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Old 07-18-2006, 12:13 AM   #1
Spon
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Default No feedback - am I being protected from myself?

I'd like to run a bunch of VST and DX effects in a feedback loop. Yes, I know I get latency delays, but that's not a problem, just a characteristic - they just behave like more delays. Given that I'm trying to build a giant oscillating behemoth with multiple distortions, compressors, delays, modulation effects, etc., a couple more short delays aren't going to hurt anything.

But, when I try, whether with sends/receives or via ReaRoute, some of the channels appear to turn off - the signal drops to zero.

Is there 'feedback loop detection' somewhere in the audio chain?

for example..
put a percussive part in track 1
send it to track 2
insert some effects in track 2 and record/monitor it post fx
send track 2 to track 3 post-fader
insert some more effects in track 3, record/monitor post fx
send track 3 to track 4
add more tracks until your CPU use gets above 50%
send the last track to track 2

as you add tracks, the meters show the signal propagating down the chain. When I add the feedback loop, they all shut off.
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Old 07-18-2006, 12:21 AM   #2
Justin
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Would feedback, with the delay being the ASIO/audio system blocksize, be sufficient? that could be done with relative efficiency...
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Old 07-18-2006, 12:50 AM   #3
Spon
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I guess I just assumed there would be either one or two buffers, depending on whether the track needed an input AND output buffer.

I also assumed that if I put all the FX in one track, I'd get one delay. If I strung them over four tracks, in series, I'd get four times the delay, and level controls at more places in the patch.

Do I care whether it's one, two, or four blocks of delay? Not really. I just want to know whether I'm missing some subtlety of the routing, or if it really didn't work.

It looks like reaper's routing ALREADY allows feedback (after this basic patch worked, I planned on using reaper's routing to set up multiple feedback paths among a network of 10 to 20 plugins.) So I'm not sure what it is you're considering implementing. If feedback is currently blocked intentionally, my dream implementation would have the options
1. warn, feedback blocked
2. no warn, feedback blocked (current reaper)
3. feedback allowed, +40db level stops feedback
4. feedback allowed and not monitored
with 1 being the default.

Otherwise, is it possible that ReaRoute allows this already, and I just don't know how to use it? I tried taking the previous patch, and sending the output of the last track to ReaRoute 14-15, and the input for the first track from ReaRoute 14-15, thinking that would work. No banana.

I DO get feedback if I use the ASIO patching in my kx driver - with latency, of course. But this requires I make a special patch for both reaper and the kx driver.

I actually do this kind of patch in AudioMulch regularly, as well has having done live performances with real hardware (guitar fx, guitar amp, no guitar). On the other hand, I think normal people are going to have little use for feedback loops in their effects patches, and it seems reasonable to me that someone who wants this ought to have to deliberately make it happen.

My best solution is for someone to tell me "reaper already does this - you just have to do this and tweak that."
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Old 07-18-2006, 01:01 AM   #4
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Currently REAPER doesn't allow feedback, as you've found. ReaRoute is for interfacing with other applications.

I was suggesting that I could add a feedback option, and that it would (as a requirement) add a delay of the asio blocksize at the time of the feedback.

You make a good suggestion about the different modes, initially I will likely just do two modes:

1) no feedback (like current reaper), with note saying that you can enable it in the preferences (or should it be project settings), if you desire.

2) feedback mode.

I just hacked it up to work, and it works quite well, actually.
It's worth noting that since the ASIO blocksize is very small, the feedback happens FAST, and can be very nasty-- so you'll want to put your own delay VST (or JS) in one of the plug-in chains..

Anyway.. I guess the real question is, is having the built-in delay of the blocksize acceptable, and is relying on the user to add their own delay in reasonable?

-Justin
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Old 07-18-2006, 01:22 AM   #5
Spon
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It's great for me. Ultimately the less delay, the more different noises you can make. But super-short delays can be speaker-blowers. Generally I hang a softlimiter on whichever outputs I'm going to monitor. Softlimiting generally makes for better-behaved feedback loops anyway.

