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Mid-side stereo techniques
Mid-side stereo techniques
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Old 8th November 2019, 10:51 AM   #1
chris661 is offline chris661  United Kingdom
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Default Mid-side stereo techniques

I thought this might be an interesting discussion.

First, a little background.
Mid-side recording is a stereo microphone setup where there's a main mic pointing straight at the musician(s), and then there's a figure-of-8 (dipole) mic with the null aimed at the musicians.

The idea is that the main mic captures the middle/centre image, and the side (dipole) mic captures the left-to-right stereo difference signal.

By putting that through a patch matrix, you can derive a standard left/right signal, but with a key benefit: you can change the stereo width after the recording has taken place - anything from purely mono to 100% stereo difference signal.


I think it'd be rather cool to have that concept operating in a HiFi system.

I have a few drivers here that I think could work to make a suitable dipole system, although I think it'll need to be a 3-way setup to keep the figure-of-8 pattern nice and symmetrical throughout the operating range.

For kicks, I'll probably do this as a baffle-less design, and I'm planning on a small 3-way setup:
2x Tang Band W6-1139 (100-500Hz) - mostly chosen for mechanical headroom
2x Bose 2.5" full-range drivers (500Hz-3kHz)
2x small dome tweeters. Haven't picked a pair yet, but am looking for 3/4" or 1/2" diaphragms to keep dispersion nice and wide.

By using pairs of drivers facing in opposite directions, they should end up mechanically nice and balanced, so I can put bolts through the mounting holes and hang the next driver below. Distortion cancellation is a bonus, and hopefully it'll even out some of the frequency response anomalies you get when listening to the magnet side of a driver.

That's all for now. Thoughts welcomed - I'll try running the Bose drivers up to 20kHz next week and get some tweeters ordered in due course.

Chris
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Old 8th November 2019, 11:02 AM   #2
billshurv is offline billshurv  United Kingdom
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Mid-side stereo techniques
I have a mid-side processing stage on the bench to go in my next preamp for experimenting with tonal adjustments but not considered trying M-S speakers
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Old 8th November 2019, 11:33 AM   #3
AllenB is offline AllenB  Australia
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Did you mean to say two crossfiring dipole mics, I'm having a little trouble picturing how one would decipher which side is which.
Quote:
Originally Posted by chris661 View Post
For kicks, I'll probably do this as a baffle-less design,
You like a challenge
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Old 8th November 2019, 11:35 AM   #4
tmuikku is offline tmuikku  Finland
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Orbit sound stuff is like this I think: Airsound | Orbitsound

And while you are at it, try this, abit more refined solution with the same idea:
Stereophonic Sound from a Single Loudspeaker
http://elias.altervista.org/html/Sin...kerStereo.html

Works well! more speaker drivers required though.

I suggest try with cheap full range drivers first how do you like it before investing too much

Last edited by tmuikku; 8th November 2019 at 11:38 AM.
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Old 8th November 2019, 11:40 AM   #5
billshurv is offline billshurv  United Kingdom
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Mid-side stereo techniques
If you think that L+R =M and L-R=S its just addition and subtraction to go from M_S to L-R
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Old 8th November 2019, 02:07 PM   #6
Charles Darwin is offline Charles Darwin  United Kingdom
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Not sure that would work on replay with speakers since the figure of 8 mic signal is split on to two recording channels one of which must be phase inverted.
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Old 8th November 2019, 06:20 PM   #7
weltersys is offline weltersys  United States
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Quote:
Originally Posted by chris661 View Post
Mid-side recording is a stereo microphone setup where there's a main mic pointing straight at the musician(s), and then there's a figure-of-8 (dipole) mic with the null aimed at the musicians.

The idea is that the main mic captures the middle/centre image, and the side (dipole) mic captures the left-to-right stereo difference signal.

By putting that through a patch matrix, you can derive a standard left/right signal, but with a key benefit: you can change the stereo width after the recording has taken place - anything from purely mono to 100% stereo difference signal.

I think it'd be rather cool to have that concept operating in a HiFi system.

I have a few drivers here that I think could work to make a suitable dipole system, although I think it'll need to be a 3-way setup to keep the figure-of-8 pattern nice and symmetrical throughout the operating range.

That's all for now. Thoughts welcomed - I'll try running the Bose drivers up to 20kHz next week and get some tweeters ordered in due course.

Chris
Chris,

Sounds like you might be after something similar to "E" in this thread:
SynTripP: 2-way 2-part Virtual Single Point Source Horn

Or the threads mentioned by tmuikku in post #4.

I tried a prototype, the stereo effect was not very convincing, little better than simply processing through a single speaker, so didn't pursue the design further.

Looking forward to hearing your observations.

Cheers,
Art

Last edited by weltersys; 8th November 2019 at 06:31 PM.
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Old 8th November 2019, 07:59 PM   #8
krivium is online now krivium  France
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Hi,
Often thought about that but as a three chanel set up lcr kind of : one mono ( m ), a pair of full range exciter on some panels with decoded side to lr ( 100% stereo from m/s dematriced to l/r).
I will follow your thread.

Last edited by krivium; 8th November 2019 at 08:07 PM.
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Old 9th November 2019, 10:09 AM   #9
turk 182 is offline turk 182  Canada
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Originally Posted by Charles Darwin View Post
Not sure that would work on replay with speakers since the figure of 8 mic signal is split on to two recording channels one of which must be phase inverted.

which pressure gradient microphone brand are you referring to? or are you referring to hybrid back to back cardioids?

Last edited by turk 182; 9th November 2019 at 10:13 AM.
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Old 9th November 2019, 11:46 AM   #10
Charles Darwin is offline Charles Darwin  United Kingdom
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Got nothing to do with the brand of mic. Any mic with switchable polar patterns that includes figure of 8 can be used or (almost) any ribbon.

To make the middle&side stereo technique work you record the output of the figure of 8 mic on two tracks and invert one of them as far as I know.
Microphone practice - Wikipedia
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