On Mon, 2009-11-02 at 10:52 +1100, David wrote: > Another thing about the that MIDI spec is where it says "optoisolators > ... rise and fall times should be less than 2 microseconds" which is > amusing because the total time of one midi bit is 3.2 microseconds. So > don't imagine you have nice square bits driving the system even if > your cable is zero length. So your optoisolators *might* be a limiting > factor depending on their speed (ie age, cost).
I think you make a factor of 10 error! One midi bit is 1/31250 = 32 microseconds, not 3.2 which makes a difference. On transmission line effects, lets see, 31,250 baud lets say you need the first ten harmonics to give a reasonable eye pattern, so say 300Khz bandwidth, and that transmission line effects become important at one tenth of a wavelength (reasonable rule of thumb), and that velocity of propagation is 0.6C, then: Wavelength = 300,000,000*.6/300,000 = ~600M, so transmission line effects can be totally ignored out to at least 60M or so. Lumped constant models look to be quite good enough, and it will almost certainly be a 5mA sources ability to charge the cable capacitance that will impose the ultimate limit. Current loops tend to have excellent interference rejection, and the fairly tight twisting in cat 5 can only help with this. Regards, Dan. _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/mailman/listinfo/linux-audio-dev
