Hi Mark and Jim, Thanks for reading my message and responding so informatively.
Regarding music synthesis, Mark wrote: > OTOH, I can't really imagine how music synthesis could use enough > compute power to keep more than a few cores busy, no matter what > programming model you choose. That may be true for playing samples, doing conventional digital reverberation or for implementing oscillators, filters and the like. However, consider the task of simulating a binaural recording, which in the physical world involves microphones in the ear-canals of a real or dummy human head, so that when the recording is listened to on headphones, the listener has reasonable left-right, and lesser front-back and above-below perception of the direction of the various sound sources, due to the way human hearing interprets the gain vs. frequency, the time delays and the phase responses generated by the head and outer ear (pinna). In a 6 sided room, with a single sound source, there are 6 first-order reflections, 30 second-order reflections, 150 third-order reflections and so on. Each path of sound, with frequency response, volume, time delay and direction should be modelled and subjected to a binaural transformation at the location of the head. (Finite element simulation of the air in the room would be way out of control, due to the need to model 5 or more cells per wavelength, such as 3mm cells for 15mm wavelengths. That would be 3 x 10^7 cells per cubic metre, and a musically interesting room or hall might be 10^6 cubic meters.) We would typically want to simulate multiple sound sources, and the sources are not isotropic, so their spectrum varies with the direction of sound emanation. To do this properly, and generate a realistic reverberation field, would also involve frequency response behaviour or the walls, and most likely many more walls. To get realistic decays involving fiftieth-order or hundredth-order reflections, the number of paths to simulate (per sound source) would be completely out of the range of any known computing resource. Likewise simulating the reverberation of a double-bass, and the string slapping on its wooden finger-board, or a sitar with its melody and sympathy strings slapping on the bridge which is mounted on a resonant gourd, or a sarod which has strings slapping both on the metal fingerboard and the bridge . . . The string tension is a function of all the waveforms at any instant, and so frequency modulates the traversal speed of all those waveforms, giving rise to a generally higher pitch at the start of the note. Stiff metal strings lead to generally higher frequencies for the upper harmonics, since these involves more bends each at a sharper angle per length of string for a given amplitude. A cymbal (or gong) might be simulated as a thousand or more interconnected zones in which waves travel in all directions in the plane of the cymbal. The speed of propagation in each zone depends in part on the tension on that piece of metal, which is an instantaneous function of the stresses on it due to all the waves traversing it at that time, with the short waves stressing it more than long waves for a given amplitude. So by injecting a single frequency or a simple low-frequency impulse (a soft mallet stroke), the waves bounce around the cymbal with all frequency components intermodulating all the other frequency components in unique ways in each of the 1000 or whatever zones. So a gong starts off with a "bong" sound which intermodulates up to a "hiss". (I think the same process occurs on the level of atom cores and atomic outer-orbital electrons in thermal motion within a solid object - any input frequency being intermodulated into a broadband random set of frequencies with an upper bound which rises as a function of the average energy.) In reality, there are no separate zones of a cymbal or gong, so better simulation would be achieved by modelling 10,000 zones or whatever. These are examples of real-world physical processes which make pleasing, familiar, sounds but which result from fiendishly complex physical processes. They would be extremely computationally intensive to model, even if it was possible to write suitable software. It is easy to take these sounds for granted, but even thinking about simulating them can provide new levels of appreciation for the richness of the physical world. It would be easier to bang a gong with a mallet, but I think it would be fun and enlightening to use complex computer modelling to create physical-like sounds and responses to other sounds which would be difficult or impossible to realise in the physical world. As far as I know, computer music synthesis languages don't work on clusters, though some may use multithreading. - Robin _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
