research
Polyphonic Guitar: Polyphonic P/U
The aim of this project is to make my electric guitar fully polyphonic. I have chosen to install the Ghost Modular Pickup System by Graph Tech Guitar Labs.
The piezo pickups come preloaded in a Floyd Rose saddle for an easy installation.
The existing saddles are replaced by the piezo saddles. The piezo connection is then threaded through the cavity of the guitar to the Hexpander board.The DIN 13 jack socket is connected to the Graph Tech “Hexpander Board” that conditions the piezo signals. “The Hexpander Modular Pre-amp features a proprietary harmonic damping system that results in tracking that is unequaled by any other system on the market today, with responsive and accurate triggering.” [1]
The term “Hexaphonic” is misleading in that it assumes that users utilise the pickup system on a six string guitar. Inventor and Musician, Matthias Grob explains this on his website.
“Some say “Hexaphonic”, which is only correct as long as the instrument has 6 strings, so we prefer “Polyphonic” here: Polyphony has its specific meaning in the music history, but the word itself simply means that there are several “sounds” and we understand several “voices” or notes. Of course this is the case for any ordinary guitar, but conventional technology treats all notes as a single sound source - which is often not in the sense of the musician!” [2]
A seventh pin is provided to allow a user to connect the sum of all the piezo pickups. Given that I am using a seven string guitar, I simply connected a seventh piezo to the seventh pin so that I have independent audio for all seven strings. I intend to mix the magnetic monaural pickups with the piezo pickups.
edit; 12/11/2009
The 7th pin (marked with a circle) on the second row of the Hexpander board ceased to function once the Fernandez sustain pickup was installed. Audio for the 7th string could be obtained once again by reconnecting the piezo pickup for the 7th string to the magnetic channel (marked with an M) on the first row of the Hexpander board. My thanks to Morgan Ahoff at Graphtech Guitar Labs for helping to resolve this issue.
Here are two early audio examples of the polyphonic guitar system. This is material being developed under the alias of Signals Under Tests, a project with DJ and programmer, John King.
Polyphonic Guitar Sample 1
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Polyphonic Guitar Sample 2
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Thanks to Michael Barkley for his Luthier skills, and to Morgan Ahoff at Graph Tech Guitar Labs for all his direction on this project. The next step is to build a break out box that provides the pickup system with power.
References
[1] Graph Tech Guitar Labs. (2009) Ghost Modular Pickup Systems. http://www.graphtech.com/products.html?CategoryID=2. Accessed on 15.07.09.
[2] Grob, M. (2008) What do we mean by Polyphonic? http://matthias.grob.org/pParad/WhyPolyGuitar.html. Accessed on 15.07.09.
Polyphonic Guitar: The Break out Box
The diagram above breaks down the pin assignments of the 13 pin DIN connection. The break out box would allow me to access individual audio for each string on my electric guitar. In researching the construction of this box, I found two excellent sources of information.
The first was Jeff Berg’s website, Unfretted.com, and the second was Dublin based Electroacoustic Composer, Enda Bates. Pins 1 - 6 correspond typically to strings 1 - 6, the 7th pin corresponds to the sum of all 6 strings, and pin 12 is where power is sent via a 9v battery. In my case, the 7th pin will correspond to the 7th string of my electric guitar. Jeff Berg’s excellent guide to building your own break out box is available here. It is very important that you read Jeff Berg’s instruction and that you ground the box properly. Do not construct this in the bath etc.
I required a female 13 pin DIN connection, 7 female jacks, and some heat shrink tubing so that I could make the connections more robust. Thanks to Taku for the recommendation of heat shrinking.
I soldered pins 1 - 7 to the tip contact of each female jack socket. It is important that you ground the sleeve of each jack along with the shield of the 13 pin DIN connection.
Once the connections began to take shape, I then built it into a cable. I used a little bit of PCB for all my grounding.
And then into a box. I managed to fit the cable into a box the size of a D.I. box. One thing I would suggest is that you use a box with a little more weight if you plan to use a loom cable so that the box does not become damaged due to the weight of the cable.
Thanks to Enda Bates, Takuro Lippit, and Jeff Berg for their direction with this project.
