An Easily Removable, wireless OpticalSensing System (EROSS) for the trumpet

Leonardo JenkinsElectrical and Computer

EngineeringUniversity of Victoria

Victoria, BCleonardo@ece.uvic.ca

Wyatt PageElectrical Engineering

Massey UniversityNew Zealand

w.h.page@massey.ac.nz

Shawn TrailDepartment of Computer

ScienceUniversity of Victoria

Victoria, BCtrl77@uvic.ca

George TzanetakisDepartment of Computer

ScienceUniversity of Victoria

Victoria, BCgtzan@cs.uvic.ca

Peter DriessenElectrical and Computer

EngineeringUniversity of Victoria

Victoria, BCpeter@ece.uvic.ca

ABSTRACTThis paper presents a minimally-invasive, wireless opticalsensor system for use with any conventional piston valveacoustic trumpet. It is designed to be easy to install andremove by any trumpeter. Our goal is to offer the extendedcontrol afforded by hyperinstruments without the hard toreverse or irreversible invasive modifications that are typi-cally used for adding digital sensing capabilities. We utilizeoptical sensors to track the continuous position displace-ment values of the three trumpet valves. These values aretransmitted wirelessly and can be used by an external con-troller. The hardware has been designed to be reconfig-urable by having the housing 3D printed so that the dimen-sions can be adjusted for any particular trumpet model.The result is a low cost, low power, easily replicable sensorsolution that offers any trumpeter the ability to augmenttheir own existing trumpet without compromising the in-strument’s structure or playing technique. The extendeddigital control afforded by our system is interweaved withthe natural playing gestures of an acoustic trumpet. Webelieve that this seamless integration is critical for enablingeffective and musical human computer interaction.

Keywordshyperinstrument, trumpet, minimally-invasive, gesture sens-ing, wireless, I2C

1. INTRODUCTIONHyperinstruments are expanded acoustic musical instrumentsthat use digital sensors to capture detailed aspects of theperformer gestures as well as provide additional expressivecapabilities through digital control. They enable the mu-sician to access the diverse possibilities afforded by digitalcontrol while at the same time leveraging the skill devel-

Permission to make digital or hard copies of all or part of this work forpersonal or classroom use is granted without fee provided that copies arenot made or distributed for profit or commercial advantage and that copiesbear this notice and the full citation on the first page. To copy otherwise, torepublish, to post on servers or to redistribute to lists, requires prior specificpermission and/or a fee.NIME’13, May 27 – 30, 2013, KAIST, Daejeon, Korea.Copyright remains with the author(s).

Figure 1: EROSS mounted on a trumpet

oped through years of training by professional musicians.Although there are examples of earlier work in this direc-tion, the term “hyperinstrument” was introduced in 1987through the work of Tod Machover at MIT [9]. Since then, avariety of different hyperinstruments, designed for the mainmusical instrument families, have been proposed. Early rep-resentative examples include: the Hypercello (strings) [12],the Metasaxophone [1] and Hyperflute [11] (winds), and theCook/Morrill trumpet controller (brass) [3]. Any acousticinstrument can serve as the basis for designing and buildinga hyperinstrument and the concept has also been appliedto non-western instruments such as the sitar [7], and theGyil african xylophone [14]. Despite the potential of hy-perinstruments to enable extended performance techniques,their adoption has been slow and idiosyncratic. We believethat this is mostly due to the following factors: 1) they areexpensive custom-made devices that are hard to replicate(typically there is only a single instance in existance); 2)they frequently require invasive modifications to the origi-nal acoustic instrument, 3) their operation and maintenancerequires significant technical expertise with electronics.

