Vocal mic feedback destroyer channel settings?

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This topic contains 13 replies, has 7 voices, and was last updated by Profile photo of coffee_king coffee_king 6 years ago.

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  • #45936
    Profile photo of coffee_king
    coffee_king
    Participant

    Hi All
    Would anyone kindly like to share their QU channel settings to eliminate feedback from vocals FOH?
    Thanks in advance.

    #45937
    Profile photo of [XAP]Bob
    [XAP]Bob
    Participant

    Depends what is driving the feedback, and at what frequency.

    Notch out the frequency as tight as you can (find it by boosting a notch by a few dB and sweeping that to find when it starts ringing).

    Or move the mic away from the FOH speakers…

    #45938
    Profile photo of timhum
    timhum
    Participant

    The settings depend on the room shape, size, position of the FOH speakers and the level of the vocal mic may depend on the amount of sound absorbing audience attending.
    In rehearsal, once your basic mix is established or before if you get to set up before the band arrive, hit the RTA tab on the Home screen and the fade up the vocal mic until you get the your first howl, notice the frequency on the RTA and notch the graphic EQ down a few dB at that frequency, repeat these steps until you achieve audio happiness.
    The skill comes in, and here I will have to defer to other more experienced practitioners, where you inevitably find yourself looking at a graphic EQ setting resembling a profile view of the Alps with serious notches in the vocal range. This may have the effect of making your vocalist sound like a duck and that is before they ask you for a “bit more middle”, “more presence” or reverb. All of which will compromise your anti-feedback settings. There is a rather nice and cheap iPad App called FFT Plot which is useful to use when doing this.
    You could but a “Feedback Destroyer” but then you are in the hands of an unthinking algorithm which will save your speakers but may have unwanted audible artefacts.
    I am interested in following this myself because I have a regular booking in a truly ghastly room with a Big Band too loud for the room and a vocalist who can not hear herself. I have tried squeaking the room with some success but am waiting for the day someone spots what I have done to achieve the nearly OK sound!

    #45939
    Profile photo of [XAP]Bob
    [XAP]Bob
    Participant

    The graphic is quite crude in terms of feedback, but can be effective.

    #45940
    Profile photo of Dick Rees
    Dick Rees
    Participant

    There’s only one setting that will guarantee no feedback:

    OFF

    Or disconnect the mics from the board.

    #45942
    Profile photo of [XAP]Bob
    [XAP]Bob
    Participant

    And sometimes I wonder about that 😉

    #45946
    Profile photo of Andreas
    Andreas
    Moderator

    …yes, switching off the mikes may also enhance the concert experience from time to time… 😉

    Maybe using a different mike (i.e. supercardioid) would help.

    As Bob said, first check what is causing your feedback. A low end boooom normally originates from the room and may be dealt easily with the high pass filter. For higher pitched feedbacks I’d check the monitors first.
    And, yes, the GEQ is (for me somewhat) too coarse to handle feedback without degrading sound, I’d prefer to use the PEQ (and sometimes wish to have more bands and higher Q).

    …and, yes, in analog times I am using the B* DEQs for feedback cancellation, their 1/60 octave notch filters are pretty effective and nearly not audible….

    #45952
    Profile photo of gilly
    gilly
    Participant

    Tim mentioned using the RTA to find the offending frequency but Bob you said using the GEQ to apply some cut to this freq is sort of crude and Andreas said PEQ is better. So let’s say we fade up the vocal mic until we hear feedback howl and we note on the RTA that the level is highest at 1khz. What is the difference in using the GEQ to notch out a 6db at 1khz against going into PEQ, selecting 1khz on one of the bands,select a very narrow width adjustment (high Q) and reducing by 6db. Is it not the same effect?

