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How to use an exciter to improve audio quality

With the development of the broadcaster TV industry, the demand for the sound quality of the program is getting higher and higher, and the improvement of the sound quality is the goal that the professional workers relentlessly pursue.

In the existing electronic field production (EFP) audio system, how to enhance the wireless microphone audio activity, improve the analog tape sound clarity, improve the human voice of the sneak sound processing, audio professionals are very concerned about the problem. In practice, we use the auditory exciter to improve the system's processing power, to improve the EFP audio quality purposes.

Exciter and its system access

Auditory exciter

At present, in the incentive mode for audio signal processing, there are auditory exciters (Aural Exciter), incentive processing software and excitation circuit. Which professional auditory exciter is more suitable for EFP.

Auditory excitator excitation of the harmonic signal is simulated by design, can be analogous to artificial reverberation simulation hall acoustic characteristics. Therefore, this artificial harmonic should not simply be seen as the original signal "false" and equivalent to distortion. The actuators are designed to restore the missing harmonic components of the audio signal, effectively expand the high frequency bandwidth and improve the signal to noise ratio, thereby improving the clarity and expressiveness of the sound reduction. Moreover, the levels of these harmonics are very low and have little effect on the power of the signal. As the exciter has the above advantages, use it to deal with the signal, can improve the sound quality.

In practice, we use Aphex Aural Exciter--250 (referred to as Ax--250) professional auditory exciters. Ax-III-250 is a dual-channel processor, and each channel includes the same two audio paths, the Main Path and the Sidechain Path. The main path sends the audio signal from the input stage directly to the output stage, beats earphones essentially without any processing; the side chain path contains all the "heart" circuits of the actuator. The two audio signals are mixed at the addition circuit level, and the mixing ratio is controlled by the Mix function. Ax--250 has a strong audio processing capabilities, and can effectively eliminate noise and distortion.

Control parameters

The main control parameters of the exciter are threshold, tuning point, harmonic quantity, sound product and mixing ratio, etc., they linkage to produce the high-frequency harmonics to be restored. The main controls of Ax-III-250 are:

(1) noise reduction threshold (NR Threshold). The control provides a threshold setting range of -60 to +30 dB in order to block the noise level out of the excitation circuit and perform noise reduction.

(2) Tuning point (Tune). The control sets the rising frequency of the second-order high-pass filter in the side-by-side path and establishes the active frequency band. The frequency control range is 700Hz ~ 7kHz.

(3) peaking (Peaking). This control provides a buffering effect for tuning points. The pre-emphasis of the tuning point frequency is gradually increased when the control amount is minimized from the minimum. At the same time, before the pre-emphasis in the tuning point, there will be a small trap, it will increase with the peak of the control and deepened. As shown in Figure 1.

(4) zero compensation (Null Fill). The effect of the zero-value compensation control is to adjust a band-pass signal, which 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-by-side path, which causes distortion of the waveform to make the sound more loud. At the same time, there will be a small notch near the tuning point on the output equalization curve, which will exacerbate the frequency near the tuning point, increasing the signal in the higher frequency band. This effect is often needed. But sometimes in order to compensate for the phase loss, with zero compensation control to de-emphasis, thereby enhancing the voice of expression and realism.

(5) Harmonic (Harmonic). Tuning control is used to adjust the amount of harmonic generation. 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 the transient and steady-state sound quality and the corresponding original signal amplitude.

If the control amount is increased, the harmonic component will be increased by the odd-even harmonic ratio of the tone control. Moreover, the harmonics generated are not harmonic distorted because they are intelligently generated and form a power envelope that increases the final sound quality rather than degradation.

(6) sound (Timbre). Sound control is used to set the type and arrangement of harmonics, that is, the ratio of odd and even harmonics. Even more harmonies sound sounds soft, odd harmonics sound more sounds some hard.

(7) Mixing ratio (Mix). The effect of the mixing ratio control is to mix the signal with the excitation enhancement into the original signal, and the control range is from 0 dB (ie, zero gain) to + 14 dB (indicating that the signal above the threshold is 14 dB boost).

In addition, Ax-III-250 also provides a single-sided bypass path (Solo) function.

System access

Exciter access is generally in two forms: In-Line (In-Line) and Side Chain (Sidechain). as shown in picture 2. In most cases, the splitter is used to connect the two devices. When using the split chain connection, use the Solo function to disconnect the audio signal of the main path, only the pure excitation signal into beats earphones the mixer, mix the original signal and pure excitation signal on the mixer. This is very important. This connection is equivalent to the exciter's Mix control moved to the mixer to use, and the mixer itself is a mixing console, so the control is more convenient and flexible, is conducive to accurate tracking and control of hearing effects.

In practice, the use of an Ax--250 dual-channel, while dealing with EFP in the multi-channel audio signal. Connect the exciter to the audio system as shown in Figure 3. Where the CH1 channel is assigned to the human voice using the CH2 channel assigned to the music used. In this case, the auditory exciter is in the form of a side chain access, the original flow of the program signal does not change, the signal is transmitted and mixed beats by dr dre according to the original channel, and two pure excitation effects are provided. These harmonics are connected with the source The signal is closely related to music and dynamics. The original signal and the pure excitation signal are only mixed on the mixer.

The specific approach is to use the CH1 set of control parameters from the wireless microphone FM audio or vocal, with CH2 another set of control parameters to deal with those who have to improve the sound quality of music or other sounds (such as electro-acoustic band, etc.). Because of the inconsistency of the sound quality of these program sources, it is necessary to determine the amount cheap beats headphones of incentive to add and adjust the mixing ratio according to the material.

The above approach is suitable for most EFP applications, safe and reliable.