Trumpet Augmentation and - IA de Investigación especializada en el MIT

Trumpet Augmentation and
Technological Symbiosis

Joseph Thibodeau and
Marcelo M. Wanderley
Input Devices and Music Interaction
Laboratory (IDMIL)
Centre for Interdisciplinary Research in
Music Media and Technology (CIRMMT)
Schulich School of Music, Universidad McGill
555 Sherbrooke Street West
Montréal, Quebec, H3A 1E3, Canada
joseph.thibodeau@gmail.com
marcelo.wanderley@mcgill.ca

Abstracto: This article discusses the augmentation of acoustic musical instruments, with a focus on trumpet
augmentation. Augmented instruments are acoustic instruments onto which sensors have been mounted in order
to provide extra sonic control variables. Trumpets make ideal candidates for augmentation because they have spare
physical space on which to mount electronics and spare performer “bandwidth” with which to interact with the
augmentations.

In this article, underlying concepts of augmented instrument design are discussed along with a review and discussion

of twelve existing augmented trumpets and five projects related to mouthpiece augmentation. Common aspects to
many of these examples are identified, such as the prevalence of idiosyncratic designs, the use of buttons placed at or
near the left-hand playing position, and the focus on measuring or mimicking trumpet valves. Three existing approaches
to valve sensing are compared, and a novel method for sensing valve position, based on linear variable differential
transformadores, is introduced. Based on the review and comparison, we created an example augmented trumpet that tests
the feasibility of a modular design paradigm.

The results of this review of the state-of-the-art and our own research suggests future directions towards a better

understanding of augmented trumpet design.

Introducción

There are musicians and instrument-builders in the
world who are not satisfied with the limitations
of acoustic instruments, bound as they are by
their physical characteristics. The existence of
augmented instruments as a field of study states
this point quite clearly. Augmenting an acoustic
instrument through the attachment of electronics
expands its identity as a controller and producer
of sound without discarding the years of practice
that a performer may already have invested in
his or her instrument. Augmented instruments
son, por lo tanto, a fascinating intersection between
traditional technique and modern technology.

Many different types of acoustic instruments

have been augmented, each posing different
challenges in design and construction. Trumpets
are particularly good candidates for augmentation
owing, in large part, to the player’s “spare
bandwidth” (Cocinar 2001)—that is to say, the parts

Computer Music Journal, 37:3, páginas. 12–25, Caer 2013
doi:10.1162/COMJ a 00185
C(cid:2) 2013 Instituto de Tecnología de Massachusetts.

of the body that are unoccupied by performing
the instrument. The left hand does not critically
affect performance and can be used to interact with
sensors instead of just supporting the weight of
the instrument. Además, there are no linkages
or other delicate mechanisms to consider when
attaching augmentations to a trumpet.

Although augmented trumpet designs have indeed

expanded the scope of sound control available
en desempeño, they have historically had the
drawback of being focused on the needs of one
particular performer and therefore have not been
widely publicized, much less standardized. Este
has led to the current state of the art, in which we
appreciate the expressive potential of augmentation
(why to augment) and we have only just begun
to systematically address the practical details
of augmentation (how to augment). If the task of
designing and constructing augmented trumpets was
easier, and if common types of augmentations were
better understood, it would eventually accelerate
development of the art and the technology.

Before going any further, we must be clear
about our terminology. The term augmented in
this article is defined as “the addition of several

Computer Music Journal

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sensors, providing performers the ability to control
extra sound or musical parameters” (Miranda and
Wanderley 2006, pag. 21). In his Master’s thesis,
Andrew McNaughton (2011, pag. 7) elaborates on this
definition:

of our own design that tests the feasibility of a
modular design approach with on-board synthesis.
Finalmente, we present conclusions and directions for
future work.

Other terms used in the description or even
title of such instruments are extended, hy-
brid, hyper, meta, electro-acoustic, cyber and
even virtual. Bowers and Archer (2005) conversar
this nomenclature and the etymology of hyper
and meta, and propose their own reactionary
infra-instruments. Despite the various names
given, they notice among these augmented
instruments a number of “recurring themes,
[como] rich interactive capability . . . detailed
performance measurement . . . engendering of
complex music . . . and expressivity and virtuos-
ity” (Bowers and Archer 2005, pag. 6). While there
are differences in these terms and the instru-
ments to which they relate, these differences
are outweighed by the similarity of intention.
These instruments are significantly different,
sin embargo, from alternate, alternativa, or “gestu-
ral controllers” (Miranda and Wanderley 2006,
pag. 19) like the EVI, which might or might not be
modelled on existing acoustic instruments, pero
either way do not produce their own sound.

