Immersive Field Recording with the Sennheiser AMBEO

Blackguard Sound specializes in immersive field recording. We’ve tried several techniques including Double Mid Side, 1st Order Ambisonics, and 2nd Order Ambisonics. We’ve even experimented with recording a solo cello with 17 mics configured for immersive playback (but that’s a separate post)! Our current favorite solution is the Sennheiser AMBEO 1st Order Ambisonics mic. Read on to find out why the AMBEO is our go-to mic for projects all over the world.

Sennheiser AMBEO on location in Iceland

Why Sennheiser AMBEO?

Flexibility

We wanted the ability to deliver B-Format for immersive media, 5.1 or 7.1.4 for post, and stereo for YouTubers.  The Sennheiser AMBEO allows us to bring one mic and generate all of these assets without complicated (and heavy) mic bars, multiple stands, careful measurements etc. We’ve recorded in different surround formats over the years and AMBEO is the only thing portable enough for the tough locations we tend to record.

Sound quality

We’re very happy with AMBEO’s sound quality.  Low end power and high end details are equally well preserved.  Upon properly decoding to 7.1.4, the surround image is immersive and accurate.  Peers that have tried other Ambisonic mics are consistently impressed with what we get from the AMBEO.

Build quality

This is the big one! Sennheiser microphones are unmatched when it comes to harsh conditions. We’ve exposed our trusty AMBEO to some incredibly dangerous conditions over the years.  From the Florida Everglades in the summer to northern Iceland in a blizzard to literally being dumped on by a waterfall in Australia, it has held up beyond all reasonable expectations, oftentimes stuffed in a backpack or hand-carried out in the elements. On a recent trip to Northern California, a rogue wave knocked the entire stand, mic and all, into the Pacific Ocean. And yet the AMBEO survives. It is the undisputed Die Hard John McClane of microphones.

Jason setting up an AMBEO with Cinela Wind Protection in Thorsmork, Iceland

Recommended Accessories

12-Pin Extension Cable - 3 meter

The 12-pin to 4x XLR fanout cable is a sensitive spot in the setup.  I find the fanout cable to be susceptible to a high amount of handling noise.  The best way to avoid this is keep the fanout completely within the sound bag, which means you will need a long enough 12-pin extension to connect to the mic, run down the stand, and into the bag.

Cinela Piani AMBEO Windshield Kit

This product was a game changer for us!  The wind noise reduction is unbelievable.  It handles near gale-force winds with ease.  We pushed it to its limits (and a little beyond) in Iceland and I was honestly amazed at where that limit is.  The shockmount is incredible and the connbox eliminates virtually all handling noise.  Pricey, but worth every bit.  Also, be sure to check out the Piani Kelly Rain Cover.  We confidently recorded behind waterfalls and exposed in the rain knowing that the mic would be protected and the sound quality would be preserved.

Sound Devices MixPre 6 II

The perfect companion for the AMBEO.  The sound quality is impeccable and the Ambisonics plugin makes recording as easy as possible.  Direct conversion to B-Format saves a ton of time in post.  Linking the gain for all four inputs ensures good imaging.  Binaural monitoring gives us the confidence we need in the field.  It doesn’t hurt that it’s also extremely tough.

Some of the best tools for mastering Ambisonics

Mastering Ambisonics

I’ve read some complaints in message boards about first-order Ambisonic recordings' ability to form a stable, immersive, multichannel image.  I believe that with careful mastering it is possible to achieve excellent results!  I’m currently decoding 1OA recordings to 7.1.4 and loving it. However, utmost care must be taken in the mastering process. Here are some things I’ve worked out through hard-fought trial and error:

First rule of Ambisonics!

Make sure you are keeping track of whether your B-Format is set to FuMa or AmbiX. It’s very easy to get this wrong and it will make the immersive image fall apart if your plugins are set to receive the wrong input type. AmbiX seems to be the more widely used flavor of B-Format and most plugins will default to that BUT ALWAYS CHECK!

