Until now, when one wanted to "augment" a piano, the approach was essentially the same as for all other augmented instruments, whether string or percussion. That is to say that one or more transducers (small membranes which vibrate like those of loudspeakers) were fixed at strategic points of the resonance box. This box was then used as a natural speaker and amplifier to transmit an electroacoustic speech, via the vibrations induced by the transducer.
This arrangement has many advantages but it does not take into account the "natural" mode of sound emission and transmission of the piano; in other words, the vibrating string, which in turn vibrates the soundboard and then the whole body. Of course, the string can be set in vibration by the electronic speech but this is a secondary effect.
This is where the idea that germinated in the minds of composers Richard Causton and Per Bloland came from: to augment the piano by transmitting the electroacoustic signal directly to the strings. To do this, the two colleagues "prepare" the piano electromagnetically.
From left to right: Per Boland and Richard Causton
The problem, however, is that you can't stick a transducer directly on the piano strings; it would prevent them from vibrating naturally. But piano strings are made of metal and they are susceptible to variations of a magnetic field. Per Bloland, who is very involved in computer music research, has developed an ingenious device.
First of all, in order for the chosen string to be sensitive to variations in a magnetic field, it must be "polarized", that is to say, it must attract more positive or negative charges to a specific place than elsewhere. A simple magnet placed next to the string does the trick (this takes advantage of the mobility properties of the electrons in the metal of the string). On the other side, facing it, we put an electromagnet (i.e. a coil of electric wire: it is the passage of electricity in the wire that creates the magnetic field, the variations of the electric current leading to variations of the magnetic field) whose one of the poles is directed straight towards the string. And the trick is done. In principle at least.
Magnets in a grand piano
The problems of development were numerous, as Per reminds us, "when we send a signal that is a little too strong, the coil can melt under the effect of the heat generated by the electricity. The sound produced is beautiful! Like a soft scream. But then, it's over, the coil is broken, it must be changed. So, we learned from our mistakes and equipped our electromagnet with a heat sink."
"You also have to make sure that the string does not hit the magnet when it vibrates," says Richard. But the result is striking. You can play any signal, even a voice and you get the feeling that the string ‘speaks’!
"The major difference with the augmented piano we know is that the electroacoustic signal passes through a natural resonant body, and takes advantage of the sound radiation pattern of the instrument: it's almost magical! Secondly, the nature of the string allows for fine and delicate control. Equipped with its fundamental and its natural harmonics, it also acts as a filter: that is to say, for example, when we send a signal that corresponds to the natural frequency of the string (an A for an A string), the sound obtained will be louder. But this also means that if we send ‘noise’, we will end up with a caressing sound. We can manage attacks in a very refined way (since we don't need the hammer), make frequencies resonate that are not part of the harmonics of the string, or even produce multiphonics (by injecting a frequency while we play the string normally, with the hammer, thus making its natural frequency sound)."
Testing setup in a grand piano
So far, the system on which the two men are working (and for which they have already composed a few pieces) is made up of 12 magnets, acting on 12 strings (which they can choose as they wish, generally favoring a chromatic distribution). It was developed by Per Bloland, Steven Backer and Edgar Berdahl at the CCRMA (Center for Computer Research in Music and Acoustics at Stanford University), and during a first residency at IRCAM in 2013 to develop a control interface, via the "Induction Connection" module of the Modalys software.
The purpose of the artistic research residency they are carrying out at IRCAM is to expand the possibilities of the system. Among the avenues considered, Per Bloland and Richard Causton would like to extend it to activate up to 24 strings - and even equip other string instruments. This involves a number of challenges, such as adapting the power of the device to the size of the string (the lower the string, the thicker it is).
"We would also like to explore the possibilities of equipping the same string with several electromagnets, or study ways to change the sound quality of the string, or even its timbre."
But the first and foremost issue they are working on, and for which they are counting on the help of researchers from the Sound Systems and Signals: Audio/Acoustics, InstruMents team at IRCAM, is the development of an active control system. This implies adding a sensor to the device. The sensor, through the signal it provides in return, can then analyze the string's vibration modes and better understand its reactions to stimuli.
"Henri Boutin, with whom we are collaborating on this subject, is an expert in active control," says Per Bloland. " He's already worked on a vibraphone and a metallophone, and we expect a lot from him, especially in terms of rigor and completeness of the research. But also, to then develop the most complete and efficient control interface possible."
"After all," concludes Richard Causton, "the ultimate goal of this whole thing is to write music for this new instrument!"