Apple (Apple is already three-dimensional! The parentheses are used here to make a difference from other conditions), you can see the changes in depth, position and angle; and a photo of the same apple although you There may be a similar three-dimensional feeling, but it is definitely different from a real "three-dimensional" apple. In terms of music, this true "stereo" broadcasting method has gradually become popular under the name "Surround sound" in recent years, and the so-called Stereo in general acoustics refers to the right and left of a sound source. , The difference in distance, not the real three-dimensional (three-dimensional in the photo). It is also worth mentioning that, whether it is the so-called Surround or Stereo, they present a situation on a plane. At present, there does not seem to be any further performance of the playback system on the market. Furthermore, whether it is Stereo or Surround, when you place the speakers, they should be on a plane at the same height (except sub-woofer). If you do not go through such a procedure, basically you ca n’t really The performance of Stereo or Surround.
Stereo Micing, as the name implies, refers to the use of special techniques when recording to make the received sounds have a three-dimensional effect when playing back in the future (that is, it can make people understand the location of one or some sound sources in space during playback Its relative relationship). So when it comes to Stereo Micing, most of the concepts refer to the use of two (or more) microphones for radio reception, and the received sound must also be completed by using two or more audio tracks when stored. The reason is that if you want to simulate the sound effect in the space, you need at least two or more positions or directions to achieve the spatial positioning situation (just like the so-called triangular positioning commonly seen on TV); as for storage, the same reason Why do you need more than two audio tracks to achieve a three-dimensional effect in Playback.
Because there are many classifications and details in the theory and techniques of Stereo Micing, here are some of the most commonly used ideas and the focus of microphone placement that I have put together. In actual use, since each sound engineer will have its own unique habits and changes, so you will not see the same method of use between each sound engineer.
After finishing, I divided the commonly used Stereo Micing theories into three categories:
1. Simulate the way of picking up a point in space
2. A way to simulate the response of a point in the space to the space sound
3. The way of simulating the human ear
After seeing the above three points, I believe it is still generally confusing. What exactly do they say, and what are they worth noting, and what are the ways of using such ideas to collect radio? Please be patient and continue to look down ~
1. Simulate the way of picking up a point in space
........ This is the most basic Stereo Micing theory. If you want to know the location of a point in space (the purpose of Stereo Micing), the simplest way is to put two microphones in this space Due to the different relationship between the time of reaching the microphone, the human brain can use this condition to localize the location of each point source.
........ The use of this type of radio, the received sound is generally less likely to have Centeral Image (for a point in space has a more accurate position idea rather than a direction in space The "one piece" feeling), the biggest reason for this situation is that the microphone only collects the sound at the position where it is located, and the sound received by the two microphones will have a problem of phase cancellation (phase cancellaTIon) during playback. , So it is not easy to produce a solid Centeral Image. Therefore, when using this type of Stereo Micing, a commonly used formula is 3: 1 (three-to-one), which refers to the "distance between two microphones" and "the line from the sound source to the microphone. The ratio of "vertical distance" needs to be greater than 3: 1 to avoid problems caused by phase reduction.
Here are some common applications and techniques:
SpaTIal Pair: Commonly used situations include live radio with only two microphones, centering, small choir (chior) radio, simple collection of a certain type of musical instrument (such as violin) in the classical orchestra, overhead of drum kits, etc. . When in use, generally need to be kept on the same plane as the sound source to be received (generally in front, the overhead of the drum kit is directly above), the axis of the microphone capsule is facing forward (or downward), remember the 3: 1 just now Mantra, omni or cardioid of the microphone pattern. The choice of microphone is usually a large-diameter (lardge diaphagm) microphone, especially when collecting human voices, some advanced large-diameter condensor microphones such as Neumann's U87, U89 ... are also commonly used microphones.
Room Mic Pair: There are many ways to receive Room Mic, including one, two or more microphones used at the same time. One of the frequently used ones is also evolved from this type of concept as shown in the figure. This kind of. When in use, the axis of the microphone capsule faces two remote corners in the space opposite to the source of the sound source. Try to make the two microphones have the same height and symmetrical angle. The pattern of the microphone can be omni or cardioid. As for the type of microphone, there is no certain shape. From cheap dynamic microphones to extremely advanced condensor microphones, people use them. The more commonly used selection criteria are the type of music, the brightness of the space itself, and the characteristics of the microphone. One of the reasons why the axis of the microphone capsule faces the corner is that strong bass will be received in the corner (bass is easy to have more bass in the corner due to the principle of sound waves), and this is often something we think Part of Room Sound to be received.
