User Guide

The Free Space is an easy to use and highly versatile binaural (3D) microphone. This manual is dedicated to educating people about binaural and the 3Dio binaural microphone.

Binaural essentially means hearing through 2 human ears. The output of the Free Space is a "stereo" signal because it has two channels (Left/Right). But it is also a binaural signal because it is sound that has been captured using realistic human-shaped ears. It captures sound just like we hear it with our own ears. You can record that sound and listen to it later using headphones.

3Dio Sound Free Space Binaural Microphone

Although the concept of binaural audio is very simple, there are recording and mixing techniques that will improve the raw recording. With these instructions, the goal is to explain how to get the most out of the 3Dio Binaural Microphone. This user guide will cover everything from the hardware, to setting up the recording environment, to actually recording, to the post production work (what to do after the 3D audio has been captured).

Those who are already familiar with audio recording, will still benefit from these instructions. Binaural recording is a paradigm shift from traditional recording practices. With binaural, you are not recording sounds individually using a plethora of mics. Binaural recording is about capturing what it "feels" like to be in a 3D place. Good binaural recordings are best described as giving the "feeling" of being somewhere else. Yes, binaural audio is just stereo sound shaped by ears, however our brains understand the directional details of that sound and tell us whether something is behind us, above us, or right next to our ear. Even if we can't see it, we can feel it, and we know it's there because the shape of the microphones provide audio localization. Once you get used to thinking about capturing a 3D environment, as opposed to individual sounds, it will easily be able to create great binaural recordings.


3Dio Sound Free Space Hot ShoeThe 3Dio binaural microphone was designed to be as universally camera-mountable as possible. The 3Dio binaural microphone comes standard with an all steel hot shoe adapter that has a fixed alignment to the microphone. We chose to use the most heavy-duty hot shoe adapter available for mounting in your video camera hot shoe or carrying on a grip handle. There is a 1/4"-20 female thread in the bottom of the hot shoe adapter for attaching to a grip handle or a tripod. The external mounting hardware can be used to mount small video cameras and external audio recorders to the 3Dio binaural mic for a portable 3D capture solution.

 3Dio Free Space Binaural Microphone with HD Camera and Audio Recorder

Both the grip handle and the externals mounting hardware are easily removable so you can use the 3Dio binaural microphone as a standalone binaural mic.

Changing the Battery

Inside view of the 3Dio Free Space Binaural Microphone

The mic capsules are powered by a 9-volt battery. The battery can be accessed by unscrewing the four screws on the top of the microphone. The 3Dio binaural microphone should operate for a year or longer on a single fresh 9-volt battery, assuming the power is off when not in use. When the battery is dead, the mic signal gets very weak.

On/Off Switch

Built-in ON/OFF switch. It is recommended to keep this switch in the OFF position when not in use to save battery life.

Bass Roll-Off Switch

The Bass Roll-Off switch is primarily used for cutting out wind noise when outdoors. It can also be helpful to reduce low frequency noise from the background of binaural recordings.

The general rule of thumb is to switch the Bass Roll-Off to "Flat" for any delicate studio recording or indoor conversation-level sound environments. If recording in the wind, a moving vehicle, or recording loud low-frequency sounds such as a kick drum, setting the Bass Roll-Off switch to "On" may result in an optimal sound quality.


The standard output of the 3Dio binaural mic is a 1/8" TRS stereo jack. There is also an option to upgrade to transformer balanced XLR outputs with phantom power support. The balanced XLR outputs allow you to run long cables and avoid picking up interference along the way.

The 3Dio binaural mic does not record audio within the microphone itself. You must record the output of the 3Dio binaural mic into an external audio recorder of some kind. This could be a video camera (external mic input), a dedicated digital audio recorder, or plug it directly into a recording studio pre-amp or mixing board.

The output is a standard mic level output. Every 3Dio binaural mic ships with an 8 inch, 1/8" male-male TRS stereo patch cable for plug & play connection to your camera or audio recorder.

