Re: [Sursound] RIR measuring, how to capture a higher order Ambisonic room responce?

[Fernando Lopez-Lezcano]

On 04/29/2018 06:13 AM, Dave Malham wrote:

Excellent - this is exactly the method I was about to suggest - steppers,
related hardware and motor control boards have been driven down in price so
much by the 3-d printing/cnc/maker revolution that it makes almost no sense
to do anything else.


Yes, I like that too... I was planning on adding a stepper and gear 
drive to my test rig (I turn it manually, not too hard).


This would have been fine for tetrahedral microphones and horizontal 
plane only measurements. The problem for me surfaced when I went to 
second order microphones and needed measurements above and below the 
horizontal plane. I built a "better" test rig that can tilt, added a 
small xy table to be able to "calibrate" the center of rotation (and of 
course 3d printed a fixture to attach the mic!), but I need to 
physically reposition the rig between each layer being measured. Not the 
best.


I was going for a different approach when it was suggested to me (both 
by my boss and a phd student here, thanks Chris & Elliot) that a robotic 
arm would be better and more general purpose. I was reluctant because of 
the cost...


(a bit off topic but maybe of interest anyway)

I was actually going to use a telescope mount (_not_ an equatorial mount 
which are the most common, apparently), I found one that would do what I 
needed, was not expensive, and I could control azimuth and elevation 
through rs232 (SkyWatcher AllView). I designed (on paper :-) a 
pantograph that would keep the microphone away from the mount, and 
replicate the movements. But again, lots of mechanical parts and tricky 
design. Better to spend time on the microphones.


So I bought a robotic arm. Len (from Core Sound) asked off-list about 
it, so I'm including some information here. I got the WidowXL from 
Trossen Robotics. Anything better (as far as I could find, not an 
expert!) would have driven the price up exponentially - this one is not 
cheap anyway. I just spent two full days assembling it (lots of pieces, 
lots of screws). Beware, ask before you buy as to delivery times - mine 
was delayed several times and they were not very upfront about it (or 
just did not know).


Anyway, I just did some preliminary tests today and it seems to be able 
to hold my microphone and move all the joints so as to point it in the 
right directions and rotate it accurately. Lots to do, but it is a start 
(to get better data).


-- Fernando



I would use the esp8266 arduino compatible wifi module
which costs about the same as a decent cappuccino - I paid about 4 euros
for one at the end of last year - which has a reasonably powerful 16 bit
processor and is quite capable of acting as a web server, so I'm doing that
and controlling my steppers from a web based interface on my mobile or
laptop. Note, however, that I've confined it to just my home network for
security sake - don't want people using it to influence the elections :-)

Dave
 PS Sorry once again I'm not currently doing this for audio - maybe one of
these days I'll get back to that.

On 24 April 2018 at 02:58, umashankar manthravadi 
wrote:


I have been using a stepper motor (of the kind used in 3d printer ) driven
by a low cost Arduino and motor control board. I 3d print a snug fitting
fixture for the microphone with the motor shaft  aligned to the array
centre. 


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Re: [Sursound] Strange 'buzz' in Ambisonic recording

[Bo-Erik Sandholm]

I suspect that depending of chosen virtual mic configuration there is so
much low frequency gain added that you boost the level of the nearly always
existing 50Hz hum so much that you actually hear it.
It has sometimes happened to me that I need to lower the input level of the
signal to the ambisonic decoder otherwise i got signal clipping in the
processing stage.

BR Bo-Erik

2018-05-07 18:30 GMT+02:00 Gerard Lardner <glard...@iol.ie>:

> I'm very much an amateur here, so please forgive what might be a stupid
> question!
>
> I recorded a concert on Saturday (John Rutter's /Gloria /and Karl Jenkins'
> /The Peacemakers/) using an Ambisonic mic and some others. I'm encoding the
> A-format to B-format using VVEncode in Reaper, and panning in the extra
> mics using Wigware Ambipan. The result is then decoded to surround sound or
> to stereo using VVDecode; all in the same Reaper set-up. I've used this
> approach before, usually successfully.
>
> I find that, when the organ and brass are playing at full volume (I mean
> in the orchestra, not just in playback), there is a 'buzzing' sound in the
> playback. It sounds harsh, pitched at about 50 Hz. But if I listen to the
> A-format files alone in Reaper or in VLC Media Player, there is no buzz.
> Similarly, there is no buzz if I encode the A-format using the stand-alone
> version of VVMic. The buzz is present both in the B-format from the
> Ambisonic mic and, less strongly, in the panned B-format from the soloists
> mic. It appears to be an artefact of my editing configuration; but it
> didn't happen in a recording I made, using the same configuration, last
> month. The only difference since then has been that my old hard disc, which
> had developed some faults, was cloned onto a new SSD.
>
> Does this description suggest a specific problem/remedy to anyone? I know
> I can produce a decent CD using the stand-alone VVMic route and panning in
> the soloists into the stereo mix; but I'd like to get to the bottom of why
> my Ambisonic configuration is doing this now.
>
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[Sursound] Strange 'buzz' in Ambisonic recording

[Gerard Lardner]

I'm very much an amateur here, so please forgive what might be a stupid 
question!


I recorded a concert on Saturday (John Rutter's /Gloria /and Karl 
Jenkins' /The Peacemakers/) using an Ambisonic mic and some others. I'm 
encoding the A-format to B-format using VVEncode in Reaper, and panning 
in the extra mics using Wigware Ambipan. The result is then decoded to 
surround sound or to stereo using VVDecode; all in the same Reaper 
set-up. I've used this approach before, usually successfully.


I find that, when the organ and brass are playing at full volume (I mean 
in the orchestra, not just in playback), there is a 'buzzing' sound in 
the playback. It sounds harsh, pitched at about 50 Hz. But if I listen 
to the A-format files alone in Reaper or in VLC Media Player, there is 
no buzz. Similarly, there is no buzz if I encode the A-format using the 
stand-alone version of VVMic. The buzz is present both in the B-format 
from the Ambisonic mic and, less strongly, in the panned B-format from 
the soloists mic. It appears to be an artefact of my editing 
configuration; but it didn't happen in a recording I made, using the 
same configuration, last month. The only difference since then has been 
that my old hard disc, which had developed some faults, was cloned onto 
a new SSD.


Does this description suggest a specific problem/remedy to anyone? I 
know I can produce a decent CD using the stand-alone VVMic route and 
panning in the soloists into the stereo mix; but I'd like to get to the 
bottom of why my Ambisonic configuration is doing this now.


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