I ran a competition on Social Sound Design (SSD) where the first person to get the Nice Question Badge would win a signed copy of David Sonnenschein’s book Sound Design: The Expressive Power of Music, Voice and Sound Effects in Cinema. The winner is Fabrice Million (what a cool name), a Frenchman living in Australia. He is a freelance web and flash developer as well as a musician. Congratulations, Fabrice! Hope you love it as much as I did.
Considering how popular this question is, I thought I’d curate a compilation of the best answers. The rest of this entry is an attempt to extract and organise all the good answers from Fabrice’s question: How to capture very low volume sound? I’m not going to quote who said what as that will get too convoluted, just think of it as the voice of SSD.
So… How To Capture Very Soft Sounds?
First off, context is important. Is the sound being recorded for scientific or creative purposes? If it is scientific, then precision and accuracy is the priority. If it is for a more creative outcome, then the way we capture, edit, process and re-contextualize the sound matters.
They are two principle ways to record soft sounds: the first is through air and the second is through mechanical vibrations.
air – condenser mics
The main problem with recording soft sounds, is that normal microphones and pre-amps on mixers and recorders all add noise to the signal. If it’s more expensive gear, chances are there will be less self-noise. So when recording a soft sound, you will probably have to increase the gain a fair bit and you also will also increase the noise floor. But even if your recording setup is dead quiet, any environmental sound will be amplified.
If the sound isn’t that soft, you can get away with being in a very quiet room such as your bedroom in the dead of night or a studio or even an anechoic chamber. You will need to be using a low self-noise microphone such as a large condenser mic. You can even go ultrasonic with Avisonics.
vibration – contact mics
A contact mic is basically the equivalent of putting your ear directly on something. It picks up mechanical vibrations rather than air. Thus making it a great option for capturing soft sounds.
One of the biggest challenges of recording quiet sounds is the medium transfer. As sounds transfer from medium to medium (such as a gas to a solid, or a liquid to a gas), you loose SPL. Let’s say you’re trying to record a light bulb filament. The sound has to transfer from the filament to the gas in the bulb, then transfers from the gas to the glass bulb, then transfers from the glass to the air around it, then to the microphone element. That’s four transfers between a solid and a gas, hence a lot of lost SPL. If you take two transfers out of the equation by attaching a contact mic directly to the glass, you have a lot more SPL to work with, and therefore can get a much better signal-to-noise ratio.
With a good contact mic, you can even pick up the sound of ants’ footsteps or the heart beat of a snail. Got $3,000 to spare? Check out the “Insect Mic” By Sanken.
So now you want to buy/build a contact mic? Check out the question: Can you suggest a good contact mic for sound design?
Most of the time, these sounds are being used in a creative context, which means we have carte blanche to re-create the sound by recording louder sources that are probably unrelated (other than sonically) to the desired sound. There is also the synthesis route, where you can create the sound from noise, oscillators, filters and so-forth, whilst bypassing the process of recording and therefore adding potential noise to a soft source .
Sound design is a mix of capturing, editing, and re-contextualiaation. Making it sound right doesn’t mean making it sound accurate. This also takes the pressure off of trying to record the impossible.