We further define an augmented instrument
as an interface comprising sensors that capture
gestures for controlling digital effects and synthesis.
A sensor is “a device that receives a stimulus and
responds with an electrical signal” (Fraden 2004,
pag. 2). The term gesture is generally defined in
this article as “any human action used to generate
sounds” (Miranda and Wanderley 2006, pag. 5). Más
discussion of gestural definitions and theory is
beyond the scope of this article.

In the rest of this article we will review and
discuss several augmented trumpets and the tech-
nologies used in their design. We begin with a
review of existing augmented trumpets and discuss
augmented instrument design concepts. Esto es
followed by a comparison of three existing valve-
position sensing technologies and an introduction
of another sensor for this task, the linear variable
differential transformer. We then detail an example

Review of Previous Developments

We know of twelve augmented trumpets that have
been constructed over the years, as illustrated in
Cifra 1 (not counting our own design, descrito
más tarde). Many examples are documented in the
literature, and several were found online. In those
cases where previously published documentation
left open questions, we contacted the original
designer for additional details. Each implements a
different set of augmentations, although there are
notable commonalities.

We will look at these trumpets mainly in terms
of the hardware elements used for gestural sensing,
comentario, and signal processing while discussing
related augmented instrument design concepts.

Gestures and Sensing

Augmenting an acoustic instrument places some
limitations on the designer’s palette of feasible
gestures because of the performance gestures and
existing mechanical interface which have been
developed over centuries of acoustic practice. El
traditional interactions between the performer
and the trumpet are relatively straightforward.
Por ejemplo, a trumpet player will press on the
mouthpiece of the trumpet with the lips and will
press on the valves of the trumpet with the fingers of
the right hand. Perhaps less obviously, a performer
will tend to consistently move and sway his or
her body and the instrument during performance
(Wanderley et al. 2005). A fundamental question
when augmenting an instrument is whether it
should be playable in the existing way: To what
degree, if any, will augmentation modify traditional
técnicas? The goal, according to our definition of
“augmented,” is to expand the gestural palette. Will
this expansion come at a cost?

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Cifra 1. Illustrated
comparison of existing
augmented trumpets.
Trumpets marked “*”
are included based on
information found

online and/or provided by
the designers, y son
labeled with their name
and the year of invention
(rather than a reference
citation).

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For the most part, the existing works expand
the gestural palette while preserving traditional
trumpet technique. Hand-operated controls (semejante
as potentiometers, buttons, and switches), familiar
from many electronic instruments, are used in
nearly every example and are clustered around the
hand positions. This maintains the original hand
positions as much as possible, while providing fast
access to additional controls. Several examples do
augment the existing mechanical interface ele-
mentos, sin embargo, particularly the valves, and several
mimic the traditional interactions on equivalent
electronic interface elements.

An acoustic trumpet’s fundamental physical con-
nection to the player is between the player’s lips and
the mouthpiece. There have been several notable
mouthpiece augmentations. Most of these sense
the force applied by a trumpet player to the mouth-
piece. Using strain gauges, Barbenel, Kenny, y
Davies (1988) introduced a two-dimensional force
transducer. Mayer and Bertsch (2005) extended this
idea into three dimensions. More recently, Bianco
et al. (2012) also used a strain gauge to measure
one-dimensional force, whereas Demoucron and
Leman used a load cell for the same task (personal
communications with the authors). A project by

Computer Music Journal

Cifra 2. Illustrated
comparison of mouthpiece
augmentations for
trumpet-related research.
These all measure force
applied to the mouthpiece,
with the exception of

Freour and Scavone (2012),
which measures lip
oscillation. The example
marked * is included
based on information
provided by the
designer.

