[Sursound] Question regarding UHJ Encoding - Decoding

[Dave Hunt]

Hi,

Thanks for finding that. I'll have to dig out the papers and see if I  
can find more info, though I remember being hopelessly confused last  
time I looked at this, several years back.


In the meantime I'll carry on just using the straight UHJ to B-Format  
equations. These work very well on 'normal' stereo recordings:  
instant ambisonic surround. How accurate is impossible to say,  
especially as none of these recordings have ever been 'surround', and  
the original event is totally inaccessible or even never existed.


It seems to work best on recordings made with a crossed pair, or even  
pan-potted mono. Hardly surprising really.


Ciao,

Dave


Date: Sat, 7 May 2011 13:54:01 -0600
From: Martin Leese 

Dave Hunt  wrote:


One of these complexities is presumably indicated by the phrase "Note
that two-channel UHJ requires the player to use different shelf
filters than for three- and four-channel UHJ (and B-Format)" at
http://en.wikipedia.org/wiki/Ambisonic_UHJ_format.

Any clues as to why this should be so ?? If we get back something
close to three-channel B-Format, why should it be filtered
differently from  a straight three-channel B-Format ?? The encoding/
decoding has no frequency conscious components. Admittedly, the gains
of the filters may need to differ between 2D and 3D decoding.


See the thread on this mailing list from
December 2008 with the Subject "decoding
an UHJ-B stereo file to Ambisonics Quad".

The thread included this post from Geoffrey
Barton:


Date: Tue Dec 30 12:16:42 EST 2008
Subject: [Sursound] decoding an UHJ-B stereo file to Ambisonics Quad

Sorry to shatter your simple world, but the shelf filters do have to
be different for 2 channel UHJ!

As the BHJ-> 'WXY' decoding has magically produced three channels from
two, there is information missing. This manifests itself as phase-
shifts between the derived WXY signals.

If you optimise the shelves to maximise rv at lf and ev at hf using
these decoded signals, the resulting values are not the same as for b-
format. You also have to watch the way MAG quoted these values as
sometimes he quoted the 'kernel' values for b-format rather than the
'normal' b-format.

Geoffrey



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Re: [Sursound] Speaker configs + subwoofers

[Bo-Erik Sandholm]

 A bit out of topic but if anyone else is into building their own speaker 
cabinets.
Let me point you to a document that is very good in explaining the design 
choices in a cabinet for the bass frequencies.

http://www.sonicdesign.se/optimum.html

Regards
Bo-Erik 

-Original Message-
From: sursound-boun...@music.vt.edu [mailto:sursound-boun...@music.vt.edu] On 
Behalf Of Bo-Erik Sandholm
Sent: den 4 maj 2011 13:48
To: Surround Sound discussion group
Subject: Re: [Sursound] Minim AD7 for sale - Speaker configs.

>From 
>http://en.wikipedia.org/wiki/Sound_localization#Evaluation_for_low_freq
>uencies

Evaluation for low frequencies

For frequencies below 800 Hz, the dimensions of the head (ear distance 21.5 cm, 
corresponding to an interaural time delay of 625 µs), are smaller than the half 
wavelength of the sound waves. So the auditory system can determine phase 
delays between both ears without confusion. Interaural level differences are 
very low in this frequency range, especially below about 200 Hz, so a precise 
evaluation of the input direction is nearly impossible on the basis of level 
differences alone. As the frequency drops below 80 Hz it becomes difficult or 
impossible to use either time difference or level difference to determine a 
sound's lateral source, because the phase difference between the ears becomes 
too small for a directional evaluation.

-Original Message-
From: sursound-boun...@music.vt.edu [mailto:sursound-boun...@music.vt.edu] On 
Behalf Of Bo-Erik Sandholm
Sent: den 4 maj 2011 13:41
To: Surround Sound discussion group
Subject: Re: [Sursound] Minim AD7 for sale - Speaker configs.

 
Yes, I have a few woofers available BUT according to what I understand from 
psychoacoustics we cannot really hear directions of sound below 80 Hz, as the 
ear/brain is changing method of decoding soundwaves between 80 to 100 Hz?
So do I really need more than a pair driven in mono (or 4) to even out the 
excitation of the room modes? 

If I where to add a low frequency decoder how should I do that?

Is it not so that the speaker feed to all of the 10 speakers are in phase for 
frequencies lower than Some "undefined" frequency? 
That is using Ambdec?

Should I have a highpass filter before or after the decoder for the 10 "small" 
speakers, if I add a low frequency feed, either mono or decoded?

Bo-Erik

-Original Message-
From: sursound-boun...@music.vt.edu [mailto:sursound-boun...@music.vt.edu] On 
Behalf Of Peter Lennox
Sent: den 4 maj 2011 11:32
To: Surround Sound discussion group
Subject: Re: [Sursound] Minim AD7 for sale - Speaker configs.

Quick suggestion: - as you're having to use more than 8 channels anyway, you're 
likely to be using a 16 channel card; thus, you would have some channels left 
to decode (horizontal only) to 3 or 4 subs

Dr Peter Lennox
School of Technology
University of Derby, UK
tel: 01332 593155
e: p.len...@derby.ac.uk  


-Original Message-
From: sursound-boun...@music.vt.edu [mailto:sursound-boun...@music.vt.edu] On 
Behalf Of Bo-Erik Sandholm
Sent: 04 May 2011 08:09
To: Surround Sound discussion group
Subject: Re: [Sursound] Minim AD7 for sale - Speaker configs.

 

I still want to suggest a setup that I will soon have in operation, I have 
written about it before.
It uses 10 channels, it is a hexagon in the horizontal plane with a speakers at 
front back.
The Z is handled by for speakers, placed where the 4 hexagon side speakers will 
end up if the Hexagon is rotated 90 degrees around a axis through the front and 
back hexagon speakers.

Fons A has created a ambdec for me of this setup.

I have the possibility to have all speakers except the 2 floor speakers 
permanently mounted due to my room geometry. I have the 2 floor speakers 
mounted on a long wooden plank letting me getting them in place quickly.

I have been rethinking my amplifier setup and will now use 3 modules of 4 
channel sure swiched amps instead of 2 Home theater amplifiers.
The shure amp modules (4 x 100W) cost 98USD including a switched power supply, 
an will give 30 watts per 8 ohm speakers, I will only be using 2 power supplies 
so the total material cost is at the moment 3 x 44 US + 2 x 48 USD, that is 
less than 240 USD.
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=320-302

I will be using second hand Kef KHT-2005.2 "Eggs" as speakers.

It is a bit of a "bother" that 10 instead of 8 channels are used, when it comes 
to the sound card setups...

Regards
Bo-Erik

-Original Message-
From: sursound-boun...@music.vt.edu [mailto:sursound-boun...@music.vt.edu] On 
Behalf Of Aaron Heller
Sent: den 3 maj 2011 20:04
To: Surround Sound discussion group
Subject: Re: [Sursound] Minim AD7 for sale

On Tue, May 3, 2011 at 10:14 AM, Fons Adriaensen  wrote:
> On Tue, May 03, 2011 at 07:15:29PM +0530, umashankar mantravadi wrote:
>>
>> in fact angelo recommended that i arrange the eight speakers as two 
>> crossed squares. two speakers in front and back, and fou

[Sursound] 5.1 Audio samples for experiments

[Junfeng Li]

Dear list,

I am now researching on how to convert 5.1-ch Audio to 2-channel Audio.
To do subjective experiments, some typical 5.1-ch Audio samples are needed.
Does anyone have these kinds of samples and share with me?

Thank you so much.

Best regards,
Junfeng
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