The XLR balanced outputs (XLR upgrade) can be plugged into any studio pre-amp and supply 48V phantom power to power the microphone. Note that when using phantom power, the battery is bypassed.

Mounting a Video Camera

When using the 3Dio binaural microphone with a video camera, be sure that it has a STEREO external microphone input. Check the camera's instruction manual to see how to adjust the input gain, and how to make the physical connection. Depending on the camera, an adapter may be required. Generally, most cameras contain a stereo input to plug in the included patch cable and immediately start filming with binaural.

NOTE: It is extremely convenient to film binaural video with the 3Dio binaural mic plugged directly into the camera. However, video cameras generally do not have a professional grade audio pre-amp in them. Typically there is a slight amount of self noise from the camera on the audio recording. For casual filming, this is not really a problem. The binaural effect is still very impressive and you tend to forget or ignore the noise after a while.

External Audio Recorders

The best way to achieve portable professional level binaural, it is recommended to use a high quality stereo audio recorder. Fortunately, portable audio recorders are relatively inexpensive.

An example of a high-quality digital audio recorder, the Zoom H6 (shown above) can record 24bit/96kHz (studio-quality dynamics) and it's self-noise is very low. There are many other options out there with various features (and various self-noise levels). The only requirements for compatibility with the 3Dio binaural microphone are that the recorder must be able to record an external stereo signal, and it must have an input gain control to allow recording level adjustments.

It is also important that the audio recorder does not have any sort of automatic gain control or compression applied to the signal. It is best to record the raw output of the 3Dio binaural microphone.

NOTE: When shooting video and recording binaural audio with an external audio recorder, manual synchronization of the audio and video in a video editor is required.

Studio Recording

The Free Space really shines when you plug it in to a studio quality pre-amp! You can achieve a much higher signal to noise ratio because the "pro-sumer" and professional pre-amps are very quiet. This allows you to capture very delicate 3D audio. Of course the quality will vary between various pre-amps and A/D interfaces, but that's another discussion.

Many audio recorders and pre-amps provide some kind of phantom power, which is designed to provide power to microphones that are not self powered.

The Free Space is self powered by a 9V battery, so you do not necessarily need phantom power. However, if you upgrade to the balanced XLR outputs with phantom power support, you can use phantom power on the XLR outputs and bypass the battery.

Equal Left/Right Gain Balance

When working with binaural recordings, its important to maintain equal gain or volume control for both the left and right channels throughout the entire recording, editing, and playback process. When using individual pre-amps for the left and right channels, take care to balance the gains as closely as you can to make sure the 3D audio image is not pushed off center.

Adjusting the Input Audio Gain

Most video camera audio inputs and stereo audio recorders have an input audio gain control. This is an important thing to fully understand. When recording the trains for my Top 8 Favorite Sounds video, I had initially set the input gain of the H1 down to around 60 (out of 100). The first train went by and totally destroyed the sound. I thought that I was going to have to re-think my entire design! That is, until I realized that it was the recorder that was maxing out, and not the mics. I brought the input gain down to 30 and recorded the next train going by. I can tell you subjectively that when that train went by and sounded the horn, it was physically painful to my own ears. I thought for sure that the mics would have peaked. However, the recording was clear and undistorted, and I ended up using footage from that second train for the final video.

You should always watch your audio signal level in the field, especially during the loudest sounds you intend to record. Bring the input gain level down as low as needed to handle those loud sounds. You can fix the overall low volume later, so relax. The only important thing you need to remember is that the further you turn it down, the more noise you will get in the final product.

To summarize, you want to set the input gain for as strong of a signal as possible, but without maxing out the recorder's pre-amp. You can find the ideal volume level by using the loudest sound as your reference point, and bring the gain down a few notches below that.