2. The theoretical basis of a type of radio in the simulation space that responds to the spatial acoustics is that the Stereo Micing theory of the previous category inevitably causes Centeral Image and sound quality distortion problems due to phase reduction. In one theory, the two points (microphones) in different positions are placed at the ideal point, so no matter which side comes from, the sound will not cause problems due to the phase reduction. So this type of Stereo Micing is also often called Coincident radio.
Of course, the theoretical point cannot be achieved in reality. There will be a certain distance between the capsules of the two microphones. Even the Stereo microphone (such as Neumann ’s SM-69, Shure ’s VP-88, etc.), the internal two The capsules will be slightly away from each other, so make sure to place the microphones as close as possible without colliding with each other (generally make the capsules of the two microphones into a vertical straight line). As for the gaps that still exist between capsules, they are generally ignored.
In fact, we generally place two microphones on the same level as the sound source, and at an appropriate distance, the two microphones are directed outward at the same angle to different sides connected to the sound source, as far as the angle is required. The angle depends on different methods, and I will have a more detailed introduction later.
Since the capsules of the two microphones are considered to be at the same theoretical point, theoretically there will be no phase cancellation, that is to say, because there is no phase cancellation, this type of radio will have a very good central image. For some solo instruments or vocals, this is an ideal way to collect sound. In addition, in terms of the three-dimensional sound, it also has the characteristics of spread out rather than making the sound very mono-like.
XY: The most commonly used technique in this type of theory. The microphone is placed at the predetermined radio reception position when placed. The capsules of the two microphones form an angle of 90 degrees (someone also uses an angle of 110 degrees). The patterns are all cardioid. It is commonly seen in the collection of solo instruments, such as guitars, sax, etc. Almost as long as I want to use Stereo Micing to collect solo instruments, I have seen people use this technique. In addition to the solo vocals, this is also one of the very popular Stereo Micing techniques. In addition, since this method is generally used to collect solo vocals or musical instruments, the commonly used microphones are all higher-level condensor microphones, but not only condensor microphones, some of which have higher sensitivity The dynamic microphone can also be used as one of the selected quantities.
Blumlein: Basically the same as XY, the main difference is that Blumlein must be at an angle of 90 degrees, and the pattern of the microphone is figure-8 (figure 8). This technique is named after the name of its inventor. Blumlein is a live sound engineer on TV, and he found that live recording in this way can not only be stereoscopic in other ways, but also has a very good central image. Therefore, it is quite often used in the reception of live programs. A technique applied. As for the sound collection in general studios, besides the figure-8 will not only receive the sound mainly from the front of the capsule, but also the reflected sound from the rear will be received, so it is rarely used in the studio, or need to be visually The situation needs to be used.
........ Mid-size Stereo (MS Stereo): This is the best mono compaTIble method. It consists of a pair of direct sound sources, a cardioid (or hyper-cardioid), and a figure-figure. 8. The microphone is perpendicular to the first microphone (remember that the two microphones should be as close as possible to the cpasule to minimize the problem of phase reduction). At first glance, it seems that it is not easy to understand how such a radio method is applied to Stereo Micing, but this is actually a bit "fraud"!
Generally, the sound recorded by Stereo Micing is either the left side of the stereo sound or the track on the right. But the sound recorded with Mid-size requires three tracks when processed on the console. The signal received by the cardioid microphone keeps its panning in the middle of the center (center); and the signal from another microphone finds a way to "copy" it (usually you can use the console's patch bay) The output point of one of the s signals, or use MULTI on patch bay), will have the phase inversion of one of the two signals. At this time, because the signals of the two tracks are the same and the phase is opposite, you can find that when the panning is about the position of the center, due to the phase reduction relationship, when the two faders are in a certain relationship, the sound of the two tracks will be heard due to the mutual cancellation. not see. Then adjust the pannig of these two tracks to completely left and right (at this time, due to the stereo relationship, the two tracks that originally canceled each other become audible again). With the first track just now, you have completed the mid-size radio and setting. Because the second and third tracks are the same as we just mentioned, when they are played in mono mode (such as most AM stations or poor portable audio), the second and third tracks will be completely inaudible. , And the first track can be left in the way you want to adjust, and in general stereo playback, you can make stereo effects with the second and third tracks. When recording to a multi-track tape drive, DTR or hard disk, it is different from the other mentioned radio methods, except that the received sound is converted into a stereo two-track signal and connected on the two tracks. The more commonly used method is to record the signals of the two microphones on different tracks (other methods usually record the sound of one of the stereo signals).
