4A is the name of the first processor realized by Italian physicist Giuseppe Di Giugno for digital sound processing. This device was designed between Naples and Paris, at Ircam, in the mid-Seventies.

Brief History – A first version of the 4A digital processor, was realized by Peppino Di Giugno, as he was called the Italian physicist, at Naples, where he worked before to went at Ircam. Just the potential of this device stimulated Luciano Berio to call Di Giugno at Ircam.
So, in Paris, at the research center wanted by Pierre Boulez, Giuseppe Di Giugno developed a new version of the 4A DSP, initiating his collaboration with the Ircam.

Reference Models – The 4A project born with goals very different, compared with those projects of the subsequent years. The main need was to have a digital instrument capable of synthesize the most number of voices. This goal was very difficult to reach with analogical devices (primarily due to superheating problems), for this reason the Italian physicist wanted to develop a bank of digital oscillators which has aroused immediately good impressions. Although the 4A could be considered an innovative instrument, at once it was clear that the first version was not able to satisfy the many needs of music composers. Two of these needs were most important: the real time and the control of the sounds synthesized. From this point of view, Peppino Di Giugno had many reference models that his project might improve. First, the Groove system by Max Mathews. This a hybrid system (with a digital part for the sound synthesize and an analogical part for his control) very powerful in the Sixties, but obsolete due to his analogical device. Di Giugno was able to achieve a same powerful device but all digital. Max Mathews offers to Di Giugno even the model of the Music V, which inspired the digital oscillator developed for the 4A by the Italian physicist. As much important has been the digital synthesizer designed by Hal Alles at Bell Labs in the same years.

Technical Features – Certainly, the 4A had to ensure a greater speed calculation, because only this technical feature would allow to reproduce 256 oscillators. This goal, for the 4A project, could be achieved easily thanks to the fact that the computer at Ircam was dedicated only to this research, not shared for general works. The faculty of synthesize 256 voices was something extraordinary for those years. To understand how extraordinary was this fact, you just know that an analogical device was capable to use ten oscillators maximum, because already a lower number of oscillators caused an overheating of components. Another new feature of the 4A was the use of variable waveform instead the fixed waveform adopted by others musical systems.[1] Since the 4A was a real time system, the sound control was run through a PDP-11/40 computer. This machine allow to control parameters such as frequency, amplitude and phase but the oscillators could not be linked togheter.[1]

Output – The output was equipped with four converters that return four channels, each able to run 16 oscillators. Certainly the 4A was not perfect, in particular should be noted that the real time capacity of the 4A, to which I’ve before mentioned, was not a very real time but it operated with a little latency, inasmuch an increased of the computational speed would generated a lot of noise. Controls in real time of musical parameters were possible thanks to a macro library and thanks to little software programmed in Fortran. The control parameters could be automated and saved in memory.

Limits – The only limit of the 4A DSP, really, was the growing need of the composers, which hoped an instrument much powerful: a simple oscillators bank was not satisfactory for musical needs. So, the next research activity of Peppino Di Giugno was a continuous improvement of this first digital signal processor, with the aim to design a DSP capable to satisfy every possible idea. For this, the 4A was rapidly set aside in favor of a new project named 4B.

For this topic I’ve read:

[1] Gerald Bennett, Research at Ircam in 1977, Rapports IRCAM, Centre Georges Pompidou, Parigi, 1977.
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