Sound - resonance, Not noise

Placing the right microphones at the best location.

 
 

Invisible Micing

The 360° camera's field of view encompasses the entire set, so it's important that the microphones must be hidden, i.e. covered or behind objects. This, however, can lead to great restrictions on both the design possibilities and recording quality, especially if the distance between the sound source and microphone is large or small.

Ambisonic microphones are used to record the entire room. During filming, they are usually placed under the camera. These are supported by individual mono microphones that capture very specific sound sources and radio microphones that are used to capture dialogue.

Ambi-Recording
To record 360° spatial sound, the '1st Order Ambisonic' format should be used for playback via headphones. In this process, four different capsules record the signals from different directions. With special matrixing, four channels are created. Three channels correspond to the 3D axes X, Y and Z; one channel corresponds to the sum of all directions, i.e. quasi a mono omnidirectional microphone. It is important to align the microphone with the camera's zero axis. This makes it easier to synchronously process both the image and sound in post-production without misalignment. It is also advisable to calibrate the alignment before the 'hot' recording. This can be done by recording a control signal in all directions when recording is in progress. The opportunity to re-synchronise/compensate for any time offset can be achieved via flap or timecode.

When choosing a microphone, it is crucial to decide the recording quality requirements. As mentioned, playback via headphones can be merciless in terms of noise, impact sound, wind or poor localisation.

Dialogue recordings
In principle, sound fishing in 360° film should only be used for 'sound-only' recordings. Depending on the scenario, hidden shotgun microphones can be used. Capturing dialogue on a 360° film set, therefore, requires some conceptual considerations. If the 360° ambience sound can be produced separately from the dialogue scenes (sound-only), the handling is the same as in conventional film; ambience via a multi-channel microphone and dialogue with hidden lavalier mics.
But, it can be difficult to connect the 'sound only' recordings with the 360° image in certain spaces. With 360° sound sources, it is possible that traffic, water noises, animals, etc. can be lightly heard in the background during dialogue.
A good option is to run everything in parallel; combine ambi-recordings with dialogue recordings. In this way, all filmed sound sources are also audio recorded at the right place and distance or with the correct movement.
The challenge:

  • Dialogues are recorded with the Ambisonic Micro

  • Dialogues are also on the lavalier mic channels

  • If the actors move away from the camera, the distance of the voice to the Ambisonic Mic changes, but not on the lavalier mics

By skilfully compensating the phase (distance or latency) of the two sources and tracking the movements in the 360° environment, this difference can be adjusted in post-production. Sometimes the lavalier signal is only needed to improve intelligibility, so it can be mixed situationally. This requires a trained ear to recognise and correct phase shifts.

Foleys/Sound-FX/O-Ton
As long as audio objects are stationary (e.g. a wall clock always ticks at the same place), they can be recorded directly with an Ambisonic Mic or separately as 'sound only' files. The advantage of using the Ambisonic Mic is that, with the correct orientation, the direction and physical characteristics of the room are accurately recorded (distances, surface characteristics, reverberation time, etc.). This saves an enormous amount of time and work in post-production. To do this, one should record the ambient sounds in the set before shooting, and then record everything that happens during the scene with invisible micing, i.e. similar to what is done in the theatre (lavaliers, boundary mics, hidden shotguns).
If, however, an event drastically changes the acoustic perception of space (window suddenly opens, people stream into the room, etc.), it is best to implement this directly as an ambisonic recording and adjust the dialogue in post.
As in conventional films, 'sound-only' can be produced directly on set at any time. The same special conditions apply: having ample time to record, quiet on set and, ideally, prepare the video sequence for picture-synchronised reconstruction on location.

From the Practice – A drone flight over Lucerne Carnival: 10’000 people, resounding Guugenmusik. The beats on the timpani, confetti bomb, and cheering crowd are visible.
How can synchronicity be achieved here?

Problems for sound:

  • Drones make loud noises. 

  • Audio dubbing is not possible with the requirement of picture synchronicity; tempo, sound, and position of the audio objects change and are thus not repeatable.

  • Multiple booming from above is not possible as the drone noise would interfere and the boom poles would be visible.

 Solution:

  • Compromise: place multiple microphones hidden directly in the scenery. Everything coming from above has to be elaborately integrated in post-production and creates an illusion that is not 100% of the real sound ratios of the on-site audio

360° SRF
The following sound equipment was used in the SRF productions INSPECTOR CRAZY, PULS and NACHTSPIEL: