- Articles

5 Tips for Recording Ambisonics | Music Production Technology | Microphones | Part 3/7


[PLAYING CLASSICAL] Hi, my name is John Escobar. And we’re going to be discussing
five tips and considerations when recording ambisonics. [PLAYING CLASSICAL] Because our image is derived from the
combination of the various capsules working together, it’s very important
to be really precise in the recording level for each channel. Ideally, you want to get them to be
within a tenth of a dB of each other. Though you could theoretically do
this with individual analog preamps, it’s going to be much easier to do
so on digitally controlled preamps via a digital recorder. This also allows you to link
pairs or groups of channels together so that one gain knob or fader
controls all the channels involved, making setting your levels much easier. Another benefit of working
with a digital recorder is that you can also record your audio
at a higher sample rate, which means that you’ve got more digital fidelity. And because we’re capturing
360 immersive audio, that means that you get more
detail out of the environment that you’re capturing. [PLAYING CLASSICAL] We’re trying to get our recorder to
within a tenth of a dB from channel to channel. In order to do that, you
can easily use pink noise or any other kind of test tone to
accurately calibrate those signals. Whatever you decide to use
as your signal test tone, as you set your gain
staging for your preamps, you’re going to want to make sure
and leave 12 to 16 dB of headroom so that as your performance happens,
you’ve got room for dynamics. Keep in mind that even though
your signal generator is now going to be showing even signals
across all of your channels, when you’re actually
capturing your recording, you’re going to see signals
vary from channel to channel, depending on the source
that you’re capturing. [PLAYING CLASSICAL] Regardless of what your recording
might be used for later, it’s really important to be aware
of the acoustic space around you when dealing with
placing your microphone. [PLAYING CLASSICAL] Large objects like walls
tend to partially absorb, but mainly reflect sound
back into the room, causing delayed and layered
arrivals at the mic. These reflections give
us a sense of distance from the sound source,
as well as the direction of where that sound is coming from. The louder a sound source is, the more
air pressure there will be in the room, and the reflections
will be more obvious. The reflections will arrive at each
capsule and provide a sonic image, much like our ears get. In this example, we
can hear the proximity to different sides of the room
and it’s reflective surfaces. [SOUND PULSE] These changes in air
pressure are what cause signal levels to vary on each channel. [PLAYING CLASSICAL] If you are making
ambisonic audio recordings to use as a bed in which to
layer other sound sources, you’ll want to pay attention to
all of the details that make up the sonic texture of that space. You can pick a central location
in the space which gives you a good balance of the
overall environment and use that as your
might listening position. The more complex that
texture is, or if you want the ability to
immerse your listener into this environment
at different areas, you will need to do a
more detailed capture. You’ll need to capture
several listening positions at the various places in the environment
where there are strong sonic changes and use those to stitch
together an overall sonic image. [PLAYING CLASSICAL] When using ambisonics to
capture a musical performance, you should have a clear idea of what
perspective you’re hoping to capture. Will this be the vantage
point of an audience member? Or will you be allowing the listener
to get a performer’s perspective? In either case, you’ll want to
be aware of the dynamic balance of the ensemble in the space, as this
balance will be reflected and perhaps exaggerated in the microphones capture. You need to either move
the microphone around until you find a well-balanced
listening position, or adjust the player’s positions
in relation to the mic. You may also choose to add spot
microphones at each instrument to help you capture find
tonal and dynamic details. Higher order ambisonic
microphones help this by having more capsules, and therefore,
dedicated points of reference in each direction. The final thing when we’re
dealing with mic placement is that often in an ambisonic recording,
we’re dealing with 360 degree video. This adds a little bit of complication,
because the camera is also seeing around itself,
which makes it a challenge to pair the microphone to
the angle of the camera. So A, you need to make
sure that the microphone is out of the sight of the camera,
yet still paired with your visual. B, you need to make sure
that the camera noises– like fans– are not affecting the
input of your microphone, or rather, what it’s listening to. And C, depending on the
type of tripod or camera stand that you’re dealing with, it
doesn’t become an obstacle of sound into your microphone. [PLAYING CLASSICAL] Generally, when making
a recording, you’re going to want to be listening to
what that sounds like in real time. Unfortunately, this
is one of the aspects that’s a little bit tricky
with ambisonic recordings. It’s not as easy as panning left
and right, because remember, the four channels that
you’re capturing– which are called an A format recording–
are not intended to be listened to as four individual channels. It’s the immersion of
those channels together. Therefore, we can’t simply
pan left, right, left, right for each of your channels. So you have a couple of choices. You can either do what we call
a fold down or do a pseudo stereo by picking two of the channels
and panning one left and one right. The other option is to do a
real time A to B conversion. You can do this on some
DAWs using plugins, or if you happen to be using one
of the more modern field recorders, they will sometimes provide real
time A to B conversion right onto the recorder. [PLAYING CLASSICAL] There’s a lot of fine details
when capturing ambisonics. Some of the details that you’re
going to want to be keeping track of are the calibration. Not only what did you
use as a test tone, but what levels were you getting
when that test tone was playing back through your system,
and into each channel. Also, you’re going to want
to make sure and document the directionality of your
microphone towards your sound source, especially if you’re pairing
that recording to a visual. Was your microphone front-facing, was
it upside-down, or was it end-fire? All of these together
later in post-production are going to help you accurately
recreate the environment that the microphone was in. Even though it might seem
like a lot to remember, keeping these five tips in
mind when recording ambisonics will result in a better recording. [PLAYING CLASSICAL]

About Ralph Robinson

Read All Posts By Ralph Robinson

Leave a Reply

Your email address will not be published. Required fields are marked *