When starting the design and construction of this musical robot, we could build further on the experiences gained through the realization of quite some automated brass instruments build since 1999: <So>, a sousaphone, <Korn>, a cornet, <Heli>, a helicon, <Bono>, a valve trombone and <Horny>, a French horn, <Bug>, a fluegelhorn and <Hunt>, a hunting horn.. This new robot, an automated trumpet, was designed and constructed to the order of Alain Van Zeveren. Musically speaking the cornet, the trumpet and the flugelhorn are very similar instruments, differing only in the timbre they produce. The flugelhorn is said to sound more mellow than the trumpet, the cornet finding a place in between. The ambitus, for Bb instruments, is the same.

Thus it made sense to start the design of this robot by examining the <Korn> and <Bug> robots and improving over them where ever possible. Main improvements we envisaged here were the sound volume, the attack characteristics and the speed of response, in particular for the valves. Again we used a membrane compressor directly coupled to the trumpet via a capillary comprised in one of the original mouthpieces that came with the instrument. The mouthpiece we first selected was one made in the Soviet Union designed specifically to facilitate sounding the highest registers of the trumpet. However, the metal alloy it was made from, caused it to explode into pieces in turning it on the lathe. That was the end of it. The alloy was clearly not heat resistent. So we reverted to a standard and completely orthodox trumpet mouthpiece. The motor driver causes resonance in the trumpet tubing, but in this case there is no unidirectional windflow through the instrument. When a note is requested from the trumpet, the firmware will calculate the optimum valve combination -including non orthodox fingerings- for the requested pitch. Thus a resonant standing wave in the instrument can be produced. Microtonal pitches are implemented such that the instrument is capable of performing quartertone music, as well as a wide range of different tunings and temperaments with great perfection. The relatively low Q-factor of the horn (compared to strings...) as an acoustic resonator renders this very well possible. The signal generated in the motor was shaped after a physical model of the air pressure waveform in the mouth cavity of a player. (Beauchamp, 1975,1980). Since there is no loop coupling from the resonator to the generator, the sound generation mechanism is a hybrid somewhere between synthetic/electronic and natural/acoustic. The advantage being that the reliability of the robot becomes very high, but this is obtained a bit at the detriment of realism, in particular with regard to the onset of the sounds, A dynamic formant filter was added using analogue electronic circuitry, in this case a pair of germanium diodes in series with a resonant LC circuit Thus the sound color will be, to a certain extend, a nonlinear function of loudness, conform to acoustic reality.

The valves are used in this instrument to tune the fundamental frequency of the instrument. The valves can be controlled independently from the mouth driver frequency. They are mechanically driven by unipolar push solenoids (Banggood types made in China, to save on cost) and use the return springs provided in the pistons in addition to the spring on the solenoids. Furthermore we mounted the trumpet upside down such that gravity also helps improving fingering speed. The notes that are normally produced using different valve combination, following theory are: Note that this is untransposed, so in reality everything will sound a full tone lower on a Bb instrument. However, we found out that using the valve combinations entailed by this system, does not lead to optimum resonance in the instrument. Thus we used the optimal valve combinations based on empirical acoustic measurement. A deficiency we encountered in our <Korn> robot was that the buildup of a sound pressure wave in the instrument was anticipating the valve movement. The valves take about 10 ms to take position, thus here we delayed the driver signal with the same amount in all cases where changes of fingering are involved. This introduces some latency but makes the sound quite a bit more realistic, in particular for the attack portion of the envelope. This idea was first implemented and fully tested on the <Bug> robot.

As we had to save as much as possible on cost, we dropped all movement as well as lights from the design. Thus the construction was a lot less involved than that of the <Bug> robot and we were able the finish the building project in a single -although well filled- month.

The electronic circuitry -in overview- consists of only two 'intelligent' PC-boards:

Overview:

1. Midi-hub board: This board, using a Microchip 18F2620 controller, takes care of the Midi I/O handling and communication as well as the control of the three valves. The circuit for the pulse/hold function here follows a recipe we applied nearly one hundreth times by now: The PCB board, is a completely new design and can in principle be applied for just about any brass instrument with up to four valves to be automated. The sizing of the Banggood solenoids used here is:

The source code for this processor is here.

