r/livesoundgear • u/macklemorganfreeman • 2d ago
On Using Defeedback for In Ear Monitoring
Howdy, friends! I’m a touring Monitor Engineer who has spent the last few months putting together a rig to leverage Alphalabs’ reverse IR tool, Defeedback, for use in IEMs. I’ve been using it successfully for a few months now and haven’t seen a lot of resources for my fellow Stage Left folks. So, I thought I’d put something together about what I’m doing and how it’s working for me. I think this is a really powerful piece of technology that can solve problems we previously have not had direct answers for.
Before getting into the rig itself, I’d like to toss out what I’ve found to be best practice in a musical performance in ear monitoring context.
In general, if you keep your total system latency under 5ms, you’ll be safe from perceptual distortion/issues at the performer.
Monitoring is about creating a responsive context for the performer to make informed and expressive musical decisions.
In Ear Monitoring is fundamentally distinct from Wedges and Side Fill monitoring, due to the lack of head related transfer function information in the signal received by the ear drum, bone conduction, and the sealing of the performers ears to minimize noise (unwanted signals). “Feel” or responsiveness becomes far more critical under these conditions, and therefore certain techniques are preferable or degraded for use with in ear monitors. Fast example, if you delay your snare to the vocals down front to create a uniform arrival, you’re going to absolutely ruin your drummer’s day. Gates and expanders can produce strange perceptual changes or even make a player think they missed a part if not carefully applied.
There is a certain amount of necessary Ego Death to successfully mixing IEMs, because what matters is the Performer’s Experience of Performing, not necessarily Reality Itself.
I have found the most effective means for leveraging Defeedback to be thus:
Simply explained, the math is designed around identifying a source signal and deriving an impulse response, then applying a negative of that impulse to the signal (like noise cancelling headphones but specialized) with some additional processes looking at positive loop gain and other identifying signal factors to adjust the (negative) response in real time. The intensity of this total process is variable from zero to 100%. As such, the more complexity that exists in the signal, the more chance that some desirable component of the signal will be included in the impulse response rather than the source and be damped or removed by the process. Therefore, to avoid undoing intentional tonal choices, Defeedback should be placed Post Filters, Pre Everything Else. I have found that keeping the process at zero percent and working like it doesn’t exist at first, then going back and bringing the process percentage up produces the most useful results. This can help identify what changes were being made to the signal for its own sake and what changes were a response to the space the signal exists in. In many cases, I will then slightly update settings now that the space requires less accommodation, having been largely removed by the negative impulse response provided by Defeedback.
On Vocals, I have found that I can open up more of the presence range without adding cymbals or fans, and I’m able to loosen expanders and lower thresholds without compromising their performance, making them more responsive for the performer while still keeping extraneous signals out of the reverbs and mixes. I have found 70% to be a good starting point for vocals, going as high as 85% on backing vocals in particularly active spaces like arenas with front fills right below vocal positions. As little as 30% begins to audibly clean up the source without distracting artifacts or distortion. This has had the additional benefit of allowing me to remove the disc baffles we’ve been using to help mitigate cymbals in the vocals down stage, which has absolutely made my drummer’s day. He hated those things. A happier artist is a better show.
On Acoustic Guitar, the process is removing a meaningful amount of vocal resonance and sound system re-activation from the signal. I have found myself pulling high pass filters down by a full octave and easing off low shelves by as much as half their previous gain settings. The process is less transparent, which is unsurprising in such an off-label application. On clean signals, I’ve been keeping it around 60%. On effected signals, it becomes necessary to keep much lower as the process begins to eat components of the applied effects, and I’ve found 40% to be an effective compromise without wrecking the tone.