Setting up the Binaural Recording Space

Recording binaural means capturing what it "feels like" to be in a 3D space. If you're recording in a tile bathroom for some reason, its going to be very echo-ey and difficult to distinguish the exact location of sound sources. If you are in a living room, the carpet and soft furniture will dampen the sound bouncing around the room, and it will be easier to distinguish the 3D location of sounds. Plus it will sound like you're actually in a living room. If you are outdoors, sounds will be very "open" and easy to localize. This is because the space outdoors is similar to an anechoic chamber (no reverberation of sound), unless you're next to a wall or other object.

When setting up an environment for recording binaural, you also have to think about the entirety of sounds and noises that are going to be captured. You have to eliminate unwanted noises, such as yourself breathing next to the ears (unless that's the desired effect;-). You might also want to turn off noise makers such as external hard drives, computers, kids, and your smart phone, etc...

It all becomes pretty obvious if you listen through the Free Space with headphones before pressing record. This can be done on some external audio recorders (like the Zoom H1) that have a headphone jack. It's always a good practice to listen through the mic before recording anyway.

Depending on your desired effect, you can also control the sonic characteristics of a room. If you can afford it, invest in some high density foam, which can be placed around a noisy room to dampen the sound. If you can't afford the foam, use blankets and/or pillows.

It's also important to think about microphone location. Placing the Free Space next to a wall will result in the feeling that there is a wall next to you. This is because your brain picks up on the part of the incoming sound that is bouncing off of the wall, and is able to identify it as a large flat surface, even though you can't see it. This is a very under-used, yet incredibly powerful ability that humans have with their ears and brains. Some blind people can actually identify the size, shape, and even the material of an object, just by listening to the way it reflects sound! That's even better than using sight! They aren't fooled by foam rocks in your yard...

So pay attention to every detail of the entire 3D space being recorded, including all sounds and noises, the room acoustics, and the location of the microphone, and you will be able to maximize the quality of your end product.

Filming Binaural ~ Close Objects and the Proximity Effect

The Free Space is excellent for capturing what it feels like to be close to objects. Distinct sounds that are located close to the microphone (less than 5 feet), have the tendency to give you chills! This is because the 3D sound is telling your brain that something is approaching you, and you might not even be able to see it! It feels so real, that your body's fight or flight response is uncontrollable, especially if the content is convincing. That's why people's first thought after hearing binaural is that it would be great to use binaural to scare the crap out of other people!

The feeling of sounds being close to you is what I think of as the binaural proximity effect. With traditional microphones, you also get a proximity effect, but that has more to do with the way the microphone responds to close sounds vs. distant sounds. With the Free Space binaural microphone, the binaural proximity effect has more to do with the 3D image than mic performance. The feeling of being close to sounds with binaural audio is a highly desirable characteristic in many cases, simply because it emphasizes the 3D human experience of "being" somewhere else (out of body). However, when you add video to the binaural, some camera lenses distort the visual sense of proximity to the object in the frame. Therefore, if you plan to film binaural video of close proximity objects, you have to think about the type of camera and lens you're going to use.

DSLRs with long focal length lenses are amazing for filming binaural video. They give you HD video with a narrow depth of field (blurry in the background), which only adds to the 3D experience. However, for filming close objects, such as a musician performing, or for ASMR videos, you will want to consider using a wider angle lens. Wide angle lenses work very well for point-of-view (POV) binaural video of close objects. This is because the image you see more closely matches the relative distance of what you are hearing.

For filming close objects with a longer focal length lens, such as 50mm and greater, you may have to physically back away from the object to get everything to fit in the frame with the right perspective. If you're filming a person playing guitar, you will have to move the camera back 5-10 feet to fit them in the frame. The problem with this is that the video will look like you are just 3 feet from the person, but if the microphone is on the camera, the 3D audio will be telling your brain that you are 5-10 feet away. This is potentially a big problem for binaural when synchronized with video. It could be confusing for the viewer to have such a discrepancy in perceived distances. You can make up for this a bit using compression (discussed later), or you can take the mic off the camera and move it closer to the object of focus while keeping it pointed in the same direction (and out of view).