Polyphonic Guitar: Fernandes Sustainer P/U
The perception of dynamic trajectories in live music performance has become of immediate importance since the conception of the Signals Under Tests project [1]. The relatively short sustain of plucked notes on an electric guitar can present limited scope in multiple speaker array performances [2]. One method of remediation has been to employ “live looping” techniques [3] and other experiments with DSP. However, at this early stage of the project, perhaps DSP is not an appropriate method to encourage sustain beyond the natural resonance of the electric guitar. A sustain pickup seems to be the most heuristic method for the time being. The Fernandes Sustainer [4] and the Sustainiac Stealth Plus [5] are the two pickups that seem the most available and suitable.
Alan Hoover at Maniac Music explains the similarities between the two models;
“The Sustainiac Stealth Plus and the Fernandes sustainer are both Electromagnetic sustainers for electric guitar. Both take the bridge pickup signal, amplify and process it, and then apply this amplified/processed bridge pickup signal to the electromagnetic driver transducer (”driver” for short). The driver then transmits a pulsating magnetic field in response to the amplified bridge pickup signal. This pulsating magnetic field causes the string vibrations of the guitar to be sustained as long as you hold the note. Simple hand-muting stops the sustain. Both systems have different “harmonic modes”. In other words, we do other electronic processing which forces the strings to vibrate differently, in such a way as to produce harmonics, kind of like a very loud amplifier does (only much more forcefully and musically, and also predictably). It is a very cool sound for many types of music. This is where the similarity stops.”
Alan Hoover at Maniac Music explains the differences between the two models;
“Our patented circuit designs allow you to use common push-pull controls which simply replace your existing guitar controls, in most cases without having to drill new holes in your guitar body. Installation of the Sustainiac circuit into most guitars can be done without having to route a new (large) cavity into the guitar. With the Fernandes, you will likely have to do a substantial route into the back of your guitar in order to fit it in. These are the main differences.”
While the Sustainiac seems to be tidier in terms of specification, the Fernandes sustainer is a little more affordable and it just so happens that I have a luthier who I trust to cut a new cavity in my guitar. Also, I have been trying to shift a little of the weight of the body since it is made of ash and it is quite heavy. I have included a short overview of the installation process below.
A new cavity had to be cut to fit the Fernandes sustainer circuit board.
The pickup system needed to be wired to the existing pots, the three way pickup selector, and the existing jack socket. The cavity was grounded with aluminum foil in an attempt to reduce any noise that was present.
Two toggle switches are present on the board to switch between the two harmonic sustainer modes and to switch the pickup on and off. These are located under the bridge of the guitar.
The pickup works relatively well and helps to further develop performance techniques in multiple speaker array based live performances. However, I am interested to see if Maniac Music will develop the polyphonic sustainer pickup they have mentioned here. [6]
A short audio sample is available below;
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Thanks to Alan Hoover at Maniac Music, Mike Barkley for your routing expertise (and patience), and to Andres Jaramillo at Fernandes Guitars.
References
[1] Signals Under Tests. (2009) Myspace. http://www.myspace.com/signalsundertests. Accessed on 23.07.09.
[2] Bates, E. (2008) Adapting Polyphonic Pickup Technology for Spatial Music Performance. ICMC, http://www.endabates.net. Accessed on 23.07.09.
[3] Looper’s Delight. (2006) Looping Tools. http://www.loopersdelight.com/tools/tools.html. Accessed on 23.07.09
[4] Fernandes Guitars. (2009) Fernandes Sustainer. http://www.fernandesguitars.com/sustainer.html. Accessed on 23.07.09.
[5] Maniac Music. (2009) Sustainiac Stealth Pro. http://www.sustainiac.com/st-pro.htm. Accessed on 23.07.09.
[6] Maniac Music. (2009) Hexaphonic Model. http://www.sustainiac.com/st-pro.htm. Accessed on 23.07.09.
STEIM - Artistic Residency - March, 2010
Polyphonic Audio and MIDI box for Polyphonic Electric Guitar
The premise of this project was to build a hardware unit which provides polyphonic audio (separate audio signal for each string) as well as MIDI data (pitch and velocity) for each note executed which could be utilised for mapping purposes. Such a hardware unit would allow the user to maximize CPU power for signal processing. Following on from a previous “break-out box” project, I purchased the Axon AX-50 board from Terratec (Germany) to allow for MIDI data for each note. The tracking is excellent in combination with Graphtech’s “Hexpander” MIDI interface.
