Tag Archives: Signal Flow

The POTH Commentaries – Turbo Surround Reverb

It was actually a “mistake,” but I kept it.

Please Remember:

The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.

Want to use this image for something else? Great! Click it for the link to a high-res or resolution-independent version.

Many things are discovered by accident. The glue for Post-It notes, for instance, was apparently an unintentional result of trying to create a much stronger adhesive. Gated reverb for 80’s-era drum tracks was also a case of “we didn’t intend to do this, but we liked it.” In the same way, Pigs Over The Horizon featured a vocal reverb with nifty characteristics that I didn’t plan out at all. In fact, at the time of the show I was a little surprised by its behavior, only realizing what I had done at a later time.

I had made the decision that any time-based FX processing for the show would be heard from the surround loudspeakers I briefly mentioned earlier. So, into the surrounds went my delay and reverb returns. What I noticed during the show was that, when Rylee, Grant, or Lisa “got on the gas” with a powerful vocal part, the surround reverb would launch like a rocket and punctuate that phrase. When they backed off, the reverb was much more tame. It was a cool bit of drama, so I kept it.

But what was really happening?

A habit that I’ve gotten into as an FOH mix human is to aggressively limit my main outputs. I don’t necessarily recommend my craziness to other people, but for me, the setup operates as a sort of automatic vocal rider, plus a method for keeping a mix in a bit of a box. I can, essentially, decide precisely how much the FOH PA gets to contribute to the overall volume of the show, and then set a “do not exceed” point. With the right settings in place (and a really excellent band on deck, of course) I can smack the limiter with the vocals – which helps to keep the lyrics on top without ripping people’s heads off. (Or, more precisely, it doesn’t rip people’s heads off any more than is necessary.)

So, for POTH, I definitely had that limiter in place. Here’s the key, though: It was NOT applied to the surround speakers. I had completely glossed over setting output dynamics for them. So, a big vocal part would happen, and go into the reverb send at full throttle. The dry signal would continue on to the main bus, where it got brickwalled…and the wet signal would blast through the unlimited surrounds. This “ex post facto” level adjustment to the dry vocal meant that my dry/ wet mix was suddenly tilted more in favor of “wet.” On the other hand, if a vocal part wasn’t smashed into the limiter, then my set proportionality was mostly untouched.

In a way, what I effectively had was an upward expander on the reverb send. A totally accidental one. Was it, technically speaking, “wrong?” Yes. Am I going to keep the basic idea around if we get to do the show again? Also, YES! It was cool! (Well, I thought it was…)


The POTH Commentaries – VCAs/DCAs

VCA/ DCA control is very handy, especially for “non-homogenous” routing situations.

Please Remember:

The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.

Want to use this image for something else? Great! Click it for the link to a high-res or resolution-independent version.

Author’s Note: This article is the first in a short series that addresses concepts and happenings related to Pigs Over The Horizon, a Pink Floyd tribute starring Advent Horizon and Friends.


When you start working with more full-featured consoles, you’ll likely run across something you might not have seen before. It’s a control feature called the VCA, or sometimes DCA on digital desks. What is this strange creature? What is it good for?

First off: A VCA is a Voltage Controlled Amplifier. The “D” comes in as a way to say that the same concept is being applied in the digital realm. (In my opinion, a digital system has it much easier, because you don’t have to work with analog circuit logic and the complexities of components or circuit layouts that come with that whole business.) The whole notion rests squarely on how it’s possible to build gain stages that modify the applied change to an audio signal in proportion to a separately applied control signal. If you have a number of control signal generators available, and can choose which control signal to apply to other gain stages, then you end up with a number of VCA/ DCA assignments. Connect a fader to the control signal generator such that the control signal is modified by that fader, and you have a VCA that’s intuitive to manage.

The VCA/ DCA concept, then, is that of a control group. When you assign faders to a control group, you are directing the console to maintain the relative balance that you set amongst those faders, while also giving you an overall level control for all of those channels at once.

“Like routing all those channels through a bus?” you ask.

Yes and no. The magic of the VCA/ DCA is that you get bus-like level management, but your routing is unaffected. In other words, VCA/ DCA groups are control groups independent of audio signal considerations. This was a big deal for me with Pigs Over The Horizon, because of how we did the playback FX.