The focus of the work presented in this paper is to aug-ment traditional trumpet playing with digital control. Thereis a long history of approaches that have been proposed toachieve this. The most generic approach is to use exter-nal controllers such as foot pedals, knobs, sliders, and key-boards to control digital processes as well as filters/effectson the audio signal produced by the horn. An iconic ex-ample of this approach was the use of electric guitar effectsby Miles Davis to modify the sound of the trumpet duringhis electric phase in the 1970s[5]. As any controller can beused for this purpose, this approach provides a very rich setof control possibilities to the trumpet player. In addition,

it requires no modification to the acoustic instrument otherthan attaching a microphone to the horn. However, inter-acting with the controllers is external to the trumpeter’stechnique. This creates additional cognitive load similar totrying to play two instruments at the same time.

An alternative approach is to directly introduce sensorsfor digital control on the body of the trumpet making it ahyperinstrument. A good overview of different approachesand sensors that can be used for augmenting the trumpt canbe found in the Master thesis of Thibodeau [13]. The pi-oneering Cook and Morrill trumpet controller [3] was builtto create an interface for trumpeter Wynton Marsalis. Sen-sors on the valves, mouthpiece, and bell enabled fast andaccurate pitch detection and provided extended computercontrol. Another well known example is the Mutantrumpet,a hybrid electro-acoustic instrument designed and evolvedover many years by composer and inventor Ben Neill [10].The Mutantrumpet started as an acoustic instrument (threetrumpets and a trombone combined into a single instru-ment). In the mid 1980s electronics were integrated tothe instrument in collaboration with synthesizer inventorRobert Moog and in the 1990s the instrument was madecomputer interactive. By attaching the sensors directly onthe instrument the digital control is more easily accessibleby the player and therefore is more naturally integrated withthe traditional way of playing the instrument. However,each instrument is unique, idiosyncratic and custom-madewhich makes replication and therefore adoption difficult.The modifications to the instrument are extensive (some-times even radically modifying the original instrument as inthe case of the Mutantrumpt) and the sensing apparatus ishard to remove if not required. Finally, the detailed designplans and component parts of most augmented trumpets(and hyperinstruments in general) are not publicly avail-able.

Here we present a low-cost, easily removable and min-imally invasive optical sensing system (EROSS) that pro-vides continuous control data from the position of the valveson the acoustic trumpet. The housing has been 3D printedmaking it fully customizable for any standard trumpet. Thesensors and housing bracket mount under the valves with-out obstructing the conventional playing position and thetwo pieces are connected together via magnets without al-tering the horn’s structure or requiring cumbersome fasten-ing. Our approach has been inspired by the Electrumpet [8]which is an enhancement of a normal trumpet with a vari-ety of electronic sensors and buttons. The Electrumpet canbe attached and detached to any Bb trumpet. It is com-mon for trumpet players to attach various types of mutesto their horn. We hope that making our sensing apparatusno more difficult to attach and remove than a mute will fa-cilitate adoption. Like the Electrumpet our design plans areavailable, the sensing apparatus is removable, and we utilizewireless communication. Our approach is more naturally in-tegrated as it focuses on providing continuous control datafrom the positions of the three (3) valves used for playing. Incontrast, the Electrumpet provides additional valve-like po-tentiometers and buttons that are not part of regular trum-pet playing. The use of magnets and 3D printing for thehousing is an additional difference and a contribution of ourwork. For sensing the continuous valve positions we utilizeoptical sensing, unlike the variable resistor potentiometersused in the Electrumpet. This optical sensing technique hasbeen proposed in the design of another augmented trumpetwhich was done as a course project at Cornell University[4]. Unlike our approach it was used for discrete ratherthan continuous control. Figure 1 shows EROSS mountedon a trumpet.

2. MOTIVATION AND DESIGNA long term objective of our research is to design and estab-lish a robust, low cost, reconfigurable sensing hardware andsoftware framework that can be adapted to various musicalinstruments in order to give them hyper-instrument capabil-ities without requiring invasive and hard to reverse modifi-cations to the acoustic instrument. We believe that there isa strong need for such a framework because of the high costand hard to replicate nature of existing hyperinstrumentdesigns. Advances in open source software, electrical sen-sors, micro-controller frameworks such as Arduino 1, and 3Dprinting open the possibility of creating reusable, adaptabledesigns that can easily be applied to existing instrumentswithout requiring extensive technical expertise and lever-aging traditional playing technique. It is our hope that aselectronics on stage are becoming more ubiquitous in manymusical genres, approaches like ours will reach larger com-munities of users. The proposed trumpet sensing system isa good case study of how such a framework can be used forinstrument augmentation.