Initially, I wanted to hack the board so that it supported polyphonic audio and MIDI concurrently, however, the Axon board is inherently noisy and a series of the DIN pins carry a rather unfortunate mains noise rendering the board unusable for audio. So, I devised a separate power supply (9v battery) acting as a piezo amplifier, powering the Axon unit separately with an adapter. I devised a DIN splitter cable so that the Axon board is able to receive the audio derived from the guitar, whilst maintaining separate power sources, ergo eliminating the ground noise issue. My thanks to Jun Kwon for his assistance with installing a series of isolator transformer to improve the quality of Audio/MIDI data translation.
In separating the ground of the piezo amplifier from the Axon AX-50 board, one is presented with a different noise problem, whereby noise generated by MIDI data is present in the audio signals. A separate MIDI interface was tested, which reduced the noise but it did not eliminate the noise altogether. To eliminate the ground noise completely, a USB isolator may be required. This project is on-going.
Mapping Strategies
The premise of this project was to reflect pitch structure in my chosen DSP during real-time performance. I built the following patch in PD (Pure Data), in an attempt to reflect pitch structure in pre-programmed signal processing during real-time performance, which can be dictated by the chosen pitches executed by the performer while maintaining an element of improvisation. The electric guitar is inherently a multi-parameter mapped instrument. For the most part, it maintains a many to one relationship, concerning many attributes of a physical instrumental technique utilised by the performer to produce a desired sonority. It is important to maintain an approach which is conceptually clear, one that maintains musical meaning versus technical mapping.
The patch collects pitches played by the performer, then generates random index via a counter. The random index is then re-called from the [coll]. In this example MIDI note 60 (C3) is mapped to an automation clip in Ableton Live. The automation clip triggers a series of signal processes specified by the user. This example is using the built in mic on my laptop.
PD to Live - Phase 2 from Ricky Graham on Vimeo.
“Killing your Darling”
After some discussion, there is further potential to develop the patch into a more modular, versatile, and interactive performance system, which may allow the patch to operate with a greater degree of independence, encouraging the performer to engage with the system via a new performance approach, versus a learned or repetitive performance practice. I intend to develop the patch to further accommodate statistical analysis of pitch class development and additional string information, such as velocity, and note onset and offset. Thus, temporal phrasing will become an interactive part of the mapping and performance process. Other approaches include the utilisation of pick position data to trigger appropriate timbral processing, resizing the [coll] size in real-time to vary the rate at which a signal process is triggered, and the real-time drawing of automation values.
My thanks to Daniel Schorno for his feedback on this project.
Performance in Antwerp
This was a great opportunity to improvise with themes I have been developing for the forthcoming album by signalsundertests. I scored some motives to work with during the performance, but I am still developing an appropriate method of scoring pitch, timbral, and spatial attributes of each theme. I would like to work with a stave per string in future, and it is my hope that the score will also be applicable to acoustic instrumentation. All in all, an excellent experience.
signalsundertests performing at the Live Looping festival at Arenberg, Antwerp.
Thank you to those who provided photography on the night, including Ingrid, Sjugge, and Benjamin. My thanks to Sjaak and Ingrid for their hospitality, and to the amazing musicians which were a part of this wonderful event. And of course, thank you to all the staff at STEIM for their support. It was a very productive and enjoyable residency.
PD to Live - Phase 3
This next phase of my live performance system project was to implement a series of algorithms to reflect pitch structure in my chosen signal processes. The overall objective is to develop this patch into an interactive live performance system for polyphonic electric guitar, which reflects a balance between salient musical cues, such as pitch, timbre, space, and time, during real-time music performance. A work in progress.
PD to Live - Phase 3 from Ricky Graham on Vimeo.
Pitch tracking is utilised in PD to obtain string class data. The data is converted to MIDI note data (pitch and velocity). MIDI data is then recorded into a [coll]. In direct MIDI mapping mode, the user can simply associate MIDI notes with automation processes in Live. In random MIDI mapping mode, the recorded notes and associated DSP are recalled at random to allow an element of improvisation. The note sequence algorithm allows faster note sequences to cease DSP in Live, foregrounding pitch. The interval algorithm allows certain interval relationships to trigger CC messages. In this example, the CC’s are mapped to a variation of spatial gestures. I will continue to develop the algorithms for live performance.
PD to Live - Phase 4
PD to Live - Phase 4 from Ricky Graham on Vimeo.
