With the development of the broadcasting and television industry, the requirements for the sound quality of the program are getting higher and higher, and improving the sound quality is the unremitting pursuit of professional workers.
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In the existing electronic field production (EFP) audio system, how to enhance the activity of wireless microphone audio, improve the clarity of analog tape sound, and improve the noise processing of human voice is a problem that audio professional workers are very concerned about. In practice, we use the auditory exciter to improve the processing power of the system to improve the quality of EFP audio.
Exciter and its system access
Auditory actuator
At present, there are an auditory exciter (AuralExciter), an excitation processing software, and an excitation circuit in terms of excitation mode for audio signal processing. Among them, professional auditory exciters are more suitable for EFP.
The harmonic signals excited by the auditory exciter are simulated and can be analogized to the acoustic characteristics of the artificial reverberation simulation hall. Therefore, the generation of such artificial harmonics should not be simply considered as "false" of the original signal and is equivalent to distortion. The exciter is designed to recover the harmonic components lost by the audio signal, effectively extend the high frequency bandwidth and improve the signal to noise ratio, thereby improving the clarity and expressiveness of the sound reproduction. Moreover, the levels of these harmonics are very low and have little effect on the power of the signal. Since the exciter has the above advantages, it can improve the sound quality by processing the signal.
In practice we use the AphexAuralExciter-III-250 (Ax-III-250 for short) professional auditory exciter. The Ax-III-250 is a dual-channel processor. Each channel includes the same two audio paths, the main signal path (MainPath) and the side chain stimulated signal path (SidechainPath). The main path sends the audio signal from the input stage directly to the output stage with essentially no processing; the side chain path contains all the "heart" circuits of the exciter. The two audio signals are mixed at the adder circuit level, and the mixing ratio is controlled by the Mix function. The Ax-III-250 has strong audio processing capabilities and can effectively eliminate noise and distortion.
Control parameter
The main control parameters of the exciter are threshold, tuning point, harmonic quantity, tone and mixing ratio, etc., which jointly generate the high frequency harmonics to be recovered. The main controls of the Ax-III-250 are:
(1) Noise reduction threshold (NRThreshold). The control provides a threshold setting range of -60 to +30 dB in order to keep the noise level out of the excitation processing circuit and to reduce noise.
(2) Tuning point (Tune). The control sets the rising edge frequency point of the second-order high-pass filter in the side chain path, and establishes the working frequency band of the excitation, and the frequency control range is 700 Hz to 7 kHz.
(3) Peaking. This control provides a buffering effect for the tuning point. When the amount of control is from the minimum to the maximum, the pre-emphasis of the tuning point frequency is gradually increased. At the same time, a small notch will appear before the tuning point is pre-emphasized, which will deepen as the peaking control increases.
(4) Zero value compensation (NullFill). The function of the zero-value compensation control is to adjust a band-pass signal that is applied to the high-pass signal in the side-chain path to compensate for "phase loss."
There is a certain delay in the signal in the side chain path, which causes distortion of the transient waveform and makes the sound louder. At the same time, small notches appear near the tuning point on the output equalization curve. This notch de-emphasizes the frequency near the tuning point, making the signal in the higher band heavier. This effect is often needed. However, in order to compensate for phase loss, de-emphasis is performed with zero-value compensation control, thereby improving the expressiveness and realism of the sound.
(5) Harmonic amount (Harmonic). Tuning control is used to adjust the amount of harmonics generated. Harmonics are generated by VCA modulation processing in the side chain path, which does not affect the signal level in the side chain path. The harmonic components generated by the internal harmonic generator are based on a complex set of simulation operations, taking into account transient and steady-state sound quality and corresponding original signal amplitudes.
If the amount of control is increased, the harmonic components will be increased in proportion to the odd-even harmonics controlled by the sound. Moreover, the harmonics produced are not harmonic distortions because they are intelligently generated and form a power envelope that causes the resulting sound quality to improve rather than deteriorate.
(6) Timbre. The sound control is used to set the type and arrangement of harmonics, ie the ratio of odd and even harmonics. The sounds with even harmonics sound softer, and the sounds with more odd harmonics sound harder.
(7) Mix ratio (Mix). The purpose of the mixing ratio control is to mix the excitation-enhanced signal into the original signal, with a control range from 0 dB (ie, zero gain) to +14 dB (a 14 dB boost on the signal above the threshold).
In addition, the Ax-III-250 also provides a single side-by-side path (Solo) function.
System access
Exciter access is generally available in two forms: In-Line and Sidechain. as shown in picture 2. In most cases, the exciter is connected between the two devices by a series connection method. When using the side-chain connection, the Solo function is used to disconnect the audio signal of the main path, and only the pure excitation signal enters the mixing console, and the original signal and the pure excitation effect signal are mixed on the mixer. This is very important. This connection is equivalent to moving the exciter's Mix control to the mixer, and the mixer itself is a mixing console, so the control is more convenient and flexible, which is beneficial for accurately tracking and controlling the hearing effect.
In practice, an Ax-III-250 dual channel is used to simultaneously process multiple audio signals in the EFP. Connect the exciter to the audio system as shown in Figure 3. The CH1 channel is assigned to the vocal use and the CH2 channel is assigned to the music. At this time, the auditory exciter is in the form of a side link, the original flow of the program signal is not changed, the signal is transmitted and mixed according to the original channel; and two pure excitation effects are provided, and these harmonics are supplied to the source of the exciter. Signals are closely related to music and dynamics. The original signal and the pure excitation signal are mixed and mixed only on the mixer.
The specific method is to process FM audio or vocals from wireless microphones with a set of control parameters of CH1, and to process music or other sounds (such as electroacoustic bands) whose sound quality needs to be improved by another set of control parameters of CH2. Since the sound quality of these program sources is inconsistent, it is necessary to determine the amount of excitation addition according to the condition of the material, and to adjust the mixing ratio.
The above method is suitable for most EFP applications, safe and reliable.
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Executive Standards:IEC60092-350, NEK606
Executive Standards:IEC60092-350, NEK606
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