A Universal Medium-An Answer
B+ Format consists of B format
ambient-recorded signal plus two channels of L/R direct recorded signal.
It is recorded on 6 channels and when reproduced it is decoded into however
many channels you have at your disposal.
By using the two channels of L/R
direct recorded signal presented only in the front we will have the directional
sound clues from the direct signal as well as the sound of the instrument.
There is no vertical height information in this pair and it is added to the
frontal speaker array.
The B format consists of 4 channels
of sound, which are W, X, Y, and Z. X, Y and Z are the differential
signal which gives the directional information to decode the W omni signal.
B format does not provide accurate localization but rather presents the ambient
information and spatial clues. This includes vertical height information.
I have chosen to use two rings of speakers to reproduce the vertical height
information.
By having the ambient and direct
information stored separately you can now chose the balance of direct and
ambient information at the time of reproduction. This will allow for
many different sized reproduction spaces. The larger space will need
less ambient information while the smaller spaces will need more. In
addition you as a listener can chose the amount of ambience that you prefer,
very much like choosing your seat in a theater.
Time, Location and Spatial
Representation
The direct sound best gives directional
and instrumental timbre information. The direct sound should arrive
earlier than the ambient signal. The direct sound doesn't have any spacious
or enveloping qualities.
The ambient sound best gives spaciousness,
spatial depth and envelopment to the reproduction of sound. It is well
known that B format presentation is not accurate in presenting location and
many are trying to improve the reproduction with higher order of B format
decoding. First order of B format is probably satisfactory for presenting
the ambient sound because it is not well localized.
Storage Requirements
B+ Format recordings require 6
channels of storage. This is now obtainable with either SACD or DVD-A
using MLP compression. The advantage of using B+ format disks is that
you are not limited to the speaker arrangement that the format will dictate
but rather a decoder will determine your listening set up or you can set the
decoder for your listening set up.
Technique of Recording B+ Format
Direct Recording
Stereo Mics
The recording of the direct channel
is done by conventional means and can use stereo microphone techniques of
X/Y, M/S or OCT and can be stored as L/R or M/S information. The direct
signal should contain little reverberant information and is recorded using
direction microphones.
Spot Mics
You can use spot microphones or
flanking microphones to help balance your recorded sound. You will need
to add ambience to the spot microphones and may need to add ambience to flanking
microphones. The ambience added should be in B format and added to the
B format channel.
Multi Track Techniques
Multi-track techniques can be
used to generate the direct signal and you will then need to add ambience
in B format. If you wish to locate images not in the frontal plane you
can present images in B format in the rear locations but remember their localization
will not be as good as the frontal image.
B-Format Recording
Room Recording
Room ambient recording is done
with the Soundfield microphone generating a B format output, which is a combination
of direct and ambient sound. The location of the Soundfield microphone
is typically at the location in the room where the direct and reverberant
sounds are equal, i.e. the critical distance. This gives accurate spatial
information about the recorded location
B-Format ambience by convolution
Another method of obtaining a
B format ambient sound is by convolution. This is a digital technique
where a room ambience is measured in B format and can then be impressed upon
another signal. This is also accurate. You can chose whether you
use any direct signal in the impulse response.
You can also obtain B format ambient
information with multiple reverberation devices. It will take at least
3 engines to generate B format reverberance, one for each axis. I have
developed a B-format mixer to help generate the B-format ambience.
Techniques for Monitoring B+
Format
Ideal decoding with 16 channels
Decoding of the B+ format is ideally
presented as 16 channels, which is arranged as two rings of 8 speakers with
45 degrees of separation between them. From stereo we know that 60 degrees
is the maximum separation between speakers without a hole in the middle.
By using an upper and lower ring of 8 speakers I am able to present vertical/height
information. You will present the L/R stereo on the front speakers without
height information. You should be able to adjust the balance of dry
versus ambient sound. I have developed decoders for 16, 12, 10 channels
of 3D surround or without height as 8, 6, or 5 channels.
Decoding in your present control
room
You can use your present control
room to work in B+ format. The decoding will be done with 60-degree
speaker spacing with two rings of 6 speakers. The front up and down
speakers will be combined and your present control room speakers will be used
for the sum of the front up and down signals. You can use your present
console to obtain the L/R stereo mix and use a pair of auxiliary sends to
sent to the B format ambience generator.
In conclusion, I believe B+ Format
is a universal media and is an answer to the delivery of surround sound now
and in the future.
