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

[canidoit]

If I was to use a hardware M/S unit, and for example:
Mid: Equaliser (6 meters away)
Side: Equaliser (30cms away)

Does the length of cable cause a delay when the M/S comes together causing a phasing in the stereo audio?
When there is a delay between Mid and Side, when it is summed back to stereo, what are the artefacts? - phasing, center is off, distortion?

Thank you.

 

[JohnRoberts]

no....

JR

 

[k brown]

no....

JR

Couldn'a said it better myself.

 

[pucho812]

I did some digging on this.

A good approximation of electrons in a wire is 11 inches of travel every nanosecond. I saw this on a science show years back and it's one of those Many audio factoids I keep in the brain bank. Just like how sound proximately travels 1100 feet every second at 72 degrees in temperature.
Anyway if the 11 inches in a nanosecond is true, we can say the speed of light through the cable is 11/12 ns/ft (considering impedance). Considering it is a minimum 20ms for our brains to interpret a delay, then the length of cable necessary to produce an audible delay is approximately 3,472 miles, or roughly the distance between Washington, DC and Sacramento, CA.

You will find that there are other things that are more likely to cause an audible delay then the cable itself.

 

[micolas]

@pucho812
About what would be the delay in the case of the distance from the Earth to the Third Stone from the Sun?
(I apologize, I couldn't help myself, sometimes my humor gets out of control )

 

[k brown]

I did some digging on this.

A good approximation of electrons in a wire is 11 inches of travel every nanosecond. I saw this on a science show years back and it's one of those Many audio factoids I keep in the brain bank. Just like how sound proximately travels 1100 feet every second at 72 degrees in temperature.
Anyway if the 11 inches in a nanosecond is true, we can say the speed of light through the cable is 11/12 ns/ft (considering impedance). Considering it is a minimum 20ms for our brains to interpret a delay, then the length of cable necessary to produce an audible delay is approximately 3,472 miles, or roughly the distance between Washington, DC and Sacramento, CA.

You will find that there are other things that are more likely to cause an audible delay then the cable itself.

One's horoscopic sign probably has more effect.

 

[pucho812]

One's horoscopic sign probably has more effect.

that was really funny.

 

[capacitorless]

Low Earth Orbit here (.63 to 6.2ms latency for 110 to 1200 miles of cable)

 

[canidoit]

Why is it though that I get a delay on my midi cable, that is 6 meters long when I play keyboard to my DAW? A 1 meter cable is unnoticeable when playing but when I used a 6 meter cable, there is a noticeable delay?

 

[radardoug]

Why dont you research before asking these kinds of questions? Midi is not audio. Midi has a baud rate of 31.25 KB/s. It takes time for a MIDI signal to be sent and interpreted. Not a lot though. See if you can research how much. Come back to class with the answer.
By the way, the MIDI cable is not doing the delay.

 

[k brown]

Why is it though that I get a delay on my midi cable, that is 6 meters long when I play keyboard to my DAW? A 1 meter cable is unnoticeable when playing but when I used a 6 meter cable, there is a noticeable delay?

You forget that Data was not human . . .

 

[canidoit]

Hi radardoug, the theory is way ahead of me. Thanks for your explanation and pucho812 as it provided it to me in laymans terms or something I can try to grasp with. Now I have terms and concepts to gain a better understanding of it which I can dig deeper into and put in practice. I mainly just plug cables and see/hear what happens.

 

[micolas]

You guys are amazing!
There is still hope in the world.
Great humor. We're a cool bunch.

 

[Newmarket]

Why dont you research before asking these kinds of questions? Midi is not audio. Midi has a baud rate of 31.25 KB/s. It takes time for a MIDI signal to be sent and interpreted. Not a lot though. See if you can research how much. Come back to class with the answer.
By the way, the MIDI cable is not doing the delay.

True but doesn't account for the perceived delay with a longer MIDI cable. I suspect it's something in the DAW / computer setup being different. I suggest to OP to try with a hardware sound module if wishing to investigate this. Plus is it a real MIDI cable or MIDI over USB ?

 

[tinn]

Why is it though that I get a delay on my midi cable, that is 6 meters long when I play keyboard to my DAW? A 1 meter cable is unnoticeable when playing but when I used a 6 meter cable, there is a noticeable delay?

Maybe your ears have been 6m away from the speaker then ? (17msec)

 

[Matt Nolan]

I did some digging on this.

