Weak current College】 【professional feedback suppressor use skills of.

First, the role of the feedback suppressor

Now that you understand the feedback suppressor role, of course, it is necessary to understand the next generation of acoustic feedback and acoustic feedback suppression method.

(A), the generation of acoustic feedback

I think as we audio Division, our headache is acoustic feedback problems, but the causes of acoustic feedback is varied, generally resulting in the sound system produces acoustic feedback reasons mainly in the following 3 ways:

1, the first is produced by pickup device: pickup the handset's voice through speakers out after this sound through speakers of direct or indirect radiation again into the microphone, microphone and speakers would form a loop. When this signal is constant loop amplification, beyond a certain range, have had positive feedback and oscillation, which produces acoustic feedback. In fact a set of sound system can be issued to a volume that has certain restrictions, like a balloon if it blow too much gas it would explode, we cannot give a sound system unlimited increase volume without a problem.

2, the second is the internal system of acoustic feedback appears: are generally caused by the effect of the channel. For example, in a mixer, we send signals AUX1-2 to effects, after effects processing if output a 2-channel signal input to the mixer of 23-24-channel, then at 23-24 in two channels of AUX1-2 knobs do not open or just after effects processing of signals and flow back to the effects, so AUX and effect between you and form a loop, when the loop level gain exceeds certain limits, it will also have an acoustic feedback.

3, the third reason is the band musical instrument of acoustic feedback: generally appear on the electric guitar and electric bass, because these two instruments also equipped with pickups, naturally also has the potential to produce acoustic feedback. Typically in this musical instrument unmanned operation, whereas the volume of the musical instruments and good through the speakers, do not switch off, subject to the volume of the speakers, and in some frequency on the frequency of resonance, when out of range, you will also have an acoustic feedback. So when the band musical instruments in unmanned operation, we should put the relevant instrument volume off, one can reduce noise, one is to prevent acoustic feedback.

(2), acoustic feedback suppression method

1, the first dealing with acoustic feedback is used to move prescaler, is going to produce sound feedback frequency shift some to prevent acoustic feedback. But this approach would seriously damage the sound quality, it is now rarely used.

2. later audio workers often use multiple simulation room equalizer to suppress acoustic feedback, but because the simulation room Equalizer adjustable frequency is fixed, when on a frequency of significant adjustment, it will seriously affect adjacent frequency, such as the frequency of occurrence the 315Hz acoustic feedback, we have to its decay 9dB, such adjustment will be affected and its adjacent 250Hz and frequency characteristic 400Hz; then a now use multi-segment simulation room Equalizer octaves are generally fixed, usually the third octaves so broadband only is a rather narrow band. It is also bound to affect the sound quality. In the light of the above shortcomings, sound engineers also developed a digital parametric equalizer, the equalizer frequency is freely adjustable and octaves are variable, so we can point to a frequency for more precise adjustments, but this kind of digital parametric equalizer also has its disadvantages, such as operation with than analog Equalizer intuitive, easy to adjust the speed to go through different menus and therefore will slow, and since there is no analog equalizers multi-segment sliding key, in the absence of relevant instruments, the use of digital parametric equalizer for sound feedback frequency is more trouble, so the sound engineers also developed a new, but to automatically look for feedback point devices: digital feedback suppressor.

3, the earliest feedback suppressor is Sabine company developed and produced by the 901 digital feedback suppressor, upgrading over the years, and now the latest model is: 2420. Feedback suppressor is a maximally suppress acoustic feedback occurs in an audio processing equipment, technically it is through the wave filter to reduce the howl. The latest feedback suppressor is a microcomputer control of multiple wave filter automatically handles the installation, when the system has a sound feedback, this device can be in a very short period of time automatically detects voice feedback frequencies and lock this frequency, and then using the filter on this frequency for narrowband, significant decay, so as to achieve a perfect acoustic feedback suppression. Using an image and metaphor: the use of traditional analog multi-segment equalizer to adjust sound feedback when, because of its frequency and octaves are immutable, so the adjusted frequency is varied, high to low; but now the digital feedback suppressor to handle acoustic feedback is precise, but also with automatic adjustment and narrow-band processing, etc. Image: If we adopt the simulation multi-segment equalizer with acoustic feedback, just like in a highway, dig a few larger, wider hole, even if not too deep, but will also have an impact by a vehicle; whereas if we adopt the digital feedback suppressor with acoustic feedback, just like in a highway, dig a few relatively narrow hole, even if very deep, do not impact through traffic. So we should analogy and contrast is very well understood.



Second, the use of the feedback suppressor method

(A) of the feedback suppressor of connection methods

1, like the equalizer, and other peripheral equipment like threaded in audio system, the advantages of such a connection is a connection and easy operation, suitable for relatively simple system. But the disadvantage is that the connection method in suppressing microphone acoustic feedback is also affected by the feedback suppressor of other sources of signals; another example we have a feedback suppressor threaded in the main channel pipeline mixerOut, that at this point the feedback suppressor can inhibit this signal channel acoustic feedback, on the other channels such as AUX output, output, etc. is not grouped.

