Any tips for quickly reducing residual feedback on a mic channel?

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This topic contains 23 replies, has 14 voices, and was last updated by Profile photo of Giga Giga 4 years, 1 month ago.

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  • #63749
    Profile photo of coffee_king
    coffee_king
    Participant

    Hi Guys
    Any of you guys and girls got tips for quickly reducing residual feedback on a mic channel?
    Its mainly on vocal mics when trailing off a vocal. (This doesnt happen all the time)
    As it occurs and then fades away that quickly its not visible on the RTA so I cant really find it to drop it out on the GEQ/PEQ

    Just to advise my speakers/etc are positioned correctly, thus is more to do with the room sound and I’ve already removed the main problem frequencies to get maximum gain before feedback.

    Any thoughts?
    Cheers guys and thanks in advance.

    #63750
    Profile photo of MarkPAman
    MarkPAman
    Participant

    So you’re trying to identify one frequency that you can hear?
    Maybe download a frequency generator to your phone or iPad, plug some headphones into it, and then match it’s output to the feedback. This one works quite well:
    https://itunes.apple.com/gb/app/signal-generator-audio-test-tone-utility/id543661843?mt=8

    #63751
    Profile photo of WaihekeSoundie
    WaihekeSoundie
    Participant

    I’m interested in this answer too. Feedback can be really hard to pin down.

    If this is in sound check then I would try to figure out if it is in the FOH or monitors first– I’d try to isolate the worst channel and then I take it to almost feed then push up FOH and monitors each in turn gently to see which makes it feed. If it is the monitors then I’d be looking at their position re: the patten I’m using and equing them– setting the GEQ or PEQ and pushing up sliders to find the most problem freqs then pulling those down once found. If it is FOH then that can be tougher– looking at speaker placement and FOH eq. Sometimes it is what it is: every room has a threshold it seems and when you are close to it get things get really edgy.

    I’m sure you know this though.

    I often do a couple of 16 channel bands in tiny bars where everything gets real loud to get over the top of the drummer and elec gats. My main fears are those feedbacks that can occur mid show and you don’t know where they have come from: Someone turned up their gain? Moved their mic or monitor? Cupping a mic? That request a few mins ago from the sax or vocalist to be turned up in the monitor? Too much reverb on a vocal channel? Sometimes it is really, really hard to find and fix except to turn everything down a few DBs..

    Don’t get me wrong– I love quiet acoustic gigs–dream of them in fact — I just get lots of really loud indy rock with out of control guitarists and drummers.
    I would really appreciate any comments too…

    #63752
    Profile photo of WaihekeSoundie
    WaihekeSoundie
    Participant

    When trailing off a vocal– do you have a lot of compression on the vocal? If you have a low threshold and the compressor is clamped right down with a full signal it can hold back a feedback that can occur when the attentuation is lifted– . this would tend to be on the tail.. might be that?

    #63753
    Profile photo of coffee_king
    coffee_king
    Participant

    So you’re trying to identify one frequency that you can hear?
    Maybe download a frequency generator to your phone or iPad, plug some headphones into it, and then match it’s output to the feedback. This one works quite well:

    Hey Mark
    If only I had the time to do that 🙂

    #63755
    Profile photo of coffee_king
    coffee_king
    Participant

    WaihekeSoundie

    Thanks for your response.
    I dont use compressors, gates or anything. The only effect I use is a small bit of reverb on vocals when needed.
    Channels – All flat (Unless REALLY REALLY needed to be EQ’d)
    Occasionally use a bit of HPF on anything thats a bit bass ringy.
    GEQ – Dialled in as needed to remove any problem frequencies using RTA. (The main thing I do over ANYTHING else) – Yeah I know its better to do this on the PEQ but its MUCH quicker to do on the GEQ. I know all about Maximum Gain Before Feedback and positioning of speakers/mics/EQing to avoid this and I always leave plenty of headroom.
    No wedge monitors used (We all use IEMs).

