SASS matrix

Posted: Sat Jan 08, 2005 7:52 am

Just wondered if anyone has used this technique. I know some people have resurrected it and have achieved good results. I'd like to try this when I get a pair of SDC omnis, but I'm not sure if I'd trust a software implimentation.
Thanks
John

Posted: Mon Jan 10, 2005 12:55 am

I am not familiar with this-- could you elaborate?

Rich

Posted: Mon Jan 10, 2005 1:04 pm

Hi Rich.
SASS makes use of the fact that omnis act like cardioids at high frequencies.

It resembles m/s in some respects, but it's done using two closely spaced omnis. With the upper frequencies, the mics are treated like cardioids using intensity differences, but below a certain frequency (at which an omni is no longer directional), these differences are almost non-existent , so phase information is used to construct left and right channels. It's yet another tecnique invented by Blumlein. I've heard examples where it's been used, but never on a commercial recording -as far as I know.

A SASS setup has a lot of practical difficulties, and is not for the faint-hearted, but when it works it's absolutely wonderful.

John

Posted: Mon Jan 10, 2005 1:49 pm

Unless I have misunderstood your description, this is what I have been doing when applying NOS to omnis-- 90 degrees and about 12 inches between the capsules.

It works much better than conventional wisdom would expect.

Rich

Posted: Mon Jan 10, 2005 4:45 pm

Hi Rich
In SASS, the mic inputs are treated like M/S below a certain frequency. One mic signal has the phase reversed and both are then added for one channel. For the other channel there is no phase reversal, and both signals are summed. The higher frequency parts are not processed in this way, and just go either left or right as a cardioid pair, as the mics aren't omnis at these frequencies.

Using SASS, the mics are quite close together.

I think that's it anyway!

John

Posted: Mon Jan 10, 2005 5:37 pm

BTW Rich

I think one of the big mic companies sells something called SASS, but it doesnt work like the setup I described. I don't know why they use the term, but Blumlein's SASS it ain't.
John

Posted: Mon Jan 10, 2005 6:33 pm

That would be the Crown SASS-P stereo mic. Basically a couple of PZM's in a big ugly mount. Sounds as bad as it looks.

--Ben

Posted: Fri Jan 14, 2005 7:41 am

John Stafford wrote:

Hi Rich
In SASS, the mic inputs are treated like M/S below a certain frequency.

John

I didn't know Blumlein invented another microphone technique! Do you have any links or references to this?

I know he invented Blumlein and MS microphone techniques. He also suggested a method of 'shuffling', which sounds a bit like what you're talking about. But it's a process, not a microphone technique, as far as I'm aware.

The basic problem he was addressing is that with any coincident technique (of which his own Blumlein and MS are prime examples) all the low frequencies end up in the centre because their wavelengths are so large that there is no amplitude difference between the capsules. And this is what you hear when you listen to a cello, for example, that is on the right channel of a coincident recording. As the note gets lower, the fundamentals move to the centre. The higher harmonics and bowing sound still provide the cues that tell us it on the side, but it's not as convincing as when the lower harmonics are coming from the same point as the higher harmonics in the stereo image.

So, the idea is to alter the M and S balance of everything below a certain frequency, typically somewhere below 700Hz, to widen out the low freqencies and realign the lower harmonics with the upper harmonics of each sound source in the stereo soundstage.

Some plug-ins offer shuffling, such as Waves S1. I use it sometimes on coincident recordings. When it's done carefully, you can make each instrument sound as if it was close-miked and panned (insomuch as its stereo image is concerned). It works particularly well on percussive sound sources, but usually destroys a string quartet unless it is a piece with lots of pizzis and so on (Shostakovich's Polka, or just about anything by Bartok, for example).

My memory is a bit foggy at the moment (it's the Himalayan air), but I think there are two different approaches to this problem, and I can only remember one of them, which is all done with amplitude. The other actually introduces time delays, if I remember correctly.

- Greg Simmons

Posted: Fri Jan 14, 2005 6:28 pm

Hi Greg
Shuffling is part of the process, but in this instance you use near coincident omnis. The cutoff frequency is 700 Hz, as you mention. I've been searching the internet for details, but I can't find anything. I read a web page on it fairly recently, but I can't seem to find it. I'll trawl through my browser's history and I hope it's still there. I want to brush up on it, but as far as I know Blumlein invented loads of mic techniques that have all but disappeared.

One thing I hate with a lot of string recordings is that the upper frequencies, such as those in bowing noise can seem separate from the sound of the sound of the instrument, especially on CD. I'll post any links that I come across.

John

Posted: Fri Jan 14, 2005 11:44 pm

John Stafford wrote:

Hi Greg
Shuffling is part of the process, but in this instance you use near coincident omnis.

This sounds like a very interesting technique. Omnis have that wonderful low frequency extension and purity and openness to their sound...

John Stafford wrote:

I'll trawl through my browser's history and I hope it's still there. I want to brush up on it, but as far as I know Blumlein invented loads of mic techniques that have all but disappeared.

Blumlein was another of those very smart guys who died waaaay too soon. (Er, is it ever *too late* to die?). Any further information would be greatly appreciated, because I have become a firm believer in knowing about as many different stereo microphone techniques as possible, so I can choose the best one for the job. My days of being a 'Blumlein bi-directionals or nothing' guy are long past! Just about every technique has its pros and cons, depending on the gig. Perhaps it is in his stereo sound patent? I know it contains Blumlein bi-directionals and I am sure it contains MS, but I'm not sure about any others.

John Stafford wrote:

One thing I hate with a lot of string recordings is that the upper frequencies, such as those in bowing noise can seem separate from the sound of the instrument, especially on CD.

I can think of numerous reasons for it, depending on the microphones, the technique, the positioning, the converters and the mastering! When using Royer's SF24, I have found that adding even a smidge (like, 0.6dB) of high frequency shelving, around 12k or above, will tend to do this. Sometimes I used it to bring the instruments a bit 'closer' on a recording that was too distant. Then I started using linear phase EQ and found it didn't happen any more. Hmmm... There's an answer in there somewhere!

- Greg Simmons

Posted: Mon Jan 24, 2005 2:09 am

Greg
I've been looking through some of my old notes, and this technique was invernted in 1931, and is the one for which Blumlein invented shuffling. I assume there is some sort of baffle for separation of the upper mids, but I recall seeing the mics quite close and pointing forward in a modern implimentation. They were in some sort of enclosure.

I think the term SASS was applied to this technique retrospectively.
I suppose it's a sort of pre-Jecklin Jecklin disc. I just can't find any info anywhere on this. I remember someone saying that it's extremely difficult to set up properly -the stereo image can be very finely etched, but that apparently doesn't mean that things will appear in the right place!

I want to start playing with the other Blumlein technique that uses an omni and a fig-8 at the side of it. I've no idea how it works, but I suppose it has something in common with M/S. I must try and find out more about this one.

Blumlein was such an amazing man. I don't know why he isn't more famed as an individual. I suppose history has a strange way of choosing heroes.

If I ever come across that website I'll let you know, but it seems to have disappeared.

John

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