JohnSwenson;680525 Wrote: > I have a theory as to what is going on, and SOME actual measurements to > back it up. > > The theory is that what is most important is main memory access, NOT > processor load. Think about it for a minute, the processor is connected > to the main memory chips with a bus that is hundreds of bits wide, when > a memory access occurs a large percentage of these switch all at the > same time (actually within 50 pico-seconds of each other). The > capacitance on a wire going from one chip to another is orders of > magnitude greater than the capacitance inside a chip, thus every time > that external bus switches huge currents flow in order to charge and > discharge those capactitances. This produces huge currents in the > groundplane and PS traces as well as EMI emitted from the signal wires > themselves. > > My analysis of groundplanes indicates that noise caused by the memory > interface is much larger than that from the processor itself doing its > thing. > > Thus the most critical thing you can do is to cut down on main memory > accesses. The easiest way to do this is to make sure that as much as > possible stays in the processor cache. This I think is where most of > these tweaks actual work. Decreasing the buffer size means that > frequently the buffer can stay in cache and the data doesn't have to go > in and out of main memory as much. Same for processes, every time the OS > switches to a new process the cache is cleared and code and data have to > come from main memory. > > This can also help explain things like flac or PCM decoding. The flac > decoding may not take all that much more processing power, but the code > is much more complex, the PCM code will have a higher probability of > staying in cache. > > This may not be everything that is going on, but I think it is a major > contributor to what is happening. Unfortunately there is no tool you > can run that gives you a graph of processor cache misses, it would take > a logic analyzer looking at the memory bus. I think that focusing on > processor utilization is a red herring and not worth worrying about as > long as it doesn't get too high. > > John S.
Fascinating! Assuming your theory is correct -- and it sure sounds plausible to a non-technical person like me -- what is astonishing is that some of the relatively minor tweaks suggested in this thread have such noticeable and repeatable effects on the sound, ad to boot, effects that are so dependent on equipment, musical tastes, expectations, and so on. I'm in awe of the complexities of this little box . . . and of the great sound that it can unleash. Guido F. -- guidof MUSIC ROOM: Marantz TT 15S1 Turntable, Virtuoso Wood Cartridge->Conrad Johnson Motif preamp Oppo BDP-83 Universal Player->Cambridge Azur 840C DAC Vortexbox Appliance->WiFi Bridge->Squeezebox Touch->Toslink->Cambridge Azur 840C DAC->Adcom GFP-750 preamp->Music Reference RM-200 Mk II amp -> Martin Logan SL3s DSpeaker Antimode 8033->REL T1 Sub BEDROOM: Squeezebox Touch (analog out)->Little Dot Mk III amp->AKG K701 headphones SECOND BEDROOM: Squeezebox Touch->Grado SR125 headphones ------------------------------------------------------------------------ guidof's Profile: http://forums.slimdevices.com/member.php?userid=40448 View this thread: http://forums.slimdevices.com/showthread.php?t=91322 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