The hex-dump for programming the PIC processor using MPLAB IPE is here.

2. Sound generator board: This board steers the 75 Watt motor compressor horn driver via a digital audio amplifier module. A 16-bit processor is used to generate the required waveform and two analog multipliers are used for envelope shaping and amplitude modulation. Thus we could maintain audio resolution even at the lowest soundlevels. Handling this in the full digital domain would have required a 32-bit processor. The analog dynamic formant filter also found a place on this board.

The power amp is a pure analogue design, using a high quality but by now obsolete LM12 power opamp, in a 5-pin modified TO3 package, rated for 150 Watt: We designed it back in 1991 (in fact to be used as a powerfull ac source for tape-recorder motors), but copies of it were used also for robots such as <So> and <Hunt>.

A note on the compression driver:

The longer we make the capilary and the smaller its diameter, the more will the mechanism reveal the true resonances and timbre of the instrument driven. However, the more we do that, the more power is required from the driver, and obviously only drivers with finite power are available... The compression ratio ought to be 1:50 at least. In no case should the diameter of the capilary be larger than the smallest diameter internal in the original mouthpiece of the instrument. A compression plate, as drawn, is not present in all makes of compression drivers. The Padu driver we favor to use, has one. Here is a picture: And, on the following picture it can be seen with the membrane and the voice coil in place: Note that making these internal guts visible this way, is a deadly operation for the compressor. The capton membrane with voice coil is glued to the front assembly. We did it on a burned out compressor that we took apart for close examination.. The construction with the compression plate helps a lot in suppressing own resonances occuring in the compression chamber. No physical air distance inside the compressor is larger than a half wavelength of the soundwaves corresponding to the highest frequencies the driver can produce. Here is a frontal view on the capton membrane: The voice coil is on the other side.

Power supply voltages and currents:

• -7.5 V dc (20 A) for the valve solenoids, pulse (SMPS)
• +5 V dc (20 A) for the valve solenoids, hold
• +5 V/ 2 A for processor boards (SMPS)
• + 3.3V 1 A derived with linear regulator from above +5V supply
• +27V-0- -27V for the power amplifier (linear)
• +15V - 0 - -15V for the operational amplifiers and the analog circuitry (SMPS)

Midi Mapping and implementation:

Midi channel: 12 (fixed in the firmware)
Midi note range: 52 to 94. (Optimum sound in the range 66-89) Note on, velocity is implemented and steers the level of the sustain phase in the adsr. We may implement the pedal notes as well, in which case the range would get the extra notes 40 to 46, with a gap between 46 and 52.

Note Off commands are required, but can be dropped for pure legato playing. Note off with release is implemented and can steer the release phase of the envelope. Note Off commands for notes that were not sounding are disregarded.

Controllers:

Controller 1: Noisiness of the sound [default = 48]

Controller 2: FM modulation delay: Delay time applied to the start of vibrato after reception of a note-on command. The range is 1 second, for a value of 127. Default is 64, corresponding to 500ms delay. It should be clear that when this controller is set to values longer than the duration of a note, no vibrato will be applied. [default = 64]

Controller 3: FM modulation depth (vibrato depth). Large values can cause audible artifacts, due to the modulation of the sampling frequency. If this controller is set to 0, the vibrato mechanism will be disabled. [default = 8]

Controller 4: FM modulation speed. (vibrato speed). This will only work if controller 3 is set to a value larger than zero. [default = 94]

Controller 5: AM modulation depth (tremolo depth) [default = 4]

Controller 6: AM modulation speed (tremolo speed) [default = 20]

Controller 7: used as a general volume controller. Note that timbre will change as the volume is changed. On high settings, the formant frequency becomes more dominant. [default = 90]

Controller 13: allows changes of valve fingering during sounding notes. Bit 0 corresponds to the 1/2 tone valve, bit 1 to the 1 tone valves, and bit 2 to the 3 semitone valve. Using this controller it is also possible to change the fingering for a sounding note whilst it is sounding, thus rendering some sound coloration possible without changing the actual pitch.