Although it sounds like a pretty good idea to use Mid-size for recording, there are actually not so many opportunities for recording with Mid-size. The main reason is that although Mid-size is a Stereo Micing technique, it should be a "fake" Stereo Micing. The stereo effect is only a different phase of a figure-8 microphone, so in fact Its effect is worse than the effect of the previous two methods, so in the use of the same need to pay attention to the timing and the final purpose. In addition, the more common application is the recording of vocals, especially when the recording is required for mono compatible or when the microphone needs to be changed frequently in the same session (Mid-size can be backed up when recording with a mono microphone when only one is used) The other one can be added immediately to make stereo recordings without the need to re-arrange the microphone, which is most suitable for recording engineers to use lazily).
3. The way of simulating the sound of the human ear In this theory, the intention is to pull the "listener" to the scene of the sound collection, that is to say, the function of replacing the human ear with a microphone. Each microphone is a virtual human ear, so it will be collected When the sound is restored, the sound heard by the human ear is also restored, which further achieves the restoration of the true hearing effect of human beings.
........ In theory, this seems to be the most perfect Stereo Micing method, but in fact, due to the different placement, angle, height, and listening space of the speaker placement, it will make The sound played is affected and the desired goal is not achieved. In fact, a further situation is that this Stereo Micing method is actually worse than the other two categories above during playback, so it is rarely used in practice.
........ However, if the final media to be played is a headset (headphones, especially advanced ones specially designed to achieve the Stereo effect), generally speaking, this type of radio will be quite real Performance. Different from the way of playing with speakers, when using headphones, because of not interacting with the playing space, the sound of the playback will be directly transmitted to the human ear, so there will be no change in sound quality due to the change of space. Under normal circumstances, when using headphones to listen to music, although the clarity of the sound quality will come better, but due to the lack of interaction with the space, the sound generally comes to be "dry" and less spatial. However, if this type of radio is used, there will be no phase reduction or blur due to spatial changes, so there will be a very high sense of realism.
ORTF (Office de Radiodiffusion-Television Francaise): A Stereo Micing technique used in live broadcasting developed by the French national broadcaster. This is similar to the XY radio mode. When used, the two microphones are spread out at an angle of 110 degrees (approximately the opening angle of the human ear), 17 cm apart (approximately the distance of the human ear), and the microphones use cardioid pattern. Because the distance between the microphones is not very large, the degree of phase reduction is not very serious, but compared to XY, its sound is more spread out and open, so it is more commonly used in this type of Stereo Micing In addition, because it is similar to coincident's radio, but the distance of the microphone is far, it is also called near coincident Stereo Micing.
Binaural: This is a Stereo Micing technique that requires auxiliary equipment to perform. You must use a dummy head when using it. This head will have a matching "hole" in the ears to let you place the microphone After placing the microphone in the "hole", the position of the microphone's capsule will be exactly where the human ear is due to the design relationship. Because there is a fake head there, and the position of the microphone is exactly the same as the position of the human outer ear, it is conceivable that Binaural's sound collection method is closer to the sound heard by the real person's ear than any other Stereo Micing. And as mentioned earlier, this is an excellent way to use headphones to play, but if the general speaker-based broadcasting method, the effect will be relatively reduced. In addition, when using this method to collect sound, some frequently used noise reduction systems (such as Dolby A, Dolby B, Dolby C or dbx) will reduce the quality of Stereo Micing using Binaural to collect sound.
The above spent some space to introduce you to some of Stereo Micing's theory and practical methods. I hope that it will be of some help to interested friends. As for more in-depth understanding of some actual situations, you can find some by yourself. Related books for research.
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