Google+

What's the Difference: Pre-Fade vs. Post-Fade

Today, we’re back to our What’s the Difference series. These are going to be short posts where we look at commonly misunderstood terms in the tech world. Nearly every audio console offers aux sends with a pre-fade or post-fade option, but what does that mean?

It’s the Pick Off Point Again

As we discussed in the last episode (AFL/PFL), pre-fade and post-fade are really all about the pick off point. That is to say, at what point in the channel strip is the aux send being picked off. A pre-fade aux takes the signal before (pre) the fader. So, the level of the fader has no impact on the level of the aux send. A post-fade aux takes the signal after (post) the fader so the level of the fader does impact the level of the send. Sometimes, it’s really that simple. See, I told you these were going to be short posts.

Options, We Have Options

Back in the days of analog consoles, it was often possible to change the pick off point. I remember reading the manual of our old Soundcraft Series 2 in which it described breaking solder jumpers to move the pick off from pre-fade, post-EQ to pre-fade, pre-EQ. Sometimes, it could be done with jumper blocks on the board.

With the advent of digital consoles and DSP, it’s now easier than ever to change the pick off point. For example, Digico allows for pre-fade, pre-mute; pre-fade, post-mute; and post-fade, post-mute options. Pre-fade and pre-mute are both pre-processing while post-fade is after the processing block. Even the Behringer X32 allows for each aux of each channel to be set pre-EQ, post-EQ, pre-fade, post-fade. 

I especially appreciate the signal flow diagram showing your aux options. 

I especially appreciate the signal flow diagram showing your aux options. 

You’ll have to break out the manual to see what options your board has.

Why Use Them?

Generally speaking, we use pre-fade sends for monitors and post-fade sends for FX. Post-fade sends are also useful for things like broadcast mixes, and feeds to ancillary rooms. We want monitors to be pre-fade because we don’t want to be changing the musician’s mixes each time we make a house mix adjustment. If you’re getting complaints from musicians that their mixes keep changing, make sure you’re set to pre-fade auxes. 

For FX, we want the level going to the FX processor to be tracking with the dry signal going to the mix. If you sent pre-fade signals to an FX processor, even if you pulled the channel down, the FX would still be in the mix. Similarly, if you’re using a post-fade aux bus to mix broadcast, you want the fader changes of the mix to track to the broadcast mix. 

Adding to the Confusion

Some manufacturers make analog boards with a few pre-fade auxes and a one or two knobs labeled FX. The FX knobs are simply post-fade auxes that often feed an internal FX system. Typically, there is an output on the board to use an external processor with those FX sends, so don’t be limited to the internal FX (which may or may not be any good). 

Many analog boards will let you switch the send for each aux or a pair of auxes to pre or post. Again, be sure the switches are in the right spot if you want to keep your musicians happy.

Pre-fade and post-fade is one of those concepts that is really quite simple, but can cause a lot of problems if not implemented correctly. Hopefully, this post helps with that.

“Gear

Today's post is brought to you by DiGiCo. DiGiCo audio mixing consoles deliver solutions that provide extreme flexibility, are easy to use and have an expandable infrastructure, while still providing the best possible audio quality. Visit their website to learn more.

Today's post is brought to you by Pacific Coast Entertainment. Pacific Coast Entertainment is the premier event production company servicing Southern California and the western states. PCE offers a complete line of Lighting, Audio, Video, and Staging equipment for rentals, sales and installs. Where old fashion customer service meets high tech solutions. PCE, your one stop tech resource.

What's the Difference: AFL-PFL

In this series, we’ll look at two things and talk about their differences. For the first installment, we’ll look at a common button on most audio consoles. The labels may vary, but the difference is important.

AFL/PFL—What’s the Difference?

AFL stands for After-Fade Listen while PFL stands for Pre-Fade Listen. Depending on the current state of your console, pressing solo in either mode may result in the same thing. Or it may be completely different. 

Both AFL and PFL are solo modes. When you press the solo button on the channel, the output of that channel is routed to the solo bus and you hear it all by itself. We use solo for auditioning an input, checking for signal, and possibly setting EQ. We’ll get to this later. 

On many consoles, you can also solo groups, VCAs and the master. So what’s the difference between AFL and PFL?

It’s All About the Pick-off Point

Pre-Fade Listen is just what it sounds like; the signal is picked off from the channel strip before the fader. Most of the time, it’s also pre-EQ, pre-dynamics and pre-Mute. You’ll have to read your manual to find out where the pick point is. Sometimes it’s after the HPF and LPF, but not always. Some digital consoles allow you to choose the PFL point, which is cool. Because PFL is pre-processing, it’s a great way to check the quality of the incoming signal before you do anything to it. 

After-Fade Listen is a pick-off point after the fader. Typically, it’s also after EQ, dynamics and mute. So that means anything you’ve done to the signal with any of those processing blocks will be reflected in the solo output. In AFL mode, you will hear the effects of EQ, dynamics and filters. If the fader is off on a channel that you AFL, you won’t hear anything. It’s after the fader, remmember. 

When To Use Them?