2.1 Design ConsiderationsThe proposed system, compared to other augmented trum-pets that have been proposed, is minimal. It only pro-vides continuous control information from the position ofthe three piston valves that are used for playing. This de-sign decision was influenced by the designed principles fornew musical interfaces outlined by Cook [2] that emphasizesimplicity (“Programmability is a curse” and “Smart instru-ments are often not smart”) and integration with existingplaying techniques (“Copying an instrument is dumb, lever-aging expert technique is smart”). We also wanted the sys-tem design to be minimally invasive and easily removablefor the reasons outlined above. The first one deals with thefact that the trumpet should remain physically unmodified,even not removing the valve bottom caps. These caps havea hole at the centre, which would work to our advantage.The location of the sensor would be such that the IR emit-ter would shoot a pulse through this hole and the reflectionoff the bottom surface of the piston would be detected bythe photo-pin-diode. All trumpet pistons are hollow cylin-ders with cylindrical tunnels welded accross and an irregularbottom surface with a hole in its centre, which is concen-tric to the hole in the valve bottom cap. This configurationmakes the optical path for the sensor multifaceted. Whennot pressed, the piston is at its maximum distance from thesensor and its bottom surface hole represent a small portionof the area covered by the sensor’s detection zone. Whenfully pressed it is at the minimum distance from the sensorand the hole represent the majority, if not all, of the areacovered by the detection zone, making it difficult to sensethe appropriate distance to the piston’s surface. Figure 2depicts a valve’s configuration and its interaction with theoptical sensor.

Another challenge was the idea of having a system thatcould be easily attached and detached to the trumpet, butat the same time be sturdy enough to keep the sensors assteadily as possible beneath the valve’s bottom cap. Opticalsensors tend to have high sensitivity, and even the slight-est of movements and/or temperature changes can affectthe system’s accuracy. To compensate for this issue a cal-ibration stage needed to be included when designing thesoftware. Also the system would have to be mounted in away such that the performer shouldn’t compromise his/hernatural grasping technique.

1http://www.arduino.cc

Figure 2: Issue with the sensor’s detection zone

2.2 Sensor PlacementA critical aspect of the design is the placement of the opticalsensors for determining the valve positions. In this sectionwe describe the empirical investigation that was carried todetermine this optimal placement according to a set of de-sign constraints. Five candidate locations near the bottomcap were considered (indicated as SL1, . . . , SL5 in Figure3b). The optical sensor consists of an emitter and a detec-tor. For each candidate location we collected the measuredoptical sensor readings for eight valve positions (indicated asV P1, . . . , V P8 in Figure 3a). The full range of possible valvedisplacement was divided linearly into these eight valve po-sitions where V P1 is the fully released valve position andV P8 is the fully pressed valve position.

The measured optical sensor readings are expected to benoisy. Thus to determine the best sensor placement, weneed multiple measurements at each candidate location toobtain the noise distribution and a clear set of criteria bywhich to score each location.. We denote the vector of mea-surements for each configuration as

xpl = xpl [1], . . . , xpl [1000] (1)

where l = 1 . . . 5 corresponds to sensor location and p =1 . . . 8 corresponds to the valve positions. For each configu-ration of l, p we calculate the following statistics:

µpl = 1

N

∑Ni=1 x

pl [i] (2)

σpl =

√1

N−1

∑Ni=1 (xpl [i]− µp

l )2 (3)

ρpl = |max (xpl )−min (xp

l )| (4)

where N = 1000 in our case, µ is the sample mean, σ isthe sample standard deviation, and ρ is the range. For eachconfiguration we calculate the number of measurements Cp

l

from xpl that fall within ±σp

l from the mean µpl . Any con-

figuration for which Cpl was less than 70% was rejected.