Freour and Scavone (2012) used two electrodes to
measure lip oscillations against a plastic mouth-
piece, albeit for trombone. These works focused
on measurements for acoustic and performance
investigación. To our knowledge, no augmented trumpet
has yet exploited lip pressure or oscillation for mu-
sical creation. The Electrumpet, sin embargo, includes
an augmented mouthpiece alongside the acoustic
mouthpiece, measuring breath pressure by means of
a relative air pressure sensor (León 2009). Estos
designs are illustrated in Figure 2.

The concept of valve augmentation was central to
several designs seen here, either through direct mea-
surement or valve-mimicking electronic controls.
Axel D ¨orner (Kartadinata 2004) used hybrid (rotat-
ing and sliding) potentiometers—mounted alongside
the acoustic valves—to capture his idiosyncratic
acoustic technique of unscrewing the valve caps
during performance. Ben Neill (2013) included a
second set of acoustic valves to control airflow to
the three acoustic bells on the Mutantrumpet. Hans
Leeuw used slide potentiometers as “electronic
valves” mounted alongside their acoustic coun-
terparts. In a similar vein, Andrew McNaughton
(2011) used three force-sensing resistors (FSRs) como
“valve sensors” mounted alongside the acoustic
valves. Three implementations included direct mea-
surements of the acoustic valve positions. Cocinar,
Morrill, and Smith (1992) used two optical switches
per valve to detect four valve positions. Craig and

Factor (2008) used a continuous optical sensor for
each valve as a threshold detector, giving binary
(up or down) positional information. Impett and
Bongers glued shielded magnets to the bottom of
the valve pistons—an intrusive but acoustically
neutral augmentation—and continuously measured
the resulting magnetic fields with Hall effect sensors
underneath the valves (Impett 1994).

Augmenting the existing mechanical interface el-
ements includes the potential to overload traditional
técnicas (analogous to the programming concept
of function overloading). The additional layer of
musical control gained through overloading can, en
doblar, modify the way that the instrument may be
played acoustically. Hay, por supuesto, various de-
grees to which one may overload a technique. Alguno
forms of technique overloading may only have negli-
gible impact on acoustic playability, whereas others
may entirely repurpose a given technique towards
augmented musical control. It is a design choice to
be understood and balanced with the musical aims
of the instrument and the desired gestural palette.
To illustrate the idea of overloading a gesture, estafa-
sider Todd Machover’s Hypercello (Machover 1992).
In one mode of operation, the bow is divided into
secciones, each controlling the playback of a different
recorded sound. The normal bowing technique is
changed by this additional responsibility and the
cello cannot be indiscriminately used as though it
were purely acoustic.

All of the trumpets that involve valve measure-

ment may include some degree of overloading,
depending on how the valve measurements are
aplicado. The Craig-Factor trumpet (Craig and Factor
2008) and Morrill-Cook trumpet (Morrill and Cook
1989) both use trumpet valve measurements purely
for informing a pitch estimation algorithm—there
is no effect on existing techniques.

There is at least one example of overloading a
trumpet performance technique that expands sound
control capabilities without significant disturbance
of acoustic playability, and that is to simply measure
the force applied to a valve near the end of its range
of motion, illustrated in Figure 3. The Sensor Horn
(McNaughton 2011) uses FSRs beside the trumpet
valves as controls unrelated to the acoustic valves
(except that they are manipulated in a similar

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Cifra 3. The force f p
applied to the valve by the
player is roughly equal to a
combination of the force of
the valve return spring fs
and the resistance of the

felt padding f f until the
limit of the valve’s range of
movimiento, at which point the
player may apply any
amount of force without
acoustic consequence.

Therefore any force greater
than that needed to
effectively close the valve
may be used as an
“after-touch” parameter.

Mesa 1. Trumpet Fingering Chart

Nota
F(cid:2)3
G3
A(cid:3)3
A3
B(cid:3)3
B3
C4
C(cid:2)4
D4
mi(cid:3)4
E4
F4
F(cid:2)4
G4
A(cid:3)4
A4
B(cid:3)4
B4
C5
C(cid:2)5
D5
mi(cid:3)5
E5
F5
F(cid:2)5
G5
A(cid:3)5
A5
B(cid:3)5
B5
C6

