Thread: Nimbus Ambisonic Recordings?

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Post by Peter June 6, 2010 (11 of 14)

Post by MartinLeese June 6, 2010 (12 of 14)
There seems to be some confusion here about Ambisonics. I will attempt to clear it up.

The key difference between Ambisonics and other surround sound systems is that Ambisonics separates transmission channels from speaker feeds. The advantage of this is that you can reproduce Ambisonics with as many speakers as you wish; it is a consumer option. The disadvantage is that you need to have a decoder in your living room (and the decoder needs to know your speaker layout).

The main transmisson format for Ambisonics is called B-Format. To include a full-sphere soundfield, this needs to contain (at least) four channels. Alternatively, three-channel B-Format is horizontal only. It is also possible to matrix the three-channel B-Format down into two-channel UHJ which is mono and stereo compatible. Unfortunately this cannot be done without compromise, the most obvious result being phasiness. The original UHJ specification contained three- and four-channel UHJ for no compromise horizontal and full-sphere, but no material has ever been released in these formats. Several hundred two-channel UHJ LPs and CDs were released by a number of companies; a discography is available.

Most Nimbus recordings were made using a Nimbus-Halliday mic which recorded in three-channel B-Format, so they were horizontal only. The three-channel B-Format was then matrixed down to two-channel UHJ for release. Unfortunately, Nimbus only archived the two-channel UHJ, not the B-Format. (There is a moral here.) All nine of the DVD-A's released by Nimbus were produced from two-channel UHJ masters. Compared to B-Format, these can sound phasey. Also the DVD-A's are pre-decoded for four speakers arranged in a square. If you do not own a UHJ decoder (currently available in all Meridian surround processors) then, obviously, you will want to use these speaker feeds. If you have more than four speakers and a UHJ decoder then you should, instead, decode to your own speaker layout. In this latter case, there is no advantage in using the pre-decoded speaker feeds. Yes, they are discrete, but they were produced from matrixed two-channel UHJ.

If you want to hear pristine B-Format then more than 200 pieces are available for free download from Ambisonia.com. Almost all of these are full-sphere. These can be downloaded as DTS images which are pre-decoded for four speakers in a square. If you want full-sphere then you will need to download the B-Format, use a decoder, and have speakers placed both above and below the level of the listener's ears. Free ad hoc software decoders are avaialble. (Note that Ambisonia.com will shortly be moving to SoundOfSpace.com.)

I hope this clears things up. Here are some links:

http://www.wyastone.co.uk/nrl/dvd_intro.html which states "These DVDs were all taken from two channel, UHJ, 44.1 kHz, 16 bit masters."
http://members.cox.net/surround/ for the UHJ discography
http://www.ambisonia.com/ to download free B-Format pieces
http://www.ambisonia.com/wiki/index.php/Playback_Software for details of free ad hoc software players
http://members.tripod.com/martin_leese/Ambisonic/ for the Ambisonic FAQ (which I created and maintain)
http://en.wikipedia.org/wiki/Ambisonics for a general introduction to Ambisonics

Post by rammiepie June 6, 2010 (13 of 14)
Mr. Leese, thank you for your rather thorough explanation of Ambisonics and directing us to the Ambisonia website. A lot of confusion abounds when discussing Ambisonics and since, especially in the States, it was almost non~existent, it's nice to realize that so many wonderful albums were recorded with multi~channel in mind, including some of the first uses of height channels. With so many competing systems vying for the multi~channel format war, it's no wonder that none really caught the imagination of the buying public in a commercial way. Everyone thought that the 5.1 video revolution would alter that landscape, but, alas, even SACD with its tri~layered versatility struggles to maintain its niche.

Perhaps, oneday, Nimbus will see fit to re~release their recorded UHJ treasures in a lossless multi~channel format which can be enjoyed by all.

Post by GROOT GELUID June 6, 2010 (14 of 14)
Ambisonics holds some wonderful nostalgic feelings and memories for me. It was during my studies at Guildford that I had the option to experiment, not only with stereo analog and digital recordings, but also with a four channel analog recorder with surround sound. In that time the theory of Prof Felgett and Michael Gurzon made a big impact on me about the possibilities to produce a much enhanced result when playing back recorded music(over the existing conventional stereo). At the university I was lucky to be able to experiment with a brand new Calrec soundfield microphone as well as an UHJ encoder. I chose to do my final project on the subject of Ambisonic recording and playback, including the possible marketing options.
Two things really stick till today: Surround recording and playback offer (potential and real) advantages over 2 channel stereo recordings, and if you offer a good playback to the general public, they can easily distinguish and favour the surround.
I did many test recording in the B format, using an omni directional microphone and 2 cross pair fig of 8 mikes, coincidentally placed, as well as recording with the soundfield mike that used 4 capsules, and can produce B format through the mixing of the output of the capsules.
The mathematical theory was quite impressive, but I am not at all convinced that the psycho-acoustical theory and explanation is very correct. After having had another opportunity to extensively experiment with surround sound recording in the early 1990's and then even more, during the development support time for SA-CD for Philips and Sony, experiencing the great advantage of the 5 channel ITU speaker set up, compared to the old fashioned 'square' quadraphonic speaker set up, and managing to dramatically improve on my former 'surround' microphone placements, it is really only the nostalgic feeling that I have left over. I would never consider using the technique for music recording any more, as I feel very lucky to have been able to do recordings in 5 channel surround, that can be realistically played back through a thoroughly tested and used consumer format, over the last 12 years.
I am writing this, just coming out of a finished recording period, recording Prokofiev violin sonatas, and having balanced the stereo and the surround to my best abilities, and thankfully being lucky enough to monitor the whole project in surround.
Now for the next week we are starting a 4 (sa)cd project with Tchaikovsky and Rimsky orchestral music and the prospect of hearing the orchestra back through the 5 loudspeakers is still, and again, very, very exiting.
By the way, I do think that if you consider the option of using many more speakers for playing back surround sound recordings, the wave field synthesis has a much greater viability, both theoretically as well as practically, than ambisonics has. It is with fond memories that I think back on ambisonics.

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