KVR Audio

pljones · Post by **pljones** » Thu Jan 21, 2010 10:36 pm

...in (passive) hardware?

I've just had a bit of a fruitless google for hardware stereo to mid/side convert schematics...

I was hoping to find a simple passive circuit I could breadboard/stripboard up. I guess as I found nothing there's a good technical reason it can't be done. (But in my head it feels like it should just be a couple of resistors and capacitors in some kind of cross-over matrix... my electronics is 25 years unused, though and was never very good!)

Any ideas anyone?

C00kie · Post by **C00kie** » Fri Jan 22, 2010 7:40 am

There should be a way to do that. But with passive components only the results won't be perfect. Anything influences everything in the components network.

Getting the side channel only is easy. It happens by accident when only the ground of a stereo audio cable gets disconnected. Then it's a matter of adding/subtracting left and right to get mid again.

pljones · Post by **pljones** » Fri Jan 22, 2010 8:29 am

I guess the other question then: would the mid be a better mono source than straight mixed L&R (i.e. wired to mono)? I'm hoping so, otherwise it's not worth pursuing.

C00kie · Post by **C00kie** » Fri Jan 22, 2010 8:35 am

You want better mono?? Wow... just, wow....

aMUSEd · Post by **aMUSEd** » Fri Jan 22, 2010 8:42 am

What is mid/side? I keep seeing this term come up

tony tony chopper · Post by **tony tony chopper** » Fri Jan 22, 2010 9:17 am

I guess the other question then: would the mid be a better mono source than straight mixed L&R (i.e. wired to mono)?

mono IS mid IS mixed L&R

I know mid/side was last year's hip term but there's nothing magic to it, mid=mono (-6dB if you wanna be picky)

deaf dunderkwac · Post by **deaf dunderkwac** » Fri Jan 22, 2010 9:18 am

mid/side is a way of recording stereo information using a directional mic for the 'mid' (front-facing) signal and a figure-of-8 or bidirectional mic pointed at the sides (90 degrees from the mid mic) The signals are recorded separately and 'decoded' back into stereo by adding the mid/side signal for one channel and subtracting the side from the mid signal for the other channel.

This is accomplisheed using three input channels to the stereo mix bus. The mid mic is panned center and the side mic in entered into two channels panned left and right with the right channel's phase reversed.
Obviously the advantages to this method of capturing audio is one doesn't need to do anything but monitor the front mic for aiming the mid/side array. Also you always have a good mono-compatible signal.

I also successfully used an omni element for capturing the side information but my mid-mic was super-hyper-cardioid (Sennheiser 816 shotgun)
My best results was using Schoeps hyper-cardioid for the front and a bi-di head for the sides (C-5 system)
Stero fm radio is a mid/side encoded system btw

deaf dunderkwac · Post by **deaf dunderkwac** » Fri Jan 22, 2010 9:26 am

actually I've run across plug-ins that can encode or decode the m-s signal but I forget where

vicious_angel · Post by **vicious_angel** » Fri Jan 22, 2010 9:40 am

Simple explanation is:
Mid = summed mono signal
Side = mid signal phazed summed with the stereo. This removes all the mid signal from the stereo file so you have the true side signal.

deaf dunderkwac · Post by **deaf dunderkwac** » Fri Jan 22, 2010 9:44 am

C00kie wrote:You want better mono?? Wow... just, wow....

LOL can I make my mono be gooder than mono?

sorry... just read that part

tony tony chopper · Post by **tony tony chopper** » Fri Jan 22, 2010 10:11 am

LOL can I make my mono be gooder than mono?

It's not that stupid, there may be tricks to convert stereo to mono in a better way, reducing phasing issues.

If I was doing that, I would probably try to correlate left & right, and sum them at the phase offset where they match the most.

It may sound like it wouldn't be "true" mono, but at the same time if you listen through headphones to a mono sound with a 180deg-shifted channel, you do hear something. So you may ask yourself if the mono sum of both channels, which would be pure silence in this case, is really the "true" mono. Mathematically it is, but in practice?

deaf dunderkwac · Post by **deaf dunderkwac** » Fri Jan 22, 2010 10:20 am

tony tony chopper wrote:
LOL can I make my mono be gooder than mono?
It's not that stupid, there may be tricks to convert stereo to mono in a better way, reducing phasing issues.

If I was doing that, I would probably try to correlate left & right, and sum them at the phase offset where they match the most.

It may sound like it wouldn't be "true" mono, but at the same time if you listen through headphones to a mono sound with a 180deg-shifted channel, you do hear something. So you may ask yourself if the mono sum of both channels, which would be pure silence in this case, is really the "true" mono. Mathematically it is, but in practice?

in analog land there will always be a difference in digital land you get silence.
I mis-read the op's statement and thought they were starting out with a mono signal panned left/right.
Yes there might be better methods to sum a stereo signal into mono and I've run across plugs that do that also. They in essence convert the stereo signal into a m/s signal and toss out the s.

There are other methods also available and a quick google will be enlightening.

tony tony chopper · Post by **tony tony chopper** » Fri Jan 22, 2010 10:27 am

They in essence convert the stereo signal into a m/s signal and toss out the s.

mmh what? That's just normal mono.

deaf dunderkwac · Post by **deaf dunderkwac** » Fri Jan 22, 2010 10:32 am

tony tony chopper wrote:
They in essence convert the stereo signal into a m/s signal and toss out the s.
mmh what? That's just normal mono.

simplified explanation

essence of phraseology. Various methods of phase correction is employed

pljones · Post by **pljones** » Fri Jan 22, 2010 8:22 pm

teleute wrote:mid side would require subtracting the two signals. the only way i can think of doing that passivly is to connect the left and right signals to either side of a transformer coil, then only the diffrence between the signals would be passed to the other coil.

you could use the transformer found in a ground loop isolator as it should be rated 1:1.

I was slowly moving in this direction... At least I have something new to google on and hit this:
http://www.diyaudio.com/forums/car-audi ... -mono.html
so I feel I'm not alone

.

You're talking about taking something like this:
http://www.djsoundkit.co.uk/proddetail.php?prod=B071A
except, rather than feeding it left and right on the two ins as you'd expect, feed it left and right as signal and ground on one in and use that out? As the mid/mono?

Can you convert Stereo to Mid/Side...