The table below gives all details:

Ctrl 13 Value	-1/2t (valve 2)	-1t (valve 1)	-1 1/2t (valve 3)
0	off	off	off
1	on	off	off
2	off	on	off
3	on	on	off
4	off	off	on
5	on	off	on
6	off	on	on
7	on	on	on

Controller 15: ADSR-period [default 24]
Controller 16: used to control the duration of the attack phase in the ADSR cycle. [default 32]
Velocity byte = attack level
Controller 17: sustain level [default = 74]
Controller 18 is used to control the duration of the decay after the attack, the time required to reach the sustain level of the sound. [default 32]
Controller 19 steers the duration of the release decay (from sustain level to zero) starting after reception of a note off command. Release will be canceled or interrupted with a new note on command if such a command comes within this time. [default 80]

The interdependencies of these controllers together with the velo byte is shown in the graph below:

CoController 20 - tuning for the trumpet. By default equal temperament and A = 440 Hz for value 64. Acceptable values for this controller are limited to:

• 48-59: sets the trumpet to just intonation mode based on fundamentals 48 to 59. The just intonation scale implemented here is: 1:1, 16:15, 9:8, 6:5, 5:4, 4:3, 10:7, 3:2, 8:5, 5:3, 16:9, 15:8, 2:1
• 61: sets <Trumpeter> to equal temperament but transposes all notes a quartertone down as compared to A = 440 Hz.
  62: sets <Trumpeter> diapason to A = 435 Hz
  63: sets <Trumpeter> diapason to A = 438 Hz
  64: sets <Trumpeter> to the standard diapason A = 440 Hz. This is the default on cold boot and reset.
  65: sets <Trumpeter> diapason to A = 442 Hz
  66: sets <Trumpeter> diapason to A = 445 Hz
  67: transposes all notes on <Trumpeter> a quartertone up relative to A = 440 Hz.
• 72-83: sets <Trumpeter> to just intonation mode based on fundamentals 48 to 59. The just intonation scale implemented here is: 1:1, 21:20, 9:8, 7:6, 5:4, 4:3, 7:5, 3:2, 14:9, 5:3, 7:4, 15:8, 2:1

Controller 25: Steers the attack force for the valve solenoids. [default = 88]
Controller 26: This controller steers the time the valves stay in their position after reception of a note-off command. This implements some resonance in the instrument after the excitation from the mouthpiece has stopped. It also avoids unnecessary mechanical noise from the valves, in particular on repeated notes or notes that can be produced with the same valve combination. [default = 32]

Controller 33: Selects different lookup tables for the fingerings. The default value 0 corresponds to our own findings in terms of optimal resonance. This lookup table differs quite a bit from the theory-book fingerings used for a Bb trumpet. Controller value 10 corresponds to the official fingering for a Bb trumpet. By setting this parameter to 9, the robot would use a lookup table as if it were a A-trumpet. With value 12, it would finger for a C-trumpet. Note that we do not treat the instrument as a transposing instrument! Acceptable value for this controller are limited to the range 0 to 12. On cold boot, this controller is always set to zero. [default = 0]

Controller 40: Selects the waveform used for the pedal tones, notes 40 to 46. The default setting here is 6. A good alternative could be 0.
Controller 41:Selects the waveform used for the low register, notes 52 to 71. The default setting here is 6.
Controller 42: Selects the waveform used for the medium register, notes 72 to 82 . The default setting is 1. Good alternatives are 6, 0 or 11.
Controller 43: Selects the waveforn used for the high register, notes 83 to 94. The default setting is 3. Good alternatives are 0,6,1

Waveforms implemented for these four controllers:

Controller 66: Power on/off switch (0 = off, any other value is on). Power off also resets all controllers to their default startup values. Also resets the wave tables to the default startup settings.

Controller 80: Dynamic range mapping. The default is 62, resulting in a 30dB dynamic range.

Controllers 100, 101, 102, 103: parameters for waveshape parametric Beauchamp. . This applies to Wave0. It is mandatory that Ctrl100 < Ctrl101 < Ctrl102 < Ctrl103. After reception of controller 103, the wave table will be recalculated. Following graph describes the waveform and its parameters:

Controller 104: parameter for setting the symmetry when waveform 2 is selected. Value 64 makes a symmetric square. Valid values are between 1 and 126.

