Professional Sound - June 2018 | Page 40

SURROUND SOUND
Figure 7 : JSON logo and SDP
There is no naturally occurring stereo sound . If that ’ s true then there is no naturally occurring surround sound . All naturally occurring sound is monophonic ; the rest of what we hear must be reflections and influences of the acoustic environment . Mono sounds must be positioned somewhere in a playback environment to give position , depth , width , and now – finally – height information relative to the listener ’ s position .
With a traditional 5.1 audio system , we are bussing signals to emulate the above . With AES70 , we can now encode a set of Open Control Architecture ( OCA ) parameters to deliver positional information with what could become sample accuracy in a stream of data . Pan , tilt , dolly , roll , truck , pedestal , and geopositional information of a microphone can be captured in the AES70 class architecture . Like with an access database , you need a key , its length , and the value . These parameters can then be rendered by a multichannel speaker system or encoded relative to head-related transfer functions in personal headphones . Why be surrounded by sound when you can be immersed in it ?
Figure 6 : OCA - http :// AES70 . audio
SWITCHING
AES67
Dante AVB / TSN CobraNet
Analog Cable IP Video whatever
OCA AES70
An audio switch toggles to make a result based on what is feeding it . If you have multiple sources and you need to switch between them , you must receive all of the sources and switch between them . Switching between multiple sources requires a lot of wiring fed from distribution systems or large-scale matrixing systems .
With AES67 , devices are capable of subscribing to any source that is on the network at anytime . A source is described in a Session Description Protocol ( SDP ) defined by AES67 to include clock source , payload format , and stream protocol information . Changing the receiver ’ s SDP switches its source . Most devices can be automated and switched remotely with the pushing of a JavaScript Object Notation ( JSON ) object containing the desired SDP . To “ switch ” between two sources , the receiver changes its choice of IGMP streams . Switching is out , choosing the SDP is in !
{ “ AES67 ”: {
“ outputs ”: [ {“ SDP ”: “ v = 0 \ n
o = -5 0 IN IP4 111.13.5.100 \ n s = Premo . AES67 . audio \ n t = 0 0 \ n a = clock-domain : PTPv2 0 \ n m = audio 5004 RTP / AVP 98 \ n c = IN IP4 239.1.5.77 / 1 \ n a = rtpmap : 98 L24 / 48000 / 2 \ n a = recvonly \ n a = framecount : 48 ”
}]
}
}
DEMUX & MUX
Something ’ s done iterating . The serialized transmission of multiplexed video is coming to an end . With a converged network , we are seeing the things that were once bundled together being split apart and scattered across the network as unique streams . With SMPTE ST2110 , the audio , data , and video are unique multicasts . The best solution to manage these devices is NMOS , or networked media open specifications . Its model refers to these elements in a hierarchy of sources , flows , and grains . The audio , data , and video are grains that can be combined to create a flow that becomes a source of the device . The flows from sources are then received and split back into individual grains . Goodbye multiplexing , hello source . Goodbye demuxing , hello flow-grains .
40 PROFESSIONAL SOUND