PFL is most useful for checking signal. When I line check a stage, I set the console to PFL and use the headphones to verify each input. Most of the time, the faders are all down (or turned off with VCAs), so nothing comes through the house. But I can hear it clearly with PFL. It’s also useful for verifying signal of a muted mic during a service. It’s not a bad idea to PFL your pastor’s mic a few minutes before he goes up to be sure you have signal. This has saved me many times. 

AFL is useful for seeing if what you’re doing is helping or hurting the sound. If you’re trying to zero in on an offending frequency on an instrument, a quick AFL while you check the EQ can save you a lot of time. Many of my FOH friends and I generally prefer to EQ channels in the context of the mix—because it is a mix after all—but sometimes some isolation is helpful to solve a particular problem.

AFL is also useful to hear the blend of a group of instruments or vocals. I use it often on the BGV VCA to hear how my vocals are blending. Because the AFL happens after faders, I hear the blend based on the fader position. A quick AFL of the VCA can make short work of getting your vocals or drum mic’s blended.

Bonus: Solo In Place

This is known by a few other names, but what it does is the same. When SIP is pressed, instead of routing the PFL’d or AFL’d signal to the headphones or solo outputs, it routes it to the main L&R buss. That means everything but the solo’d channel is shut off and all you hear is that solo signal.

This can be useful or incredibly dangerous, depending on the situation. When you’re running a rehearsal, SIP can be helpful to identify a channel that might be lighting up a room resonance or something similar. But during a service, it can be devastating. It’s so dangerous that Digico requires you to press the SIP button for full two seconds just to engage it, and then it blinks red the entire time. 

Don’t try out SIP during a service—ever! I rarely use SIP as I much prefer to EQ and alter dynamics within the context of the mix. But that’s what it does. Proceed with caution.

“Gear

Today's post is brought to you by Heil Sound. Established in 1966, Heil Sound Ltd. has developed many professional audio innovations over the years, and is currently a world leader in the design and manufacture of large diaphragm dynamic, professional grade microphones for live sound, broadcast and recording.

CHCC Renovation: Main PA and Lobby

Because of the cool rigging bar, we only needed two pick points to fly the array and get the angle we needed. Gotta love good hardware.

Because of the cool rigging bar, we only needed two pick points to fly the array and get the angle we needed. Gotta love good hardware.

By now it should not be news to anyone that we put in a Bose RoomMatch PA in Coast Hills. I have taken no small amount of flack for that decision, but I stand by it, especially now that we really have it dialed in. As I’ve said before, there are other PA’s that we could have used, but none fit the budget and provided the directivity control RoomMatch does. And in that room, we really need control.

Asymmetric and Symmetric Boxes

As far as I know, we are one of the first installations to use both types of boxes in the arrays. Now, I should point out that RoomMatch may look like a line array, but it’s not. It’s billed as a Progressive Directivity Array. That means each box covers a specific part of the seating area. There is some combining at lower frequencies, but for the most part, the boxes don’t interoperate much. 

Because of that, we were able to mix and match boxes for a very specific design. I wanted to provide some sense of stereo imaging across a wide chunk of seating in the middle, and keep as much sound off the walls as possible. To meet those goals, we used boxes that were narrow on the outside and wider in the middle at the top of the array. The arrays are mirror imaged and the coverage is indeed pretty tight.

I do love a good rack. Amp rack, that is...Get your mind out of the gutter.

I do love a good rack. Amp rack, that is...Get your mind out of the gutter.

Keep The Colors Straight

Apparently, when I wired up the arrays, it was dark and I was tired. I inadvertently wired a few NL4s wrong and we had some phase issues initially. But once we got that sorted out and began the tuning process, it was all fun. 

A couple of guys from Bose came down and started taking measurements throughout the coverage area. They averaged those together and we came up with a room curve. Interestingly, the curve they came up with was shockingly similar to the one I put in using a LAMA transfer function with the measurement mic at FOH. 

We ended up with about 4 filters in the system, and two of them are there to tame room anomalies. Otherwise, the system sounds really good out of the box. We did a little gain shading in the amps to dial out some summing that was happening with the LF elements in the arrays, and to compensate for the air loss at the HF end. But otherwise, the system is pretty flat. 

Stereo Imaging for Days

I really wanted to have an LR system, but didn’t expect to get great stereo imaging. I was surprised to be wrong on this point. Throughout almost the entire center four sections and much of the back outside sections, there is an excellent sense of stereo. We played a bunch of tracks through the system and each time we kept looking at each other saying, “Wow, the stereo field is amazing!” It’s some of the best I’ve heard in a live PA. 

But vocals image right in the center where they should and speaking sounds fantastically present. So I’m very pleased with that. Time will tell if they really utilize the stereo image as well is can be, but it’s nice to have it available. 

This is a terrible photo of the subs. but you get the idea.

This is a terrible photo of the subs. but you get the idea.

Big Bottom

The system also has four dual-18” subs in a cardioid pattern flown over the center of the proscenium. They are in a 2x2 arrangement and once we got the timing right, it’s pretty remarkable how little low end there is on stage. But throughout the whole seating area, there is plenty. We ended up dialing those back a little bit because Coast Hills has never been thumping the bass. There’s headroom there, however, should the new style of worship desire more bass. 

