Stereo, quad, 5.1, 7.1,… Ambisonics to the rescue
Prelude
Imagine you did a nice recording of an oratorio. You created a fine stereo mix when the client calls you...
"Hey, did you see the guy with the video camera at the concert? That was just the angle for details. He also had a camera on a tripod, and his montage looks great. Wouldn't it be great if we had a 5.1 up-mix of your recording?"
No problem as you had two outriggers for ambience. Lucky they were there! So you dutifully do a 5.1 mix that will shake things up. Soon afterwards your client rings you up again.
"Nice work on that! The video guy is very happy. Actually I'd love to hear it as well, but I've just got this quad setup from way back. I wired it all up now so could you please give me a 4.0 mix?"
OK, back to mixing it is, and guessing as to how the balance will work for him, as you are loath to tear apart your standard conforming monitoring rig.
"Thanks mate, I feel like I'm back in the 70's, but with a much better sound of course! Now, the video guy said he'd love to release this recording--not on DVD but on Blue-ray, do you dig it? He'll want 7.1 for that though, can you please do that?"
OK, stereo, 5.1, quad, now 7.1, every time requiring a dedicated mix to accomodate the discrete speaker feeds. So you do the 7.1 as well, moving to a friends mixing space that takes some getting acquainted to, but you get it done in the end.
"Lovely man! Your 7.1 mix really rocks! I get great feedback from everyone who saw the clips, and even the local TV wants to broadcast the performance. Say, is your mix mono compatible?"
Mixing to B-format
Ambisonics, developed in the early 1970's by the mathematician Michael Gerzon has a solution for this problem: Mix in B-format.
"In the basic version, known as first-order Ambisonics, sound information is encoded into four channels: W, X, Y and Z. [...] The W channel is the non-directional mono component of the signal, corresponding to the output of an omnidirectional microphone. The X, Y and Z channels are the directional components in three dimensions. They correspond to the outputs of three figure-of-eight microphones, facing forward, to the left, and upward respectively." [Wikipedia]
For a lot of music (and most playback configurations; really, how many setups with height channels have you encountered so far?) the Z-channel can be omitted leaving the need for three channels for 1st order B-format.
What do you need to do when recording?
If the ensemble is rather close and not too expansive a Nimbus-Halliday (developed by Dr. Jonathan Halliday, research director at Nimbus Records) can do the job. If not a main mic setup based on symmetry or better yet arranged in an a isotropic configuration can be used. Use directional spot microphones according to taste.
What do you need to do when mixing?
Configure your DAW for a 3 (or 4) channel main bus. Put an Ambisonic decoder (e.g. by Bruce Wiggins / WigWare or Daniel Courville) onto that bus. Now use an Ambisonic panner (see previous links) to pan the sources to specific locations, and that's about all there is to it.
To be continued...
Imagine you did a nice recording of an oratorio. You created a fine stereo mix when the client calls you...
"Hey, did you see the guy with the video camera at the concert? That was just the angle for details. He also had a camera on a tripod, and his montage looks great. Wouldn't it be great if we had a 5.1 up-mix of your recording?"
No problem as you had two outriggers for ambience. Lucky they were there! So you dutifully do a 5.1 mix that will shake things up. Soon afterwards your client rings you up again.
"Nice work on that! The video guy is very happy. Actually I'd love to hear it as well, but I've just got this quad setup from way back. I wired it all up now so could you please give me a 4.0 mix?"
OK, back to mixing it is, and guessing as to how the balance will work for him, as you are loath to tear apart your standard conforming monitoring rig.
"Thanks mate, I feel like I'm back in the 70's, but with a much better sound of course! Now, the video guy said he'd love to release this recording--not on DVD but on Blue-ray, do you dig it? He'll want 7.1 for that though, can you please do that?"
OK, stereo, 5.1, quad, now 7.1, every time requiring a dedicated mix to accomodate the discrete speaker feeds. So you do the 7.1 as well, moving to a friends mixing space that takes some getting acquainted to, but you get it done in the end.
"Lovely man! Your 7.1 mix really rocks! I get great feedback from everyone who saw the clips, and even the local TV wants to broadcast the performance. Say, is your mix mono compatible?"
Mixing to B-format
Ambisonics, developed in the early 1970's by the mathematician Michael Gerzon has a solution for this problem: Mix in B-format.
"In the basic version, known as first-order Ambisonics, sound information is encoded into four channels: W, X, Y and Z. [...] The W channel is the non-directional mono component of the signal, corresponding to the output of an omnidirectional microphone. The X, Y and Z channels are the directional components in three dimensions. They correspond to the outputs of three figure-of-eight microphones, facing forward, to the left, and upward respectively." [Wikipedia]
For a lot of music (and most playback configurations; really, how many setups with height channels have you encountered so far?) the Z-channel can be omitted leaving the need for three channels for 1st order B-format.
What do you need to do when recording?
If the ensemble is rather close and not too expansive a Nimbus-Halliday (developed by Dr. Jonathan Halliday, research director at Nimbus Records) can do the job. If not a main mic setup based on symmetry or better yet arranged in an a isotropic configuration can be used. Use directional spot microphones according to taste.
What do you need to do when mixing?
Configure your DAW for a 3 (or 4) channel main bus. Put an Ambisonic decoder (e.g. by Bruce Wiggins / WigWare or Daniel Courville) onto that bus. Now use an Ambisonic panner (see previous links) to pan the sources to specific locations, and that's about all there is to it.
To be continued...
posted by Andrew Levine at Wednesday, December 29, 2010
0 comments