Recording in Windy Environments

Wind is a big problem for binaural. When wind hits the microphone capsules it produces all kinds of unwanted noise, especially in the low end frequencies. There are two weapons available to take care of wind completely. The first is the bass roll-off filter, which I already mentioned. Turn it on any time you anticipate even the slightest amount of wind. The second weapon available is a pair of the Windy Space Muffs. These muffs will eliminate all wind at lower wind speeds, and will sound completely realistic at higher wind speeds. I've even boosted the low end EQ around 60-80Hz in one video just to bring out more of the low end wind noise! These things are the ultimate solution for wind with the Free Space, and they are a must have for any field recording.

Windy Space Muffs

Using Compression with Binaural Audio

If you know what compression is, you can skip this paragraph. Compression is a tool that audio engineers use to control sound, and is typically applied in "post", which means after the audio is recorded. It is either a software plug-in, or an external hardware compressor. Compression boosts the volume of quiet sounds, while limiting the volume of the loud sounds. Compression allows you to bring out a lot of the detail of a recording (quieter parts), and make it sound bigger and more full. Basically every radio station, music album, and TV show use compression extensively to finely balance all the sounds so that nothing gets drowned out.

Compression is a very valuable tool for binaural. Many people say to avoid it completely, but I disagree. The argument to avoid it comes from the idea that for binaural, you really want the full dynamic range of the sound to remain intact. This means that you would just need to turn up your volume when you're listening back so that the loudest sounds would be just as loud as they actually were at the time, relative to the quiet sounds. I would agree that in an ideal world, this would absolutely be true. But we don't live in an ideal world. We live in a world with an ongoing "volume war" over music and TV and every other media we produce. Because of this, people who do not know that they should turn it up, will not have a good listening experience. But beyond that, there are other benefits for using compression with binaural.

When you apply compression to binaural audio, the resulting effect is that objects appear to sound closer than they really are. This is because the quiet, distant sounds are now boosted in volume, and our brains interpret that as being closer. This "proximity distortion" sounds like a problem, but the effect only becomes a negative one if you over-use it. You can use it to your advantage in situations where you want things to sound closer, like I mentioned above with a long focal length DSLR camera lens. But overall, using just enough compression to boost the overall presence of a binaural recording without distorting it will result in a much more immersive listening experience.

I will discuss how to actually use compression in the post processing section.

Synchronizing Video & Binaural Audio

When you plug the Free Space directly in to your video camera's external microphone input, the binaural audio is automatically recorded in perfect synchronism with the video. This is great, and very nice for casual binaural video! But as I mentioned above, if you want higher quality audio, you may choose to use an external audio recorder to capture the sound. When you do this, you must then manually synchronize the binaural audio to the video. You can do this on your computer using any standard video editing software. There are many choices for software, but the minimum requirement is that it must be able to handle multiple tracks of audio, so that you can see/hear the camera's built in microphone audio, at the same time as the audio captured from the Free Space. If you don't have any camera audio, you can snap your fingers in front of the camera before shooting the scene and carefully align the audio to that.

If you do have an audio track from the camera, you can use that as a reference for aligning the binaural audio. All you do is zoom in on the audio tracks, and align the peaks and valleys as closely as possible. You should really get down to the frame level and get it as perfectly aligned as your software will let you. Our brains are sensitive enough to detect even a half of a frame discrepancy in synchronization. Once it's aligned, don't forget to mute or delete the camera's audio track. You'll realize it later if you don't, because the sound will not be binaural anymore with the other audio playing.

In case you're wondering about available video editing software packages, I have successfully used Final Cut Express, Sony Vegas Pro, and iMovie to synchronize binaural video, but nearly every other software editor will work as well.

Post-Production Binaural Audio

I've talked a lot about "post", so here it is. Post production is what you do with video and audio after it's been recorded in raw form. I will leave video post production out of this and focus just on the binaural audio. It applies for both video and audio editors.

