Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Courville, Daniel]

Politis Archontis wrote:

> https://github.com/polarch/JSAmbisonics
> - WebAudio_FOA.js: Implements B-format encoding, rotations, virtual 
> microphones, acoustic intensity analysis, and binaural decoding
> - WebAudio_HOA.js: Implements HOA encoding, rotations, virtual microphones 
> and binaural decoding for a user-specified order

This looks great. My only concern is regarding terminology: you seem to use the 
term "B-Format" only for 1st order (and I presume it's of the FuMa kind), and 
you drop it for HOA.

So, on the GitHub page, we read:

• HOA_bf2acn: converts a B-format stream to an ACN/N3D HOA stream
• HOA_acn2bf: converts the first-order channels of a HOA stream to B-format

This could be confusing for ambisonic newbies, I think...

- Daniel

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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Politis Archontis]

Hi Daniel,
> On 19 Jun 2016, at 19:21, Courville, Daniel  wrote:
> 
> Politis Archontis wrote:
> 
>> https://github.com/polarch/JSAmbisonics
>> - WebAudio_FOA.js: Implements B-format encoding, rotations, virtual 
>> microphones, acoustic intensity analysis, and binaural decoding
>> - WebAudio_HOA.js: Implements HOA encoding, rotations, virtual microphones 
>> and binaural decoding for a user-specified order
> 
> This looks great. My only concern is regarding terminology: you seem to use 
> the term "B-Format" only for 1st order (and I presume it's of the FuMa kind), 
> and you drop it for HOA.
> 
> So, on the GitHub page, we read:
> 
> • HOA_bf2acn: converts a B-format stream to an ACN/N3D HOA stream
> • HOA_acn2bf: converts the first-order channels of a HOA stream to B-format
> 
> This could be confusing for ambisonic newbies, I think...

Good point, I’ll add some clarification in the dcumentation that whenever I 
mention B-format I mean first-order B-format (which should be unambiguous).

Were the examples working for you at all?

BR,
Archontis
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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Marc Lavallée]

Excellent work! :-)

The examples are working. The ones for HOA are impressive.

I may "steal" some of your code for ambisonic.xyz ;
I was unable to use Firefox a year ago.
--
Marc

On Sun, 19 Jun 2016 17:08:20 +,
Politis Archontis  wrote :

> Hi Daniel,
> > On 19 Jun 2016, at 19:21, Courville, Daniel
> >  wrote:
> > 
> > Politis Archontis wrote:
> > 
> >> https://github.com/polarch/JSAmbisonics
> >> - WebAudio_FOA.js: Implements B-format encoding, rotations,
> >> virtual microphones, acoustic intensity analysis, and binaural
> >> decoding
> >> - WebAudio_HOA.js: Implements HOA encoding, rotations, virtual
> >> microphones and binaural decoding for a user-specified order
> > 
> > This looks great. My only concern is regarding terminology: you
> > seem to use the term "B-Format" only for 1st order (and I presume
> > it's of the FuMa kind), and you drop it for HOA.
> > 
> > So, on the GitHub page, we read:
> > 
> > • HOA_bf2acn: converts a B-format stream to an ACN/N3D HOA stream
> > • HOA_acn2bf: converts the first-order channels of a HOA stream to
> > B-format
> > 
> > This could be confusing for ambisonic newbies, I think...
> 
> Good point, I’ll add some clarification in the dcumentation that
> whenever I mention B-format I mean first-order B-format (which should
> be unambiguous).
> 
> Were the examples working for you at all?
> 
> BR,
> Archontis
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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Courville, Daniel]

Politis Archontis wrote:

> Good point, I?ll add some clarification in the dcumentation that whenever I 
> mention B-format I mean first-order B-format (which should be unambiguous).

Thanks. But I'm curious: any reason why you don't want to use the term 
"B-Format" in HOA?

People working with HOA in the last ten years or so have kept the B-Format 
moniker for the spherical harmonics stage in Ambisonics.