The playback FX were in surround. Two channels were routed up front (in mono, actually), with two more channels that were sent directly to surround left and surround right, respectively. Once the surround channels were “lined up” with respect to each other and the feeds to the front, I didn’t want to change that relationship – but I DID want to be able to ride the overall FX cue volume if I had to.

I couldn’t achieve what I wanted by busing the four FX channels together; They would all have ended up going to a single destination, with no way to separate them back out to get surround again. By assigning them to a DCA group, though, it was a cinch. The routing didn’t change at all, but my ability to grab one control and regulate the overall volume of the unchanged balance was established.

Of course, busing is still a very important tool. You need it whenever you DO want to get a bunch of sources to flow to a single destination. This might not just be for simple combining. You might want to process a whole bunch of channels with exactly the same EQ and compression, for example, and then send them off to the main output. If that’s not what you’re after, though, a VCA/ DCA group is a great choice. You don’t chew up a bus just for the simple task of grouped volume control, and if you change your mind on the routing later it’s not a big deal. Your grouped controls stay grouped, no matter where you send them, again, because of that “independence” factor. The VCA/ DCA has nothing to do with where signals are coming from or where they’re going – it only changes the gain applied.

I personally am not as heavy a user of VCA/ DCA groups as some other audio humans, but I see them as a handy tool that I may end up leveraging more in the future. I’m glad I know what they are, because they’re a great problem solver. If your console has them, I definitely recommend becoming familiar with their usage. The day may come when you need ’em!


The Pro-Audio Guide For People Who Know Nothing About Pro-Audio, Part 6

I believe in life after the console.

Please Remember:

The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.

Want to use this image for something else? Great! Click it for the link to a high-res or resolution-independent version.

“The point of loudspeaker management is to make final, overall adjustments to console output so that devices which actually create acoustical output (speakers, that is) can be used most effectively.”


The rest of this article is available – free! – right here.


The Pro-Audio Guide For People Who Know Nothing About Pro-Audio, Part 5

Buses are what put the “mixing” in mixing consoles.

Please Remember:

The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.

Want to use this image for something else? Great! Click it for the link to a high-res or resolution-independent version.

“The most common destination for a channel’s signal is a bus. Buses are really what make a mixer a mixer: They’re signal lines meant to carry and combine a number of individual channel signals fed into them.”


I wrote this article for Schwilly Family Musicians. The rest of it is available for free, right here.


The Pro-Audio Guide For People Who Know Nothing About Pro-Audio, Part 3

Onward to the microphone preamp…or trim.

Please Remember:

The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.

Want to use this image for something else? Great! Click it for the link to a high-res or resolution-independent version.

“Signals at mic-level may require large, positive gain changes to correctly drive downstream electronics, and so a jack that can be connected to a microphone preamp is needed in that case.”

Read the whole thing, free, at Schwilly Family Musicians.


Console Questions

A few simple queries can get you going on just about any console.

Please Remember:

The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.

Want to use this image for something else? Great! Click it for the link to a high-res or resolution-independent version.

Back when I was in school, we were introduced to “The Four Console Questions.” The idea behind the questions was that, if you walked up to a strange mixer, you could get answers to the questions and be able to get work done. Mixing desks come in many varieties, but there aren’t very many truly different ways to build them that make sense. In any case, all the basic concepts have to essentially stay the same. If a console can’t take some number “a” of audio inputs, and route those inputs to some number “o” of outputs, you don’t have a mixing console anyway.

With the growing commonality of digital mix systems, I feel that the essential “console questions” need some expansion and tweaking. As such, here’s my take on the material that was presented to me over a decade and a half (GEEZE!) ago.

1. Do I Know What I Want To Do?

You might say that this isn’t a console question at all, but in truth, it’s THE most important one. If you don’t know what you want to do with the console, then knowing a bunch of information about the console’s operation won’t help you one iota. The unfortunate reality is that many people try to engage in this whole exercise backwards; They don’t know what they want to accomplish, but they figure that learning the mixer’s whys and wherefores will help them figure it out.

Certainly, learning about a new feature that you haven’t had access to previously can lead you to new techniques. However, at a bedrock level, you have to have some preconceived notion of what you want to accomplish with the tool. Do you want to get a vocal into the FOH PA? Do you want to get three electric guitars, a kazoo, and a capybara playing Tibetan singing-bowls into 12 different monitor mixes?

