The compressor limiter is a professional audio processing device that compresses audio signals and compresses and limits the dynamic range of audio signals. Its main function is to protect the safety of the amplifier and speaker system in the speaker system, while preventing the occurrence of overload clipping distortion, and can also improve and create some acoustic effects. For example, when the original sound with a large volume change is compressed, the volume can be changed smoothly; when the vocal component of the vocal is compressed, the squeaking of the microphone or the tuning can be excessively restricted; a special sound effect can be produced when processing certain instrument sounds.
In order to facilitate the regulation of the pressure limit, the main function circuit of the compressor has two adjustment units, one is the threshold level, the other is the compression ratio, and the regulation of the two units to process the dynamic range of the signal is lower than that allowed by the latter equipment. The dynamic range is the principle, and the function of processing the audio signal by the compressor is fully utilized.
The compressor has three treatment schemes depending on the application, namely, overall compression processing, high-level compression processing, and peak compression processing.
1. Overall compression processing
The overall compression processing is used when the dynamic range of the signal source blown by the device is larger than the dynamic range of the device itself, and is mostly used for recording sound reinforcement. The compression ratio of the overall compression is determined by the ratio of the dynamic range of the program signal to the dynamic range of the device. For example, the dynamic range of the recording microphone source is about 100dB, and the dynamic range of the device is 70dB. At this time, the compression ratio should be positioned around 1.5:1.
The threshold level of the overall compression is generally set at 8 dB of the weakest signal level of the sound source or 10 dB above the local noise level. The overall compression action time is generally set at the lowest position, and the recovery time can be determined according to the slow Chengdu pronunciation. In order to make the weaker part of the tail sound more natural, it can be set at about 1s under normal circumstances.
2. High level compression processing
In the process of sound reinforcement in many programs, the signal level above the average of 20dB is only 5% of the short time. The sound system of the general performance sound reinforcement, especially the sound reinforcement system of pop music singing, has a large average volume, and the sound system generally works close to the full load output state, and it is impossible to have a dynamic margin of 20 dB. At this time, in order to prevent the impact of the large peak signal of about 5% of the short time, a high level compression process is often used, and the compressor is only compressed against a short high level.
Since it is not an overall compression, the compression process will have a significant impact on the original signal at the inflection point. In order to solve this problem, the following methods can be used: First, in order not to frequently operate the compressor in the working/recovery state, the threshold level after the compressor is processed should be determined to be more than 3 dB in the average sound source rating, and secondly, Reproduce the original dynamic characteristics of the loud loudness signal that has been compressed, and add a suitable sound head during the initial process of the device entering the compressed state. This processing can cause the large loudness segment that is actually compressed to audibly produce an effect that is louder than the segment. In order to simulate the auditory feature, the operating time of the compressor to enter the compressed state can be adjusted to 5 to 10 ms. Thus, when a loudness signal appears, it can be compressed for a short distance before compression.
3. Peak pressure limit processing
When the professional audio equipment is near the overload distortion state, the smile of the input level rises to cause the signal to be topped. In order to effectively control the overload distortion of the device, peak pressure line processing is often used.
Threshold levels for peak pressure processing are usually very close to the highest limits of system dynamics. Here, the level for forming the head sensation is small, and the action time is generally set at 150 μs, and the compression ratio is generally greater than 10:1, usually between 10:1 and 20:1.
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