From Brian Willoughby Sent Thu, Dec 27th 2018, 05:11
On Dec 26, 2018, at 6:54 PM, Michael E Caloroso = <xxx.xxxxxxxxxxx@xxxxx.xxx> wrote: >> 3) Although 99% of MIDI devices have MIDI Thru wired properly with 0 = latency from MIDI >> In, I seem to recall hearing about a few MIDI devices that have CPU = processing on the >> MIDI stream for MIDI Thru, and that would introduce latency. That = would be in violation of >> the MIDI standards, so I hope you don=E2=80=99t have any devices like = that. >=20 > The telltale is a device with a port labeled "MIDI OUT/THRU" or only > IN/OUT ports but no THRU. Buried in the menu system may be a > configuration to change the OUT port to a THRU. Under this condition > the "THRU" signal isn't the circuit spelled out by the MMA and is > actually coming from the CPU on the device, which WILL have some delay > to it. Theoretically, a MIDI device could use a digital multiplexer to switch = the MIDI jack between CPU output and a textbook MIDI Thru circuit. I=E2=80= =99m not aware of any synths actually doing this, but it would be = possible to have a switchable port that doesn=E2=80=99t introduce = latency when set to Thru. > I'm not a fan of chaining THRU ports as one too many can distort MIDI > signals to the point where they are not recognized at the receiving > device or can appear as another erroneous MIDI message. I'm not > talking clock messages, I'm talking performance messages like note > on/off and CC messages. Perhaps I=E2=80=99m missing your point, but there is nothing = electrically different between MIDI clock messages and MIDI Note On/Off = and CC messages. They=E2=80=99re all 8-bit serial words with 1 start bit = and 1 stop bit. If distortion were to occur, it could affect any bit, = and there=E2=80=99s no reason that MIDI clock messages would be immune = to such bit errors. 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. If someone has a = reproducible test case to the contrary, I=E2=80=99d be very interested = to read the details. Brian Willoughby