I’m working on designing and building a string resonator feedback instrument based on a resonator I built in 2019. It was originally intended as an instrument to add sympathetic string resonance to any instrument in a way similar to those found on a Hardanger fiddle. This works well, but what I find most exciting to do when playing this instrument is to use it as a feedback instrument by sending the output back into the input. This feedback means that the instrument rings loudly when left to its own devices because each string is continually fed back into itself. It is played by muting strings and touching harmonic nodes, creating a subtractive performance technique.
I have been testing the original version of this instrument in conjunction with a modular synth setup and my own breadboarded circuits to help develop the full instrument. This page is a journal of the specific design decisions I am making in small details of the instrument. It will be occasionally updated as I develop and build the instrument.
PHYSICAL DESIGN
Strings
The strings are laid out in a distinctive fan shape. They are electric guitar strings in varying weights. Electric guitar strings are used because they work well with the pickups. There are two main reasons I chose this design:
1. It is conducive to the primary playing technique. By holding my left hand with the base of my palm near the bridge I can mute large groups of strings partially or fully with the base of my palm. At the same time, my fingers are free to mute individual strings, touch harmonic nodes, or pluck strings to help initiate feedback (though plucking is not the primary mode of interaction and is more of an ‘extended technique’ on this instrument). They are on the left because I am left handed and this instrument (so far) is intended mostly for my own use.
2. It allows for different string lengths within the rectangular shape. The middle strings are longest and are therefore better suited to lower pitches (though there is not a standard tuning for this instrument!). This layout is similar to a thumb piano and in some ways feels more intuitive to me than the low-to-high pitch layout of most stringed instruments.
Pickups
The pickups are single-coil electric guitar pickups. They are wound individually on each string because the fan-shape of the strings precludes the use of typical electric guitar pickup layouts. The signal from each pickup is sent through a trimmer pot before being summed and sent into the rest of the signal patch. These trimmers are to help balance the feedback reactivity of each string, which will change depending on string weight and tuning.
Tuning Pegs
These are typical guitar tuners but are places on the underside of the instrument. This is purely for aesthetic reasons.
Transducer + Bridge
Transducers are essentially speakers without a speaker cone. Rather than moving air directly, they transmit motion/vibration (usually audio) into whatever they are placed against. The bridge conducts the transducer’s vibration into all the strings. The bridge has an unusual wide, arc shape at the top in order to be perpendicular to each fanned string. It tapers to a round base at the bottom to create good contact with the transducer. I will be testing bridge shapes using 3D printed models but have not yet decided on a material for the final version. It will most likely be CNCed from a very hard wood, but other options include 3D printed plastic, softer woods, aluminum, and bone.
Body
The body of the instrument is a single piece of wood that will be shaped using a CNC machine. This is same basic technique used on the prototype version. I will be sourcing the wood from Willard Brothers Woodcutters, a local shop that specializes in slabs of hardwood responsibly sourced from storm-damaged trees or other trees otherwise scheduled to be taken down.
Knobs
The knobs control the analog effects circuitry of the feedback path. They are laid out in columns from left to right that follow the signal flow. They are meant to be operated with the right hand to manipulate the behavior of the feedback path.
Touch Plates
It is important to me to have elements of unpredictable, chaotic behavior on this instrument. In my roles as a composer, improvisor, and instrument builder, I always want to be at least somewhat surprised by how my artistic creations behave. This is especially relevant when improvising. I don’t want the instruments I play to disappear; I want them to play back at me, giving me sounds and reactions to respond to rather than simply a blank slate for creation. The touch plates will connect different parts of the circuit to each other in “wrong” ways to create new pathways and behaviors. I was inspired to do this by several instruments including the MakeNoise Strega, but the biggest inspiration was the work of Landscape, whose Stereo Field instrument is built entirely out of “wrong” routings in amplifier circuits, and whose Touch Points allow for touch-based patching of modular synthesizers.
Power
This instrument is powered by a typical 9V power supply. I am also hoping to incorporate a battery to allow for standalone playing but transducers use a lot of power and I will decide if a battery is practical once I have determined the total power draw of the instrument.
Audio In
This instrument is best played with others (though I love playing is solo through a modular synthesizer as well). Audio is sent into the instrument and through the strings and feedback path. This can create a range of behaviors ranging from a subtle addition of sympathetic resonance where my instrument only lightly colours my collaborators’ sound, to behaviours where dramatic feedback on my instrument is shaped in chaotic ways by the influence of their sound.
Effects Send/Return
This instrument is self-contained and includes the effects that I have found most rewarding to work with to transform the feedback path. However, I also want to be able to add other effects or processing to the feedback path such as guitar pedals or modular processing. These can be plugged into the Send/Return jacks to be added to the feedback path.
Audio/Headphone Out
These are the final output of the sound. The instrument makes sound acoustically as well because of the transducer, but transducers are not ideally suited for transferring audio to the air, so better sound quality is achieved by outputting the sound through a ¼” jack to be recorded or played through speakers. I have also included a headphone out for private playing.
CIRCUIT DESIGN
Amplifiers
Amplifiers are present at the start and end of the electronic portion of the feedback path. This instrument depends on a large amount of amplification to set the strings in motion and create feedback. But the signal level must also be adjusted before entering the electronics to ensure that it is at an appropriate level for their operation. The amplifiers are soft clipping to preserve tone and emphasize the lower partials while preventing runaway feedback.
Wavefolder
I am still experimenting with different choices for wavefolding. I am focusing on designs that allow for the emphasis of different odd partials. Odd partials are particularly useful on this instrument because they introduce more new pitches than even partials. The presence of the wavefolder creates timbral possibilities and aids in producing new pitches on the strings by touching harmonic nodes.
Delay
My delay is based on 2 PT2399 delay chips that can be toggled to operate in series or in parallel. Operating in series allows for a longer maximum delay time, while operating in parallel allows for two simultaneous delays of different lengths. These dual delays are useful on this instrument because the delay length has a strong effect on what pitches are emphasized in the feedback loop. Using two delays at once enables more complex pitch material as well as new timbral and rhythmic possibilities. These delay chips are noisy at longer delay times, but for this instrument that noise can help to instigate feedback, especially when played solo.
Tilt Filter
A tilt filter, also known as a DJ-style filter, is a simple tool to alter the balance of high frequency and low frequency sound. Like the trimmers on each string, it can help to balance the feedback of the individual strings, and can be used performatively to change that balance.
Wet/Dry Amount
Each effect includes a knob controlling the wet/dry amount to determine how much of the effect is present in the feedback loop.