Due to the complexity of the optical path, we used three(3) criteria to score the possible locations. The first one isLinearity, because it is desired that the system’s transferfunction (valve position vs. output data) is as linear as pos-sible. The second one is Dynamic Range, to ensure a bettersignal-to-noise ratio. The third one is Robustness, becausewe want a location that robustly handles noise, such as theones induced by the sensor and the mechanics of the sys-tem, providing consistent output measurements. A scorewas calculated for each criterion and each sensor location l.

(a) Valve Positions (VP)

(b) Sensor Locations (SL)

Figure 3: Parameters for sensor placement analysis.

• Linearity

The curve fitting cost Ll from a least squares linear fiton the means µ1,...,8

l of each VP instance correspond-ing to a particular location l (each curve is fitted to8 points). Lower cost signifies a more linear responsefrom the system.

• Dynamic Range

The distance in measurement space between the min-imum and maximum of two adjacent valve positions:Hp

l = |min (xpl )−max (xp

l )| where p = 2, . . . , 8. To ob-tain a single score for a particular location l we weighteach valve position with the following weights:whp = [1.05, 1.15, 1.25, 1.35, 1.45, 1.55, 1.65]. The weigthswere determined empirically in order to emphasize theaccuracy at the fully pressed position (p = 8). The fi-nal Dynamic Range score is Hl =

∑8p=2 wh

p×Hpl . A

higher score implies better dynamic range.

• Robustness

The ratio Rpl = σp

l /ρpl between the standard devia-

tion and range for each configuration l, p (the d indexis dropped based on the first experiment). As defined,this criteria is likely to be sensitive to outliners, but infact this might work to our advantage because we aretaking into account any possible noise, such as the oneinduced by the EROSS not being mechanically lockedwhen mounted. To obtain a single robustness score fora particular location l we weight each valve positionwith the following weights:wrp = [1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7]. The final ro-bustness score is Rl =

∑8p=1 wr

p × Rpl . The weights

were determined empirically in order to emphasize theaccuracy at the fully pressed position (p = 8). A lowerscore implies better robustness.

The scores for the three most suitable sensor locations arein Table 1. These scores show that, while SL4 is the morerobust location, SL1 has the least variation from a linearcurve (Linearity criteria) and the wider dynamic range.

Table 1: Test results for critical valve position (Valve fullypressed)

Sensor Loca-tion

Linearity(Ll)

DynamicRange (H8

l )Robustness(R8

l )SL1 752 270 8SL4 2511 316 6SL5 1714 402 20

The scores Rl, Hl, Ll were normalized and added withequal weight to yield a final score Sl. The sensor location l̂that yielded the highest score l̂ = arg maxl Sl was selectedfor the placing of the sensor and corresponds to the detectorbeing positioned at the center, while the emitter sits at theedge, of the cap’s hole (SL1).

3. SYSTEM DESCRIPTIONThe use of optical sensors provided the least invasive optionout of different valve sensing approaches considered, such asthe ones described in [13],[6]. Since the system is intendedto perform range control on the trumpet valves rather thanjust event detection, a tightly focused sensor implementa-tion was needed in order to achieve accurate results. As inprevious work, the system’s sensor location is at the bottomof the valves, below the bottom caps for easy retractabilityof the system. The system’s main components are the opti-cal sensors, the microcontroller and the wireless transceiver.All the details such as circuits schematics, part numbers, 3Dmodels for the casing, software are available upon request.