A good approximation of electrons in a wire is 11 inches of travel every nanosecond.

Just a little pedantry here, but in the spirit of education. Electrons in a wire move at somewhere closer to a few millimeters per second. Your 11 inches per nanosecond is the speed of the wavefront. Think of it more like a Newton's Cradle or whipping a long rope (not perfect analogies, but examples of wavefronts moving somewhat independently of the actual material through which they propagate).

 

[Newmarket]

Just a little pedantry here, but in the spirit of education. Electrons in a wire move at somewhere closer to a few millimeters per second. Your 11 inches per nanosecond is the speed of the wavefront. Think of it more like a Newton's Cradle or whipping a long rope (not perfect analogies, but examples of wavefronts moving somewhat independently of the actual material through which they propagate).

fwiw I do think that's it's good to clarify that point.

 

[ccaudle]

Considering it is a minimum 20ms for our brains to interpret a delay

Perceptible delay is not really the relevant measure here. In M/S processing (or any kind of processing which involves summing) a substantial delay will create comb filtering.
The measure of "substantial" is how many degrees at a particular frequency. A fixed delay will be a higher percentage of a full cycle at higher frequencies, so generally for worst case you would consider the effect at 20kHz (even though for most adults behavior at 20kHz is not particularly relevant it gives a nice consistent worst case target to use).

The propagation velocity at low frequencies is not quite the same as at high frequencies, but for a quick analysis you can just assume it is the same, and then dig into more precise details if it is within an order of magnitude of something you care about.
Propagation velocity in twisted pair is around 70% of free air, so about 200Mm/s, or equivalently about 5ns/m.
Period of 20kHz is 1/20k or 50us.

So the difference in propagation delay between 6m and 0.3m is the propagation time through 5.7m, or just under 30ns.
30ns/50us is 0.00057, or 0.057% of a wavelength. One degree is 1/360=0.28% of a wavelength, so the difference in propagation delay through an extra 5.7m of cable is around 0.2 degrees. And of course relatively less at lower frequencies.
I don't have time to whip up a Matlab script that shows the effect of summing two identical 20kHz sine waves with a 0.2 degree offset, but needless to say it will be very small.
In a real system that will be down in the noise, and for a M/S setup you should not typically have the M and S signal at almost the same amplitude in both channels, so any combing will be even less if the signals are not identical amplitude.

A little bit long winded, but an example of how you can think through questions like this and get a little better understanding of when you should be concerned rather than just looking to someone to give you a yes/no answer.

 

[pucho812]

Perceptible delay is not really the relevant measure here. In M/S processing (or any kind of processing which involves summing) a substantial delay will create comb filtering.
The measure of "substantial" is how many degrees at a particular frequency. A fixed delay will be a higher percentage of a full cycle at higher frequencies, so generally for worst case you would consider the effect at 20kHz (even though for most adults behavior at 20kHz is not particularly relevant it gives a nice consistent worst case target to use).

The propagation velocity at low frequencies is not quite the same as at high frequencies, but for a quick analysis you can just assume it is the same, and then dig into more precise details if it is within an order of magnitude of something you care about.
Propagation velocity in twisted pair is around 70% of free air, so about 200Mm/s, or equivalently about 5ns/m.
Period of 20kHz is 1/20k or 50us.

So the difference in propagation delay between 6m and 0.3m is the propagation time through 5.7m, or just under 30ns.
30ns/50us is 0.00057, or 0.057% of a wavelength. One degree is 1/360=0.28% of a wavelength, so the difference in propagation delay through an extra 5.7m of cable is around 0.2 degrees. And of course relatively less at lower frequencies.
I don't have time to whip up a Matlab script that shows the effect of summing two identical 20kHz sine waves with a 0.2 degree offset, but needless to say it will be very small.
In a real system that will be down in the noise, and for a M/S setup you should not typically have the M and S signal at almost the same amplitude in both channels, so any combing will be even less if the signals are not identical amplitude.

A little bit long winded, but an example of how you can think through questions like this and get a little better understanding of when you should be concerned rather than just looking to someone to give you a yes/no answer.

o.k. sounds good except I wasn't asking the question or looking for a yes or no answer.

 

[ccaudle]

I wasn't asking the question or looking for a yes or no answer.

The original poster was, I just used your reply as an easy jumping point to respond to the original question.