Microphone distance
The microphone distance is the distance from a microphone (also a main microphone ) to a sound source or a sound body . This trivial-sounding explanation is necessary to create a demarcation from the microphone base , with which no confusion can occur. The microphone base is the distance between two microphones, regardless of the distance to the sound source.
The microphone distance to the sound body must be chosen with care:
In closed rooms, the microphone should always be within the reverberation radius . If the microphone is set up outside of the reverberation radius, direct sound and more or less diffuse reflected sound are superimposed , which leads to indistinctness and “blurring” of the recording. A typical value for the reverberation radius in a reverberant room, e.g. B. a church, depending on the size of the room volume, the reverberation time and the directivity of the microphone is around 2 meters. This means: the closer a microphone is in the direct field of a sound source, the louder and less spatial the recorded signal. However, if the microphone is more than 2 m away from the sound source, the diffuse field signal predominates and the entire sound signal is recorded unclear and blurred. That is why microphones should always be located within the reverberation radius in recording technology.
If the distance is too small, the spatial impression that may be desired may not be effective and, when using directional microphones, lead to close-up effects that are noticeable in an increase in the low frequencies. However, both effects can be used specifically for a specific and desired sound impression.
Outside there is mostly a lack of reflective surfaces and the reverberation time is zero. In this case the reverberation radius is infinite. If the microphone distance is too great, however, there is the possibility that unwanted interference may be recorded.
Sound film and video recording problems
Many cameras, both professional and amateur, have microphones attached directly to the camera body. If a sound film is recorded in closed rooms from too great a distance, usually corrected with a zoom lens , the sound is often recorded outside the reverberation radius and the microphone distance is too great, with the consequences mentioned above. When making professional film recordings, an "unleashed" microphone, ie detached from the camera, is used whenever possible. Attempts are also made to prevent the problem of background noise.