The basic theory of capturing the voice
The radiation pattern of the human voice is complex and requires correct treatment of the audio to maintain a high degree of speech intelligibility. In order to be able to alter the frequencies of a recording, you have to be able to rely on consistent and linear microphones. Make a recording at reference position, one meter (3’) from the talent to know the natural/true sound of the voice.
Microphones placed on the chest are below and sometimes also behind the mouth, which is the most challenging placement.
Directional microphones are seen in a number of variations, i.e. cardioid, hypercardioid and supercardioid. They differ in their rejection of sound aiming the microphone from the sides and behind but also in the pureness of the sound around the microphone.
An omnidirectional microphone will in principle pick up sound equally from all directions. The microphone will though become more and more directional the higher the frequency. The smaller the capsule, the more true omni the microphone is.
Ambient – Stereo Techniques
The workflow in a recording studio often includes adding ambient mics during the session. It’s an easy task to accomplish, which usually gives great sounding results. Be aware that there are a few challenges that you will need to deal with. To achieve ambience, you need distance. Depending on the style of music and the type and tonal balance of your room, you will need more or less distance.
Stereo ambience or mono ambience?
Stereo ambience can be tricky to record and blend into your mixes correctly. This is due to the many different ways of combining the stereo setup with the actual width and stereo spread / image of your mix in progress.t
To match and balance these elements together as natural as possible, requires you to measure out and carefully place the stereo ambience microphone setup. This will ensure you avoid random negative frequency dips, also referred to as phase cancellations.
That said, using the 3:1 rule as a reference will help identify the correct mic placements and minimize phase issues.
Mono ambience is the quick fix and will work just fine in your mixes and due to only one ambience mic placement you won´t have to deal with time differences between your mics.
3:1 rule explained
The 3:1 rule deals with minimizing the audible phasing problems when summing a number of microphones to mono. The rule states that the source-to-microphone distance of numerous microphones should be three times the distance between the sound source and the nearest microphone.
Phase peaks and dips from the same sound source occur when panned to the same position at the same level, which will be the case if you’re using more than one microphone. The effect is equivalent to having your ear at two different places at one time!
A rule of thumb for minimizing phasing issues is to have around a 10 dB difference in level between the microphone contributions. The 3:1 distance rule achieves this. Another workaround is to pan microphones in the mix. Due to the nature of panning, this also creates level differences.