2. use a mixer channel in the plug INS inserted/out interface feedback suppressor threaded in the channel, so that the connection has the advantage that you can maximize the feedback suppressor to adjust, no need to take into account the impact of other audio sources. The disadvantage is: use this connection method one feedback Suppressor up to control the mixer of 2 channels, the device is not fully utilized.

3. use a mixer marshalling of plug INS inserted/out interface feedback suppressor threaded in the Group channel, this connection is: you can compile into this group within the microphone for centralized processing, without affecting other audio sources. The disadvantage is: prone to malfunction, for example: a 1-8-channel mixer is the microphone, we take the 8-channel microphone series to a mixer for 1-2 classification for centralized processing, but if 1-8-channel microphone in any way accidentally also arranges to 3-4, if the 3-4 group, without feedback suppressor, that at this point it is also possible to produce acoustic feedback. So you want to know the sound mixer, operation with very carefully before using this method. On the whole as a result of this approach can fully utilize the feedback suppressor, and therefore the current maximum connection method.

4. If there are some sound mixer for marshalling channel no plug INS inserted into/out of the interface, we do not want to leave feedback suppressor concatenated primary output channel, and want to centrally control the handling of the microphone, then we can take a look less standardized, textbooks without method, for example: a 1-8-channel mixer is the receiver, we can take the 8-channel microphone volume through the AUX sends to the feedback suppressor, if is AUX5-6 channel. Through the feedback suppressor processing and flow back to the corresponding channel mixer, if is 23-24 channel. This connection method and connection effects almost require AUX to set send after the faders, also called for 23-24 channel AUX5-6 can no longer open, otherwise it will produce a signal loop; but the difference is now 1-8-channel volume cannot be made into any marshalling and main channel, which is the main channel of the marshalling channel L-R, 1-2, 3-4, 5-6 ... Single channel, and so on the appropriate button is not dark, let this eight channel volume only through AUX5-6 sent out, and then after 23-24-channel mixed with a mixer, and finally a mixer and then pass the corresponding signal channel output. It is also possible to play a good role, but felt this way is a bit of excess, but my opinion has always been emphasized: flexible and practical.

5, another method is to use two sound mixer, a dedicated connection to the phone, through the feedback suppressor for processing and then enter the volume to another mixer. Such advantages are: maximum on microphone for centralized control of processing, and completely avoid the interference of other audio sources; the disadvantage is: devoted to microphone, usually small mixer, its quality is better in General, and the dataI is also not enough rich functionality, and therefore the quality of the treatment may not be ideal; there are two mixer operation with some trouble, skillful sound engineers tend to be got flustered.

(B) feedback suppressor works

Different feedback suppressor although adjustment methods are varied, but the principle is the same, here we are with Sabine FBX2420 feedback suppressor of as an example for everyone to brief introduction:

Sabine's FBX2420 feedback suppressor using SMARTFilter technology during the performances, not the system adjustment during the feedback process. It is built into a very advanced automatic parameter adjustment device, this device filters can automatically search for feedback frequencies and accurately lock feedback frequency bandwidth, a very narrow, absorption depth enough filter to automatically eliminate worry of squealing voice. FBX2420 automation levels are high, and its adjustment speed than other feedback suppressor faster.

The feedback suppressor really work?, of course, the most important thing is to look at the feedback control filter quality. Filter quality which you can use the adjust speed, accuracy, resolution, and the consistency of the sound.

1. speed: in the new FBX2420 SMARTFilter is running in the algorithm of the speed of digital signal processors, obvious advantages can be in less than 30 seconds of time in the automatic adjustment of all parameters. Work, will continuously monitor feedback FBX2420, when discovered feedback point cannot be processed automatically.

2. accuracy: some of the feedback suppressor sometimes it's difficult to tell which ones are useful music signal which is harmful to the feedback signal, this is the most difficult to resolve feedback controllers. Bad judgement means wasting filter also affect sound quality. FBX outstanding performance is always able to accurately judge, new SMARTFilter technology make it more effective. FBX2420 use patented technology to analyze programs in harmonic components, because of the harmonic components of feedback is low, but music and language program contains rich harmonic components, so you can correctly answer the FBX is music or feedback.

3. resolution: this is a big problem, we know that feedback is a fortuitous event, we need accurate lock feedback point, but a lot of feedback suppressor general filter adjustment to the feedback frequency of nearby, and relies on increased filter bandwidth and attenuation depth to eliminate acoustic feedback. While FBX2420 takes a more complex solution, it can be done 1Hz resolution, truly the fast and precise:.

4. voice of consistency: Sabine on digital filter innovation process is unique in the industry, providing digital filter number exactly the sound better, with smaller phase distortion and smooth frequency response. Sabine absorption filters in allDepth to maintain consistency of the sound, providing a true constant Q values of characteristics.