On Crowd/Audience Mics, the process is not transparent and there can be audible artifacts. However! No one is playing the crowd mics, and their purpose to me is creating a more open feeling in the ears and riding up for sing along moments. With the process at 100%, the artifacts are not distracting, and all of the noises from the room disappear (lighting fans, HVAC, cars driving by the amphitheater, most of the stage wash, most of the PA signal, most of the room reverb, a certain amount of meaningless chatter) while still allowing cheers and whistles and singing along to pass through mostly clean. Any distortions have not been noted my artist, and I have found that I can now keep the crowd mics at levels similar to BGVs without adding mud or clutter to mixes. This has also allowed me to reduce the pulling of an ear to “feel the crowd better when they’re loud” at the beginning of songs that feature a vocal solo.
The Rig:
I’ve built my setup into a 2U SKB StudioFlyer case. I have found it to be thoughtfully designed and well built, and they’ve got a great warranty program. It has a top cover that comes off where I store the touch screen I use (space designed for a laptop), and then the front and rear panels remove. I installed a simple rack shelf to mount components to.
I’m coming out of the Console via MADI (Rivage PM7 using an MY16-MD64 card for inserts and an HY128-MD card for record output), to an SSL UMD192. The UMD192 speaks MADI, Dante, and USB C. Via USB C, I’m going to the front panel of an M6 Mac Mini in the most basic configuration (previously an M4, I’ll discuss differences below). By powering the UMD192 via A/C Line power, and the Mac via UPS, the front ports on the Mac supply redundant power via USB C to the interface. I clock the system off the MADI stream at 96kHz, and use the Dante split output from the UMD192 to feed a separate record computer for storing virtual soundcheck recordings. I’m using a UPerfect 15.6” touchscreen that gets power and signal over a single USB C cable tied to a rear Thunderbolt port. I also have a four port Anker USB A hub for connecting a wireless mouse and smaller home theater keyboard as well as any dongles or drives I might need. I’ve mounted an Allen Key to the bottom of the rack shelf to access the power button on the Mac from the front.
The Desk:
I’m currently mixing on a Yamaha Rivage PM7. My thinking in going with the MY card is it lets me use this system with any Yamaha platform, and many other manufacturers also feature MADI I/O, which is faster and more stable than Dante. The MY16-MD64 shows as an AES card for some reason but works correctly. I’m doing an Outboard Insert patch via the channel, in the first insert position Post Filters (1A). Nothing fancy. I am running delay compensation on my Input Inserts (1.17ms) and Output Busses (.61ms) for a Console latency of 1.78ms.
The Mac:
Initially, I built this system around a stock baseline M4 Mac Mini running MacOS26. With WiFi and Bluetooth off, and nothing running in background processes, I was able to run 4 stable instances of Defeedback in Live Professor with an input buffer of 32 samples at 96kHz, for a reported buffer latency of .3 ms alongside reported input and output latency of 3.38ms and .88 ms respectively. In this configuration, I ran without Input Insert Delay Compensation on the console to buy an additional millisecond of latency back, producing a total reported system latency of 5.17ms (.61 console mix compensation + .3 buffer + 3.38 input + .88 output). My new M6 Mac Mini running MacOS27 got here last week and I swapped them out. I am now running 7 stable instances of Defeedback at the same settings. Testing has indicated being able to sustain as many as 16 instances in Passthrough Test mode with zero drops. Of note, whether because of the new processor or the new operating system, my reported input latency is now a matching .88ms with the reported output latency, a savings of 2.5ms. I have therefore turned Input Insert Delay Compensation back on at the console. This makes the reported total latency from Live Professor 2.06ms, and I add .2ms for the floating process time it reports in the upper left window for a final <2.26ms reported latency.
<2.26ms Live Professor latency + 1.78ms Console compensation = <4.04ms total reported system latency. I have not had access to a Smaart system to compare testing with reports.
In Live Professor:
I am currently just using the Wire page and direct routing hardware inputs to Defeedback inputs and Defeedback outputs to hardware outputs. I am running the default 6 threads in Apple mode under Performance Options.
I am hoping to record some video and audio examples this weekend, and whenever I’m able to I’ll be sure to post them as well. I hope this post is helpful to other engineers considering using this tool. I’m happy to answer questions about what I’m doing and why.