Optical Sensors.A fully integrated proximity sensor from Vishay2 was cho-

sen so the constraints on spatial resolution and robustnesscould be achieved. This sensor is a small surface mountdevice measuring 4mm (L) x 4mm (W) x 0.75 (H). It in-cludes an IR emitter, photo-pin-diode and processing cir-cuitry such that up to 16 bits of effective proximity reso-lution are possible. This sensor has an effective angle ofhalf sensitivity of ±55◦, meaning that if we assume a cone-shaped detection zone with a ±55◦ angle (see Figure 2),then the intensity of radiation of the IR signal is at its max-imum in the middle, and half the maximum on the edges.For proximity measurements, the emitter sends a train ofpulses at a specific frequency and the detector, tuned tothat same frequency, captures the reflected signal, which issubsequently processed and converted into the 16-bit out-put value, known as counts. The inherent noise from thecircuitry is between ±5 and ±20 counts. It features an I2Cinterface which is supported by the chosen microcontroller,and its performance features are configured by writing toregisters in its internal processing unit.

Although it seem counterintuitive, the optimal locationSL1 allows for the IR signal within half of the detection zoneto enter the valve chamber, while allowing full exposure ofthe detector to capture the reflected signal (see Figure 3b).Also, in principle this location ideally eliminates reflectionsoff of the bottom cap. This is supported by the results fromthe analysis described in section 2.2.

Development Board.A ready-made wireless development board developed by

Texas Instruments (eZ430-RF2500)3 was used. This pack-age was chosen because of its immediate availability as wellas ease of integration with the optical sensors via I2C, plusthe integrated wireless RF transceiver. Also, the fact that

2http://www.vishay.com/docs/83798/vcnl4000.pdf3http://www.ti.com/tool/ez430-rf2500

this board’s size is 33mm (L) x 20mm (W) x 4mm (H) makesit more suitable for a minimally-invasive system. In addi-tion, the microcontroller (MSP430F2274) in this board hassome performance features that are relevant for this applica-tion. Perhaps the most important feature is the Low-Powermode (LPM), in which the microcontroller shuts down itsCPU while in idle state (i.e. waiting for the user to pressthe activation button). Since the transmitter’s side (Tx)is powered by a battery and not a power supply from thewall or a computer, this feature is very advantageous, asdescribed in the section 4.3. It is also worth noting thatthe RAM size for this particular microcontroller is 1KB,so the system’s software design had to be constrained bymemory availability. The Flash memory size is 32KB andcan be used when RAM is not available, however its slowerperformance must be taken into account.

3.1 Hardware DesignThe system consists of three optical sensors located under-neath the bottom valve caps connected via I2C to the wire-less development board.

Figure 4: EROSS mounted under the valves

Unfortunately all three sensors come preprogrammed witha fixed slave address, which basically defeats the purpose ofthe I2C protocol multi-drop capability. To overcome thisissue an I2C-based multiplexing device (TI’s PCA9544A)4

was incorporated into the design. An actuation button(SENSE), strategically attached to a trumpet valve guard soit doesn’t interfere with the natural grasp of the instrument,gives the user control over the system to enable/disablesensing operation. Three (3) LED’s (one for each valve)convey basic status information for the sensors. At the bot-tom part of the system the battery pack was attached, aswell as an On/Off switch and a Calibration button (CAL).A removable mounting structure was 3D-printed using aThing-O-MaticTM printer from MakerBotTM. The struc-ture consists of two (2) C-shaped sliding brackets coupledaround the valve chambers for mechanical support. Onebracket holds the circuit and sensors attached to the bot-tom, and the valve guard with the actuation button andstatus LED’s attached to the side. The other bracket slidesapart in order to detach the sensing apparatus. Figure 4shows a close up picture of the mounted system and Figure5 shows the 3D-printed mounting bracket with the attachedsensors from a top view.

