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zemlin
Location: USA
Posts: 1156
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 Posted - Mon Jun 30, 2003 8:19 am
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Just a thought inspired by my first M-S recording yesterday. Maybe this is a "DUH!" for the rest of you, but I don't recall seeing this mentioned before - I generally ignore surround-related threads as I only have 2 speakers.
Using the same idea as the SIDE mic for left/right information, a figure-8 MID mic could provide the REAR component by inverting that channel.
Front Left = +M+S
Front Right = +M-S
Rear Left = -M+S
Rear Right = -M-S
Center channel = +M
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MusicConductor
Location: USA
Posts: 1524
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Posted - Mon Jun 30, 2003 9:23 am
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In theory there is some validity to what you're saying, as what you're suggesting is similar to traditional "passive" surround setups. However, what you're suggesting would make, for example, the right rear information identical to the front left, except that its polarity would be flipped. Traditionally, the "passive" surround approach would merely place the "S" information alone in the rear speaker(s).
(BTW, "passive" surround simply means that four channels are derived from summing or subtracting, and "matrix" surround, such as Dolby Pro Logic, means that processing, steering logic, and other phase tricks are employed to manage the sound.)
Unfortunately, when all is said and done, what you have here is still a 4-channel process derived from 2. I think when you get to the point (here's wishing for you!) of monitoring in 4 or more channels, your ears will immediately recognize the difference in surround quality when at least 4 microphones are used to capture the sound. For example, you could still use an M-S or X-Y pair for your main front source, or if you feel a phantom center channel isn't adequate, use 3 spaced cardioids for a L-C-R approach (but there are plenty of dangers with this). Position your front mics from the source so it's just a tad drier in ambiance than you'd normally prefer. Then use another pair to literally mic the ambiance. I've heard of more than one engineer aiming cardioids at the corners and getting rather lovely results, but this will always depend on the room.
Then, assign each of these signals to the correct speaker locations, and you'll hear why discrete 5.1 is such a vast improvement over Dolby Pro Logic and every other "4-2-4" matrix system.
Of course, this crude example assumes an empty room and acoustic music, perhaps classical. I don't recommend miking an audience as the primary source for surround information because their racket is distracting and uncohesive to the music. Audience mics are valuable for spots of limited duration like applause, or participation through singing or clapping. Non-acoustic music needs a different approach for surround that is not dependant on acoustics alone to work, which is best done in the studio or with lots of musicians (overdubs, chorusings, , artificial reverbs and effects, etc).
A little voice is telling me that this is way more than you wanted to know, Karl!
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zemlin
Location: USA
Posts: 1156
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Posted - Mon Jun 30, 2003 10:55 am
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| MusicConductor wrote: |
| A little voice is telling me that this is way more than you wanted to know, Karl! |
Like I said - I only have two speakers anyway, so I won't be doing surround mixing for a while. It was just a thought.
The examples I had in my little brain would be more "ambient" sounds - crowd noises, nature sounds, traffic, etc. It seems to me that you could get a pretty realistic playback of sounds that surround you. Perhaps it would be easier to set the mics up as XY with figure eights (not a new invention, I know - I don't recall the name of this setup) and assign LF/RF the normal way and reverse phase for RR/LR
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SteveG
Location: United Kingdom
Posts: 6695
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Posted - Mon Jun 30, 2003 11:51 am
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| zemlin wrote: |
| It seems to me that you could get a pretty realistic playback of sounds that surround you. Perhaps it would be easier to set the mics up as XY with figure eights (not a new invention, I know - I don't recall the name of this setup) and assign LF/RF the normal way and reverse phase for RR/LR |
It's called a 'Blumlein' array, and it's been around since 1931. It is regarded as having excellent lateral imaging, and giving a good sense of the 'acoustical space' that it is in. And it has placement problems with large groups - since you can't alter the mic angles without screwing up the response (this is almost always a pure gradient sin-cos response) you find yourself getting too far away from large groups to get the imaging correct. That's when you revert to the classic 135 degree crossed cardioids.
So the 'pseudo' or passive rear information will be of a better quality from a pair of crossed figure-8's, certainly, but as MC says, this isn't a good idea with an audience. Unless of course you are into recording audience 'participation'...
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ozpeter
Location: Australia
Posts: 3200
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Posted - Mon Jun 30, 2003 7:26 pm
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I've hear a couple of excellent string quartet live recordings by Mike Skeet using crossed fig of 8's - one of which was at Wigmore Hall, where the audience know not to even think of even breathing! The sound did have a special something about it, spacially.
Any more feedback on how your recording itself went, Karl?
- Ozpeter
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zemlin
Location: USA
Posts: 1156
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Posted - Mon Jun 30, 2003 8:08 pm
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| ozpeter wrote: |
| Any more feedback on how your recording itself went, Karl? |
The recital was for voice and flute students. Some pieces had Piano too. The room was pretty live, but not bad accoustically. The crowd was much larger than anticipated and I left my big stands at home so the mics were surrounded by audience. I think it would have been better to have the mics futher off the floor.
I had the C3s setup as MS and my NT5's as XY all on top of a single straight stand about 6' off the floor. The room had a flat, tile floor.
The flute pieces sound pretty good with the MS setup - a much fuller sound than the XY - to be expected considering the resulting pattern. They benefit from the reverb.
For the vocal pieces I think I'm going to mix the cardiod C3 and the XY - the MS mix is too "roomy" for the vocals, and the XY pair sounds a bit thin without the C3. I haven't mixed it much - I might also try just MS with less "S".
Once I get through it I'll post some samples for comparison.
Some of the performances were pretty good - there were a few beginners, and one that should seriously consider trying something else. 
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ozpeter
Location: Australia
Posts: 3200
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Posted - Tue Jul 01, 2003 1:54 am
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How close were you? IMHO, an MS setup will tend to sound best a bit closer to the source than an XY setup would. I've been trying to work out in the lounge here what sort of distance I'd be from a small chamber group, if using an MS pair - as a sweeping generalisation, it looks like between 2.5 metres to 4.0 metres to get good focus and presence, and for the performers to have width, with perhaps a tad more side in the mix than 50/50 (55/45?). Of course it's partly room dependent, though thinking through various rooms/halls in my head, not that much so long as it's not downright nasty. Same thing with levels - not much variation seems necessary - I have a little line drawn beside my mic preamp's gain control which I know will give me the right level at the recorder with most sources, because if it's a symphony orchestra the mics will be somewhat further back compared with a guitar - so it's the distance which varies the level rather than the gain at the preamp. (BTW I understand from Sennheiser UK that the MZA MS-1 preamp is still available for around 400 pounds sterling; I'd alleged in another thread that it was discontinued).
- Ozpeter
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zemlin
Location: USA
Posts: 1156
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Posted - Tue Jul 01, 2003 11:54 am
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| ozpeter wrote: |
| How close were you? |
I would guess they were about 5'-8' from the mics - it varied with each performance.
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MS for Surround mixes