- Daniel

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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Politis Archontis]

No reason specifically, 
I always thought that most people associate B-format with the traditional 
1st-order specification, and maybe the FuMa definition up to 3rd-order. I 
wasn’t sure if that’s the common term for general HOA signals. 

So, you think something like HOA B-format is better (if I don’t have to go into 
the details, channels, normalization etc.) ?

Archontis


> On 21 Jun 2016, at 00:14, Courville, Daniel  wrote:
> 
> Politis Archontis wrote:
> 
>> Good point, I?ll add some clarification in the dcumentation that whenever I 
>> mention B-format I mean first-order B-format (which should be unambiguous).
> 
> Thanks. But I'm curious: any reason why you don't want to use the term 
> "B-Format" in HOA?
> 
> People working with HOA in the last ten years or so have kept the B-Format 
> moniker for the spherical harmonics stage in Ambisonics.
> 
> - Daniel
> 
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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Albert Leusink]

Politis Archontis  writes:
> 
> Were the examples working for you at all?
> 
> BR,
> Archontis
>
Well done Archontis!. I was hoping this could be possible, somebody just had
to put the work into it...thanks so much for this.

The examples are (sort of) working for me but sound very low res and dull. 

When I switch between 1,2,3 and 4th order in the HOA decoder, it seems that
each time when you increase the order, it extends the frequency range
upwards by half an octave...

Most of the first order samples reproduce nothing above 10k and a lot of
them sound severely saturated/clipped.

You note on your Github that you used an Eigenmike for the recordings, could
this be the issue? I've never heard anything musical sounding coming out of
that microphone, of course the localization is stellarbut it seems to get 
duller and duller the more orders you truncate


I'm on Mac OS 10.11.5 using Firefox 48.0b1

Greetings,

Albert

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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Michael Chapman]

> No reason specifically,
> I always thought that most people associate B-format with the traditional
> 1st-order specification, and maybe the FuMa definition up to 3rd-order. I
> wasn’t sure if that’s the common term for general HOA signals.
>
> So, you think something like HOA B-format is better (if I don’t have to
> go into the details, channels, normalization etc.) ?
>

IMHO each of A-, B-, C-, D- and -formats are generic terms.

So B-format is " the spherical harmonics stage in Ambisonics" regardless
of channels present or what order they are in.

As for (your) "HOA B-format", no criticism, but my take is that unless
context implies/demands otherwise then 'an ambisonic file' (or 'ambisonic
signal set') is implicitly B-format. (To be pedantic there is a reasonable
presumption that it is B-format.).
But, there must be much to be said for instructions to novices being
explicit (if only once).

Michael




> Archontis
>
>
>> On 21 Jun 2016, at 00:14, Courville, Daniel 
>> wrote:
>>
>> Politis Archontis wrote:
>>
>>> Good point, I?ll add some clarification in the dcumentation that
>>> whenever I mention B-format I mean first-order B-format (which should
>>> be unambiguous).
>>
>> Thanks. But I'm curious: any reason why you don't want to use the term
>> "B-Format" in HOA?
>>
>> People working with HOA in the last ten years or so have kept the
>> B-Format moniker for the spherical harmonics stage in Ambisonics.
>>
>> - Daniel
>>
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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Politis Archontis]

Hi Albert, 

Thanks for the feedback!

> On 21 Jun 2016, at 07:38, Albert Leusink  wrote:
> 
> Well done Archontis!. I was hoping this could be possible, somebody just had
> to put the work into it...thanks so much for this.
> 
> The examples are (sort of) working for me but sound very low res and dull. 
> 
> When I switch between 1,2,3 and 4th order in the HOA decoder, it seems that
> each time when you increase the order, it extends the frequency range
> upwards by half an octave…

The low-pass effect at the moment is the effect of order truncation. HRTFs at 
higher frequencies have too much directional variability, and that means that 
these high-frequencies are reflected to the higher-order filters. Dropping the 
HO generates the low-pass effect. Note that this is also due to the basic 
implementation of the decoding filter examples. You can correct (on average) 
this high-frequency loss in a systematic way, and generally you can improve the 
colouration by tuning the decoder, which is something that these filters do not 
have. You cannot correct however the spatial spreading or blurring of the lower 
orders (or decreased externalization and elevation effects).

