Four channel recording with two figure 8 mics ???

[Analok]

Oy, my head hurts!

[boojum]

To revisit the jiggery-poke associated with the Pearl. As the mic is four cards, all +, an opposing card must be phase inverted before combining to make it like a true figure-8, + and -. Then after combining the one side must be inverted back so that both sides of the channel are now positive, a figure-8 manipulated for M-S. I finally realized this was the underlying reason for the double flipping. It takes me time but if I live long enough I can figure out things. Hopefully

Thanks, all, for the instruction and patience. This forum is the foundation of most of what I have learned about this wonderful game of pursuing and capturing sound.

[bigdaddyrox4574]

I have a question that seems relevant to this thread: When I have used my CAD M179s in Blumlein before, I have noticed that the low end is rolled off a good bit. I have considered adding an Omni to this array, placed directly between the two figure 8s, and then processing the signals with with a hi-pass filters on the figure 8s and a lo pass filter on the omni. If it works with my somewhat low end setup, I might consider investing in some better quality figure 8s (and an omni, of course!) in the future. Anybody have any input on this idea? ...I know, if it was a really good idea, somebody would have already mentioned it

[aracu]

Originally Posted by bigdaddyrox4574

I have a question that seems relevant to this thread: When I have used my CAD M179s in Blumlein before, I have noticed that the low end is rolled off a good bit. I have considered adding an Omni to this array, placed directly between the two figure 8s, and then processing the signals with with a hi-pass filters on the figure 8s and a lo pass filter on the omni. If it works with my somewhat low end setup, I might consider investing in some better quality figure 8s (and an omni, of course!) in the future. Anybody have any input on this idea? ...I know, if it was a really good idea, somebody would have already mentioned it

It's a good idea and is used by some recordists. The two fig 8 + one omni can also be used as a B-format array, which allows adjusting the polar pattern, stereo width and horizontal direction during or after recording.

[John Willett]

Originally Posted by aracu

It's a good idea and is used by some recordists. The two fig 8 + one omni can also be used as a B-format array, which allows adjusting the polar pattern, stereo width and horizontal direction during or after recording.

Not quite correct as you need three fig-8s and an omni for true B-format. WXYZ.

But what you described will work fine in the horizontal plane as you still have the WXY elements and are only missing the Z (vertical) one.

[aracu]

WXYZ: b-format
WXY: native b-format

[WiFiJeff]

Originally Posted by bigdaddyrox4574

I have a question that seems relevant to this thread: When I have used my CAD M179s in Blumlein before, I have noticed that the low end is rolled off a good bit. I have considered adding an Omni to this array, placed directly between the two figure 8s, and then processing the signals with with a hi-pass filters on the figure 8s and a lo pass filter on the omni. If it works with my somewhat low end setup, I might consider investing in some better quality figure 8s (and an omni, of course!) in the future. Anybody have any input on this idea? ...I know, if it was a really good idea, somebody would have already mentioned it

Josephson C700S. My go-to mic, got it in September and have done about 20chamber music concerts with it since. I usually just go Blumlein, but when the piano lid is on the short stick the omni cap does wonders for the sound.

Jeff

[Haimis]

So, I didn't quite understand this: If in a Blumlein we have 2 fig.8 microphones in a coincident 90-degree angle, why couldn't it be used to surround? I have understood (probably incorrectly) that the fig. 8 has sort of a "+"-side and a "-"-side, so most of the stuff from the front of the mic will be "+ phase" and the stuff from the rear "- phase" - sorry for the unscientific terms. But:

-If I recorded my ambience (I'm talking nature sounds and other kinds of ambience for film use) with a Blumlein pair, could I put the output of the left-facing fig.8 to the front left channel and the same thing, phase-reversed, to the rear right speaker, and vice versa for the other microphone, and get somewhat usable results on a shoelace-duct tape -budget?

I'm pretty green as an engineer, so please bear with me

...and I'm pretty sure the answer lies in the previous posts, but I failed to understand...

[aracu]

Originally Posted by Haimis

So, I didn't quite understand this: If in a Blumlein we have 2 fig.8 microphones in a coincident 90-degree angle, why couldn't it be used to surround? I have understood (probably incorrectly) that the fig. 8 has sort of a "+"-side and a "-"-side, so most of the stuff from the front of the mic will be "+ phase" and the stuff from the rear "- phase" - sorry for the unscientific terms. But:

The + and - represent a difference in polarity, which is different than phase.

[2pulse]

Originally Posted by Haimis

-If I recorded my ambience (I'm talking nature sounds and other kinds of ambience for film use) with a Blumlein pair, could I put the output of the left-facing fig.8 to the front left channel and the same thing, phase-reversed, to the rear right speaker, and vice versa for the other microphone, and get somewhat usable results on a shoelace-duct tape -budget?