    Its nothing to do with cupping mics, turning up gain, too much reverb etc

    I really have next to no time to set up and sound check as I’m doing both sound and performing at small to medium sized wedding venues, but would just like to be able to tweak this problem ever so slightly when it occurs. Its more of a trailing high ring (That dies off) than a full on feedback though.

    I appreciate any further comments/info.

    #63757
    Profile photo of Andreas
    Andreas
    Moderator

    No wedges and high pitch ring? Sounds like the PA is directly bleeding into the Mic(s). What kind of mics are you using? Tried supercardioids?

    #63758
    Profile photo of Roy
    Roy
    Participant

    You mention that all channels are EQd flat – I would be tempted to change that, especially for the vox channels. Get hold of the frequency response chart for your brand of mic and adjust the PEQ to compensate any peaks. I use only SM58s and a small cut from around 2k-7k helps with controlling the vibrancy. Some mid-cut (a little) helps too – at one gig I did several months ago (which had 5 vox channels), I had auto EQd the room using a DBX DriveRack, which caused a slight tail exactly as you describe on every mic. A small cut in the mids cured it. And to the point I could happily go beyond unity on the master fader and never get near feedback. And that also had 4 stage wedges as this band doesn’t like to use IEMs.

    #63762
    Profile photo of coffee_king
    coffee_king
    Participant

    No wedges and high pitch ring? Sounds like the PA is directly bleeding into the Mic(s). What kind of mics are you using? Tried supercardioids?

    This isnt an ongoing issue, just something I’d like to learn to avoid in the future.

    Vocal mics are all Sontronics STC-80.
    They do not really need EQing as such. (Check out some SM58 to STC-80 comparisons) – Like I said only when necessary. Although might be worth an look at if it was all happening all the time.

    My entire ethos for mixing audio is FLAT UNLESS NECESSARY.

    #63763
    Profile photo of Lee7
    Lee7
    Participant

    For all live work I use either Sennheiser e945’s or Audix OM-7’s and 11’s as they are Supercardioids and hypercardioid mics that are great for feedback rejection. But, on some occasions even these mics can struggle and that is using wedges that have been set up properly for the environment they’re in.

    Some rooms are just horrible to work in no matter what you do to try and tame the sound reflections.

    So one mic that I have turned too to get me out of a situation that is cheap as chips to buy, but sounds great is the RED5 RDV30. Also work well on guitar cabs.

    #63765
    Profile photo of [XAP]Bob
    [XAP]Bob
    Participant

    If you think it is the same each time then use the multitrack recorder and then do a very short loop to apply the RTA to find the frequency. Of course it’s never the same twice – figure what the feedback loop is, and try to eliminate it…

    #63768
    Profile photo of Dick Rees
    Dick Rees
    Participant

    When the note goes off, just find the pitch. For example, if it’s an “A”, it’s a multiple of 440. Pitch>frequency charts are easily found. Print one out and keep it handy.

    If you can’t tell find the pitch of the offending sound, hire help…

    #63769
    Profile photo of Dick Rees
    Dick Rees
    Participant

    OK, further suggestions.

    See what happens without the reverb. If it goes away with no ‘verb, EQ the reverb return.

    #63770
    Profile photo of airickess
    airickess
    Participant

    If you think you are going into a situation where that might happen again make sure you do a multitrack recording on the Q-Drive. Then if it happens you have it recorded and can listen to it to find out the frequency. Then you can notch it out on either the mic channel or, as Dick suggested, the FX return channel.

    #63771
    Profile photo of DoctorG
    DoctorG
    Participant

    As has been pointed out, the key to eliminating the feedback is finding the frequency at which it occurs. The RTA on the QU console should help you do that. Remember that the RTA follows the PAFL selection.

    I suspect that the problem may be that you’re trying to push too high a sound level for your room and the associated equipment. When the band quits playing, the signal that excited the feedback goes away. It could even be related to one device, such as an electric guitar, that puts out a particular frequency that sets off the feedback. Perhaps a guitar string or piano key is not being muted quickly enough.

    Fixing a problem like this can be difficult. Be sure you’ve tried all the things suggested here. Carefully listen and analyze your sound, then do the one thing that should work – turn down the sound level.

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