The idea of the examples was to show that you can include your own decoding 
HRTF-based filters. If somebody has their own optimized binaural decoding 
filters, I can provide the same examples with their own filters (or gradually 
write some proper documentation).

If filters are not provided, then the decoder just creates two opposing 
cardioids, which have much less colouration (and worse binaural effects) - I’ll 
try to add this mode on the examples too for comparison.

> 
> Most of the first order samples reproduce nothing above 10k and a lot of
> them sound severely saturated/clipped.

Hm, that seems to be my mistake, I noticed it too at some other browser 
recently. 
I think it’s due to having normalized the decoding filters to peak unity, which 
may result in clipped output after all processing. I’ll check it when I can.

> 
> You note on your Github that you used an Eigenmike for the recordings, could
> this be the issue? I've never heard anything musical sounding coming out of
> that microphone, of course the localization is stellarbut it seems to get 
> duller and duller the more orders you truncate

In a sense the Eigenmike provides a much better first-order B-format. Using 
proper encoding filters the range of the dipoles and omni are close to the 
ideal ones for up to ~9kHz, for the Soundfield the patterns start to deviate 
from ideal at lower frequencies. But you are right, I also haven’t managed to 
get from the Eigenmike the great sound quality I’ve heard from Soundfield 
recordings.

Regards,
Archontis
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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Politis Archontis]

Hi Michael,

On 21 Jun 2016, at 10:35, Michael Chapman 
mailto:s...@mchapman.com>> wrote:

No reason specifically,
I always thought that most people associate B-format with the traditional
1st-order specification, and maybe the FuMa definition up to 3rd-order. I
wasn’t sure if that’s the common term for general HOA signals.

So, you think something like HOA B-format is better (if I don’t have to
go into the details, channels, normalization etc.) ?


IMHO each of A-, B-, C-, D- and -formats are generic terms.

So B-format is " the spherical harmonics stage in Ambisonics" regardless
of channels present or what order they are in.

As for (your) "HOA B-format", no criticism, but my take is that unless
context implies/demands otherwise then 'an ambisonic file' (or 'ambisonic
signal set') is implicitly B-format. (To be pedantic there is a reasonable
presumption that it is B-format.).
But, there must be much to be said for instructions to novices being
explicit (if only once).

I agree with that, I’ll just add explicit definitions in the documentation, SH 
conventions and channel ordering for the first-order and high-order processing, 
and leave to people to pick the term they prefer. In the end they all descrbe 
the same thing..

BR,
Archontis
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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Stefan Schreiber]

Politis Archontis wrote:



In a sense the Eigenmike provides a much better first-order B-format. 



Only in a directional sense, and not that much IMO. (vs. "much better")



Using proper encoding filters the range of the dipoles and omni are close to 
the ideal ones for up to ~9kHz, for the Soundfield the patterns start to 
deviate from ideal at lower frequencies.

Does this really matter, in this case?? (means: 1st order directivity 
won't go to 9kHz anyway...)




But you are right, I also haven’t managed to get from the Eigenmike the great 
sound quality I’ve heard from Soundfield recordings.
 



Exactly. An SF mike records over the complete musical spectrum. The 
Eigenmike tries to (via signal processing/HF correction) but doesn't do yet?


Too simplistic?

Best regards,

Stefan


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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Stefan Schreiber]

Stefan Schreiber wrote:



Exactly. An SF mike records over the complete musical spectrum. The 
Eigenmike tries to (via signal processing/HF correction) but doesn't 
do yet?