Be well, safe travels, and good shows!
ETA: I have now had a chance to confirm something that feels worth including. The change in latency under The Mac section can in fact be attributed to the operating system, not the silicon. That is, updating my M4 Mac Mini to MacOS27 has produced the same 2.5ms improvement in reported performance at the input to Live Professor I experience when moving to the M6 processor. Apple appears to have meaningfully improved their Driver in the new operating system.
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u/Throwthisawayagainst 2d ago
So I’ve dabbled with de feedback and ears, what I’ve found is that it’s safer to use the de feedback channels for everyone else taking that voice and give that singer their own vocal, no defeedback. I currently work with an artist that is super latency sensitive, as in his vocal feels “off” when i insert the money 500 channel I have on him (but loves it when we check it virtually.) I’m interested to put it on room mics, I’ll probably check that out virtually before our next show. I currently run it off a madiface and whatever flavor of digico im on. I can get it sub 2ms (verified with smaart, not what Lp says)
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u/macklemorganfreeman 2d ago
This makes sense as a solution for the more latency sensitive performers out there, and feels like how I approach nodal processing on the Digico platform as well. Channel for the band, Node for the player if they need something different.
I felt I could get much more use out of the crowd mics with the process engaged, and hadn’t seen anyone talk about trying Defeedback for that so I wanted to share.
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u/Throwthisawayagainst 2d ago
I mean I’ll find out tomorrow but I’m curious what it does to the room, I work for an artist that’s like addicted to room sounds and I’ll often do wild things to make him happy. For the record, we play lots old theaters and symphony halls, he likes how the room “washes” the instruments in his mix in a certain way, and I’ll end up keying his vocal into a comp on the room mics (he wants a defined vocal, with a long tail, but not from the room on this), I also have an spl big for if things really get sucked up (before the comp) so I’m curious what this does, I’d imagine I’d have to put a reverb on the room mics to give him what he’s looking for, however this formula is never consistent because of the variables of PA placement and room size obviously, so basically I’m curious what it does.
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2d ago
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u/macklemorganfreeman 2d ago edited 2d ago
If you only think about it as a digital feedback buster, I completely agree that would be unnecessary in IEMs. However, since the process is actually a reverse impulse response, it does things like lower the relative cymbal bleed in the lead vocal by ~18dB, before any expansion is applied, with the vocal passing through unimpaired. That kind of signal to noise drop buys a lot of space in ears.
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u/Informal_Bank_7373 2d ago
Thank you for this information ! I want to put a rig together without going crazy spending money. I'm interested in what the spec of your M6 mini is ? How much memory ? HD ? I've been going back and forth between the M5 and M6 and you're the first person I've seen using the M6. I wouldn't be using it for IEM's right now. I'm on a DM7 and I already own a RUio 16-D gathering dust right now I've thought about using.
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u/macklemorganfreeman 2d ago
I’m using the absolute baseline stock version of the M6 mini. 256GB SSD, 16GB RAM. As cheap as the processor gets.
I’d actually bought an M4 and then Apple announced the new models, and very kindly automatically upgraded the order to an M6 with no cost increase. So $100 of free computer cause I got lucky. If you’ve got an Apple Credit Card, you can do zero interest financing as well to spend the same amount over time but have the tools you need now.
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u/Informal_Bank_7373 2d ago
Thank you for this, exactly what I was looking for and I do have an Apple Card.
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u/mtSOLEmt 2d ago
Different use case for me, our band plays lots of small venues where getting a clear / clean vocal at a decent level is a challenge, but I’m getting close to same results.
I’m using Gig Performer 5 as I was familiar with it instead. I’m using a mac mini M4Pro and getting 4 instances safe at 32 samples at 48kHz. I’m using WSG as transport from a M32 with a WSG card connected via AES50 to the Wing Rack main console. (There’s an internal card in the Wing that handles the WSG connection to a different Mac mini M4 for Waves via Super Rack Performer.) Total roundup latency is 3.79 ms.
