Mid Side - does cable length affect the phase/delay of stereo result?

[Newmarket]

It was a good question from the OP ignoring the speed of electrical signal propagation through wires being extremely fast compared to the relatively pedantic audio wavelength/periods.

In other slower mediums sum and difference combinations of audio traveling over different path lengths (like through air) can interfere..... and for much higher frequencies than audio the propagation speed through wires can result in constructive or destructive interference (and more).

"No" was just my succinct answer to the original question. There is nothing wrong with more information but at some point it can get confusing "Blinding them with science".

Just to be clear you are comparing the speed of an analog audio signal passing through wire vs, MIDI digital bit stream passing through wire. Apples and Grapefruit... not the same. There is propagation delay in both the midi send end and midi receive end.

The delay has nothing to do with the length of the midi cable. I recall experimenting with sending MIDI signals through 100' long audio snakes with no appreciable delay (while I wasn't measuring for that, I just wanted to see if it worked).

JR

Yes. Except that ime "propagation delay" refers only to the transmission of a signal in a cable (or eg optical fibre). But, as you point out, any delay of the type the OP has experienced is not down to the cable length (or construction fwiw).

 

[radardoug]

again please clarify... are you experiencing a signal delay related to the length of your midi cable? i.e. short midi cable passes signal faster than long cable?

IIRC midi uses RS-485 serial data protocol that is supposed to be good for thousands of feet (at least for slower data rates).

JR

Its not really RS485 John. It is a standard UART, but uses an optical coupler. RS485 uses differential send and receive ics.

 

[Newmarket]

Roughly the speed of light, only a lil slower?

The commonly used "Speed of Light" figure refers to the speed in a vacuum. Speed in other media is slower. Speed of - let's call it an electromagnetic wave here - in a wire/cable depends to some extent on construction. But from memory somewhere between 60 - 70 % is ballpark.

 

[Newmarket]

IIRC midi uses RS-485 serial data protocol that is supposed to be good for thousands of feet (at least for slower data rates).

JR

It's not RS-485. At an electrical level it's a current loop (how many mA escapes me atm) with opto-isolation at one end.
Regardless, in reality it works for a lot longer than the specification and is not the cause of the delay
Unless you make a mistake and get a resistor value wrong by an order of magnitude making it very susceptible to noise interference Ask me how I know 2am when we found it (not my error tbf). At least thirty years ago - I still remember it

 

[Chrisfromthepast]

A room full of college students gasped when our E&M professor walked us through the derivation of the actual electron travel speed. .0004m/s is close enough to whatever made us all gasp. (10^-4)
Please forgive me for confusing that figure with the electrical impulse speed, which was really the subject of this thread before all the derailments. I apologize for my part in the confusion.

 

[Ike Zimbel]

IIRC I tested sending midi down a 100' audio snake. But this was last century.

JR

I ran it down a longer snake than that in the 90's. We had a requirement for the FOH engineer to trigger an effect in the artist's mix at monitors. We just made XLR-DIN adapters and ran it down the snake. I forget if it was the mic snake or the return snake, but either way it was 250-300'. It's been a while, but IIRC, there were duplicate FX units (SPX-somethings...) at FOH and Mons. It made more sense to keep the audio local to each desk rather than send the effected signal back down the return snake.
I never heard of a single issue with this arrangement.