    #45954
    Profile photo of cornelius78
    cornelius78
    Participant

    The geq centres the cut at 1kHz, but will also affect get 1/6th of the octave either side of the centre freq (for a total of 1/3 of the octive for that geq fader: that’s why it’s called a 1/3rd geq.) If you use the peq and get the Q to be narrower (can go as narrow as 1/9th of the octave on the Qu, other desks (eg Midas Pro,) can get even narrower,) you’re cutting out less of the sound and still eliminating the feedback. To borrow an old analogy, using the geq instead of the peq is like using a hatchet instead of a scalpel; it works, but it does a lot of collateral damage in the process. Furthermore, what if the feedback isn’t precisely at 1k, what if it’s a bit higher or lower? The freqs on the geq are fixed and to get rid of the feedback you might have to adjust multiple ones, butchering the sound even further. The peq is sweepable, so you can sweep to the exact frequency that’s feeding back and notch it out properly.

    #45956
    Profile photo of [XAP]Bob
    [XAP]Bob
    Participant

    Yep, it’s all about accuracy – that’s why (if you have time) sweeping a narrow “boost” will find feedback frequencies more accurately than the 1/3 octave RTA.

    #45957
    Profile photo of timhum
    timhum
    Participant

    Thanks for the clarification cornelius78, I think that next time I am in that awful room I will use the PEQ to notch out the primary offending howls and use the GEQ to deal with the rest of the offending frequencies. I think I took out about 6 or 8, rolled off the bass and ever so carefully edged up the level during the performance to establish the max loudness possible. It was nearly enough, pushing the level even further, the room became very lively like I had added some sort of reverb and I backed off from that a tad. My first PA job and I nearly wished I had not volunteered! Perhaps it is a good case for the automatic howl suppression kit.
    I was somewhat vague in my previous post about the iPad app. It is called FFT Plot and gives a graphic showing the entire frequency analysis of what is going on in the room including the value of the loudest frequency, ie. the howl but it does not have to be loud enough to offend the ear as you can see the ringing develop before the full blown howl develops.

    #45958
    Profile photo of Dick Rees
    Dick Rees
    Participant

    The geq centres the cut at 1kHz, but will also affect get 1/6th of the octave either side of the centre freq (for a total of 1/3 of the octive for that geq fader: that’s why it’s called a 1/3rd geq.)

    No. GEQ filters affect program material over as much as an octave, 1/2 on either side, depending on the depth of the cut.

    It’s called a 1/3 octave EQ because of the spacing of the filter centers at 1/3 octave intervals.

    I think I took out about 6 or 8, rolled off the bass and ever so carefully edged up the level during the performance to establish the max loudness possible. It was nearly enough, pushing the level even further, the room became very lively like I had added some sort of reverb and I backed off from that a tad. My first PA job and I nearly wished I had not volunteered! Perhaps it is a good case for the automatic howl suppression kit.

    If you are having to use more than 3 or 4 filters to deal with room/system issues, you have other problems such as speaker type and placement, mic type and placement, etc. You’ll learn these things in time. It will be better with PEQ since you will be able to get more “surgical” with the narrower filters.

    As to the “automatic howl suppression”…forget that. They are not a cure-all and will not function effectively for you until you understand what they can and cannot do and how to make them do it…hardly “automatic”.

    Once you understand SYSTEM DEPLOYMENT and can effectively use the PEQ to deal with pesky room resonances you will have enough knowledge to get a “feedback destroyer” to work for you as an “automatic parametric equalizer”, which is what it really is. There are some good ones such as the Sabine GraphiQ, but not exciting the room with the system in the first place is the way to go. But that’s the basic live sound knowledge you’ll have to get.

    You cannot use EQ of any type to compensate for poor speaker/mic choice and placement. Prevention/cure as the old adage reminds us.

    #45967
    Profile photo of cornelius78
    cornelius78
    Participant

    No. GEQ filters affect program material over as much as an octave, 1/2 on either side, depending on the depth of the cut.

    It’s called a 1/3 octave EQ because of the spacing of the filter centers at 1/3 octave intervals.

    My bad, thanks for the correction.

    #46556
    Profile photo of coffee_king
    coffee_king
    Participant

    Thanks for your help everyone I’ll be trying out your advise later on this evening.

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