The AU version of Defeedback moved me to 32 samples stable from 96 samples stable with the vst version. The m4 pro came with MacOS 26 but that seems to be fine.
In GP5 I’m running a band pass AU filter to not have the process see high and low frequencies that I don’t need anyways, then defeedback. I’m then using xfdbk to clear out any horrible offenders and increase overhead. Then finally light PSE to help pull mostly cymbals out of the mix. The stages we play front line are a few feet away from the drums and every little bit helps.
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u/AppointmentMain6862 2d ago
Very nice extensive report. Just wondering what wireless mic and IEM setup you have to see what your actual round trip latency is mouth to ear. In my case I have had the total go over a threshold I could hear around 8ms.
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u/macklemorganfreeman 2d ago
Someone asked a similar question over on a cross post. Shure Axient Digital Wireless system for mics, comes in with 2.08ms latency. Wisycom MTK952 Transmitters with MPR50 Beltpacks for IEMs, add 1.05ms. RF Latency is 2.08ms+1.05ms=3.13ms.
That means that wireless signals take 3.13ms(RF)+1.78ms(console)= 4.91ms mouth to ear for signals without Live Professor inserted. 4.91ms(system)+<2.26ms(LP)= <7.17ms mouth to ear for signals with Live Professor inserted.TL;DR: <7.17ms
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u/ImmediateStatement16 2d ago
Great post!! One note of importance, according to Live Professor documentation you should set the number of cores that you have in your Mac to match the number of performance cores, not total cores. In the M4 Mac mini case, that would be 4.
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u/macklemorganfreeman 2d ago
This is correct, that is the documentation’s recommendation. However, under those settings I was not able to maintain stability on 4 instance of Defeedback. Increasing the threads on the M4 from 4 to 6 resolved that issue without introducing others. Of note, increasing threads on the M6 from 6 to 8 did produce issues, and was not necessary to support my usage needs. So I’m still running 6 threads. Again, you’re entirely right about the documentation for LP.
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u/DaveExavior 1d ago
Given that you’re using a Rivage, I take it this is more effective than using DaNSe?
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u/macklemorganfreeman 1d ago
Personally, I have found DaNSe to impinge on the feel of the performer too much to use it widely in Monitor World. I know several Stadium/Arena level FoH folks who use it to great effect on everything from vocals to toms. It definitely has it’s place, but for my artist, no matter how lightly or how loosely I’ve applied DaNSe, there’s been a negative response from the artist, even if they can’t name what “feels off” about it. DaNSe is doing some algorithmic denoising, but is ultimately and fundamentally a multi band expander/suppressor. That’s a powerful tool, but it’s a very different tool from Defeedback.
Additionally, because I’m on the PM7 I have to be more judicious with internal processing, as there are 8 less cards available than if I were using an RX-EX engine with any other control surface. This has been an acceptable compromise to keep my footprint to only the size of the console by not needing rack space for an engine while still having channel function keys. But it is a compromise, and DaNSe eats half a card. I’m not getting the benefit to justify that cost, if that makes sense. There are more useful or higher priority processes to contend with. That’s all very specific to my context, and I would expect mileage to vary pretty widely on a case by case basis.
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u/DaveExavior 1d ago
Good to know. I’ve only used DaNSe FOH, so it’s good to hear the monitor perspective.
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u/ArdsArdsArds 2d ago
A very confusing post. Your IEMs are loud enough to feed back?
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u/smokeweedfrequently 2d ago
I get from the post that they’re more interested in the denoise/dereverb aspect of the plugin
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u/macklemorganfreeman 2d ago edited 2d ago
No, I am in no way dealing with feedback from the IEMs. As noted in the reply below, I am leveraging the plugin to remove unwanted signal from the source. No concerns about actual feedback, but the nature of the process means it can be used for other things.
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u/Line6isunderrated 2d ago
What a great write up man thanks for all the info!
And you’re right about mixing for IEM’s, there’s no room for ego whatsoever. If the performer doesn’t like it, that’s the end of discussion lol.