Since zero delay is pretty much impossible, one ASIO block is godlike awesome. And unless you are trying to do accurate physical modeling in reaper, the small delays have an effect, but they aren't important. It's just hideous noise, after all. Seriously, six distortions, three phasers, six flangers, a graphic EQ and an FFT diffuser - are you really going to notice an extra 15ms of delay in the loop?

BTW, what happens to plugins that try to compensate for latency while in a feedback loop?
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Old 07-18-2006, 01:36 AM   #6
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Quote:
Originally Posted by Spon
It's great for me. Ultimately the less delay, the more different noises you can make. But super-short delays can be speaker-blowers. Generally I hang a softlimiter on whichever outputs I'm going to monitor. Softlimiting generally makes for better-behaved feedback loops anyway.

Since zero delay is pretty much impossible, one ASIO block is godlike awesome. And unless you are trying to do accurate physical modeling in reaper, the small delays have an effect, but they aren't important. It's just hideous noise, after all. Seriously, six distortions, three phasers, six flangers, a graphic EQ and an FFT diffuser - are you really going to notice an extra 15ms of delay in the loop?

BTW, what happens to plugins that try to compensate for latency while in a feedback loop?

Delay compensation should still function as normal, just when there's feedback present, at some point a track starts reading the last block of a receive instead of the current..

But just to be clear, some effects that have latency that is compensated (say, an FFT-based EQ like ReaFir), and phasers/distortions, may not really introduce delay... i.e. for experimenting I had to throw in a long jesusonic delay .. anyway expect something usable for this in .990 sometime tomorrow I hope.

-Justin
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Old 07-18-2006, 01:40 AM   #7
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I'd be very keen to have some kind of safety mechanism on this - user proof too. Not only for speakers but also for ears. Yes, I realise that it's along the lines of warning people not to dry their dog in the microwave, but a few times a year I do something feedbackky accidentally, and every time my brain just freezes and heaven knows how many seconds go by before I hit the right button. Maybe something on the master - more than x number of samples at more than +5db, mute the master? It's only monitoring...
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Old 07-18-2006, 03:47 AM   #8
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+1
what Art said.

All of us will, sooner or later, "accidentally" create a feedback loop and promptly blow our speakers / ears/ bank balance.
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Old 07-18-2006, 06:13 AM   #9
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Quote:
Originally Posted by DarkStar
+1
what Art said.

All of us will, sooner or later, "accidentally" create a feedback loop and promptly blow our speakers / ears/ bank balance.
+2
Sounds like an accident waiting to happen.....if there is ever an option for this, it should be kept under lock and key and a big 'WARNING' sign..

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Old 07-18-2006, 11:30 PM   #10
Spon
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Hmm.. some people dislike it so much they FR something to protect themselves from it...Muhahaha! I must be onto something!!!

I agree - the anti-feedback protection currently in reaper should be default. The more professional side of me understood why it didn't feedback. But if it did, I would definitely use it.

On the other hand, people complain of feedback already happening, and ask for a built-in limiter or detector - I'm not sure how, I worked at it and didn't find it easy to get feedback at all.

One option is a detector that turned the volume down (say a 20db mute with a 3 second recovery time). This could be a godsend in a studio or workstation situation, but it would be so damaging if used badly (i.e. front-of-house mix) that I'd want it to be a plugin or obscure option too.

Another option is to just patch a limiter or softclipper in the master or monitor path. This tames feedback to some extent, and some limiters can be tweaked to produce the effect of option 1.

Another option (does reaper already do this?) is a "limiter" that turns down the master mixer whenever the output level goes above 0db, *and* remembered the old setting, so you could see what change happened. This is a bit more general a tool than feedback reduction. Even so, it isn't something I'd want messing around on a live track while I recorded.

The people who actually HAVE problems with feedback - what are you doing when it happens? What reaper settings lead to feedback?
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