000

010

100

110

011

101

001

111
•

•

◦

•

◦

•

◦

•

◦

•

◦

•

◦

•

◦

•

◦

•

◦

•

◦

The column heading above a fingering shows the state of the
three valves, with the binary number 000 indicating all valves
open and 111 indicating all valves closed. The standard or most
common fingering for a note is indicated by the • character;
◦ indicates alternate fingerings. Adapted with permission from
Spang (1999).

can use four different fingering positions (000,
110, 111, 001) of which one is the primary (000)
and the other three being alternates. Alternate
fingerings are not used in every register, but of
particular interest is the fact that the third valve
is never used on its own during normal trumpet
actuación. Admittedly, the traditional use of
alternative fingerings—including the solitary third

manner). If the FSRs were mounted at the valve
finger pads, pressure applied to the valve during
valve manipulation could be used as an overloaded
control. In such a way one could augment the
trumpet with a sort of after-touch capability. Este
highlights the importance of identifying which
performance gestures (or parts thereof) have an
acoustic consequence.

The use of nonstandard performance gestures
can also be exploited for augmentation and is,
de este modo, a form of technique overloading. These are
performance gestures that are acoustically usable
on the original instrument but are not normally
usado, for whatever reason (economy of motion,
imperfection of tone, strength of tradition, etc.). On
a trumpet there are several examples.

A trumpet can be de-tuned while playing to
bend notes in a trombone-like manner. The Mehta
Gluiph trumpet (Kartadinata 2003) incorporates a
trombone-like slide and associated sensor in order to
exaggerate and capture this nonstandard technique.
As previously mentioned, Kartadinata (2004) usos
the nonstandard technique of unscrewing the valves
during performance. This could be measured for use
in sound control, perhaps with an optical sensor.
Además, removal of the valves after unscrewing
them would be measurable with a valve-position
sensor like those we have already seen.

Any trumpet with valve-position sensing can
take advantage of nonstandard fingerings. Mesa 1
shows the notes produced by depressing different
combinations of the valves. Por ejemplo, to play
an E5 (concert D5, given the most commonly used
tuning of trumpets in B-flat), the trumpet player

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Cifra 4. Usando
nonstandard technique
(shown in gray) to allow
unobtrusive interaction
with augmentations
attached to the bell pipe.

valve—isn’t unheard of, but for the purposes of
augmentation it can be exploited with minimal
obtrusion upon the playability of the instrument.

Trumpeters can press down the valves with the
insides of their knuckles instead of the fingertips,
as shown in Figure 4. This frees up the fingertips
to interact simultaneously with augmentations
such as switches or distance sensors mounted on
the bell pipe of the trumpet. The Meta-Trumpet
(Impett 1994) could be used this way. It has buttons
mounted on the bell pipe alongside the valves,
although the buttons are not explicitly intended for
this technique. Similarmente, the Mutantrumpet (Neill
2013) includes two joysticks just left of the rear set
of valves that could be manipulated in this manner.
The Sensor Horn’s valve-adjacent FSRs could serve
this purpose if one were to play the valves with the
left hand instead of the right (McNaughton 2011).

Besides existing and nonstandard gestures there
son, por supuesto, those gestures that are normally not
intended to produce sound—what Wanderley et al.
2005 refer to as “ancillary gestures”—or indeed
ones that are designed “from scratch.” Among the
augmented trumpets seen here, there are some
examples that exploit the position and kinematics
of the instrument and player by measuring distance,
velocity, aceleración, and rotation. The Meta-
Trumpet (Impett 1994) uses ultrasonic distance
sensors, accelerometers, and tilt switches to measure
posición, movimiento, and rotation, respectivamente, en el
tip of the trumpet bell. The Amphibious Destroyer
Trumpet (Tomayko-Peters 2006) and Hithering
Thithering Djinn (Bithell 2009) both incorporate an
accelerometer mounted near the valves. The Sensor
Horn (McNaughton 2011) uses an accelerometer
clipped to the bell (it could presumably be clipped
to other parts of the instrument instead, or even

to the player’s right hand). The Mehta Gluiph
Trumpet (Kartadinata 2003) has a gyroscope beside
the bell to measure the instrument’s rotational
movimiento.

