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  • Question about VST feedback loop technique

    Can somebody elaborate here about VST feedback loop technique?

    I tried to build some constructions from VST plug-ins in VSTHost,
    but so far the only result is kind of "speaker-blower" or "ear driller" ;)
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  • #2
    Pretty obvious to suggest a gain vst in the feedback loop and a limiter after the final plug?

    Only time I've really played with this was using a Reaper fx chain, you can use bufsaves to send the audio back to earlier in the chain. Plenty of opportunity for speaker-blowers too...
    Latest release: never to be repeated

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    • #3
      Originally posted by GaryG View Post
      Pretty obvious to suggest a gain vst in the feedback loop and a limiter after the final plug?
      I tried only GGain between links in my FX chain. Now I will try to go with limiter. Thanks for tip!
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      • #4
        conceptually feedback works in most vsts work like this:

        You go through the first instance of the program following the entire effects chain.
        When you get to the end of the effects chain, if you wish, you may run a certain portion of the master output through a feedback loop, which does nothing more than reinsert the sound coming from the master to the base input.
        In simpler terms, you take the output and put it back in the input.

        SO, if you have too much of your feed going through feedback, you will start gaining more volume because the feedback module is not set low enough so that the output drains away over time.
        If you're aren't careful you will get your explosive speakers all explodey and the like.

        My suggestion regarding feedback modules is that you start from 0% feed and work your way up in small increments.
        3%
        5%
        8%
        etc.
        give each new increment a few seconds to either stack in volume or dissipate so that you don't jump too far in the danger zone.
        as soon as you hear it start to get loud, back down one increment and that is your 'safety ceiling'

        waves with higher harmonics are less prone to this reaction.
        raw waves, though. Such as sine waves, are quite prone to the explodiness of feedback, so be careful.

        ProTip?: Use a limiter when experimenting with modulated sound design, especially in sequences where you will be matching waves. (whenever I'm experimenting making my own synths I tend to just put a limiter on my master during the session)

        Pros?
        Feedback can, if used effectively, double down your vocal formants which makes it quite an effective 'humanoid pad' generator.
        It can also help establish and maintain volume, along with extending release times by a small amount of time.
        If rerouted, you can apply 'fed-back' signal to other effects chains to build a complementary to the original. This also negates the possibility of untimely explosions.
        If Distorted you can get some raw mechanical resonation if you control your overtones appropriately. (I would suggest closely monitored unisono)

        Cons?
        Your speakers might explode, and the dynamic changes can easily cause hearing loss.
        Sometimes, if you're not careful, your dynamic layer will absolutely shatter and it may interfere with your use of the stereo field.

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        • #5
          I have used many times feedback loops to create interesting sounds. Mostly I have done it in Ableton Live, but I have also used Reason and Reaper.

          A feedback loop in your signal chain creates 2 problems:
          a) general volume buildup
          b) specific frequency buidup

          These are the two things that will result in ear-piercing, speaker-shredding and generally unpleasant and unusable sounds.
          If you want to create a feedback loop that is useful for sound design,, you must first eliminate these two problems. And here's how...

          In Ableton Live, you create feedback loops by directing the output of one channel (call it C1) into another channel (call it C2). You now also direct the output of C2 back into C1.
          Imagine you have another 2 channels. One called Input (which is directed to C1) and another channel called Output which feeds from C2.

          Any sound from the Input channel will enter the feedback loop between C1 and C2 and the sound that is "circulating" in that feedback loop is 'collected' at the output channel (which outputs to the Master channel)

          Before you start inputing any sounds. There are some things you must (or really should) do.

          1) lower the gain on C2 to, say, -10dB. You can adjust this later, but you definetely don't want it to be 0dB, otherwise any sound will build up to ridiculous levels.
          2) To be sure your speakers and your ears don't explode, you want to put a limiter on the Output channel. Set the max level to, say, -3dB.
          This assures that the sound comming out to the speakers or headphones will never exceed a sensible level. Make sure also that you keep the volume knob on your sourcard / stereo / amplifier at a low setting.
          3) Even if you apply point 2 above, volumes can still build up in the feedback loop between C1 and C2 to very high levels. Although these sounds will be tamed to an acceptable volume by the limiter on the Output channel, digital clipping would still occur inside the feedback loop and produce horrible sounds. So I suggest adding a second limiter inside the feedback loop. You can set this one also to -3dB.