Just to be a bit more clear:

An Eigenmike has some aliasing limit frequency, if I remember well at 
about 7.5 kHz. (I also remember that they do "s.th." above to extend HF 
range.)


If you use an Eigenmike as a main microphone and combine this with some 
spot microphones, the HF problems might become manageable.


You have very few tonemasters (actively) on this list, so this is not 
what people here or "we"  would do/aim for.


A SF mike has some aliasing problems at high frequencies (probably above 
about  the same range), too - but these should be more benign.


Any corrections of my crude views are highly welcome...O:-)


Best,

Stefan

P.S.: It is very hard to obtain or "google" the price of an eigenmike. 
The eigenmike could be a nice tool for VR/AR recordings, so probably 
they could start to become a bit more transparent on this.

(Nokia also doesn't "hide" its VR camera prices...)


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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Steven Backer]

Hi Archontis et al.,

Nice work!  It’s great someone is taking the time to put together the 
infrastructure for web-based ambisonics.  I enjoyed watching your Intensity 
Analyzer.

How did you encode the raw Eigenmike signals?  Using some of our software 
(EigenUnits-Encoder or EigenStudio), or something else?  

We did recently give access to the encoded “Eigenbeams” (spherical harmonics) 
with the exact intention of making it easier for people to pair em32 recordings 
with their own ambisonics decoders.  There are some subtleties to consider in 
the encoding process, especially for higher order.  In fact, we’ve found that 
some decoders, specifically for HOA, do present some challenges that can 
degrade parts of the spatial image and spectral response.  There will be a 
paper presented on this topic at the upcoming AES Sound Field Control 
conference in Guildford.  

In the past, we had control of both ends of the signal chain (i.e. the 
beamforming in EigenStudio), and we could “do the right thing”.  Now without 
knowing a-priori what the decoder is doing it becomes more difficult.  This 
could explain some of the effects discussed earlier in this thread.  We will 
soon be releasing some software updates that will hopefully address some of 
these issues.  So perhaps reserve some judgement for a later date ;-)

> An Eigenmike has some aliasing limit frequency
You are correct that the Eigenbeams will spatially alias around ~8kHz.  We do 
implement a workaround for traditional beamforming, but for ambisonics 
applications we just let it alias.  There is still usable signal up to 
(temporal) Nyquist and I’ve heard plenty of material that sounds just fine up 
there.A future version of the microphone may not have this issue anymore 
(at least in the audible spectrum)…

> It is very hard to obtain or "google" the price of an eigenmike.
We are happy to provide this information.  Feel free to send a request for a 
quote via email: cont...@mhacoustics.com
 
> The eigenmike could be a nice tool for VR/AR recordings
Absolutely!  We think so, too.  We’ve actually been pretty busy recently making 
quite a few recordings (some with video!), and have some great material we are 
going to share publicly very soon.  Hopefully some of it can convince folks 
about any sound quality issues as well, especially for musical recordings.  We 
will demo some of this also at the Guildford conference.  If you are there, 
please stop by, have a look/listen, and continue to share your feedback.

-Steven

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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Politis Archontis]

Hi Steven,

There seems to be a misunderstanding, your seem to address the considerations 
raised by Stefan here on the list , not me :-) …

I am quite a fun of the microphone and I have gotten excellent results 
rendering to large loudspeaker arrays (>25ch) using both ambisonic decoders and 
the parametric decoders that we are developing here in Aalto University.

On 22 Jun 2016, at 00:31, Steven Backer 
mailto:s...@mhacoustics.com>> wrote:

Nice work!  It’s great someone is taking the time to put together the 
infrastructure for web-based ambisonics.  I enjoyed watching your Intensity 
Analyzer.
Thanks a lot! The intensity analyser it’s a bit incomplete at the moment, cause 
it’s showing the broadband intensity vector, so it’s hard to show multiple 
different sources from different directions. I’ll soon add a band-passed 
version.