Feedback

Feedback is the visual, auditory, or tactile-
kinesthetic mechanism by which a performer
senses the state of his or her instrument (Miranda
and Wanderley 2006, pag. 11). An acoustic instrument
inherently provides performance feedback to the
player in the form of vibrations and perceivable
instrument state. An electronic instrument, y
for that matter electronic augmentations, needn’t
have any feedback mode at all except the sound
produced (Tanaka 2000). También, visual feedback can
help the audience understand the instrument in
actuación, as exemplified in Gabriel Vigliensoni’s
SoundCatcher (Vigliensoni and Wanderley 2010).
Among existing augmented trumpets there are
three that use a feedback mechanism. The Mehta
Gluiph Trumpet (Kartadinata 2003) uses a small
LCD display mounted on the top of the bell, como
does the Electrumpet (León 2009). Hans Leeuw
has since switched to an iPhone for visual feedback,
which is the same mechanism used in the Hithering
Thithering Djinn (Bithell 2009), except that Bithell’s
iPhone is mounted on the left side of the valves to
double as a touchscreen interface for sound control.

Signal Processing and Sound Generation

The sensor signals in an augmented trumpet must
be processed before they are usable for controlling
sound generation. All the augmented trumpets we
have found incorporate hardware that collects and
conditions sensor data. There are a variety of hard-
ware platforms among these augmented trumpets,
from general-purpose microcontrollers such as the
Arduino used in the Electrumpet, field-progammable
gate arrays (FPGAs) such as the Gluion used in the
Do¨rner Gluion Trumpet, and repurpopsed USB
gamepads used in the Amphibious Destroyer Trum-
pet and the RobotCowboy Augmented Trumpet
(Wilcox 2008). In terms of function there are few

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Cifra 5. Three trumpets
we made. Top: An early
test project with force
sensors on the valve caps.
Middle: A valve sensor
comparison trumpet

mounted in a wooden
support structure. Bottom:
Our modular proof-of-
concept prototype, called
Symbiote. In the ﬁrst and
last examples we used a

Yamaha “Silent Brass”
combined mute and
pickup (not shown) a
capture the instrument’s
sound.

diferencias. Every example discussed here acts
as a sensor interface with sound generation and
mapping outsourced to a PC or MIDI synthesizer.
In most cases the communication with offboard
hardware involves cabling the augmented trumpet
sensor interface to the sound generator. Wireless
communications and battery power, as used with
the Electrumpet (León 2009), can help mitigate
problems due to cabling but can also introduce
problems of their own (Cocinar 2001).

Comparison of Valve Sensors

For a given gesture, there will be many possible
sensing solutions, each with distinct advantages
and disadvantages. Consider the desired level of
detail in the measurement and the properties of
the outgoing signal. Is it important to continually
or completely measure a gesture? Are discrete
steps or partial measures sufficient? Después de todo,
with clever conditioning and analysis a simple
type of measurement can adequately represent a
complicated gesture. There is a wealth of published
information about the quantitative performance and
general use of different types of sensors in print (p.ej.,
Bongers 2000; Nyce 2004; wilson 2005; Miranda
and Wanderley 2006) and online (p.ej., “Sensorwiki”;
Wanderley et al. 2006) allowing instrument designers
to more easily choose those that best fit their needs.
In the case of valve-position sensing, augmented
trumpets have taken, hasta la fecha, different approaches
to the level of detail. Por ejemplo, the Craig-Factor
trumpet produces a binary threshold as output
(Craig and Factor 2008), whereas the Morrill-Cook
trumpet produces four positions (Cook et al. 1992).
Other augmented trumpets (Bongers 2000; León
2009) provide continuous valve measurements.

Cifra 6. We made a signal conditioning board for
the LVDTs based on a design by Jean-Loup Florens
for the ERGOS force-feedback device (ACROE 2013).
Threaded rods were used to actuate the valves. El
output signals of the set-up were sampled at 10 kHz
by a National Instruments PCI-4472 capture card
in a nearby desktop computer. The experimental
trials focused on one valve (first valve—i.e., closest
to the mouthpiece) with four sensors and a second
valve (middle valve) with one sensor hooked up as a
“marker,” and progressed according to the following
procedimiento:

We compared three of the valve-position sensors

1. Lower the actuation rod until it just touches

seen in previous examples: slide potentiometer,
hall effect, and visible-red (as opposed to infrared)
LED, to a fourth position sensor: the linear variable
differential transformer (LVDT), to determine their
suitability for different types of augmented trumpet
projects (Thibodeau 2011).