You have to know your application.

2. How Do I Correctly Clock The Console?

For an analog console, the answer to this is always: “No clock is required.”

For a digital rig, though, it’s very important. I just recently befuddled myself for an agonizing minute with why a digital console wasn’t showing any input. Whoops! It was because I had set it to receive external clock from a master console a few weeks before, and hadn’t returned it to internal clocking now that it was on its own.

You need to know how to indicate to the console which clock source and sample rate is appropriate for the current situation.

3. How Do I Choose What Inputs Are Available To The Channels?

This is particularly important with consoles that support both on-board input and remote stageboxes. You will very likely have to pick and choose which of those options is available to an individual channel or group of channels. What you need to discover is how those selections are accomplished.

4. How Do I Connect A Particular Input To A Particular Channel?

You might think this was covered in the previous question, but it wasn’t. Your global input options aren’t the end of the story. Many consoles will let you do per-channel “soft-patching,” which is the connection of a certain available signal to a certain channel without having to change a physical connection. Whether on a remote stagebox or directly at the desk, input 1 may NOT necessarily be appearing on channel 1. You have to find out how those connections are chosen.

5. How Do I Insert Channel Processing?

In some situations, this means a physical insert connection that may be automatically enabled…or not. In other cases, this means the enabling and disabling of per-channel dynamics and/ or EQ, and maybe even other DSP processing available onboard in some way. You will need to know how that takes place, and with all the possible variations that might have to do with your particular application, it is CRITICAL that you know what you want to do.

6. How Do I Route A Channel To An Auxiliary, Mix Bus, Or The Main Bus?

Sometimes, this is dead-simple and “locked in.” You might have four auxiliaries and four submix buses implemented in hardware, such that they can only be auxiliary or mix buses, with the same knobs always pushing the same aux and a routing matrix with pan-based bus selection. On the other hand, you might have a pool of buses that can behave in various ways depending on global configuration, per-channel configuration, or both.

So, you’ll need to figure out what you’ve got, and how to connect a given channel to a given bus so that you get the results you want.

7. How Do I Insert Bus Processing?

This might be just like question 5, or wildly different. You will need to sort out which reality is currently in play.

8. How Do I Connect A Given Signal To A Physical Output?

Just because you have a signal running to a bus, there’s no guarantee that the bus is actually going to transfer signal to any other piece of equipment. Especially in the digital world, there may be another layer of patching to assign signals to either digital or analog outputs. Bus 1 might be on output 7, because six matrices might be connected to the first six outputs. Maybe output 16 is a pre-fader direct out from channel 4.

You’ll have to figure out where all that gets specified.


Obviously, there’s more to being a whiz at any particular console than eight basic questions. However, if you can get a given signal into the desk, through some processing, combined with other signals you want to combine, and then off to the next destination, you can at least make some real noise in the room.


Is The Crossover Leaky?

A lot of low-end can still get into your mains.

Please Remember:

The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.

Want to use this image for something else? Great! Click it for the link to a high-res or resolution-independent version.

Every so often, I get to chew on a question that a reader asks me directly. I kinda wish that would happen more often (hint, hint, hint…). Anyway, I was sent a message on The Small Venue Survivalist’s Facebook page, asking if I could render an opinion on why a bass guitar seemed to have a surprising amount of LF information in the main speakers. The mains were being used alongside a subwoofer, with the sub providing a crossover filter at 100 Hz. What could the issue be?

There are a few explanations that would seem reasonable, if one discounts “catastrophic” issues like the crossover filter simply failing to operate as advertised.

1. Crossover filters, especially those implemented in active electronics, have a tendency towards a relatively steep slope. Even so, they usually aren’t brick-wall implementations. Everything below the cutoff doesn’t simply disappear – rather, it’s attenuated at a certain rate. With a filter set to roll off everything “below 100 Hz,” the mid-highs are still being asked to do a fair bit of work at the crossover frequency. The general vicinity of 100 Hz is actually quite bassy (depending on who you ask, of course), so the mains might be perceived as doing more than they should when everything is quite normal.

