[LAU] ssr and alternatives

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Mon Mar 1 21:47:31 CET 2021

On 2/26/21 7:26 AM, Brandon Hale wrote:
> I'm not really looking for environments for making compositions. I'm 
> mostly looking for that decoder that can decode to arbitrary and weird 
> speaker arrays on Linux.

Hi Brandon,
You will need two things:

- a way to design a decoder
- a way to run that decoder

For designing Ambisonics decoders I use ADT (the Ambisonics Decoder 
Toolkit, by Aaron Heller):


You will probably want to read through the references there to learn 
about the different design methods available, the respective tradeoffs 
and tricks. It is not extremely difficult but like everything else you 
have to learn stuff.

This is definitely not a "single button, press here for decoder" solution.

ADT will generate a proper Ambisonics decoder, dual band with phase 
matched filters, near field compensation filters for the speakers and 
(optional) level and delay compensation for your array. It can output 
ambdec configuration files (but limited to 3rd order, of course) and 
also Faust source code for the full decoder (which is what I currently 
use). Faust can be compiled to any number of plugin and whatnot formats. 
I have used standalone QT/Jack apps in linux and supercollider plugins - 
I think it can easily generate pd as well.

For very irregular arrays and "weird speaker locations" there is, sorry, 
no magic. In some cases you might conclude that Ambisonics is not the 
correct solution (for very irregular arrays).

I have successfully used ADT to create decoders for our concert systems 
(up to 32.8) and for our Stage small concert hall with a 56.8 system and 
Listening Room (full 3D 22.8). A LOT of work to get properly calibrated 
arrays but the result sounds pretty darn good (if I may say).

My experience with fairly regular "dome" speaker arrays is that ALLRAD 
works best (Slepian decoders have the appeal of using the "right" 
harmonic functions but in my experience they are not good with highly 
irregular arrays).

If your speaker coverage has "holes" then it is all about tradeoffs. You 
can optimize for even energy (loudness) but then you will have 
directional errors and/or mismatches of perceptual cues at low and high 
frequencies, if you minimize directional errors you will have uneven 
loudness. If you want Ambisonics you need decent speaker coverage for 
best results.

You can look at the plots of meaningful parameters when designing your 
decoder with ADT and see what you get for different configurations.

This is all with the caveat that there are limits to your perception, so 
what looks like an error on paper might not be significant in practical 
listening conditions, and as Fons rightly points out, going above order 
7 does not make much sense.

Some data from a composer's point of view here (Natasha Barrett):

In the paper she explores the limits of what was for her significant in 
terms of max ambisonics orders. My current compositional work uses mixed 
5th/2nd order Ambisonics and I am quite happy with the results (in a 
56.8 system that can potentially decode 6th order[*]).

Hope this helps,
-- Fernando

[*] https://lac.linuxaudio.org/2019/doc/lopez.pdf

> On 2/25/21 4:42 PM, Jeanette C. wrote:
>> Hey hey Brandon,
>> Feb 25 2021, Brandon Hale has written:
>> ...
>>> Are there any good alternatives for rendering ambisonic and wavefield 
>>> synthesis audio files?
>> ...
>> It's no surprise that I willmention Csound, which can do quite a bit in
>> the way of ambisonics. I'm sure PD (PureData) and SuperCollider (SC) can
>> do the same and they have good graphical interfaces.
>> There are also LADSPA/LV2 plugins to produce ambisonic outputs, not sure
>> what exactly there is. Fons has released a few plugins.
>> For Wavefields synthesis I only know of SWONDER, which is older than SSR
>> and - I think - no longer maintained, but it's been ages since I looked
>> at that.
>> Csound, PD and SC also offer many utilities for building good
>> soundscapes and sound design in general. Depending on what you are
>> looking for in the way of textures, Luigi Verona has talked about his
>> way of creating melodic textures, scapes and clouds. Perhaps that would
>> serve your purposes?
>> HTH.
>> Best wishes,
>> Jeanette
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