          Points 1 to 3 deal with problem A "general volume buidup".
          Before we look into problem B, I must explain something else about feedback loops. A feedback loop has a 'time constant', this is the time that takes the signal to complete the feedback loop and come back to the point where it is mixed with the input sound. Lets call the time constant T.
          If a sound enters the loop and has a frequency of 1/T, it will be in phase with the input, so the waves will add up perfectly producing a new sound of the same frequency but higher volume. As that new sound goes round the feedback loop again and meets itself again at the input, the volume is boosted again, and so on.
          This means that the feedback loop will strongly boost sounds around the frequency 1/T (and the harmonics 1/2T, 1/3T, and so on...)
          That is why the classic feedback between a mic and a speaker produces those whistling sounds - that is the 1/T frequency being boosted to ear-piercing levels.

          So here we introduce some new rules
          4) You want your feedback loop to include a delay plugin. Make it 100% wet and with feedback = 0 (if feedback is different from 0 you are creating a second feedback loop inside your loop!). You probably want this to be 50-200ms at this point.
          5) At this point you can open the Input channel and start feeding sound to your feedback loop and listening. All you will get is a simple boring delay, check that the volumes are OK and adjust if needed.
          6) You now need to add effects that will make your feedback loop do something interesting. I suggest effects that mess up the frequency contents of your sound (pitch shifters, ring modulators, some granular effects) are good ones to try. By messing up the frequency contents of your sound, you prevent that certain frequencies build up creating problem B. This should also create some good and interesting sounds.

          From this point on the 'rules' are less important and your creativity should now take over.
          7) You can now add other effects (chorus, flanger, distortion, etc) and also play around with the delay time and even introduce delay feedback.
          8) the delay effect witin your feedback loop may already create a kind of "reverbering" or "ringing" effect, but often things sound better with a reverb effect added (either in the output channel or inside the feedback loop itself).
          9) if you are after drone-like effects go crazy on the reverb. Granular effects also work well for this.

          Have fun and do let me know if this was useful (sorry for the post being a bit long)
          Some sound examples:
          http://www.freesound.org/people/AlienXXX/packs/11333/
          http://www.freesound.org/people/AlienXXX/packs/8399/
          Last edited by AlienXXX; 06-20-2014, 01:57 PM.

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          • #6
            How to build feedback loop in Reaper? I am kind of lost in its routing options... :(
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            • #7
              If you select to display the routing matrix [Menu View -> Routing Matrix] should be easy to assign which channel(s) output into which channel(s) with just a few clicks.
              Remember to disable the Master Output out (leftmost column) on the channels that are supposed to be part of the feedback loop, and just leave it on for the one channel you intend as output.
              Remember to include the limiters, lower gain on the feedback channel and use sensible volume settings for your speakers/headphones.

              Let me know if it worked.

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              • #8
                Originally posted by AlienXXX View Post
                If you select to display the routing matrix [Menu View -> Routing Matrix] should be easy to assign which channel(s) output into which channel(s) with just a few clicks.
                Remember to disable the Master Output out (leftmost column) on the channels that are supposed to be part of the feedback loop, and just leave it on for the one channel you intend as output.
                Remember to include the limiters, lower gain on the feedback channel and use sensible volume settings for your speakers/headphones.

                Let me know if it worked.
                C1 sends to C2. C2 sends to C3. C3 sends to C4 and C2. C4 sends to master. Limiters on C2 and C3. Source synth on C1, FX on C2 and C3.
                But no sound on channels different than C1 (I checked enabling sends to master for a while and bypassing FX).

                routing.jpg
                Last edited by MetaDronos; 06-20-2014, 05:02 PM.
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                • #9
                  Go to File -> Project Settings
                  Select the Advanced tab and tick 'Allow Feedback in Routing'
                  (this option is off by default)

                  Should work now.

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                  • #10
                    Originally posted by AlienXXX View Post
                    Go to File -> Project Settings
                    Select the Advanced tab and tick 'Allow Feedback in Routing'
                    (this option is off by default)

                    Should work now.
                    And that was the element I always missed before (And I tried more than once ;) )
                    What a vast universe of sound I just opened!

                    AlienXXX, thank you very much! :highfive:
                    SoundCloud // FreeSound // Twitter
                    Get exposure for your electronic music through WEATNU.COM independent promotion network.
                    "Shortwave" - collaboration album with Ager Sonus

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                    • #11
                      And here is my fresh track, involving feedback loop technique (in drone layer):

                      http://soundcloud.com/metadronos/ailivimphos
                      SoundCloud // FreeSound // Twitter
                      Get exposure for your electronic music through WEATNU.COM independent promotion network.
                      "Shortwave" - collaboration album with Ager Sonus

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                      • #12
                        Originally posted by MetaDronos View Post
                        And here is my fresh track, involving feedback loop technique (in drone layer):

                        http://soundcloud.com/metadronos/ailivimphos
                        You are fast!

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