This would basically null the signal at the listener's position.

[Haimis]

Originally Posted by 2pulse

This would basically null the signal at the listener's position.

Ahh, you're right. What was I thinking again?

Maybe I'll research the double-M+S instead. Sounds like a viable option. Thank you for waking me up to reality!

[JEGG]

Originally Posted by bigdaddyrox4574

I have a question that seems relevant to this thread: When I have used my CAD M179s in Blumlein before, I have noticed that the low end is rolled off a good bit. I have considered adding an Omni to this array, placed directly between the two figure 8s, and then processing the signals with with a hi-pass filters on the figure 8s and a lo pass filter on the omni. If it works with my somewhat low end setup, I might consider investing in some better quality figure 8s (and an omni, of course!) in the future. Anybody have any input on this idea? ...I know, if it was a really good idea, somebody would have already mentioned it

Try EQ'ing your mic's in addition to adding an omni-not at the same time, though. The two approaches will yield very different low end behaviors.

[Bibster]

Originally Posted by JEGG

Try EQ'ing your mic's in addition to adding an omni-not at the same time, though. The two approaches will yield very different low end behaviors.

Errr.... The way he describes it, or at least: how I'm reading it, is that the only low-end in the mix will be the low-end from the omni.

So there are no two approaches here, but only one. (Two complementary processes, yes)

[aracu]

Another alternative is to use the two fig 8 and omni in a native b-format array, for a more coherent and manipulable stereo image than adding a
center omni in mono.

[Gutbucket]

Originally Posted by Haimis
-If I recorded my ambience (I'm talking nature sounds and other kinds of ambience for film use) with a Blumlein pair, could I put the output of the left-facing fig.8 to the front left channel and the same thing, phase-reversed, to the rear right speaker, and vice versa for the other microphone, and get somewhat usable results on a shoelace-duct tape -budget?

Originally Posted by 2pulse

This would basically null the signal at the listener's position.

No, it will not. Summing signals in air is very different than summing them electronically. Try it.

[Gutbucket]

Originally Posted by bigdaddyrox4574

I have a question that seems relevant to this thread: When I have used my CAD M179s in Blumlein before, I have noticed that the low end is rolled off a good bit. I have considered adding an Omni to this array, placed directly between the two figure 8s, and then processing the signals with with a hi-pass filters on the figure 8s and a lo pass filter on the omni. If it works with my somewhat low end setup, I might consider investing in some better quality figure 8s (and an omni, of course!) in the future. Anybody have any input on this idea? ...I know, if it was a really good idea, somebody would have already mentioned it

To compensate for the low frequency rolloff of the 8's, lowpass the omni with an inverse of the response rolloff of the 8's. You needn't highpass the 8's. Their exisiting response you wish to correct is already 'highpassed'. The stereo information will trasition to omni below the corner frequency, which is most likely perfectly acceptible.

Other option is to attempt to extend the bottom end response of 8's with EQ. That retains stereo information down there, but you are more likely to run into noise/rumble issues.

If you want to get technical and play around a bit, add the filtered omni and try boosting only the Side component of the Blumlein pair in that frequency region.

[2pulse]

Originally Posted by Gutbucket

No, it will not. Summing signals in air is very different than summing them electronically. Try it.

I think we all know what a speaker pair with opposite wiring sounds like... The entire signal doesn't just vanish to the listener, mainly because of things like room reflections and the fact that we have spaced ears and that we occasionally move our heads about--but there is definitely acoustic nulling happening at all points equidistant from the speakers. You can absolutely hear it in the low frequencies without having to take pains to position your head correctly.

I figured that was worth mentioning to someone contemplating whether or not to send an opposite-polarity signal to opposite speakers.

[JEGG]

Originally Posted by Bibster

Errr.... The way he describes it, or at least: how I'm reading it, is that the only low-end in the mix will be the low-end from the omni.

So there are no two approaches here, but only one. (Two complementary processes, yes)

The two approaches will yield very different results. Not time to write a book here. Even a synthesized 8 behaves as a velocity mic-completely insensitive to standing waves and the like. Omni's are not. There is always a difference, and it can be dramatic, especially in large rooms.

An omni puts a big fat monaural pressure component in the middle of your image, which is *exactly* what is *avoided with Blumlein*, and largely the point of it, and why it images so well.

There are times when that is OK and even beneficial. But then the best way is to use MS with omni mid, a technique I sometimes use to very good effect.

The OP could try Blumlein with omni flanks. That makes more sense.

But EQ's the 8's would be a lot simpler, given the proper geometry of forces.

It's not the same at all. (Blumlein plus omni mid vs Eq'd or non Eq'd 8's)