The wooden support structure shown in Figure 5

held a trumpet and sensor chassis illustrated in

the valve cap.

2. Start the data acquisition.
3. Position a digital caliper for measurement
and zero its position to the valve position.
4. “Mark” the data point by pushing down the
middle valve, then wait a moment to let the
sensor signals stabilize (in case they were
jarred by the movement of the valve).

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Cifra 6. Valve-sensing
conﬁguration. First valve
is shown in cross-section
at right.

Cifra 7. Results of an
experiment comparing
different methods of
tracking valve position.
Notice the linearity of the
potentiometer and linear
variable differential
transformador (LVDT).

Cifra 6

Cifra 7

5. Lower the actuation rod until the caliper

reads a displacement of 1 mm.

6. Repeat Steps 4 y 5 to generate all of the

data points across the range of motion of the
valve.

The quantitative results shown in Figure 7 espectáculo
the advantage of the LVDT in terms of linearity and
sensitivity.

En efecto, the LVDT is well known to have very

linear, accurate, and repeatable characteristics
(Nyce 2004), making it well suited for trumpet
augmentation experiments requiring exact and

reliable measurements (such as laboratory gesture
analiza). The complexity of signal conditioning
and the obtrusiveness of attaching the LVDT to the
trumpet make it less than ideal for general use as
a musical controller. The attachment mechanism
En figura 6 is heavy and bulky owing to the need
to securely mount the LVDTs parallel to the valves
on the far side of the bell pipe. It could be lightened
by using a different material, but the bulk would
remain an obstacle.

LED reflectance and Hall effect sensors, respetar-

activamente, based on those used by Craig and Factor
(2008) and Impett (1994) occupy the other end of
the spectrum. As seen in Figure 7, the full-scale
response curves of the these sensors are far from
linear, although there is an almost linear segment
in the response of the LED sensor. This nonlinearity
is made up for by low weight, noncontact sensing,
and ease of installation. These types of sensors are
therefore well suited to performance environments
where an exact linear measurement is not necessary
for the practical control of musical parameters.

Note that the sensors involved in this experiment
were approximations of their equivalents in the lit-
erature, not necessarily identical hardware. Our ex-
periment compares technologies for valve-position
sensing rather than comparing the efficacy of specific
augmented trumpet designs against each other.

Symbiote

Electronic augmentations and the instrument to
which they are attached form a kind of technological

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Cifra 8. Arquitectura
underlying the Symbiote
design platform.

symbiosis. De este modo, the inspiration for our own work
in trumpet augmentation was the concept of a self-
contained technological organism that lives, grows,
and mutates as it expands the capabilities of its host
and builds an aggregate identity: a Symbiote.

Based on the existing augmented trumpets,
we built a proof-of-concept prototype to look at
practical results stemming from our notions of
standardization by modular design and on-board
synthesis.

With the exception of the Trumpet MIDI Con-
troller (Craig and Factor 2008), which was designed
for trumpet players in general, existing augmented
trumpets have been custom-designed for a par-
ticular performer or composition—tailored to an
idiosyncratic performance style. A significant de-
gree of technical skill is necessary to develop and
maintain these instruments, limiting widespread
access to (and experimentation with) augmentation
tecnología.

This is not to say that customized implementa-
tions are undesirable. On the contrary, an augmented
trumpet intended for performance by a specific artist
should conform to that artist’s idiosyncratic needs.
The general needs common to all augmented trum-
pets (sensor interface[s], signal routing, parameter
mapping, and sound synthesis), sin embargo, could be
provided by a common design platform.

By standardizing the common elements of an aug-
mented trumpet, development efforts could be dedi-
cated to optimizing the instrument to match the per-
anterior. Además, a modular augmented trumpet
design platform would allow different designers to
easily share and implement each other’s ideas.
dicho eso, there are obvious advantages to
application-specific implementations. Sobre todo,
they use only the resources needed for the intended
purpose (low overhead), allowing them to be op-
timized to their specific task (high performance).
Por otro lado, the inevitable need for mainte-
nance and possible reconfiguration require the same
technical expertise as needed for the initial con-
estructura, which can be viewed as a disadvantage.
A modular system would ensure that parts could
be replaced, if needed, and even reused, staving
off obsolescence and minimizing electronic waste.
Expanding in scope, a carefully designed modular

system could make augmented trumpets accessible
to performers who lack the technical expertise and
resources to build an instrument from scratch. El
fruits of a designer’s labor would be available to
a larger population who could in turn apply and
expand upon augmentation ideas through musical
and technological dialogue.