(3) feedback suppressor of adjustment methods

Feedback suppressor in tuning generally use AutoFit, some also with manual adjustment method, here we still to Sabine's FBX2420 feedback suppressor, for example to talk about the simple adjustment method, adjusted in the following order:

1. put the microphone placed in several key areas of performance, you can use a microphone fixed, or you can let the actor simulation performance.

2. press the reset RESETDYNAMICS key until all the LEDs go out to clear the previous filter settings, then Clip-level lights flash, this step also is used to adjust the parameters to clean up.

3, because the sound inside the two-channel speaker placement, therefore producing acoustic feedback frequencies vary, so a single channel to adjust, or you will waste your filter. At this point we can use the Bypass button to turn off one of the channel. Press the STEUP key officially entered the need to make an adjustment channel Active activation mode, which is ready, you can adjust.

4, slow and push up the receiver channel faders, when producing sound feedback when the feedback suppressor is automatically suppressed and its corresponding one filter indicator will light up. So repeatedly, when filter channel full activation, the system automatically suspended. At this point READY key in the blue lights begin to light up, indicating that the setting is completed. Then Bypass the channel, go to debug another channel.

Basically a large order is, of course, there are some details you need to reference the product specifications. Actually use feedback suppressor to handle sound feedback and take advantage of multiple pieces of simulation room Equalizer processing method of acoustic feedback, but a basic is automatically adjusted a depends on our manual adjustments.

See here some audio engineer may find the feedback suppressor was a baby, so is panacea! virtually any audio processing equipment are not a panacea, imagine: If we adopt a six group's mixer, mixer main output signal to the main speakers; 1-2 formation signal to the subwoofer; 3-4, and 5-6 Group gave different auxiliary speaker; then AUX 1-2 signal also gave the stage that at this point the listening, sound mixer had 5 groups signal output, should we be able to buy 5 feedback suppressor? General, of course, is impossible. Even if you use Group focused on the microphone to be processed, and that there is no way to control AUX listening channel signals, so if you want the perfect treatment of acoustic feedback, a sound system at least configure 2 feedback suppressor. Even if your system has a sufficient number of feedback suppressor, that's not likely to be all, but don't be naive to think that the current feedback suppressor can 100% tell what is what is microphone music signal feedback sound, the truth is good music signal often give feedback suppressor suppression, and harmful microphone feedback sound but not very good control. There are also some audio system acoustic feedback point too much feedback suppressor per channel 10 several filter is simply not enough. So for feedback suppressor use and evaluation or benevolent see benevolence Moses.

Third, use the feedback suppressor-time issues

1, in the use of microphone for feedback point suppression, it is best to find a few frequently used the microphone, but when you want to continue to transform the location of the handset, you can also place the point when the adjustment of background music or microphone to speak some words, which can make the sound more active, more precise and fast find acoustic feedback frequencies.

2. the system if you have to press the device, also note the compressor for pass-through, and adjust the completed and then restored. Whereas the system of other audio processing equipment such as: equalizer, Exciter, divider, amplifier, etc, to adjust to normal working state, you cannot pass through.

3. takes note of the detection of a system in the feedback suppressor on the music signal and microphone feedback signal detection method of resolution is: turn off all the microphone, the feedback suppressor thread in any of the music signal channel, it is best to put a disco music, constantly increasing volume of this channel, if it is found that the feedback suppressor started working and serious impact on the sound quality, it proves that this feedback suppressor is also not very perfect, and if we want to continue using it, you can use it alone microphones, not with other sources of signals.

4, there is one thing to note: If you have to readjust the feedback suppressor, the on-site performance, do not press the Reset button, as this will give you a previously set all parameters in the clear, the feedback suppressor into just the factory's original state, it is very dangerous, the system will probably appear strong screech, serious but also equipment.

5. some of the feedback suppressor with automatic and manual work mode, if you think you have a perfect adjustment of the system does not occur with acoustic feedback, then you can leave feedback suppressor on manual or lock mode, so that both preserves the device in the original parameters, not because the device error detection and false starts and change the parameters have been adjusted well.

6, there's one more thing: feedback suppressor is impossible both inhibit acoustic feedback and adjusting the sound field, adjust the sound field need to have a dedicated simulation multi-segment room equalizer or professional digital parametric equalizer.

Hope the above presentation enables you to have some feedback suppressor, owing to the current high-tech feedback suppressor cost is too high, so in general engineering use of quantity, nor popular, so it has caused a lot of audio engineers have never contacted the high-end of the feedback suppressor. But I think that as long as there is a better sound field, configure a better speaker, selection of a suitable microphone, multi-stage room equalizer toSimple adjustment, in such a system, even if no feedback suppressor, acoustic feedback is still very good processing; on the contrary more upscale feedback suppressor is also no use! so I hope everyone can feedback suppressor role have a clear understanding.