3.2 Software designDue to the I2C-bus’ topography the sensing needed to bedone sequentially. For the purpose of this system, the pro-cess of reading each sensor once is referred to as a sensingcycle. The transmitter’s side of the system is the maincomponent and its operation is described in this section.4http://www.ti.com/product/pca9544a

Figure 5: Top view of system housing

When powered-up, the microcontroller first makes surethe sensors are connected by testing the I2C bus. Then itconfigures the sensors for proximity measurements by writ-ing into the IR LED current; Proximity MeasurementSignal Frequency; and Proximity Modulator TimingAdjustment registers. Once the sensors are initialized thesystem shuts down the CPU and waits for the user to pressthe CAL button. When the calibration (CAL) button ispressed the system goes into Calibration mode. In thismode the system performs ten (10) sensing cycles and av-erages the measurements. This process is done twice, onefor the valves up to determine the lower boundary or min,and one for the valves down to determine the upper bound-ary or max. In this stage the slope of the linear model iscalculated as:

m =1024

max−min (5)

After calibration the CPU is shut down while it waits for theuser to press the SENSE button. Due to the complexityof the optical path, there was a concern that there may notbe a monotic relationship at the output (one value countfor each position); and in that case it would be impossibleto linearize the readings from the sensor, but in practicethere was in fact a monotonic relationship. Linearizationwas done through the equation Y = m(x −min), where xis the value from the sensor and Y is the linearized outputvalue. m is the slope and min is the lower boundary, ascalculated in the Calibration stage. In Sensing mode thesystem wirelessly transmits the linearized, averaged mea-surements from three sensing cycles. It stays in this modeuntil the system is powered-down again.

4. PERFORMANCECalibration is done everytime the system is powered-upand it compensates for any gain and offset error that thesystem may introduce. Main performance parameters areSpatial/Temporal resolution, System Robustness and PowerConsumption.

4.1 Spatial / Temporal resolutionThe trumpet valve has a range of 17mm (0.669”), and theoptimal sensor position produces a full scale dynamic rangeof about 1000 counts or 10 bits, so the spatial resolution of16.5µm/value (micrometers per value). In practice we havefound that there is a variation in full scale dynamic rangeacross valves of 1-bit, possibly due to a variation in the re-flective properties of the bottom of pistons. This small lossin resolution has minimal effect on practical performance.Latency is determined by the time it takes the system toread data from the sensors and send it over to the receiver.When using the microcontroller’s Low-Power mode, the la-tency is 3.6 msec. The threshold for noticeable latency is

Table 2: Estimated Battery-life time (hours).Idle Sensing

Type LPM no LPM LPM no LPMAAA (700mAh) 170 94 77 78LiPo (850mAh) 206 114 94 94

20 msec for the average human ear, but could go as lowas 15 msec. This difference of 11.4 msec gives room to domore sensing cycles and average them, thus perhaps im-proving the robustness of the system. Operating the mi-crocontroller in low-power mode has no significant effect onthe latency.

4.2 System RobustnessUnder repeated trials involving attaching and detaching thesystem, the greatest non-linearity transfer error, or vari-ance, was of 5%, or about 50 counts in 1000. From thiswe can say that the system is robust in its ability to per-form consistently after attaching/detaching. Time and us-age would probably decrease the system’s performance asthe bottom of the pistons become less reflective, due to dustand spit. This issue is largely mitigated by the calibrationstage.

4.3 Power ConsumptionAn estimation of the current drawn by the system wouldhelp determine the battery’s life expectancy. For the firstprototype two (2) rechargable AAA batteries with 700mAhof capacity were used; for the second implementation, aLiPo battery with a capacity of 850mAh was used. To es-timate the battery’s life cycle two (2) performance scenar-ios were studied: 1) Idle: After Initialization and SensorCalibration, the system stays on but never goes into Sens-ing Operation mode. 2) Sensing: After Initialization andSensor Calibration, the system goes into Sensing Operationmode and stays there until the battery is depleted. Thesetwo (2) scenarios cover the range of use of the system fromminimum performance to full Sensing Operation. Two es-timations were done, one with use of the microcontroller’sLow-Power mode (LPM) and the other one without. Basedon the results of Table 2, it is clear that the long batterylife will ensure that changing or recharging batteries is in-frequent.

5. IMPLEMENTATION & FUTURE WORKThe main goal of this paper is to describe the technical as-pects of EROSS and motivate minimally invasive and easyto remove digital sensing systems for musical instrumentsin general. Therefore, we refrained from describing any ex-plicit artistic mappings and performances with the systemas we hope it can be used by many artists in different andunique ways.