Conceptual Design

There are already many platforms on which to
design musical controllers, such as the Gluion
(Kartadinata 2006) and the now ubiquitous Arduino
board. These are intended to acquire sensor data
for mostly PC-based processing. Their acquisition
infrastructure is limited by their number of analog
inputs and outputs, and their architecture is not
predisposed to on-the-fly hardware reconfiguration.
In the case of the Gluion, the hardware is FPGA-
based and therefore able to accommodate virtually
any number of inputs/outputs but it is programmed
with one specific configuration around which the
rest of the instrument must be built. The Arduino
has a limited number of analog inputs (the exact
number depends on the model) and lacks built-in
analog output. Por otro lado, it provides an
intuitive programming interface and is easy to set up.
The Symbiote aims to combine the advantages
of the Gluion and Arduino platforms. Idealmente, él
represents a flexible and accessible system in terms
of both hardware and software, and it has the power
to perform sound synthesis on-board. Its design is
based on modularity and distributed processing. A
central module, the hub, connects to any number
of peripheral node modules using a standardized
communication infrastructure (ver figura 8).

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Cifra 9. Symbiote
implementation and inset
illustrated functionality.
The hub is attached to the
bell pipe, and the pitch
estimator node is attached

to the lead pipe (neither
shown in inset). Fader and
valve measurement nodes
are attached to the valve
assembly.

Cifra 10. Symbiote
implementación. See text
for explanation.

Cifra 9

The hub is the “brains” of the Symbiote. Él
performs mapping and digital sound synthesis in
addition to managing the nodes—providing bus
addresses and subsequently pulling and pushing
data as needed. It also performs analog conversion
on necessarily high-speed inputs (such as audio
inputs). An important function of the hub is direct
communication with a PC for programming. El
hardware used for the hub, whether an FPGA or
microcontroller, must have significant processing
power to perform digital sound synthesis.

A node can interface with sensors and displays,

Cifra 10

condition data, detect salient events, or perform
specialized computing functions. It acts as an
extension to the capabilities of the hub, but can
be removed without disasterous consequences. A
node only needs to be as powerful as is necessary
for its task, and it uses a standardized physical
connection to the hub for communications and
fuerza.

Bus networks are ideal for connecting an un-
known or changing number of nodes. El COM-
munication lines are shared and therefore the
number of connected nodes has a minimal impact
on the hardware requirements. The disadvan-
tage to a bus is that its throughput is limited
by the number of nodes. The previously men-
tioned high-speed inputs on the hub handle signals
that need to circumvent the limitations of the
bus.

Implementation

We implemented the fundamental elements of
the conceptual design (Hollinger, Thibodeau, y
Wanderley 2010), como se muestra en la figura 9. The goal
was to test the idea that two standardized design
elements—the bus communication protocol and the
distributed processing architecture—could form a
useful foundation for modular augmentation. Allá
are four modules, a hub and three nodes, that are
arranged as shown in Figure 10. Ribbon cables
connect all of the circuit boards to power and bus
signals. It is similar to the design used by Craig and
Factor (2008) with embedded synthesis instead of
MIDI output.

An inter-integrated circuit (I2C) bus was the most

attractive option for the communication system.

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Cifra 11. The three nodes:
a pitch estimator based on
the Programmable
System-on-Chip (PSoC), a
PSoC-based four-fader
interface, and an
Arduino-based interface to
the valve-position sensors.

It needs only two wires (cutting down on physical
bulk), it is simple to control, and it is implemented
as a custom hardware block on many different
embedded devices. It is not the fastest type of
low-level bus communication but it is capable of
serial communication speeds of up to 400 kbit/sec,
which is fast enough for the control rates used in
popular audio programming languages such as Pure
Datos. The nodes can be successfully connected to
the hub at run time without needing previously
defined I2C addresses so that the hub “knows” at
any given moment which nodes are connected and
what each of them can do. This information is vital
for mapping and synthesis.

