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tutorials : working with ambisonics

Tha acousmodules plugins are made for being used with real loudspeakers systems and can work with every spatial arrangement you may need.
Nevertheless, they can be easily integrated in a binaural virtual space workflow or be used together with ambisonics coding thanks to free plugins like GRM-Tools SpaceVR and IEM / Sparta / Ambix series.

You will find here some users' cases that must cover the most common situations together with Reaper's host.

Note : all the examples below suppose that you are already efficient with Reaper and the use of multichannel plugins.
You can see also : Utiliser Reaper (avec les Acousmodules) (in French)
and the video Configuration de base dans Reaper (sorry, also in French)

 

1. Integrate ambisonics sounds in a multichannel work
2. Use the acousmodules (and other multichannel plugins) inside an ambisonics workflow
3. Export a multichannel work in ambisonics

 

 

1. Integrate ambisonics sounds in a multichannel work

1. insert an ambisonics coded sound into an existing track or put it directly in the Arrangement window :
> by default the track will have the same number of channels than the file :

ambix0.jpg

> reminder : 1st order = 4 channels / 2nd order = 9 channels / 3rd order = 16 channels
> if the sound has been recorded with a microphone there is a lot of chances that it will be 1st order
> you have to know if the file is A-Format (original 4 thetrahedron, needs a specific conversion plugin *) or B-Format (already processed into ambisonics)
> if you don't know : if the first channel is louder than the others there is much chances that it is B-Format, otherwise... ask or search...
> if the 3rd or the 4th channel is silenced it is a "2D only" B-Format Ambix (3rd) or FuMa (4th)

2. if you want to use it as a mono sound, you don't need a decoder, just have to change its channels format in the Properties panel to "Mono / Left",
since the first ambisonics channel (B-Format) always corresponds to the omnidirectionnal virtual microphone (W) :
ambix2.jpg 

3. in all other cases you MUST know if the channels numbers are in the old FuMa or the newer Ambix order
> here you may need to insert on the track a format converter like the plugin Ambix Converter

ambix1.jpg
(since it is higly recomended to use the ambix numbering, you may have to convert only old recordings coded in FuMa)
 

4. if you use the single channel mono conversion, you can use the sound directly, for instance with a Spat3D plugin placed on the track or on the object :

ambix3.jpg

> attention : don't forget to set the track channels number to the same value as the plugin's spatial output (on the picture "10")

 

5. if you want to use the original full space, you will have to decode it, for instance with the IEM's AllRADecoder plugin :
- insert the plugin on the track or on the object

ambix4.jpg

- unless you wish to decode it in stereo or in quadriphony, the track's channels number (or the file's) will be too small, and the plugin will indicate "bus too small")
> you have to set the number of channels to match the higher value between the coding order and the spatial format.
> for instance :
- a 1st order file will not benefit, in this plugin, from a higher decoding order than 4, and the spatial format is Auro-9.1, so the tracks channels number must be 10
- with a 3rd order file you will need 16 decoding channels even if the spatial format is also 10
> you can also use a non linear decoder like the Sparta Compass Decoder which can upscale a 1st order input to 3rd with a higher spatial accuracy (at the cost of a possible sound degradation)

ambix5.jpg

 

6. As soon as you are in the multichannel domain, every plugin is available to process the whole space or some specific channels :
 > Cinema 32 bits acousmodules : 5.1 / Auro-3D, 17.1 and 22.2
> Sphere based and Domes (32 bits too)
> and of course all the 64 bits series...

 

 

 

2. Use the acousmodules (and other multichannel plugins) inside an ambisonics workflow

You can stay in the ambisonics domain from the begining to the end of a project, for instance if you just need to assemble field or music recordings,
with eventually some common effects like filter, compress, reverberation and spatial Yaw, Pitch, Roll (all provided with the IEM, Sparta and Ambix plugins)
as long as they process all the channels in exactly the same manner.
But you may also want to use them in a more creative way for special effects, sampling etc. that be only available in the multichannel domain.

 1. decode the sound to a format that will preserve both the sphere based speakers arrangement and will minimize the effects of the decoding/re-encoding process.
> it is highly recommended to do it in 7th order (64 channels), for instance with IEM AllRADecoder, if you want to process the whole space :

ambix6.jpg

with a Scatterizer :

ambix8.jpg

 

or a 8 channels circle :

ambix7.jpg

to process with an AnimaSpat 864X :

ambix9.jpg

. . .
 

3. once it is done, you have to encode the plugins'output in ambisonics, using also the higher available order, with IEM's MultiEncoder,
of course using the same spatial settings (they can be exported / imported between the plugins and are also compatible with the Sparta ones) :

ambix10.jpg

 

 

 

 

3. Export a multichannel work in ambisonics

If a production is compatible with sphere based spaces like domes, it may be useful to render it as an ambisonics file together with a multichannel one.
It may be then faster and safier to adapt it to a different loudspeakers number and spatial arrangement (as long as it is more or less spherical).
Using ambisonics in this way is like working in linear PCM and, at the end only, exporting in mp3 to make the diffusion easier (lower bitrate) and wider (universal compatibility).
Here the odds are that the number of needed channels risks to be higher...

It is imperative to use the higher possible coding order, in Reaper it means 7th order (64 channels), or if the file's size really matters 5th order (36 channels).
The reason is that all the interchannel space is already done in the multichannel domain, and since the ambisonics coding will inevitably add its own side effects,
the result will tend otherwise to be spatially more confused and sonically less sharp.

1. insert a MultiEncoder (IEM) at the end of Reaper's Master bus

2. set its spatial format according to the multichannel's one

3. set the order if possible to "7th"
note : it is alas not possible to keep the current loudness calibration since the encoding process, depending on the input channels number, will result in a different level.
In general, a higher multichannel space needs to lower the Master output to prevent clipping.
 > doing the Rendering in 32 bits can be safe but will result in a really big file ! 

4. Render !

ambix11.jpg

note : the Wavepack format (lossless) will result in a smaller file than every other file compression system like Zip or Rar, and will be directly playable in Reaper :-)