Direct sound and reverberation

Direct sound, diffuse sound and reverberation

The propagation of one or more sound waves and their interactions are collectively called the "sound field". This sound field includes the signal emitted directly by a sound source as well as all signals generated by reflections from objects and the room's boundary surfaces. The direct signal of the sound source is also called direct sound . The part caused by reflections is divided into early and late reflections. Especially the early reflections have to be considered and treated selectively, because they are very similar to the direct sound and can lead to unwanted effects in the auditory perception like phantom sound source shifting or comb filter effects. After the sound waves have been reflected a few times in the room, they are called late reflections. These are approximately diffuse, i.e. they are distributed homogeneously in the room and arrive at the listening position equally from all directions. This mixing of reflections that can no longer be distinguished forms the reverberation and gives the room its vividness. When treating the first reflections, it is essential to ensure that sufficient reverberation remains, otherwise the room will sound flat and dull.

Reverberation

The reverberation time "RT" is an important acoustic parameter for rooms. It indicates the time in seconds until a sound field has decayed by 60 dB, i.e. to one thousandth, after excitation.

Reverberation times of specific rooms

Depending on the size and utilization of a room, different requirements apply to the optimum reverberation time. Rooms with a neutral behavior for monitoring and mixing should generally have a very low reverberation time. Rooms for recording instruments, on the other hand, should have a somewhat higher reverberation time. Some instruments, such as stringed instruments, even rely heavily on a high reverberation time and a large room to develop a natural sound. "The perfect room" or "the perfect reverberation time" therefore does not exist.
In practice, it has become common practice that control rooms, for example, usually have a reverberation time of 0.25-0.3s. The reverberation time is frequency-dependent and should be kept as linear as possible over the entire spectrum.
Recording rooms in the rock/pop area usually have a reverberation time of 0.5s. This is slightly above the reverberation time of the control room. The larger the recording room, the longer its reverberation time can be. If you still need relatively dry recordings, either move to another, smaller room or set up absorptive partition walls.