There is not much you need to do to binaural to polish it up. The great thing about it is just how good binaural sounds straight out of the microphone. However, when you want to present a recording or a video of many different sounds recorded in different places at varying sound levels, it's important to "balance" everything out for a nice consistent sound. In post, the goal is also to improve the raw recordings by bringing out the best of the tracks.

One of the most important items to cover in post is the low end. Whether or not you recorded with the bass roll-off filter turned on, you should pay attention to the low end when mixing. You should try to balance the low end so that it's neither lacking, nor too strong. You should be able to feel the low end as naturally as you would if you were using your own ears. A binaural track that is lacking low end feels weak and thin. But a heavy low end is very distracting and unnatural sounding.

We are talking about cutting or boosting frequencies below about 200 Hz, so the tool of choice is a low shelf filter. I set the "knee point" of my low shelf filter to around 200 Hz and either increase or decrease the gain. As a point of reference, if you recorded using the Free Space with the bass roll-off filter turned on, a gain of about +9dB at this knee point will approximately recover the low end.

It is also good to use compression in post to make the binaural experience more "lively". I currently use Final Cut Express to edit my binaural videos. FCE has a "Dynamics Processor" audio effect, which is a compressor/limiter. Most of the time, I will use the default settings of the dynamics processor and only adjust the gain setting, but I also turn on the limiter function, just to avoid peaking beyond 0dB (the maximum). You can adjust the other settings if you know what you are doing, but for the average person, the default settings in most audio compression plug-ins will work fine.

What you want to do with compression is to find the loudest part of your recording and adjust the gain based on that. Push the gain up as far as you can until the loudest part of the recording begins to sound unnatural. Then you can bring it down a few dB, and back into a "natural" level. The rest of the track should appear much louder and more lively now, but will retain full 3D localization. It's helpful if your compressor plug-in has a visual meter to indicate that the compressor is in action. This way you can see exactly how many dB you are squishing.

The only other setting I adjust occasionally with compression is the "threshold" setting. This setting tells the compressor what the cutoff volume level is for any sound that will be compressed. So any sounds that are at a higher volume than the threshold setting will be limited (squished), and anything below that level will be boosted by the gain setting. If this is set at 0dB, then nothing will get compressed. You generally will bring this down to -6dB for moderate or -12dB for strong compression. Here is a great link for an overview on compression.

NOTE: Make sure NOT to decouple a stereo compressor such that each channel is compressed individually. Both channels should be compressed together. Independent left/right compressors will ruin the binaural effect.

Binaural Audio File Formats

Let me clear up a potentially confusing term, "Compression". We already spoke about using a compression tool to condition your binaural recordings for a full and balanced signal. Now I'm going to talk about compressed and uncompressed file formats. This is completely different than the compressor tool in the studio.

Compressed audio files like MP3 files, are "compressed" in the sense that the file size is smaller. They accomplish this by removing some of the higher frequencies that we are less likely to notice missing. They also reduce the dynamics of the sound. This means that compressed audio will have less impact for strong sounds, and will also lose some of it's pristine higher end "bling". For binaural, the lower the file compression quality, the worse the 3D effect will be.

Binaural audio is best recorded and manipulated using an uncompressed file format such as WAV or AIFF. These file formats preserve the entire frequency spectrum and all of the dynamic detail of the signal. When recording and doing all of your post production work, you should always use an uncompressed file format. You want the EQ and audio compression (studio tool) to act upon the highest resolution signal possible. I always work with WAV files at 24bits/sample and 96kHz sample rate.

That being said, you can mix down to a compressed file format for the final mix. Compressed file formats include MP3, AAC, and OGG, along with several others. All of these will work fine for the final mix as long as you use a high bit rate. I generally use the highest available quality settings for compressed file formats. When uploading a binaural video to YouTube or other video site, they will do additional file compression, which will result in further loss of quality, so it's important that you start with the highest available quality.