2. If a sizeable pile of low-frequency energy has been dialed into the bass-guitar channel, or the bass-guitar’s pre-console tone, that big hill-o-bass won’t be tamped down by the crossover. It will be split up proportionately, but following on from the first point, the mid-highs will still be tasked with reproducing their allotted piece of that big LF mound. Consequently, a surprising amount of energy may be present in the tops.

3. I have a suspicion that plenty of modern, two-way boxes receive some degree of “hyping” of their low-end at the factory. This makes them sound more impressive, and the manufacturer can get away with it because of safety limiters placed post-EQ. (The limiter prevents the low-frequency amplifier from supplying more voltage than the woofer can handle, and there may even be a level-dependent high-pass filter in play.) A low-frequency boost that occurs after the crossover reduces the crossover’s apparent effectiveness. Sure, the signal leaving the crossover might be down 12 dB at 75 Hz, but a +6 dB shelving filter put in place by the manufacturer at 100 Hz “undoes” that filtering to only lose 6 dB. Once again, a potential situation develops where the mid-highs are being asked to reproduce more “boom” than you expected.

It is entirely possible that an apparent problem isn’t covered by the three possibilities above, but they should catch quite a few scenarios where everything is hooked up properly and configured correctly.


EQ Propagation

The question of where to EQ is, of course, tied inextricably to what to EQ.

Please Remember:

The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.

Want to use this image for something else? Great! Click it for the link to a high-res or resolution-independent version.

On occasion, I get the opportunity to guest-lecture to live-sound students. When things go the way I want them to, the students get a chance to experience the dialing up of monitor world (or part of it). One of the inevitable and important questions that arises is, “Why did you reach for the channel EQ when you were solving that one problem, but then use the EQ across the bus for this other problem?”

I’ve been able to give good answers to those questions, but I’ve also wanted to offer better explanations. I think I’ve finally hit upon an elegant way to describe my decision making process in regards to which EQ I use to solve different problems. It turns out that everything comes down to the primary “propagation direction” that I want for a given EQ change:

Effectively speaking, equalization on an input propagates downstream to all outputs. Equalization on an output effectively propagates upstream to all inputs.


What I’ve just said is, admittedly, rather abstract. That being so, let’s take a look at it concretely.

Let’s say we’re in the process of dialing up monitor world. It’s one of those all-too-rare occasions where we get the chance to measure the output of our wedges and apply an appropriate tuning. That equalization is applied across the appropriate bus. What we’re trying to do is equalize the box itself, so we can get acoustical output that follows a “reference curve.” (I advocate for a flat reference curve, myself.)

It might seem counter-intuitive, but if we’re going to tune the wedge electronically, what we actually have to do is transform all of the INPUTS to the box. Changing the loudspeaker itself to get our preferred reference curve would be ideal, but also very difficult. So, we use an EQ across a system output to change all the signals traveling to the wedge, counteracting the filtering that the drivers and enclosure impose on whatever makes it to them. If the monitor is making everything too crisp (for example), the “output” EQ lets us effectively dial high-frequency information out of every input traveling to the wedge.

Now, we put the signal from a microphone into one of our wedges. It starts off sounding generally good, although the channel in question is a vocal and we can tell there’s too much energy in the deep, low-frequency area. To fix the problem, we apply equalization to the microphone’s channel – the input. We want the exact change we’ve made to apply to every monitor that the channel might be sent to, and EQ across an input effectively transforms all the outputs that signal might arrive at.

There’s certainly nothing to stop us from going to each output EQ and pulling down the LF, but:

1) If we have a lot of mixes to work with, that’s pretty tedious, even with copy and paste, and…

2) We’ve now pushed away from our desired reference curve for the wedges, potentially robbing desired low-end information from inputs that would benefit from it. A ton of bottom isn’t necessary for vocals on deck, but what if somebody wants bass guitar? Or kick?

It makes much more sense to make the change at the channel if we can.

This also applies to the mud and midrange feedback weirdness that tends to pile up as one channel gets routed to multiple monitors. The problems aren’t necessarily the result of individual wedges being tuned badly. Rather, they are the result of multiple tunings interacting in a way that’s “wrong” for one particular mic at one particular location. What we need, then, is to EQ our input. The change then propagates to all the outputs, creating an overall solution with relative ease (and, again, we haven’t carved up each individual monitor’s curve into something that sounds weird in the process).