The hub is an ARM development board. Uno de
the hub’s ADCs reads the microphone signal from
the trumpet, from which it derives an amplitude
envelope. On the software side, the hub manages I2C
communications and generates three pulse waves
controlled in part by the outputs of the three nodes.
The lower computing demands on the nodes
allowed us to choose less powerful devices in their
implementations. Two of them are based on Cypress
Semiconductor’s Programmable System-on-Chip
(PSoC), which have programmable analog and
digital hardware blocks, thereby cutting down on
peripheral circuitry and making them behave like a

hybrid between a microcontroller and an FPGA. El
Symbiote implementation shown in Figure 10 usos
two PSoC-based nodes (one pitch tracker and one
four-slider interface) and one Arduino-based node
(valve sensing), detailed in Figure 11. Details of the
signal processing are shown in Figure 12.

In operation, our prototype fulfilled its purpose,
demonstrating the feasibility of a modular design
platform with built-in synthesis. During the devel-
opment process it was easy to isolate problems in
the system, as the modularity made it very clear
where a given problem originated, and any or all of
the modules could be easily disconnected from the
sistema (even while running) without catastrophic
resultados. The project took longer than it would have
if we had developed it as a fixed architecture, similar
to the existing augmented trumpets. Sin embargo,
the overhead of designing and implementing a mod-
ular architecture was a long-term investment. Una vez
we had finished implementing the hub and one of
the nodes, the other two nodes took very little time
to complete because so many design elements were
standardized across the system. The system has
survived countless disassemblies and reassemblies,
and to date it has never failed to operate in a live
demonstration, which is as simple as powering it on
and plugging the output into an amplifier.

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Cifra 12. Symbiote signal
Procesando.

Conclusions and Future Work

There are numerous challenges in designing aug-
mented trumpets and many questions about the
effects of augmentation on the performer and their
música.

It is clear from our review of existing projects
that there are commonalities in the design and
construction of augmented trumpets, Por ejemplo,
valve-position sensing, which we investigated
by comparing four different sensing technologies
including the LVDT.

Documenting the existing commonalities and
commonalities that may emerge in future designs
is essential to make the task of creating augmented
instruments faster and easier.

Our experience developing Symbiote seems to
indicate that a modular design platform would be
ideal for projects that justify the initial overhead:
long-term augmented trumpet projects with easily
modifiable, expandable, and interchangeable parts.
There are necessary improvements to the Sym-
biote for it to grow from a proof-of-concept prototype
to a performance-quality instrument. The hub’s pro-
cessing power must be upgraded to support more
complex synthesis techniques. We are currently
working on a version that integrates a Raspberry
Pi development board running Pure Data as a
more general on-board synthesis solution. A larger
“palette” of nodes would allow for the kind of
widespread modular experimentation that we envi-
sión. Integrating the on-board mapping and synthesis

system with the Digital Orchestra Tools LibMapper
(Malloch, Sinclair, and Wanderley 2009) via Open
Sound Control would streamline the process of
configuring the instrument. Finalmente, it would be
extremely beneficial to foster an online community
of trumpet augmenters, whether or not they adopt
the Symbiote paradigm.

Trumpets, after hundreds of years of acous-
tic development, are growing beyond the limits
of acoustic behavior. Actualmente, an augmented
trumpet is an acoustic trumpet with symbiotic
electronics attached to it. It has been modified
after the fact. There may come a time when an
augmented trumpet is a refined instrument whose
acoustic and electronic elements are manufactured
together—and the term “augmented” may become
irrelevante. The designers and performers of today’s
augmented trumpets are only just beginning to
explore the potential of this instrument. Each one
is an experiment and each experiment contributes
to our understanding of how our technology shapes,
reflects, and manifests artistic expression.

Expresiones de gratitud

We owe many thanks to Avrum Hollinger for his
help in designing and programming Symbiote, a
Antoine Lefebvre for building the sensor chassis,
to Jean-Loup Florens from ACROE for designing
the LVDT signal conditioning board, and to Francis
Paris for his experiments in embedded DSP. Parte

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of this research was made possible by a Natural
Sciences and Engineering Research Council of
Canada Discovery grant to the second author.

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