Natural reverberation control in a music studio
Over the past more than 20 years, music recording studios have developed rapidly, and their forms are changing. It coordinated and promoted each other with recording technology and pickup technology, and greatly promoted the development and update of sound quality processing equipment and technology. During this period, there were natural reverberation music recordings, short reverberation music recordings, strong sound absorption music recording rooms, and the silent end music recording studio, and so on. At the same time, sound insulation rooms (Booth) and sound isolation screens and other ancillary facilities are widely used in the recording room. Nevertheless, the natural reverberation music recording room plays an irreplaceable role in music recording.
1. Reverberation time in China's large music studio
2, room volume: the long reverberation music recording studio used to record a kind of serious music, such as symphony, requires considerable volume. This is not only the requirement of reverberation time and sound diffusion, but also in order to avoid sound saturation in the room.
The indoor sound saturation is the high indoor sound pressure level. The high sound level is sound "frying" and deafening; and for music with wide frequency distribution (especially the serious music of Symphony), it is possible to pass the highest sound level of the microphone in some frequency bands, so it is difficult to correct the sound attenuation after the microphone. It has been known that the size of the indoor sound level is mainly determined by the constant of the room and the sound power of the sound source. For smaller volume rooms, if we want to ensure a longer reverberation time, we will correspondingly reduce the sound absorption of the indoor surface. When the sound power of the source is the same, the indoor sound pressure level will increase correspondingly. Roughly speaking, the highest sound level of listening to music is around 100 decibels. Common sense tells us that a piano with a sound power of about 0.4 watts is played in the ordinary living room (about 0.8 seconds of reverberation) and a large Symphony Orchestra (sound power about 60 watts) in a concert hall of 2 seconds in the reverberation time, and listeners think their sound levels are appropriate. If the environment is replaced, it feels that the former is too small (so many concert halls have to use the sound expansion system), and the latter (perhaps if possible) is bound to be intolerant. The general view is that the best use of the natural reverberation music studio is the concert hall with a volume of more than ten thousand cubic meters.
The effective way to solve the problem of acoustic saturation is to increase indoor acoustic absorption. The increase of the sound absorption coefficient of the indoor interface is equivalent to increasing the volume of the room, but it also inevitably reduces the reverberation time inside the room. As far as recording is concerned, of course, it can be supplemented by artificial reverberation, but such a recording studio can no longer be used as a natural reverberation type.
3. Diffusion of rooms: Although the strict diffusion of sound fields is difficult to achieve, most of the body shapes are irregular or long, wide, and high proportions, and the large music recording rooms with sound absorption surfaces or reflective surfaces in the interior are likely to meet the basic requirements of the diffusion sound field, such as no clear intermittent sound, sound field distribution. Basically uniform, directional diffusion is better (D value is above 0.9).
It is worth noting that due to the large volume of such music recording studios, if necessary, it is likely that there is no necessary early reflection. Although the exact relationship between early reflection and sound quality is not yet clear, it is certain that it will have an important influence on the feeling of music, the sense of depth and intensity. In the room, early reflection and direct sound and reverberation also play an important role in the sense of distance and the size of the room. Even if the reverberation time is appropriate, if the pickup point is short of the initial reflection within 50 milliseconds, there may also be audible quality problems, such as "fluttering" of voice.
4, reverberation radius: Although the reverberation radius of the room is not an independent parameter to describe the acoustical state of the room, it is of great practical significance to describe the reverberation at different positions in the room. In other words, with the help of reverberation radius, different reverberations can be picked up at different locations in the room until the maximum reverberation is determined.
In the recording of natural reverberation music, a basic requirement is to keep all the information as much as possible when playing music. Because of the large volume and reverberation time of this kind of recording room, the theoretical value of reverberation radius is not much different from the measured value. The reverberation radius can be obtained through the volume and reverberation time of the recording room. Using the concept of reverberation radius and selecting pickup points properly, it is possible to pick up the whole band's voice successfully with only one microphone. The usual practice is, first of all, based on the reverberation radius, and then the specific adjustment according to the hearing sense to accurately select the distance between the microphone and the sound source and the specific position of the microphone.
It must be pointed out that for a large music recording room with a certain reverberation time, the reverberation radius is not a fixed value in the whole frequency range of the band. It is not only related to the frequency characteristics of the reverberation time in the recording room, but also to the directivity of the instrument and the directivity of the microphone.
In the case of the influence of the microphone directivity, which is discussed in the next chapter, only in terms of the source and room factors, the low frequency reverberation time of the music studio is longer than that of the middle frequency (500 Hz) and the high frequency. When the volume is constant, the corresponding reverberation radius will be shorter than that of the medium and high frequency.