Upscaling

The Audio Brewers ab Upscaler plugin is pure magic. It can take a 1st Order Ambisonics recording from the AMBEO (or any other 1OA mic) and upscale it all the way up to 7th order! The gains in spatial resolution are astounding. As a rule, I am highly skeptical of anything that claims to enhance an existing recording but Alejandro at Audio Brewers has figured out a way to do it in a simply breathtaking manner. Lately, I’ve been going up to 3rd Order (anything more and the number of channels gets a bit unwieldy) before decoding to my desired monitoring format. Just be sure to do any EQ or other processing BEFORE the Upscaler exponentially increases the number of channels!

Decoding

I use Audio Brewers ab HOA Decoder for decoding B-Format down to stereo, 5.1 or even 7.1.4. It is an amazing tool, but there are some important things to consider.  First, be sure to monitor in whatever format you are decoding to.  This will require that you do separate passes for the 7.1.4, 5.1 and 2.0 versions.  Do not assume that the settings for one decode will work for the other.  They often don’t!  Next, be sure to rotate the image all the way around to make sure you’re achieving balance and focus.  Despite my best efforts at mic setup, I rarely use zero degrees for the optimal ‘viewing’ angle.  Finally, don’t be afraid to mess with the mic spacing angle, especially in the stereo render.  Don’t be dogmatic - sticking to tried and true stereo miking methods - the best sounding result may be something unexpected.

EQ

I use Fabfilter Pro-Q3 for EQ duties.  First, it supports multi-channel formats, which rules out many other EQ plugins (however, it will not support 1OA except in multi-mono mode - please fix that Fabfilter!).  Next, it is a phase linear EQ, so it won’t mess with the time alignment of the 4 channels - very important if you want to preserve that immersiveness!  Finally, it has a dynamic EQ function which is essential.  I like to use a low shelf EQ set to dynamic mode to take care of intermittent bursts of low energy (like in wind or wave recordings) without sucking all the low end power out of the rest of the recording.  AMBEO-specific tip:  I find that the AMBEO has some buildup in the mid-500Hz range.  I like to scoop out 3dB in this area to compensate.  Be sure to use a light touch and listen carefully.  If your EQ notch is too narrow or too deep some negative artifacts will be introduced.  Never apply EQ without good reason and be mindful of the how and why.

Noise Reduction

I use iZotope RX for light noise reduction.  Rule number one - never apply broadband noise reduction to an Ambisonic recording!  There’s no quicker way to add artifacts, chirps, swirliness - whatever you want to call it.  I limit my RX use to a few surgical functions when performing Ambisonic mastering.  First, Spectral Repair, set to a conservative setting, can remove unwanted birds, ticks, clicks, pops and so on.  Don’t expect it to completely remove every unwanted sound.  You may have to concede that an unwanted sound will remain slightly audible or you may need to cut around it.  Listen carefully and LOOK carefully.  If Spectral Repair is cutting a hole in your spectrum, discerning ears will notice!  I also use De-Plosive to take care of intense low-end energy.  Be sure to set the frequency threshold based on the source material.  Avoid the temptation to use De-Wind.  It’s designed to remove wind noise from voice recordings - not wind recordings!  It will leave musical artifacts all over the place near the cutoff frequency, which is tolerable in location dialog, but never in a nature recording!

Sennheiser AMBEO on location Mendocino County, CA

In Conclusion

The Sennheiser AMBEO is a workhorse. Ambisonics recordings are underrated. Mic drop (don’t worry, it won’t break).

Check out our immersive ambience libraries or hire us for your next field recording expedition.

Don’t Fear the LFE - A Practical Guide to Using the LFE Channel for Music Mixers

Hello Dolby Atmos music engineers! Welcome to the world of immersive audio! We post mixers have been here for a while, now. We know you’re excited to use all the new toys at your disposal. Here are some tips from the film department to make the most of the LFE channel in Pro Tools.

First and most important tip - do not use the LFE send control in the Pro Tools Panner. It has never worked correctly and likely never will!

LFE Send in the Pro Tools Panner

So what’s wrong with the Pro Tools Panner? It sends the audio to the LFE channel, right? Yes it does. Here’s a simple setup where I have a mono audio track playing pink noise. That track feeds into a 7.1.4 aux that goes to the speakers. You can see in the video that the signal is being sent into the LFE channel when I turn up the LFE control. So far, so good.