How did you encode the raw Eigenmike signals?  Using some of our software 
(EigenUnits-Encoder or EigenStudio), or something else?
All the examples use the Encoder plugin provided by you. We have created our 
own encoding filters too here, based on dense anechoic measurements of the EM, 
which get some decent 4th-order components with a range of 2kHz~7kHz, but they 
lack some bass on orders 2&3 compared to your Encoder (I guess you’re using a 
thresholding approach at LF?)

In fact, we’ve found that some decoders, specifically for HOA, do present some 
challenges that can degrade parts of the spatial image and spectral response.  
There will be a paper presented on this topic at the upcoming AES Sound Field 
Control conference in Guildford.
This is an interesting point you raise cause ambisonic research itself has 
avoided it pretty much. I think because it breaks the useful separation between 
microphone encoding and loudspeaker decoding. Hence, decoding becomes 
frequency-dependent with respect to the array size, mics etc. We have used both 
an order-limited approach here (a n-th order decoding matrix per band that the 
EM delivers properly the n-th order signals), and a decoding filter matrix 
approach. But we have gotten good results one way or another so I know that EM 
can deliver :-).

In the past, we had control of both ends of the signal chain (i.e. the 
beamforming in EigenStudio), and we could “do the right thing”.  Now without 
knowing a-priori what the decoder is doing it becomes more difficult.  This 
could explain some of the effects discussed earlier in this thread.  We will 
soon be releasing some software updates that will hopefully address some of 
these issues.  So perhaps reserve some judgement for a later date ;-)
That sounds great! (and no judgment from my side..)

An Eigenmike has some aliasing limit frequency
You are correct that the Eigenbeams will spatially alias around ~8kHz.  We do 
implement a workaround for traditional beamforming, but for ambisonics 
applications we just let it alias.  There is still usable signal up to 
(temporal) Nyquist and I’ve heard plenty of material that sounds just fine up 
there.
Let aliasing above that HF is reasonable. Another approach that may improve 
slightly compared to that, and something we have used in the past for 
parametric decoding, is to point your alias-suppression HF-beamformers towards 
the speakers.

The eigenmike could be a nice tool for VR/AR recordings
Absolutely!  We think so, too.  We’ve actually been pretty busy recently making 
quite a few recordings (some with video!), and have some great material we are 
going to share publicly very soon.
Please do! The 3-4 recordings you have at the moment on the website do not do 
justice to the EM potential!

Best regards,
Archontis Politis

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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Politis Archontis]

(Sorry for the re-posting, sursound seems to destroy indentation from my mail 
manager, making the previous one hard to read..)

Hi Steven,

There seems to be a misunderstanding, your seem to address the considerations 
raised by Stefan here on the list , not me :-) …

I am quite a fun of the microphone and I have gotten excellent results 
rendering to large loudspeaker arrays (>25ch) using both ambisonic decoders and 
the parametric decoders that we are developing here in Aalto University.

>On 22 Jun 2016, at 00:31, Steven Backer 
>mailto:s...@mhacoustics.com>> wrote:

>Nice work!  It’s great someone is taking the time to put together the 
>infrastructure for web-based ambisonics.
>I enjoyed watching your Intensity Analyzer.
Thanks a lot! The intensity analyser it’s a bit incomplete at the moment, cause 
it’s showing the broadband intensity vector, so it’s hard to show multiple 
different sources from different directions. I’ll soon add a band-passed 
version.

>How did you encode the raw Eigenmike signals?
>Using some of our software (EigenUnits-Encoder or EigenStudio), or something 
>else?
All the examples use the Encoder plugin provided by you. We have created our 
own encoding filters too here, based on dense anechoic measurements of the EM, 
which get some decent 4th-order components with a range of 2kHz~7kHz, but they 
lack some bass on orders 2&3 compared to your Encoder (I guess you’re using a 
thresholding approach at LF?)

