Old 08-13-2018, 06:59 PM   #1
Philbo King
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Default Distinctions between the Ambisonic Orders

Distinctions between the Ambisonic Orders?

I haven't run into a good description of Orders.

If I had to guess:
1st Order: Mono + L-R (AKA mid-side stereo)
2nd Order: 1st Order + Front-Back (basic surround)
3rd Order: 2nd Order + Top-Bottom (3d surround)

Am I close here? Are there more higher Orders?

Thanks in advance.
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Old 08-13-2018, 10:17 PM   #2
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Hi Philbo.

I'm planning on creating a topic to explain the fundamentals of Ambisonics and your question here is one of those I plan to address with that topic.

For now though, basically first order Ambisonics is akin to combining three m/s techniques into one recording. A first order Ambisonic recording contains four audio channels. They are known as W, X, Y and Z. This is also commonly referred to as B-format.

As you no doubt know, with a regular m/s recording, we have either a cardioid and figure 8 mic or an omni and figure 8. The omni gives us a mono signal and the figure 8 gives us the sides which when combined during m/s decoding, creates a stereo field.

In Ambisonics, a complete first order configuration gives us an omni (W channel), a front/back figure 8 (the X signal), a left/right figure 8 (the Y signal) and an up/down figure 8 (the Z signal).
When decoded, these four channels give us a full 3D sound field with depth, width and height information.

The sound field resolution is determined by the Ambisonic order. First order gives us one lobe per direction and the lowest spacial resolution. As we increase the Ambisonic order, we add more channels which basically split the lobes into smaller lobes which gives us increasing spacial resolution. This is also referred to as spherical harmonics.
A second order Ambisonic signal has nine audio channels instead of four and a third order signal has sixteen channels. They all still contain the basic mono omni (W) channel but add to the complexity of the spherical harmonics (the lobes in each direction) using pre determined mathematical formulae. The extra channels in each increasing order contain additional spacial information and greatly increase the ability for the listener to perceive accurate spacial cues.

REAPER is ideal for higher order Ambisonics because it can have up to 64 audio channels per track which equates to seventh order Ambisonics. The free IEM plugin suite mentioned in various posts here supports up to seventh order Ambisonics and the man in charge of IEM development, Daniel Rudrich, is a member and contributor here as well.

This is the IEM website..
https://plugins.iem.at/
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Old 08-14-2018, 02:14 AM   #3
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My simple-minds memory aid:

- First order: 4 mics (2D)
- Second order: 8 mics (3D).

Of course, this is just for basic understanding, as it leaves out 3rd order, or mics like the Zylia (that has 19 capsules, IIRC).
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Old 08-14-2018, 02:47 PM   #4
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Quote:
Originally Posted by cyrano View Post
My simple-minds memory aid:

- First order: 4 mics (2D)
this is incorrect. As readave says, 1st order ambisonics that can be captured with a tetrahedral mic like the soundfield can capture the 360 degree (3D) soundfield. Confusingly you can do ambisonics with only horizontal info, by omitting certain spherical harmonics. For example the Zoom H2n, can record horizontal only FOA.

Peter stitt's blog provides a nice introduction IIRC: https://spatialaudio.xyz/blog/ doesn't seem to be working right now
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Old 08-14-2018, 03:51 PM   #5
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Thx, Oli. I was confusing mics and speakers.

Could that blog have been moved here?

https://www.ssa-plugins.com/blog/category/what-is/

Mind you, there are several dead links on these pages too. Images are missing, fi.

Oh, and beware, spatialaudio.com is currently serving malware.
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Old 08-14-2018, 05:00 PM   #6
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Thanks for that. I doubt I'll ever have enough speakers to go past 1st order though.
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Old 08-14-2018, 11:08 PM   #7
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Quote:
Originally Posted by Philbo King View Post
Thanks for that. I doubt I'll ever have enough speakers to go past 1st order though.
One of the great things about Ambisonics is that it is speaker agnostic. You decode the Ambisonic mix to suit the speaker configuration you have. That speaker configuration can be anything from a single mono speaker to as many as you want.
The Ambisonic order is about the spherical resolution of the recorded material. Ambisonic channels do not equal speaker channels. That is determined by your decoder.
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Old 08-15-2018, 08:28 PM   #8
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Perhaps this microphones doc may be helpful https://docs.google.com/spreadsheets...DinIub/pubhtml
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Old 08-15-2018, 10:11 PM   #9
jm duchenne
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Quote:
Originally Posted by junh1024 View Post
Perhaps this microphones doc may be helpful https://docs.google.com/spreadsheets...DinIub/pubhtml
A very good chart !

But, you have written "Zoom H4n" as a 4 channel ambisonic recorder.
Isn't this a mistake since it has only 2 external mic inputs ?
And even the H6 which has 4 phantom powered inputs is not suitable since their level cannot be synced.
To my knowledge, only the F4 (and the F8 of course) from Zoom can be used for 1st order ambisonics.

Also, the LG 360 cam don't use ambisonics but a multichannel ring (which is by the way not bad at all).
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Old 08-20-2018, 05:39 PM   #10
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Quote:
Originally Posted by jm duchenne View Post
A very good chart !

But, you have written "Zoom H4n" as a 4 channel ambisonic recorder.
Isn't this a mistake since it has only 2 external mic inputs ?
And even the H6 which has 4 phantom powered inputs is not suitable since their level cannot be synced.
To my knowledge, only the F4 (and the F8 of course) from Zoom can be used for 1st order ambisonics.
Thanks. I've updated to show F4.

Quote:
Also, the LG 360 cam don't use ambisonics but a multichannel ring (which is by the way not bad at all).

Apparently it can https://www.google.com/search?q=LG+360+CAM+ambisonics
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Old 08-21-2018, 12:26 AM   #11
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Oh, thanks, silly me !
I had only the 5.1 option on mine, but with the update I found now there is a 3D option and gives a 4 channels soundtrack instead of the previous 6 channels one.
Of course it is only horizontal, but it is a nice addition for this cheap camera.
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Old 09-28-2018, 12:04 AM   #12
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Quote:
Originally Posted by cyrano View Post
Thx, Oli. I was confusing mics and speakers.

Could that blog have been moved here?

https://www.ssa-plugins.com/blog/category/what-is/

Mind you, there are several dead links on these pages too. Images are missing, fi.

Oh, and beware, spatialaudio.com is currently serving malware.
That is indeed the new link. All of the images have been fixed and (hopefully) all of the links now redirect to the new site. The spatialaudio.xyz domain is no longer mine so I don't know what sort of content it is now hosting.
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