But there’s a problem - it’s simply sending a copy of the pink noise into the LFE. Here’s a quick illustration. I added a mono audio track set up to record just the LFE subpath of the 7.1.4 aux from earlier. When I record onto that track and then solo it, you still hear full frequency pink noise.

What’s so bad about that? Well, a couple of things:

Bass Management

In most music Atmos setups, the subwoofer is pulling double duty. It’s getting the content of the LFE channel but it’s also doing bass management for the other speakers. It helps to keep in mind that the subwoofer and the LFE are not the same thing. The subwoofer is a speaker and it gets fed from two sources, the bass management settings in the Dolby Renderer or your monitor controller, plus whatever you elect to send to the LFE channel.

So let’s say you have a kick drum you want to send to the LFE. That kick is panned to the front left and right speakers (phantom center). Being a kick drum, a lot of the energy is already going to the subwoofer because of bass management. Now, if you turn up the Pro Tools LFE control it sends a copy to the sub. This results in the same sound, just twice as loud (assuming the LFE send is set to unity, but you get the idea). Additionally, if your room is not setup carefully and the speakers have not been phase aligned, you may have phase cancellation and actually make the kick LOWER in the mix!

No Filter

The Pro Tools LFE send control does not filter the source audio before it hits the subwoofer. It’s relying on the crossover in your subwoofer to low pass. This could lead to inconsistent results as different subwoofers may have different crossover settings. Dolby recommends that all LFE content be low pass filtered at 120Hz, preferably with a phase linear-capable plugin. They also recommend a hi pass filter at 20Hz to clean up any infrasonic mess. Unfortunately, there’s no way to insert a filter on the Pro Tools LFE send.

The Solution

With that in mind, here’s the fix that post mixers have been using for years.

First go to the I/O Setup and make a mono bus called ‘LFE SEND’.

Making a mono bus called ‘LFE Send’ in Pro Tools

Still in the I/O Setup, make a mono subpath of your 7.1.4 bus, name it ‘LFE RETURN’ and make sure it is routed to the LFE channel.

Making a mono subpath called ‘LFE Return’ in Pro Tools

Then, add the ‘LFE SEND’ you created to any track that you may want to send to the LFE. Leave the fader down for now and you can automate it later.

Adding the LFE Send to a track in Pro Tools

Next, make a new mono aux track in Pro Tools and name it ‘LFE RETURN’. It will get its input from the ‘LFE SEND’ bus and it will output to the ‘LFE RETURN’ subpath.

Creating the LFE Return Aux Track in Pro Tools

Finally, insert the following plugins onto the LFE RETURN aux track:

Filter

In this case, FabFilter Pro-Q 3 with a high pass set to 20Hz and a low pass set to 120Hz. Make sure it’s in linear phase mode. Other options include iZotope Neutron.

Fabfilter Pro-Q3 settings

Subharmonic Generator

In this case Avid Pro Subharmonic Generator set to 100% wet. This ensures that the original signal is completely transformed. We will only hear the artificially generated subharmonics. Adjust the input controls on the left of the plugin window to the frequency range that best suits the source material. You’ll have to toggle between while listening to find out what works best. Other subharmonic options include Cargo Cult Subquake and Waves LoAir.

Avid Pro Subharmonic settings

Limiter

In this case Avid Pro Limiter, but any limiter will do. This is just to keep the LFE channel from clipping if you get over zealous with the send level. Netflix recommends a limiter ceiling of -2.3dB. That’s for film content, but it’s something to aim for.

Avid Pro Limiter settings

Now, we have a properly derived LFE channel! Simply turn up the aux send level to taste.

An added benefit - managing the LFE this way makes it Bed/Object agnostic. Using the Pro Tools Panner will only work if the track is assigned to the bed.

One more tip - LFE stands for ‘Low Frequency Effect’. That means it’s best used as an effect. Sure, you can turn up the send a little to give your instruments some extra weight, but it’s best reserved for particular moments you want to accentuate. A sub drop at a transition, for example. Or to beef up the chorus. Or whenever you want the song to be even bigger. In movies, we will use the LFE to accentuate explosions, gunshots, particularly heavy punches - stuff like that.

OK, now get out there and don’t be afraid to use the LFE!

Finally, do you use a different DAW that handles the LFE better than Pro Tools? Let us know!