>In fact, we’ve found that some decoders, specifically for HOA, do present some 
>challenges that can degrade parts of the spatial image and spectral response.
>There will be a paper presented on this topic at the upcoming AES Sound Field 
>Control conference in Guildford.
This is an interesting point you raise cause ambisonic research itself has 
avoided it pretty much. I think because it breaks the useful separation between 
microphone encoding and loudspeaker decoding. Hence, decoding becomes 
frequency-dependent with respect to the array size, mics etc. We have used both 
an order-limited approach here (a n-th order decoding matrix per band that the 
EM delivers properly the n-th order signals), and a decoding filter matrix 
approach. But we have gotten good results one way or another so I know that EM 
can deliver :-).

>In the past, we had control of both ends of the signal chain (i.e. the 
>beamforming in EigenStudio), and we could “do the right thing”.
>Now without knowing a-priori what the decoder is doing it becomes more 
>difficult.  This could explain some of the effects discussed earlier in this 
>thread.
>We will soon be releasing some software updates that will hopefully address 
>some of these issues.  So perhaps reserve some judgement for a later date ;-)
That sounds great! (and no judgment from my side..)

>>An Eigenmike has some aliasing limit frequency
>You are correct that the Eigenbeams will spatially alias around ~8kHz.
>We do implement a workaround for traditional beamforming, but for ambisonics 
>applications we just let it alias.
>There is still usable signal up to (temporal) Nyquist and I’ve heard plenty of 
>material that sounds just fine up there.
Let aliasing above that HF is reasonable. Another approach that may improve 
slightly compared to that, and something we have used in the past for 
parametric decoding, is to point your alias-suppression HF-beamformers towards 
the speakers.

>>The eigenmike could be a nice tool for VR/AR recordings
>Absolutely!  We think so, too.
>We’ve actually been pretty busy recently making quite a few recordings (some 
>with video!), and have some great material we are going to share publicly very 
>soon.
Please do! The 3-4 recordings you have at the moment on the website do not do 
justice to the EM potential!

Best regards,
Archontis Politis
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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Politis Archontis]

Hi Albert,

> 
> Most of the first order samples reproduce nothing above 10k and a lot of
> them sound severely saturated/clipped.


I re-normalized the decoding filters in the examples, could you confirm if that 
fixes the clipping issues you mentioned on your browser?

Best regards,
Archontis 

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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Steven Backer]

Thanks for the detailed reply, Archontis!  Good feedback for us.  Yes, sorry, I 
did kind of group all of my responses to various comments in this thread into 
one reply.

Keep an eye out for an update to our encoder plugin (including 4th order, in 
approximately the same range you mention).  Everything is working in the lab 
here; just need to find time to package, document, and post to the website.

Looking forward to seeing how your Web Audio project evolves.  My wife is 
always telling me to stop writing native apps in archaic C++, and that the web 
is the future.  Guess we have arrived!

