Over the last few weeks, I have been researching into recording techniques I have never tried. The first was binaural which I had heard of and have listened to before. The other is hydrophones which I have never really thought about in the creative sense only the scientific sense.
For creating binaural recordings there is two ways to create the effect. The first is the use of binaural mics the other is the use of HRTF (head-related transfer function) plug-ins that manipulate the phase to create a similar sound. Binaural is the use of two inputs that create spatial aspects (Blauert, 2005). For the microphone technique you can use blocked (outside ear canal) or unblocked which both have the same spatial information (Blauert, 2005). This is proven through the Thévenin equivalent which is a lot of algebra that I don’t understand anymore (much to my dismay due to all the complex maths I did in school) (Blauert, 2005). A method to create blocked recordings that avoids reflections from the ear canal is to set two small condenser elements in earplugs (Blauert, 2005). Binaural mics have been tested for accuracy over the years for directionality and distance, them most effective are the ones that are more human-like (Blauert, 2005).
The use of HRTF is also known as synthesised binaural which reduces localisation errors to almost non-existent including in non-individual recordings (Blauert, 2005). Due to the distance between ears the time for the sound to reach and the phase change due to the body it changes the signal to both ears (“Binaural Recording Techniques”, 2019). If the sound is towards one ear it raises the Mids to the ear however, it creates a shadow to the other ear (“Binaural Recording Techniques”, 2019). These recordings are made to be played back in complete isolation from headphones (Blauert, 2005). The type of headphone can change the playback as closed-back headphones can create internal resonance (Approaching Static Binaural Mixing with AMBEO Orbit, n.d.). Open-backed have a flatter response for the best playback whilst speakers can remove the 3D impact (Approaching Static Binaural Mixing with AMBEO Orbit, n.d.). A rough parametric EQ to correct playback for speakers is as follows:
480Hz low shelf +2dB
4kHz Bell -11dB Q1
8kHz Bell +8dB Q2
Master 0dB
(“Binaural Recording Techniques”, 2019).
I have been focused on AMBEO Orbit by Sennheiser as it is a free binaural HRTF plug-in. It can be used to support the binaural recording to help reinforce sounds through spot mics (Approaching Static Binaural Mixing with AMBEO Orbit, n.d.). It can also be used on MIDI recordings to make them binaural. For the plug-in you set the elevation and position of the sound for the initial spatial sound (Approaching Static Binaural Mixing with AMBEO Orbit, n.d.). This plug-in also allows you to set clarity and room size (Approaching Static Binaural Mixing with AMBEO Orbit, n.d.). The other factor to be considered is the time delay between the binaural recording and the spot which is easily fixed in editing but is necessary to fix for live sound (Approaching Static Binaural Mixing with AMBEO Orbit, n.d.).
I also have been looking at hydrophones. This is because for the meditation project we are recording the beach and my client suggested a hydrophone for crashing waves. Now I had never heard of hydrophones or if I had I didn’t remember the name. However, once I read the quick wiki explanation, I remembered I had heard of them for science. I don’t have access to a hydrophone, and it is a little late to order one as they all ship from the US or UK. Also, the most affordable one is made to order so it could take 3 weeks just to be made and then shipping. I was a little concerned and was thinking that it probably wouldn’t happen as I had already booked equipment and scheduled a time that suited both me and Ethan for recording at the beach. I then discovered a few DIY hydrophone plans one of which looked pretty sturdy for this and that I could make. It was a design done by the musician Leafcutter John which had clear instructions and I had the equipment to make minus a few speciality pieces. He used piezo disks with a pre-amp to make the transducer element and a steel can which allows solder to stick (Soundfly Partners, 2017). One thing another person noted was that piezo disk based hydrophones have limited frequency response however, I am using this more as a learning experience to see whether I would invest in one in the future. I have made cables before and was fortunate enough to be given some XLR ends and have a soldering kit, so it is only the piezo disks that I need. Now sound travels at around 1450/1500 m/s (metres per second) so it has different characteristics to normal recordings (Duck, 2019). The wavelengths are longer levels differ by about 62dB to air and the highs reach quicker than the lows (Duck, 2019; Emge, 2016). One main thing to keep in mind with hydrophones for recording is the impedance of some mics will need to be converted as most are designed to plug into phones (Emge, 2016). You also can’t usually record in stereo and still have localisation (Egme, 2016). To create a stereo image, you have to either use proximity effect or editing (Egme, 2016). Water size matters due to how far sound can move. You may get noise pollution in small bodies of water so the deeper it is the less likely that will happen (Emge, 2016).
These are all interesting things to keep in mind. I should be able to make a hydrophone by the field recording session however, with COVID-19 shipping is a little messy (at least they are all coming from within Australia). I also haven’t done much on A Quiet Place II as I was unwell for some of last week and so will be implementing my notes on trailer mixing (which is mainly automate volume) during this current week.
References
Binaural Recording Techniques. DPA Microphones. (2019). Retrieved 23 October 2020, from https://www.dpamicrophones.com/mic-university/binaural-recording-techniques.
Blauert, J. (2005). Communication Acoustics. Springer.
Duck, T. (2019). Some things I have learnt about Hydrophones [Blog]. Retrieved 26 October 2020, from http://versed.com.au/some-things-i-have-learnt-about-hydrophones.
Emge, A. (2016). How to record underwater sound effects with a hydrophone [Blog]. Retrieved 26 October 2020, from https://blog.prosoundeffects.com/how-to-record-underwater-sound-effects-with-a-hydrophone.
Sennheiser Electronic. (n.d.). Approaching Static Binaural Mixing with AMBEO Orbit [PDF]. Retrieved 19 October 2020, from https://en-au.sennheiser.com/ambeo-orbit.
Soundfly Partners. (2017). How to Build a DIY Hydrophone [Blog]. Retrieved 26 October 2020, from https://flypaper.soundfly.com/produce/how-to-build-a-diy-hydrophone/.
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