control gain distortion, learning its parameters will give you better control over the aural picture and the chance to control feedback for your own ends. Until you have heard a vibe playing controlled feedback, you have not heard a truly unique sound from the instrument. As you explore the shaping of the sound wave, you will find that each effect has a particular way of manipulating your tone color. As in painting, some effects blend, some clash, and some transform.

Next is the fuzz tone,10 a gain effect: a type of distortion that amplifies the waveform and then clips it to produce an over-driven, compressed semblance of a square wave. It was developed in much the same way as the wah pedal, by a guitarist turning up an amplifier until the sound was distorted. One of the first uses of gain distortion with a vibraphone was by Gary Burton, on his recording Good Vibes (issued by Atlantic Records, 1970) on the track Vibrafinger.

This is followed by an envelope filter, an automatic wah that lets you control the blend, sensitivity, and sweep of the frequencies. The wah pedal is foot-operated and can be used with the damper pedal to create a one-of-a-kind sound. The envelope filter gives a more predictable sweep, and gives you back your balance.

The next effect is vibrato. This is the effect that best simulates the acoustic-vibe sound with a motor-driven baffle system, but it gives you control over more of the signal than an acoustic rotor effect: an acoustic instrument lets you vary the speed and position of the rotors to influence the sound picture; an electric vibrato gives you control over speed, depth, doppler, and phasing -- and that's just the beginning.

So far, the signal has passed through and been shaped by a wah pedal, distortion, envelope filter (automatic wah), and vibrato. These effects all control the sound wave in predictable reflections of the original signal. The ring modulator processes the wave into a hybrid sound. Ring modulation takes an instrument signal as a frequency, couples it with a carrier frequency (controllable through the effect) and transmits the sum and difference of the frequencies as a complex wave output. It can also change the signal output from a sine wave to a square wave. It is a world of sound by itself and works well with a variety of input signals.11

The final treatment in this signal path is a rotary sound processor. This is a reproduction of a Leslie effect.12 It is an adjustable rotating tremolo and chorus, with additional sound mods built in to fully sculpt the sound.

Regardless of your particular signal path, there is now an instrument output cable. It can go to an amplifier with speakers, a P.A. head (multiple inputs), and usually, multiple speakers. It can go to a direct box for the house sound system (and personal amplification for stage volume). It can go to a mixer, providing a monitor feed for the player's headphones, or send the signal to be further modified or redirected to alternate processing, stereo or surround sound, recording, a plug-in of your choice, or all of the above.

You are on the verge of being heard.

On-Stage Considerations

In any musical situation, instrument placement plays a part in overall mix and sound quality of the performance. This doesn't change when utilizing an electric keyboard. The criterion now extends to instrument position (always put your instrument up front!) coupled with speaker direction, height of the enclosure, and stage plot. There is a great deal of scientific and psychoacoustic information available on this subject, and you should certainly do considerable homework. There are some general considerations: elevate (or tilt) the speaker enclosure to approximately audience ear level; do not bury your amp behind anything on stage; use a sight line to configure sound direction; if you can see the back of the room from your speaker, chances are good the audience in the back will be able to hear you. Then you need to be able to hear yourself. A larger stage will require a monitor of some sort. Headphones or earbuds are effective, as is a separate monitor speaker enclosure, which will require a monitor mix. This mix can be your sound, or any combination of the unit you are playing with. You might require bass in the mix or bass drum, some hi-hat, keys, guitar -- whatever you need to hear to get the musical message across. One excellent rule of thumb when playing larger venues with bigger crowds: maintain a balanced stage mix, where everyone can hear everyone else. This makes the reinforcement more efficient and the sound engineer much easier to work with.

Whatever method you choose to generate a signal path, you are on the verge of getting your mallet message across to all the fans that need to hear electric/electronic keyboards and the music being made with them.

Plug it in, turn it up.

Wear hearing protection.

An Example Setup

Sample Photo

My rig includes the following signal path: Musser M-48 vibraphone with K&K pickups and pre-amp going to:

  1. wah wah pedal
  2. fuzz tone
  3. envelope filter
  4. vibrato
  5. Moog ring modulator
  6. rotary sound processor.

This single-signal path is plugged into a Kustom rolled and pleated P.A. head (200 watts) driving two enclosures, each consisting of two 12-inch speakers and a horn.


  1. Kurt Gartner. N. Cameron Britt: Presenting the Emvibe -- An Electromagnetically Actuated Vibraphone. Percussive Notes, Vol. 51, No. 5, September 2013, 62-63.
  2. MIDI (Musical Instrument Digital Interface) is a system that allows electronic instruments to communicate with computers and other related devices. It translates striking velocity, pitch, note length, and other information from the instrument into ones and zeroes, the language of computers.
  3. The need for a wireless setup for the mallet instruments has yet to be felt, but as you embark on the wiring diagram for specific stage settings you might like one less wire to trip over.
  4. There is a vast amount of information related to electronic sound production and reproduction. Guitar magazines, string and keyboard catalogs, music stores, and word of mouth will reveal all the options and selections.
  5. Multiple enclosures allow the instrumentalist to pinpoint coverage and allows the use of stereo, quad, or surround-sound capabilities.
  6. The best procedure is to try every system you come across. Take your vibraphone to a sympathetic music store and try every amp and pedal in there. After exhaustive research and many sound checks, the cabinet that functions best overall for an amplified three-octave vibe is an enclosed four-speaker bass cabinet (in the author's opinion).
  7. Moving equipment safely and efficiently is of prime importance. Using hard cases and road cases with packing is highly recommended. Reducing set-up time becomes a priority when you are on the road.
  8. Chet Atkins first used the electronic wah effect in 1958 on his recording of Boo Boo Stick Beat. Jimi Hendrix started using the effect in 1967. Listen to any of Hendrix's work, particularly Voodoo Child (Slight Return), All Along the Watchtower, or his version of The Star-Spangled Banner. Listen to Eric Clapton with Cream: White Room and Tales of Brave Ulysses. The wah-wah can be percussive, rhythmic, lyrical, and everything in between. It is now heard in a myriad of contexts in contemporary and popular music. Dave Rubin, The Wah Wah Pedal, Guitar Archives, Guitar One (October 1998): 131.
  9. Feedback is a reaction of an amplified signal being picked up by the reinforcement and within a closed loop, beginning to amplify itself -- resulting in a powerful noise event. As reference, watch Jimi Hendrix or Stevie Ray Vaughan effectively use their instruments and amplifiers to create new sonic possibilities.
  10. This particular fuzz is an Ibanez Tube Screamer TS9. The Ibanez TS808 was introduced in the late '70s and was followed by the TS9 produced from 1982 to 1985. The effect pictured is from 1982. This fuzz provided a benchmark for all gain-distortion units and has been reissued. As reference, the Tube Screamer was the only effect used by Stevie Ray Vaughn on his album Texas Flood, issued by Epic Records in 1983. Click here to read the author's review (with video) of the TS9.
  11. See for an example of square-wave output.
  12. The Leslie speaker enclosure was developed to provide an authentic organ sound for electric organs. The system utilizes rotating speakers to create a 360-degree sound projection. There is a treble and bass speaker that can rotate at various speeds by way of a foot pedal. The actual Leslie cabinet is worth hearing; its sound is unique. Technology has converted this type of envelope shaping into a more compact version.

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