Stereo recording is the process of recording multiple track soundtracks during film production. The signal-to-noise ratio, dynamic range, bandwidth, distortion, and crosstalk and phase shift of the main vocal material of the movie stereo are more stringent than those of the mono video. The recording system is a system in which a digital camera captures audio. The recording system of most digital video cameras is a PCM stereo digital recording system, which can record in 12 different modes (recording frequency is 32KHz, two channels) and 16 bits (recording frequency is 48KHz, two channels). Let's take a look at the recording technology of the digital recorder.
The stereo recording of the digital recorder has a cross-arranged microphone shape, which is much more complicated than the one we imagined.
Recording two-channel stereo, mainly adopts the time difference and the sound pressure difference to create a three-dimensional sense of space. The time difference is that the time when the sound source reaches the left and right ears is different, and the stereoscopic feeling is generated. The sound pressure difference is different from the intensity of the sound received by the ear.
Another important factor for stereo recording is the phase. When using a speaker or mixing the left and right channels to mono, the left and right channels have the same phase to increase the volume, and vice versa. The active noise reduction device used in airplanes and some cars reduces noise by outputting opposite phase sounds.
The way in which stereo recording microphones are placed (also known as the standard) is very complicated. The following are commonly used:
A/B mode: The two microphones are pulled apart by a certain distance, parallel or at a certain angle toward the sound source. Simple and convenient, but easy to produce sound field and phase problems.
ORTF mode: The two microphones are 17cm apart and face the sound source at an angle of 110 degrees.
X/Y mode: The two microphones are placed at an angle of 90 degrees, and the microphone diaphragm is very close. Stereo recording with sound pressure difference has the advantage of solving the phase problem, but the pairing requirements for the microphone are higher.
M/S mode: A cardioid directional microphone (Mid) is placed at a 90-degree angle with an 8-shaped directional microphone (Side). The MS mode requires an encoder to generate left and right channels for stereo recording. The encoding mode is left channel = M+S, right channel = M-S.
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