The same idea applies to FOH. If the whole mix seems “out of whack,” then a change to the main EQ effectively tweaks all the inputs to fix the offending frequency range.

So, when it’s time to grab an EQ, think about which way you want your changes to flow. Changes to inputs flow to all the connected outputs. Changes to outputs flow to all connected inputs.


A Weird LFE Routing Solution

Getting creative to obtain more bottom end.

Please Remember:

The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.

Want to use this image for something else? Great! Click it for the link to a high-res or resolution-independent version.

This is another one of those case studies where you get to see how strange my mind is. As such, be aware that it may not be applicable to you at all. I had a bit of a conundrum, and I solved it in a creative way. Some folks might call it “too creative.”

Maybe those people are boring.

Or they’re reasonable and I’m a little nuts.

Anyway.

I’ve previously mentioned that I handle the audio at my church. We’ve recently added some light percussion to complement our bass-guitar situation, and there was a point where our previous worship leader/ music director wanted more thump. That is, low frequency material that was audible AND a bit “tactile.” In any case, the amount of bass we had happening wasn’t really satisfying.

Part of our problem was how I use system limiting. I’ve long nursed a habit of using a very aggressive limiter across the main mix bus as a “stop the volume here” utility. I decide how loud I want to get (which is really not very loud on Sundays), set the dynamics across the output such that we can’t get any louder, and then smack that processor with a good deal of signal. I’ve gotten to a point where I can get it right most of the time, and “put the band in a box” in terms of volume. Drive the vocals hard and they stay on top, while not jumping out and tearing anyone’s face off when the singers push harder.

At the relatively quiet volume levels that we run things, though, this presents a problem for LF content. To get that extended low-frequency effect that can be oh-so-satisfying, you need to be able to run the bass frequencies rather hotter than everything else. The limiter, though, puts a stop to that. If you’re already hitting the threshold with midrange and high-frequency information, you don’t have anywhere to go.

So, what can you do?

For a while, we took the route of patching into the house system’s subwoofer drive “line.” I would run (effectively) unlimited aux-fed subs to that line, while keeping the mains in check as normal, and we got what we wanted.

But it was a bit of a pain, as patching to the house system required unpatching some of their frontend, pulling an amp partially out of a cabinet, doing our thing, and then reversing the process at the end. I’m not opposed to work, but I like “easy” when I can get it. I eventually came to the conclusion that I didn’t really need the house subs.

This was because:

1) We were far, far below the maximum output capacity of our main speakers.

2) Our main speakers were entirely capable of producing content between 50 – 100 Hz at the level I needed for people to feel the low end a little bit. (Not a lot, just a touch.)

If we wouldn’t have had significant headroom, we would have been sunk. Low Frequency Effects (LFE) require significant power, as I said before. If my artificial headroom reduction was close to the actual maximum output of the system, finding a way around it for bass frequencies wouldn’t have done much. Also, I had to be realistic about what we could get. A full-range, pro-audio box with a 15″ or 12″ LF driver can do the “thump” range at low to moderate volumes without too much trouble. Asking for a bunch of building-rattling boom, which is what you get below about 50 Hz, is not really in line with what such an enclosure can deliver.

With those concerns handled, I simply had to solve a routing problem. For all intents and purposes, I had to create a multiband limiter that was bypassed in the low-frequency band. If you look at the diagram above, that’s what I did.

I now have one bus which is filtered to pass content at 100 Hz and above. It gets the same, super-aggressive limiter as it’s always had.

I also have a separate bus for LFE. That bus is filtered to restrict its information to the range between 50 Hz and 100 Hz, with no limiter included in the path.

Those two buses are then combined into the console’s main output bus.

With this configuration, I can “get on the gas” with low end, while retaining my smashing and smooshing of midrange content. I can have a little bit of fun with percussion and bass, while retaining a small, self-contained system that’s easy to patch. I would certainly not recommend this as a general-purpose solution, but hey – it fits my needs for now.


The Power Of The Solo Bus

It’s very handy to be able to pick part of a signal path and route that sound directly to your head.

Please Remember:

The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.

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The Video

The Summary

Need to figure out which channel is making that weird noise in the midst of the chaos of a show? Wondering whether your drum mics have been switched around? Wish you could directly hear the signal running to the monitor mix that’s giving people fits? Your solo bus is here to save the day!