Re: [Sursound] O.T.: Android (was: installations)

[Marc Lavallée]

On Sun, 11 Mar 2018 20:17:38 +
st...@mail.telepac.pt wrote:

> Citando Marc Lavallée :
> >  GAFA is the main provider of spyware (a well documented subject).
> >  At least Android is free software (or “open source”),
> >  so some versions of Android are free of Google’s spywares,
> >  There’s also quite a lot of free software for Android,
> >  available from the F-Droid repository (and there’s probably
> > others).  
> 
> Ok, now I see your point: You can install your own version of Android.
> 
> (But most people just use the Android they "get" i.e. buy, even not  
> being able to replace the OS.)



Most people won't know and won't care, but it's fairly "easy" (or not
too difficult) to disable many Google apps and services on any Android
devices; as a new user, skip the creation of a Google account, then
disable all things related to Google in settings/apps. It won't get
rid of all surveillance activities, but it's a good start... When
possible (not all devices are supported) it is just easier and safer to
install a custom Android firmware, because none of that extra
customization is required. Then, as a rule of thumb, use only free
software from the F-Droid and Guardian Project repos, install a safer
browser (Firefox Klar or OrFox), and if the phone is rooted install an
ad-blocker based on firewall rules. A safer device also runs faster
and requires less power, which is a good thing when used as an
ambisonic recorder or player...

 
--
Marc
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Re: [Sursound] oktava 1st order mic

[Len Moskowitz]

Peter wrote:


Thank you for your opinion Len. I am tempted to ask 'why' but let me
ask instead what are the most difficult things to get right when
building a first-order microphone.


The incomparable Aaron Heller covered the main points in his response.


Len Moskowitz (mosko...@core-sound.com)
Core Sound LLC
www.core-sound.com
Home of TetraMic and OctoMic

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Re: [Sursound] oktava 1st order mic

[umashankar manthravadi]

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Re: [Sursound] oktava 1st order mic

[umashankar manthravadi]

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Re: [Sursound] oktava 1st order mic

[Aaron Heller]

The radius of the tetrahedral array determines the frequency at which the
B-format polar patterns start to breakdown. The formula given by Gerzon is
c/(pi*r), where c is the speed of sound and r is the radius of the
array[1]. Depending of the design, the acoustic radius is about 10% larger
than the physical radius, because the sound has to diffract around the
structures. So, in round numbers 10/r kHz, with r in cm. In a Soundfield
mic, the physical radius 1.47cm, so around 6.8 kHz. The Octava is over 4
cm, so less than 2.5kHz.  Note that very small capsules tend to be noisy,
so there is a tradeoff between noise and integrity of the patterns at high
frequencies.

In many of the 3D printed designs, the array is not open enough and the
interior space behind the capsules becomes a resonant chamber. This causes
peaks, dips and phase shifts in the response of the individual capsules
that are difficult to correct and affect the resulting patterns. There is
also the general geometry of the microphone body that tells you how much
care went into the design in terms of acoustic shadowing, reflections, and
diffraction. The large flat surface on the top of the preamp enclosure in
the Octava does not look good to me.

Part of the magic of a tetrahedral microphone is that the free- and
diffuse-field responses track each other. To achieve this, it is important
that the directivities of the four capsules are well matched [2].
Calibration can compensate for this to some degree, but the better the
capsules match, the better the result will be.  The only way to do this is
have a large collection of capsules, measure them individually, pick sets
of four, and then calibrate the entire array.  I know that Core Sound does
this (and Calrec did this). I don't know about other companies. In general,
I am suspicious of any tetrahedral mic that uses generic A-to-B conversion,
with no individual calibration.

[1] M. A. Gerzon, "The Design of Precisely Coincident Microphone Arrays for
Stereo and Surround Sound," 50th AES Convention Preprints, London, no. 20,
1975.

[2] A. J. Heller and E. M. Benjamin, "Calibration of Soundfield Microphones
using the Diffuse-Field Response," 133rd AES Convention Preprints, San
Francisco, no. 7811, 2012.


On Sun, Mar 11, 2018 at 3:13 PM, Peter P. <peterpar...@fastmail.com> wrote:
>
> * Len Moskowitz <lenmoskow...@optonline.net> [2018-03-11 18:48]:
> > Gerard Lardner wrote:
> >
> > > Fons Adriaensen in Italy calibrated my Oktava. I believe Richard Lee
in
> > > Australia might still offer a calibration service, though he appears
to
> > > be less active on the internet these days, and I think Core Sound in
the
> > > USA also will do it - they used to say it on their website, but I
> > > haven't checked lately.
> >
> > We could, but in general we can confidently state that Oktava doesn't
> > understand how to build a first-order ambisonic microphone, and the
cost and
> > effort to calibrate it is not worthwhile.
>
> Thank you for your opinion Len. I am tempted to ask 'why' but let me
> ask instead what are the most difficult things to get right when
> building a first-order microphone.
>
> best, P
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