Old 02-25-2019, 08:43 AM   #1
lamacchiacosta
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Default mic surround techniques to Ambisonics

Hello,
I am trying to make my head around how to convert/decode stereo, multichannel surround techniques to Ambisonics, (pretty much the way round of most Ambisonics decoders). I would like to adapt my old recordings to my new spherical projects. Let's say I have a recording made with a stereo technique for the front and a stereo technique for the back. I know the distance between the mics: how can make that into ambisonics stream (AmbiX)?
So far I found some plugins that could be in the right direction but they don't seem to do what I need:

Waves B360 Ambisonics Encoder - looks like more a mix-to-ambisonics tool
Harpex-X - It seems the only technique it can manage is DoubleMS (which I never used).
SPARTA Array2SH - to me is not very clear what it does.

Thanks.
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Old 02-25-2019, 02:42 PM   #2
ReaDave
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What are you using for decoding and what Ambisonic order are you using?

Pretty much all my Ambisonic mixes are third order and I'm using Blue Ripple Sound for the majority of my needs as well as some of the very good encoding and upmixing tools in the IEM Plugin Suite. The IEM plugins are free and can work right up to seventh order. There's a stereo encoder and a multi encoder included in the suite.
The Blue Ripple Core plugins are free and include a stereo upmixer (encoder) which is also very good and works in third order.

For front/back stereo pairs, I'd use two stereo upmixers (encoders) and feed the front pair to the left and right front at 45 degrees either side of the front center position. Do the same for the back stereo pair at 45 degrees left and right of the back center position. This is assuming a square mic setup. Adjust the angles to match if your mics are in a rectangle.

There's a sticky in this section of the forum with links to various Ambisonic resources and the Blue Ripple Sound and IEM plugins are listed there.

Here's a direct link to the IEM plugin descriptions....
https://plugins.iem.at/docs/plugindescriptions/

And here's a link to the sticky with other links.....
https://forum.cockos.com/showthread.php?t=210108
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Old 02-25-2019, 02:50 PM   #3
ReaDave
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Also, Daniel Rudrich from IEM is a member of this forum. This is his profile here....
https://forum.cockos.com/member.php?u=119131
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Old 02-26-2019, 05:55 AM   #4
RDan
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Hi there,

in general what you can do is simply encode your microphone signals with their directions during recording, as ReaDave has already proposed. There are quite a lot of tools available which are capable of this, as it's basic Ambisonic panning:
- IEM MultiEncoder or StereoEncoder
- ambix_encoder
- O3A panner

I personally would recommend using tools which support higher order Ambisonics, at least third order, as anything below is not very good in my opinion. Unfortunately, Waves B360 Encoder only supports first order.

Double-MS is basically 2D Ambisonics. You can see first order Ambisonics as a tripple-MS, as you have one Omni-signal (mid) and three figure of eights (sides).

Regarding the array2sh by SPARTA: this plug-in is brilliant, however it's not what you are looking for. It encodes spherical (and cylindrical) microphone arrays into Ambisonics. Those arrays should be as coincident as possible, we are talking about a radius of only few centimeters. I suppose your front/back stereo pairs had a bigger distance.

tl;dr; treat your microphone signals as separate sources, and encode them with their directions into higher order Ambisonics.

best
Daniel
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Old 02-27-2019, 01:50 AM   #5
lamacchiacosta
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Thanks guys for your answers, I will play with the mentioned plugins to see if I can find the right set-up for my specific technique, which of course won't have the Z signal as it's only orizontal surround.
All my projects are in 3OA so if I could implement all my old recordings would be fabulous. The following step will be how to create a fake but convincing Z plan out of those, but hey, a step at a time. :-)
Many thanks.
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Old 02-27-2019, 04:48 AM   #6
ReaDave
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Quote:
Originally Posted by lamacchiacosta View Post
The following step will be how to create a fake but convincing Z plan out of those, but hey, a step at a time. :-)
Many thanks.
I've had my eye on this for a while but haven't tried it yet because I'll probably want to purchase it straight away. It is quite expensive and I don't have the funds right now.
It has had some very positive reviews though.....

https://nugenaudio.com/haloupmix/
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