Controllers 105 and 106: parameters for the minimum and maximum points of a triangle wave, selectable with waveform 4. The parameters will be clear from following waveform graph:

Controller 107: parameter for the pulsewidth. This is waveform 12. The range for the parameter is 2 - 126. The graph illustrates the parameter:

Controller 108: parameter for setting the symmetry when waveform 13 has been selected. This is an assymmetric sinewave. Value 64 makes a symmetric sinewave. Valid values are between 1 and 126. The graph illustrates the parameter:

Controller 109: parameter for setting the symmetry when Waveform has been set to 14 (dirty assymmetric sine wave) .

Controller 110: parameter to set the level of noisiness in the waveform 14.

Controller 123: switches the sounding note off.

Pitch bend: The <Trumpeter> robot can be used in any tuning system. In the drawing below we give the coding example for a quartertone scale:

Most good sequencer software (such as Cakewalk or Sonar) uses the signed 14 bit format. Note that one unit of the msb corresponds exactly to a 0.78 cent interval. To convert fractional midi to the msb only pitchbend to apply follow following procedure: if the fractional part is <= 0.5 then msb= 63 + (FRAC(note) * 128), if the fractional part is larger than 0.5, we should switch on the note + 1 and lower the pitch with msb= (1-FRAC(note)) * 128. Note off does reset the pitch bend for the playing note! The resolution implemented on <Trumpeter> for pitch bend (and vibrato) is limited to 1/10th of a semitone.

Technical specifications:

• size: w= 660 mm, d=260 mm, h=520 mm (without stand), with stand and wheels h= 1500 mm
• weight: 17kg (without the stand)
• transportation: may need a flightcase.
• Power: 230 V ac / 150 W. At rest, power consumption is ca. 5 W.
• Tuning: based on A = 440 Hz (within 1 cent). Programmable.The tuning can be adjusted.
• Ambitus: [40-46, pedal tones] 52-94, normal notes
• Sound pressure: > 102dBA @ 1m, frontal.
• control: MIDI-input, 3 MIDI-Thru (differential).
• Insurance value: 6.550 Euro (production cost)

Design, research and construction: dr.Godfried-Willem Raes (2021)

Collaborators on the construction of this robot:

• Mattias Parent
• Bert Vandekerckhove
• Alain Van Zeveren

Music composed for <Trumpeter>:

• Alain Van Zeveren - in the making.

Some more pictures:

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Construction & Research Diary:

• 27.05.2021: Alain Van Zeveren brings in a trumpet, made in the DDR (former East-Germany) with a proposal to have it automated by us.
• 28.05.2021: First rough inventarisation of the project, taking into account the dropping of all movement from the design.
• 30.05.2021: Sketches for the construction of the chassis. The structure ought to be really strong and vibration free. Could we use Banggood solenoids (Chinese) for the valves to save on building costs?
• 31.05.2021: Power supply for the power amp recalculated: 50 VA at 2 x 18 V should give more than enough margins and overload protection.
• 02.05.2021: It appears required to design a new hub board handling the midi parsing and the pulse-hold hardware for the valves. This could become a pretty universal board for robotic brass instruments with three (and maybe four...) valves. Circuit drawing worked out and calculated. PCB designed. In this approach we can do the project with just two microprocessor PCB's.
• 03.05.2021: Lathe works to adapt the trumpet mouthpiece to the orifice of the membrane compressor. We ruined the Russian made mouthpiece as it was made of a kind of composite brass-like material. It flew away from the lathe and broke in two parts... The second, and original East-German made mouthpiece came out too small to guarantee a tight fit. So we turned one of the trumpet mouthpieces we had in stock. Here is the result: This is how it mounts to the robot:
• 04.05.2021: Start bringing together chassis parts. A very first and tentative rough presentation for a possible mount...: Start welding and drilling of the mounting clamp for holding the trumpet. For this construction we use regular steel, as stainless steel is about three times more expensive. Regular steel is also easier to weld and to work in general.
• 05.05.2021: Design of a PCB for the compressor driver/synth board. This is a further derivative of the last most recent board made for <Hunt>.It's a pretty expensive board because we are using high precision Burr-Brown analog multipliers here. Saving on cost at this point, leads to limitations in dynamic range and to a much worse signal/noise ratio. First step in soldering the components on the board: Further work on the support chassis. The first thing to get done, is fixing the trumpet in a rigid clamp without doing harm to the trumpet. Only once we get this done, we can position the solenoids for driving the valves as well as the compressor assembly. By the end of the day, we got most of the relevant mechanical parts sawn out and welded together. The disadvantage of using regular steel reveals itself again: the structure needs to be painted or sprayed... Here are some pictures made today: The construction of the limiters for the anchor trajectory, serving as silencers on fallback of the anchors as well, will be for tomorrow...
• 06.06.2021: Cutting and drilling of the fall-back stops and dampers. Here we use slices of square 50 x 50 x 3 steel profile. Mounting with bolts and nuts rather then welding, for ease of adjustment. The felt for the cushions should be 10 mm thick. Considering to use our LM12 power opamp design, as we still have one single copy in stock. It's pretty large though ( 300 x 160 x 60 mm). Playing around with the diferent design possibilities for the chassis with the circuitry. Seems that it' s hard to proceed if we dont have the power supply components. So maybe we should first solve this problem before we go on with the construction... Two power supply modules ordered from Farnell: Mean Well 7.5 V - 20 A and 5 V - 20 A, order numbers 2816032 and 2816022. Cost ca. 150 Euro.
• 07.06.2021: Decided to paint the regular steel parts with silver paint. PCB-files sent to Polo to have the films made. Here is the PDF file.
• 08.06.2021: Expecting delivery of the ordered power supplies from Farnell... In the meanwhile, we made an insulating backplate in blue polyacrylate ('Plexiglass') for the solenoid holder.
• 09.06.2021: The ordered power supply modules came in. A piece of very strong rectangular steel profile (180 x 80 x 5) digged up and cut out to hold these two power modules. Experimenting with the assembly and the different possibilities for bringing the components together. Reminding myself: make sure it can be disassembled for maintenance and repair!
• 10.06.2021: Further drilling work on the 160 x 80 x 5 steel profile: Mounting holes for the 5 V and 7.5 V power supplies. Large ventilation holes (20 mm) drilled.
• 11.06.2021: Cut out for the mains entry finished (IEC connector). Holes drilled and M4 thread tapped for mounting the power amp module. Square steel profile 250 mm x 25 mm x 25 mm drilled with 8 mm mounting holes for the trumpet assembly. This profile welded on the large steel profile. However, now we have to rework the Plexiglass plate fro the solenoid driver board. The films for the PCB's came in from Polo, so in the weekend we can proceed with some manufacturing and electronics.
• 12.06.2021: Further work on the chassis components: We could even add an optional and demountable stand using this wheelbase: . How much protection do we have to provide for the non-insulated heatsink on the LM12 opamp? The heatsink metal carries the negative supply voltage for the amplifier and should never get shorted to ground. All M4 threads for mounting components made. All feed-through holes drilled. New layer of silverpaint applied.
• 13.06.2021: Once more, test assembly... Can we weld the mounting flanges underneath? We did. The trumpet robot can now be mounted on a stand with a flat surface of 150 mm x 250 mm with four M8 bolts and nuts. This is the chassis without any component: Paint corrections and again, assembly.