Because the main boxes go down so low, the subs are really only working at the very low end, just like they are supposed to. Off hand, I don’t recall where they are working, but I believe it’s from about 30-90 Hz. 

Good Lobby Sound

For the last 5 years I’ve been frustrated by the sound in our lobby. It was terrible, really. We had a bunch of ceiling speakers mounted in the walls. Under the best of conditions these won’t sound good, and these were not good conditions. 

I spent a little more money in the lobby than I ordinarily would have, but I’m glad I did. We hung four RMU208 Utility Speakers from Bose up in the corner where the wall meets the ceiling. The RMU208 is a dual 8” plus a horn configuration, and it’s driven by a PowerMatch 8250. The 8250 puts out 250 watts into 8 channels, so each speaker is powered individually. I went with 8 channels because someday, they want to blow the front of the building out and put speakers out front. So they have 4 channels to expand into. 

I didn’t have time to do any tuning of the lobby speakers, but I thought they sounded acceptable out of the box. At some point, I want to go in and play with the Smaart rig and tweak them a little bit, but for starters, it works. My choice of Bose speakers for the lobby was based on the idea that I wanted them voice matched to the mains. As you walk in from outside into the lobby, then into the sanctuary, it just keeps getting louder, but it sounds the same. I think we hit that goal. 

Overall, I’m very pleased with the system. It has enough headroom to get really loud if they want, but it sounds clear at lower volumes. It’s very present without being harsh and has a nice, warm low end that doesn’t mask the midrange. And the lobby sounds good. That’s a win in my book.

Roland

Gear Snobs

Audio guys can be snobs when it comes to gear. But the reality is, we can’t always have our favorites. Sometimes, it’s a simple budget issue. For Coast Hills, we didn’t have the budget for Meyer, d&b or L’Acoustics. If I had held out for those brands because they have more cachet, we would not have a new PA at all. The money is just not there. But the church can afford RoomMatch. And having heard it, and after some considerable evaluation, I’m convinced we haven’t sacrificed that much. 

Is RoomMatch as good as a L’Acoustics Kara rig? Maybe not. Will the average person notice a big difference between those two? Probably not. Will the average person notice the upgrade from what we had to RoomMatch? Absolutely. I’ll take that outcome over no change at all.

Be Open

Lighting guys can be snobs, too. Some will say, “If it’s not Varilite, it’s not in my rig.” Or Martin. Or High End. Whatever. In the past, we’ve rented about 6 VL2500s for Easter. Those are great fixtures, to be sure. But this year, we rented 18 Elation Platinum Spot 5R Pros. Are they as good of a fixture as the VL2500? Not really. The panning isn’t as smooth, the color mixing isn’t as nice and we had one go flaky on us. However, we made a bigger visual impact with 18 of them than we ever did with the 6 VLs for the same money.

And you know what? If I were buying moving head fixtures for Coast Hills, I would probably go with Elation. No, they’re not as rugged as a Varilite. But, we can afford more of them, and they would be fine for what we’d need them for. 

Use What Fits

When I say “fits” I mean both budget and application. If you’re at a big church with big budgets and can afford the best gear, go for it. But if you’re at a smaller church with small budgets, don’t feel bad about going with brands with lower cool factor. Sometimes, the smaller companies innovate really well and come up with great solutions at great price points. Don’t discount them because they are not what the big church or big tour is using. 

I’ve talked with guys who are at smaller churches with all volunteer tech teams who are convinced they need a Digico at FOH and a Grand MA at lighting. Those are great pieces of kit, but they do have a steep learning curve, as well as big price tags. In a smaller setting with lower production demands, there are better options. Never feel bad about choosing the best option for your church; even if it’s not what all the cool kids are using. 

Get Good Advice

In my new role, I find myself helping churches decide what to buy. While I have my preferences on what I like, I have to set those aside and make sure I’m recommending what is best for them. I recently steered a church toward a Yamaha QL away from a Digico SD9. Personally, I would prefer the SD9 any day. But in this setting the QL makes much more sense. Not only is it considerably less money—and they were already at the top of their budget—it’s much more friendly to non-professional operators with zero digital console experience (and 20 years of analog experience). 

When purchasing equipment, make sure whoever is recommending what they are recommending knows your situation and how it will be used. Make sure they aren’t just giving you their stock solution. It would be a lot easier for me to have a “small church package” of gear that I can price and sell. But it would not likely be the best fit for everyone. So we stay custom for each church. 

I’ve always been a contrarian, so this concept is not foreign to me. But I write this to encourage those of you who are nervous about not doing what everyone else is doing. They used to say, “Nobody ever got fired for buying IBM.” That may have been true, but a lot of companies missed out on better options because someone took the safe route. 

Don’t be a gear snob. Get what works for your church. Everyone will be better off for it.

Today's post is brought to you by CCI Solutions. With a reputation for excellence, technical expertise and competitive pricing, CCI Solutions has served churches across the US in their media, equipment, design and installation needs for over 35 years.