From Brian Willoughby Sent Thu, Dec 27th 2018, 09:21
From Brian Willoughby Sent Thu, Dec 27th 2018, 09:21
On Dec 26, 2018, at 10:34 PM, Michael E Caloroso = <xxx.xxxxxxxxxxx@xxxxx.xxx> wrote: >> However, there=E2=80=99s no evidence that any synth manufacturer has = problematic MIDI >> Thru circuitry that would actually cause bit errors, no matter how = far down the chain >> they are placed. There are actually a pair of inverter gates ahead of = every MIDI >> Thru circuit, and if those are Schottky inverters, such as common = 74LS04/14/06 hex >> gates, then they=E2=80=99ll actually clean up any slew rate problems = on the input such that >> the output is just as good as the original. >=20 > The '04/06 are not Schottky types, but you are correct that Schottky > '14 gates can clean up dirty logic signals. If you buffer the input > to the Schottky gate and add a cap of the right value, it can turn a > narrow input pulse into a nice square one. That=E2=80=99s why I listed 74LS, as in Low-power Schottky. There=E2=80=99= s also 74S High-speed Schottky, 74AS Advanced Schottky, and 74ALS = Advanced Low-power Schottky. You might be thinking of the Schmitt trigger, which the 7414 is. A = Schmitt trigger would certainly clean up any problems at the end of a = MIDI chain. They=E2=80=99d prevent any such problems from building up in = the first place. Schottky is just fast, so it should sharpen up the edges on Thru. = Schmitt actually implements hysteresis, which sort of gets rid of any = analog uncertainty in the rising or falling edges. But Schmitt is = probably only necessary when the signal actually changes directions = while rising (or falling), and I doubt that even a long chain of MIDI = Thru would start exhibiting those kinds of problems. > Interestingly enough, the MIDI spec - my 1983 or 1988 specs - do not > specify a Schottky inverter, they even suggest a discrete inverter. True. It just seems like 74S or newer have been common in synths. I = can=E2=80=99t remember the last time I saw a literal 7404 or 74L04. Brian