• 14.06.2021: Attempt to produce the missing MIDI-hub and valve-control board. Discovered that the scaling of the PCB films is fully wrong. The PCB size on the films is 100 x 153 instead of 100 x 160... how can that have gone wrong?
• 15.06.2021: New PCB made, drilled and soldered. Running out of XP-Power 5V-2A power modules. At Farnell delivery wouldn't be any sooner than december 5th... So, we ordered a few from RS-Components. All components in the pulse-hold circuit recalculated for operation with the Banggood solenoids and the 5V/7.5V power supplies. This is the result: The dissipation in the IRLZ34NPBF mosfet, with an Rdson=0.046 Ohm is only 0.5W during hold. Thus no heatsink required. This mosfet is specified for 55V - 30A. For the velo-pulse mosfet, we went for a AU_IRF3710Z type. This type is specified for 100V - 59A and its Rdson is 0.018 Ohm at Ug=10V. Thus the dissipation of this mosfet when the velo input is on becomes 1.15W. As the velo pulse duration is maximum 32 ms, the real dissipation will be a lot lower. So here also, no heatsink required. Board fully populated and soldered, except for the missing XP-Power module. Just got a message from RS-components: the modules should get here on friday... This is the copper side: Start coding the firmware for the midi hub and the valves. It's a bit more work than just adapting code done for <Bug>, mainly because here we have the valve-bits mapped on more than a single port. Start wiring of the mains power leads and some connector. Slowly it's getting into shape. Soon we will have to make up our mind in regard of the question as to where to hold it... The assembly is quite a bit heavier than what we first thought.
• 16.06.2021: Further work on the firmware for the valve and midi hub board. Code testing and debugging on the 8-bit PIC test- and development board. Controller 33 introduced for the selection of different lookup tables for the use of valves and fingerings. The default value for this controller should be 10, corresponding to the theory-book valve table for a Bb trumpet. Shouldn't we also implement the -for human players virtually unplayable- pedal tones? That would give us an ambitus 40 to 46, followed with a gap and then the normal noterange 52 - 94. This of course also entails serious modifications for the 16-bit processor responsible for the wave-generation..
• 18.06.2021: Correction of the drilled holes for the valve solenoids. Programming firmware V1.0 for the valves done. The 5V-2A power modules came in, so we can finalize this board.
• 19.06.2021: Mounting and wiring finished. First firing up... a smoke stack as a result! Apparently, one of the mounting holes for the power amp shorted the -37V voltage to ground. As a result, the negative 7918 regulator went to heaven as well as the balanced receiver/driver amp (SSM2141). A copper trace on the PCB was found to have molten away. Some repair work at hand, before we can go on. This is the circuit for the power amp:
• 20.06.2021: Power amp repaired: Start working on the code for the compressor driver. First preliminary version compiled and uploaded in the PIC's. First test report: valves work fine, but need some fine tuning and different defaults. Mounting holes still need corrections and a lot of filing, a tedious job. Sound generation works but the power amplifier still seems to fail: it gets very hot... There is a strong DC component on the output... First thing to do: check the signal from the generator on the oscilloscope and verify levels as well as DC-offset. The power supply (+37V -0- -37V) is a bit on the high side but seems o.k. There seems to be failure in the +/-15V supply for the multipliers and the opamps. Not the NMA0515 tiny SMPS is in error, but one of the Epcos 100uH inductors - the one in the negative supply lead- seems to be unconnected...
• 21.06.2021: Further hardware debug of the wave generator board. Finally we got it all working. <Trumpeter> plays. To do now: Empirical lookup tables for the fingering, wavegenerator algorithms and lookups. Controllers 40 to 43 added for wavetable research. ADSR implementation changed as compared to earlier robotic wind instruments. Now the velo byte steers the attach volume. Sustain level is controlled with controller 17. As a consequence, midi files edited for <Korn> and <Bug> will need some changes if they are to be played on <Trumpeter>.
• 22.06.2021: Development of testcode in the <GMT> framework. Research on the driver waveforms.
• 23.06.2021: Empirical lookup tables for the fingerings measured and implemented in the valve PIC firmware. A small report recorded on video for our stream from the logos labs tomorrow. <Trumpeter> dismantled again, to make adjustment of the valve solenoids possible.
• 24.06.2021: Further programming work on the waveform generators. We include both resynthesized acoustic waveforms as pure algorithmic models. Revision of the midi implementation. Rewriting test software in <GMT>.
• 25.06.2021: PIC-firmware for the pitch processor upgraded. Stand welded for the robot. The trumpet-assembly mounts on the stand with 4 M8 bolts. The mounting plate has embossed markings ('mot' and 'horn') that should be observed. The central 2" tube can be fixed on the 4-wheel stand with two M6 bolts. The holes are threaded for this purpose. Complete disassembly of the robot to make milling of the mounting holes possible. The whole procedure disassembling/reassembling takes about five hours of work. By the end of the day we had the robot up and running again.
• 26.06.2021: Demonstration of <Trumpeter> for Alain Van Zeveren.
• 28.06.2021: Painting of the stand: blue, RAL5012. Here it is, fully mounted on its stand:

To do:

• - Implement a larger delay between fingering and membrane compressor drive?
• - add eyes?
• - add more excitation waveforms?
• - make a demo recording?

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Last update: 2021-10-10 by Godfried-Willem Raes

The following information is not intended for the general public, but is essential for maintenance and servicing of the robot.

Technical drawings, specs and data sheets:

Compression driver unit: Model PADU 100, power rating 100W, impedance 16 Ohms. (Made in China) We have measured this component carefully when making <Asa> and found the impedances in function of applied frequency as follows:11.4 Ohms @ 100Hz, 23.68 Ohms @ 1kHz, 26.7 Ohms @ 10kHz and 45 Ohms @ 25kHz. The acoustic load does influence the measured impedance at 1kHz over a 1:2 range: with the mouth completely closed it measures 32.8 Ohms and with the mouth completely opened but without any resonator, 15.35 Ohms. This phenomenon does not occur for the very low neither for the very high frequencies. The measurements were performed in 2016 with our Hameg LCR meter, model HM8018. The frequency response is 100Hz to 10kHz. The thread for mounting is 1 3/8"-18 TPI.

Valve lookup tables (according to acoustic theory)

Power supply:

Circuit drawing for the valve control and MIDI hub board:

Firmware for the hub board:

• source code
• hex dump:

PCB for this hub board designed for 3 or 4-valve brass instruments:


[scale 200%]

Power supply modules for this board:

• Negative supply: Mean Well 7.5 V 20A - RSP-150-7.5 Farnell order nr. 2816032
• Positive supply: Mean Well 5V 20A - RSP-100-5 Farnell order nr. 2816022

Compressor driver board (monophonic synth with acoustical modelling):

Circuit drawing:

PCB for this circuit: [scale: 200%]

Current drawn by this board 310mA @ 5V supply.

Soldered board:

References:

Beauchamp, J.W. "Analysis and Synthesis of Cornet Tones Using Nonlinear Interharmonic Relationships". In: j-aes, volume 23, number 10, pages 778--795, 1975.

Beauchamp, J.W., "Analysis of Simultaneous Mouthpiece and Output Waveforms of Wind Instruments" . In: j-aes, 1980, Preprint No. 1626,

Benade, Arthur .H., "Fundamentals of Musical Acoustics". Ed.: Oxford University Press, 1976.

Fletcher, N.H. & Tarnopolsky, A. "Blowing pressure power and spectrum in trumpet playing" In: J. Acoust. Soc. Am., volume 105, number 2, part 1, 1999.

Martin, Daniel W., "Lip vibrations in a Cornet Mouthpiece", In: J.Acoust.Soc.Am. vol13 . 1942

Raes, Godfried-Willem, "Kursus Akoestiek", Ghent University College 1982/2014, Internet: http://www.logosfoundation.org/kursus/4023.html

Raes, Godfried-Willem, <Bug> an automated Fluegelhorn, 2016.

Raes, Godfried-Willem, "Expression control in musical automates", 1977/2021,

Raes, Godfried-Willem, "Logos @ 50, het kloppend hart van de avant-gardemuziek in Vlaanderen", ed. Stichting Kunstboek, 2018

Rose,Nicholas and Holloway, Damien, "Finite element modeling of brass musical instruments', in: Proceedings of Acoustics, Fremantle, Australia 2012.

Smith, Bob H., "An Investigation of the Air Chamber of Horn Type Loudspeakers", in: The Journal of the Acoustical Society of America 25, 305-312 (1953); https://doi.org/10.1121/1.1907038

Cost calculation for <Trumpeter>:

1. Parts and components

2. Consumables

3. Depreciations on tools and equipment used (calculated over 1 month)

4. Labor and design (45,-/hour)

[EOF]