Nimbus DVD Music
A series of Surround Sound releases on DVD launched in August 2004 
Three audio formats on one disc 
90 minutes playing time 
Playable on DVD-Video and DVD-Audio players

Nimbus Records has pioneered Surround Sound since 1972. All Nimbus 
recordings have been made using Ambisonics, a system we prefer because
it can capture the acoustic quality of each hall and recreate it in a
domestic environment with great fidelity. Until now users have needed a
specific Ambisonic decoder to be able to enjoy Nimbus recordings the way
they were intended. As only a handful of manufacturers have made these,
the full effect of our recordings has only been available to a dedicated
minority of listeners.

Now, DVD makes it possible to deliver Nimbus Surround Sound recordings to
home listeners with standard, readily available equipment - all that is
required is a DVD Video player connected to a DTS capable Surround Sound
system, or a DVD Audio player with multi-channel playback. We believe that
Surround Sound will enhance your listening experience more dramatically than
all other technical innovations combined.

What's On the Disc

The Surround yourself with ... series of discs present up to 90 minutes of
music (up to 180 minutes on double sided discs) in three different formats.
You should choose the format that is appropriate for your home playback system.

Stream 1 - 2 channel, UHJ encoded, PCM, 48 kHz, 24 bit (DVD-Video players)

This stream is the most appropriate if you only have two channel playback or
if you have your own Ambisonic decoder set up for your specific playback system.
The audio quality is a close equivalent to what you would hear from a standard CD.

Stream 2 - 4 channel, DTS compressed, 48 kHz, 24 bit (DVD-Video players)

This stream is the one to use if you have a DVD-Video player connected to a
surround sound amplifier with a DTS decoder. DTS compression is a lossy compression
system (see paragraph below), but does give very good audio performance. DTS
decoders are built into the vast majority of domestic surround sound amplifiers now

For more information on DTS please try

Stream 3 - 4 channel, MLP losslessly compressed (see paragraph below), 88.2 kHz,
20 bit (DVD-Audio players)

This stream is playable only by DVD-Audio players. All DVD-Audio players are capable
of decoding MLP data streams. The four channels will be delivered from the analogue
multi-channel outputs of your DVD-Audio player - these must be connected to the 
multi-channel inputs on your surround sound amplifier.

For more information on MLP please try

Audio Compression Systems

Audio compression systems fall into two categories, referred to as lossless and lossy.
When using a lossless compression system, the audio data you get from the decoded
stream is identical to the information you put in - the compression reduces the size
of the data without any impact on the data itself. When using a lossy compression
system, the size of the data can be reduced further but the data you get out is not
identical to the original. Different lossy compression systems offer different
compromises between data size reduction and data accuracy.

The Speaker Arrangement

The four channels delivered by both the DTS and MLP streams are four speaker feeds -
front left and right, back (or surround) left and right. When decoding Ambisonic
material it is possible to decode for a specific number and layout of speakers -
these four channels were decoded assuming four matched speakers arranged in a square
with the listener(s) in the centre. While this arrangement may not match exactly many
domestic playback systems, after extensive tests we found it to be the most flexible
target layout. It works well for systems where the listener is closer to the back
speakers and this has been compensated for with gain adjustments on the amplifier.
It also works particularly well for the standard ITU speaker layout, which is most
likely to be recommended in surround sound amplifier manuals.

The decision was made to decode for a target layout of four rather than five speakers
for two reasons:

For a centre speaker to work well as part of a music playback system it must be well
matched to the other speakers in terms of its sonic character and its relative level
must be set correctly. The majority of domestic surround sound playback systems are
used for movie playback, where the centre channel is used primarily for on-screen
dialogue. For movies it is much less critical if the centre speaker does not match
the others, or if the level is set incorrectly. It is likely that many of the centre
speakers in domestic playback systems are not appropriate for music reproduction for
these reasons. The conclusion was that excluding the centre speaker would reduce the
danger of bad surround playback.

Ambisonics is fundamentally best decoded for regular arrangements - that is to say
four speakers in a square, five in a pentagon, six in a hexagon etc. The centre 
speaker in the standard five speaker layout biases the sound towards the front, 
making Ambisonic decoding more difficult and requiring more compromises than for the
four speaker arrangement we have chosen.

For these reasons the front speaker is intentionally silent.

Similarly, there is no LFE (low frequency effects, normally sent to the system
subwoofer) channel data. The reason for this is more straightforward. There is no low
frequency information in classical music recordings which cannot be reproduced
satisfactorily by a normal, full range speaker - even the cannon in Tchaikovsky's 1812
Overture. If you have a system with smaller speakers and a subwoofer, then your
surround sound amplifier's bass management system will automatically redistribute the
low frequencies that your main speakers cannot handle to the subwoofer. There is no
need to include any of this information in the dedicated LFE channel on the disc.


The Ambisonic system used by Nimbus Records was developed in the early 1970s. It
comprises methods for recording and reproducing Surround Sound with great fidelity,
and remains unchallenged as the most coherent and effective Surround Sound system.

Ambisonics can be helpfully divided into four areas - microphone, post-production,
transmission, replay.