-Steven


> On Jun 22, 2016, at 12:56 AM, Politis Archontis  
> wrote:
> 
> (Sorry for the re-posting, sursound seems to destroy indentation from my mail 
> manager, making the previous one hard to read..)
> 
> Hi Steven,
> 
> There seems to be a misunderstanding, your seem to address the considerations 
> raised by Stefan here on the list , not me :-) …
> 
> I am quite a fun of the microphone and I have gotten excellent results 
> rendering to large loudspeaker arrays (>25ch) using both ambisonic decoders 
> and the parametric decoders that we are developing here in Aalto University.
> 
>> On 22 Jun 2016, at 00:31, Steven Backer 
>> mailto:s...@mhacoustics.com>> wrote:
> 
>> Nice work!  It’s great someone is taking the time to put together the 
>> infrastructure for web-based ambisonics.
>> I enjoyed watching your Intensity Analyzer.
> Thanks a lot! The intensity analyser it’s a bit incomplete at the moment, 
> cause it’s showing the broadband intensity vector, so it’s hard to show 
> multiple different sources from different directions. I’ll soon add a 
> band-passed version.
> 
>> How did you encode the raw Eigenmike signals?
>> Using some of our software (EigenUnits-Encoder or EigenStudio), or something 
>> else?
> All the examples use the Encoder plugin provided by you. We have created our 
> own encoding filters too here, based on dense anechoic measurements of the 
> EM, which get some decent 4th-order components with a range of 2kHz~7kHz, but 
> they lack some bass on orders 2&3 compared to your Encoder (I guess you’re 
> using a thresholding approach at LF?)
> 
>> In fact, we’ve found that some decoders, specifically for HOA, do present 
>> some challenges that can degrade parts of the spatial image and spectral 
>> response.
>> There will be a paper presented on this topic at the upcoming AES Sound 
>> Field Control conference in Guildford.
> This is an interesting point you raise cause ambisonic research itself has 
> avoided it pretty much. I think because it breaks the useful separation 
> between microphone encoding and loudspeaker decoding. Hence, decoding becomes 
> frequency-dependent with respect to the array size, mics etc. We have used 
> both an order-limited approach here (a n-th order decoding matrix per band 
> that the EM delivers properly the n-th order signals), and a decoding filter 
> matrix approach. But we have gotten good results one way or another so I know 
> that EM can deliver :-).
> 
>> In the past, we had control of both ends of the signal chain (i.e. the 
>> beamforming in EigenStudio), and we could “do the right thing”.
>> Now without knowing a-priori what the decoder is doing it becomes more 
>> difficult.  This could explain some of the effects discussed earlier in this 
>> thread.
>> We will soon be releasing some software updates that will hopefully address 
>> some of these issues.  So perhaps reserve some judgement for a later date ;-)
> That sounds great! (and no judgment from my side..)
> 
>>> An Eigenmike has some aliasing limit frequency
>> You are correct that the Eigenbeams will spatially alias around ~8kHz.
>> We do implement a workaround for traditional beamforming, but for ambisonics 
>> applications we just let it alias.
>> There is still usable signal up to (temporal) Nyquist and I’ve heard plenty 
>> of material that sounds just fine up there.
> Let aliasing above that HF is reasonable. Another approach that may improve 
> slightly compared to that, and something we have used in the past for 
> parametric decoding, is to point your alias-suppression HF-beamformers 
> towards the speakers.
> 
>>> The eigenmike could be a nice tool for VR/AR recordings
>> Absolutely!  We think so, too.
>> We’ve actually been pretty busy recently making quite a few recordings (some 
>> with video!), and have some great material we are going to share publicly 
>> very soon.
> Please do! The 3-4 recordings you have at the moment on the website do not do 
> justice to the EM potential!
> 
> Best regards,
> Archontis Politis
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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Albert Leusink]

Politis Archontis  writes:

> 
> Hi Albert,
> 
> > 
> > Most of the first order samples reproduce nothing above 10k and a lot of
> > them sound severely saturated/clipped.
> 
> I re-normalized the decoding filters in the examples, could you confirm if
that fixes the clipping issues
> you mentioned on your browser?
> 
> Best regards,
> Archontis 
> 


Hello Archontis,

Much better, I hear no longer any clipping except for the choir (sample 3)
which has some distortion on the right at about 4 seconds in, but that could
have been from the original capture. Thanks!



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Re: [Sursound] Ambisonics on the web pt.1: Web Audio FOA/HOA ambisonic objects

[Politis Archontis]

Hi, 

just a note that I replaced the binaural decoding filters in the examples with 
others that fix most of the decoding colouration issues that were very strong 
in the first version. 
I‘ve also added some Matlab routines that can show how these filters can be 
computes from an HRTF set, with two different approaches, a virtual decoding 
and a “direct” approach.

I’d like to get some feedback (does it sound better?) from people that are 
interested in this. (You can find and listen to the examples at the bottom of 
the webpage https://github.com/polarch/JSAmbisonics).

The library will soon be packaged as a more formal javascript library, with 
NodeJS - thanks to David Poirier-Quinot from IRCAM for the massive work!

Best regards,
Archontis

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