In the curent configuration the added weight of EROSS(180g compared to the 880-1130g of a typical trumpet) stillallows the trumpet to be held comfortably, but the highprofile of the system, along with its low center of gravityaffect the robustness of the EROSS by applying unwantedmechanical torque when tilting the trumpet. Replacing theAAA batteries with a slimmer LiPo battery, as well as de-signing a printed circuit board would reduce the system’sprofile, therefore reducing the torque and improving uponthe robustness.

Future plans include providing versions of our system toother researchers experimenting with augmenting the trum-pet as well as expert trumpet players that do not have atechnical background. This way we can get feedback abouthow intuitive the system is to use, how stable and robustit is, what are possible improvements, as well as more sub-

jective aspects such as whether or not it is inspiring to use,whether it hinders performance, and whether it fits intoa particular artist’s workflow. An easy to remove audiopickup in conjuction with real time pitch detection can beused to provide accurate pitch tracking information thatcan also be informed by the valve positions.

One interesting application of the proposed system thatwe are planning to explore is real-time transcription andlatency compensation. This involves the concept of whatwe have been referring to as “Negative Latency”. This con-cept is associated with the time it takes for the valve togo down when is pressed. In order to play a note, a trum-peter generally has the valve(s) already fully pressed down(open valve positions are a special case) when she/he startsto blow into the mouthpiece. From previous tests, it wasdetermined that a player is able to fully press a valve in50ms. If the instant that he begins to blow is consideredt = 0ms, because is when the sound is being produced,then at t = −50ms he would have been starting to pressthe valve(s). This negative instant could be used to givethe system a head start to perform calculations and predic-tions in effect compensating for any system induced latency.Based on a 90%-to-10% rise time (see Figure 6), character-istic of analog eletronics, the valve depression time is 30ms.The idea is to study how this ”Negative Latency” could im-prove time accuracy in real-time transcription, as opposedto more discrete approaches of valve sensing [3, 4].

Figure 6: Rise time of an analog step function

6. CONCLUSIONSThrough this work, we aim to provide a low-cost and adapt-able platform that artists can utilize without much back-ground in engineering and electronics. This way they canrealize their own specific vision while still taking advan-tage of a flexible framework for interactive physical com-puting. The use of minimally invasive and easy to removeaugmentations to instruments has the potential to widenthe adoption of hyperinstruments. We believe that EROSSdemonstrates the potential of an easily removable, mini-mally invasive wireless sensing system for augmenting thetrumpet with digital control capabilities.

Although in practice the dynamic range of the systemis below the desired 10-bit range, it provides a fluid, dy-namic and fairly linear response. The noise induced by theEROSS not being mechanically locked when mounted tothe trumpet, plus the sensor’s inherent noise, presented adecrease in the system’s robustness. With a non-linearitymeasure of the system’s transfer function in the order of 5%,it still proved to be robust enough to give consistent outputwhen detaching and attaching the system. In summary, wehave achieve our objectives of devising an easily removablesystem that provided continuous gesture control from thetrumpet valves

The system was made possible by leveraging advancesin sensors, micro-controllers, wireless transmission, and 3Dprinting. The system is stable and works as intended under

the design constraints we posed. It does not affect acoustictrumpet playing and is tightly integrated with the gesturesused for playing. We look forward to evolving our designfor the trumpet as well as for other instruments. It is ourhope that because of the open design of the system it willbe adopted, used, and improved by others.

7. ACKNOWLEDGMENTSStephen Harrison, Duncan MacConnell, Dr. Eric Manningfor their feedback and support in the development of thisproject. Ben Neill for inspiration. Dr. Mantis Cheng andNeill MacMillan for introducing us to the wonderful worldof 3D printing. The UVic ECE Technical Support Staff(Brent Sirna, Paul Fedrigo, Rob Fitchner) for their wisdom.Lorena Mibelli for ongoing support.

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