In its simplest form an Ambisonic Surround Sound recording is made using a Soundfield
microphone - this is a microphone with four cardioid capsules in a tetrahedral
arrangement. The outputs of these four capsules can be processed to give a B-format
signal. (The raw output of these four capsules is sometimes referred to as A-format).
B-format is the core of the Ambisonic system. It consists of four channels best
described in terms of four coincident microphones - three figure-of-eight patterns
each aligned with one of the three axes (channels X, Y and Z) of a three dimensional
graph, and one omnidirectional (channel W). These four signals together describe a
full, three dimensional soundfield.

Nimbus uses a slightly different microphone arrangement developed by our Reseach
Director, Dr. Jonathan Halliday, which consists of two figure-of-eight microphones,
one directed along the front / back axis, the other along the left / right axis, and
an omnidirectional microphone, all held togther as closely as possible in a frame.
The result from this arrangement is single plane B-format, comprising channels X, Y
and W, without the Z (height) information.

The post-production part of the sequence, although not relevant to the way Nimbus
makes recordings, allows multitrack recordings to be mixed to produce an Ambisonic
result. There is both analogue equipment and now plugins for various audio processing
software that allow the mixing engineer to manipulate sources recorded in more
conventional ways, either mono or stereo, as part of a B-format soundfield.
These include tools to select location and movement within the soundfield in three

The finished, Ambisonic recording can be delivered to the user in a number of ways.
B-format itself is a very efficient transmission format, conveying full three
dimensional sound in only four channels. For single plane recordings, three channel
B-format can be used. It is also possible to decode the B-format to a common, regular
speaker arrangement for transmission as speaker feeds. The most basic method for
transmission of an Ambisonic signal uses a system called UHJ. UHJ is a matrixing
system developed to allow Ambisonic material to be transmitted via only two channel
media. The two channels are stereo compatible - that is to say you can listen to them
as a normal stereo recording on standard equipment - but with a UHJ decoder you can
decode them to your chosen multichannel speaker layout.

An important aspect of Ambisonic transmission and replay is that nothing in the
production chain to this point has made any assumptions about the number or arrangement
of playback speakers. Ambisonic material can be decoded to any number of speakers.
Decoding works best for regular speaker arrangements, as mentioned above. Decoding for
irregular layouts is possible, but it becomes more difficult to recreate a convincing
soundfield. Even using speaker feeds as a method of transmission, if the target
arrangement of speakers is known a decoder can reconstruct the original B-format from the
feeds and then redecode to any other chosen speaker layout.

For much more information on Ambisonics please try

The Production Process

When Nimbus started to make digital recordings in around 1980 until the late 1990s all of
our master tapes were two channel, UHJ encoded, 44.1 kHz, 16 bit - exactly the same
format as we deliver on CD. Before that we recorded to four track analogue tape, in
either A-format or B-format. More recent recordings have been made using three or four
channel magneto-optical discs in B-format, 48 kHz, 20 bit. The significance of all this
is that each of these master formats requires different treatment to derive the four
speaker feeds on the DVDs. The first batch of five DVDs were all taken from two channel,
UHJ, 44.1 kHz, 16 bit masters.

The process of establishing exactly how best to treat these various master formats was
started some time ago, at the prompting of Richard Lowe (Periphonix), a long time supporter
of Ambisonics. His initial work creating test material and his collaboration during the
development of the production process has been a crucial part of the project.

The material on the DVD-Video part of the disc must be presented at 48 kHz - this is part
of the DVD-Video specification - so the material was sample rate converted for those
streams using a software solution. The Ambisonic decoding was undertaken using software
written specifically for this project and supplied by Meridian Audio.

The DVD-Video streams are presented at 24 bits. It can be demonstrated that correctly
dithered 16 bit audio contains information well below its expected noise floor. Analysis
of our earliest digital recordings indicates that there is at least 18 bits worth of 
information available, and later recordings made using more sophisticated A to D 
converters have even more. The DVD-Video specification allows for digital audio streams
of 16, 20 or 24 bits. The 20 bit option would give enough capacity for the data
available in the recordings, however support for 20 bit audio files is not implemented
correctly in the majority of DVD Authoring systems, so the decision was taken to use a
24 bit stream, even though the bottom four or more bits may have no useful data. 20 bits
is used for the DVD-Audio stream, as the MLP encoder does handle 20 bit streams correctly.

The DVD-Audio stream is presented at 88.2 kHz. While there is little obvious benefit to
be had from such a high sampling frequency when the original recording was made at 44.1
kHz, it has been observed that D to A converters sound better when working faster. The 
choice of this sampling frequency has no impact on the total playing time of the disc, as
the MLP lossless compression system is very good at not encoding information that is not
there - a stream at 88.2 kHz, 20 bit compresses more efficiently than the same material
at 48 kHz, 24 bit. 88.2 kHz was chosen over 96 kHz as it is a simple multiple of the
original 44.1 kHz, and therefore avoids the complex 44.1 to 48 kHz sample rate conversion

Later in the series there will be DVD releases of some of Nimbus' earlier, analogue
recordings. For these the production process will be different - it will be possible to
make new digital transfers from the original analogue masters at higher sampling
frequencies and with more bits. This will change the decoding process somewhat, although
the same software has the facility to decode B-format sources.

If you have any questions about these discs, or about the recording and decoding
technology used, please send an e-mail to

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