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The Veritable TechNinja

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[Dec. 6th, 2005|02:24 pm]
The Veritable TechNinja
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Can any of you live sound people/band members explain to me why anyone would want do deal with the complications of micing a speaker cabinet instead of using a DI box/transformer to put it directly through a mixer? It seems like the dumbest thing ever to me to purposefully take a signal from an instrument, run it through an aplifier (distortion), put it out through a speaker (more distortion, phase issues), pick it up with a microphone (gain issues, bandwidth issues, feedback, distortion, general shittiness), then repeat the whole amping process. Is the coloration of a collector's guitar cabinet really worth incurring that much garbage in the signal? Is it something to do with cohesiveness between the coloration of the sound coming out of the guitar cabinet versus the PA cabinets? I come from a different world of audio, where signal paths are as short and free of detouring as possible to retain sonic intergrity.

While we're at it, can someone please explain to me _why_ compression is so prevalent in PA setups? Don't you want dynamics in your sound? To me, it seems like cheating to purposefully limit sonic headroom in order to get your volume flat. Getting the volume flat is a matter of proper gain settings as far as I know. Here's another thing that I recently addressed with my camp, the hi-fi folks. Why over-amp a speaker? Yes, under-driving a speaker can cause the amp to choke, but overdriving it can cause the speaker to distort (and die). I understand bi-amping, in fact it makes perfect sense. To have a crossover that's set for the frequency ranges that each driver in your cabinet reproduces properly, you essentially have a per-driver amp and don't end up robbing your tweeters. Wouldn't it make the most sense to have as direct a path as possible to the mixer, set all your gain correctly, cut useless frequencies per channel, go through a single stereo graphic EQ to correct room acoustics, cut up your signal in the crossover to the exact ranges of your drivers, and run one amp channel per driver?
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Comments:
From: princeadam
2005-12-06 07:52 pm (UTC)
If you need answers to these questions and don't get them, I would suggest checking out the LJ user avsquad and asking him. He's my friend from Hope, Ryan, and he is a total audio god.

As far as the micing the speaker, I think you hit the nail on the head when you were speculating about coloration. Yes, it does sound distorted and shitty-esque, and that's the point. It's pretty much the entire point of The Strokes. They get the vintage feel and sound because they at least master their shit to sound like they miced an amp. At least that's what it sounds like to me.
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[User Picture]From: arcsine
2005-12-06 08:12 pm (UTC)
Mind pointing him towards this entry for me?

It seems to me like that's more the musician's job than the audio engineer's, to get the sound they want (with effects processors). The engineer's job is to preserve that sound, mix it with the other sounds, and make them all loud.
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[User Picture]From: ego_likeness
2005-12-06 09:24 pm (UTC)
Miking an amp does not *have* to sound shitty, just as using digital gear doesnt have to sound cold. There are billions of amazing recordings out there that were done before the age of direct recording that sound amazing. The Strokes have a very specific asthetic that they are trying to get, which has more to do with EQ and mixing than it does with using mikes or not.

Mikes are like any tool, its how you use em. People argue that analog sounds better than digital, but really they are just means to an end, and have different strengths and weaknesses.

As to whos job is whoms, it just depends on how much work you want to do, and what you want your end result to be. If you are a guitarist in a rock band, and that is all you are concerned with, ie: just playing the guitar, then you are correct to an extent, tho it is also your job to help the sound as a whole by eqing properly so as not to interfear with other people instruments. If however, you are like me, and most of the people we play with then its a whole other ball game.

It depends on what you are going for, different producers also have different sounds, and sometimes a band or label will work with them specifically for that sound. Flood, Rave Gotell, Rick Rubin all come to mind. Some producers like Steve Albini prefer to be more transparent it depends on what the client wants.
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[User Picture]From: arcsine
2005-12-06 09:49 pm (UTC)
I'm of the mind that it's easier to make a signal more complex than to strip out only the unwanted additions to an already complex one. If you're working on a digital mixer, you're going to get less interference and a "brighter", more clear sound. From there, you can add reverb, distortion, what-have-you until you have the sound you want. I have a feeling a lot of people get too subjective when working with audio, and make up for lack of knowledge of what's actually going on with their signal by using subjective terminology. Same thing happens in hi-fi, people buy $20/foot speaker cable because the package says it'll make their music "brighter/softer/warmer/quicker/whatever".

I guess I'm from the Albini camp, but I'm not going to knock the undefinable alchemy of producers like Rick Rubin.
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[User Picture]From: avsquad
2005-12-08 12:41 am (UTC)
as i haven't read through all the other replies i'll probably end up sounding redundant, but i'll do my best:

as for micing guitar amps, you've got to remember that electric guitars were developed in the 30s, well before multitrack recording was starting to be developed. pickup and amp technology have grown hand in hand and both cater to one another's needs...most pickups are designed to sound best when played through a guitar amp and vice versa (which is why we don't use guitar amps as pas). distortion (and i'm not talking about fuzz here) in a guitar's case is extremely important, as it's what makes an electric guitar sound like an electric guitar. when you take a direct off of a guitar, you're getting a nice clean signal but the signal isn't going to the destination it was designed for...a pa cab that's designed to be as clean and even as possible vs. a guitar cab that's going to compress the shit out of the sound, roll off all the top end, and add a bunch of harmonic distortion. the same is true for distortion (and other) pedals. when you take a direct off a distortion pedal, you're invariably going to get a nasty, buzzy mess, because the pedal is expecting the amp to smooth it out. it's the same reason sm57's are so popular on guitar amps...if you look at a frequency response chart on one, they roll off almost everything over 15k. sounds like a crappy idea, but what in reality it just helps take some of the edge off.

essentially, you've got good distortion and bad distortion: good being the kind you get from a guitar amp or a piece of tube gear (the advantage to tube stuff is the harmonic distortion and gentle compression it adds) that's a part of the design, the bad being what we're used to thinking of (overdrive, phase distortion [which can be pleasing itself - chorus, flanger, etc]). more than likely modern day pickups could be designed to sound best when taken direct, but with all guitars/amps/effects having been developed together under the assumption that they would be passing through a typical guitar amp at the end nobody's about to try to change things.

when you get into fancier direct boxes like the sansamp or pod, you're actually getting into a more complex signal chain in a lot of ways. instead of putting an amp and mic in between your guitar and the pa, you're putting a complicated piece of electronics whose sole purpose is to emulate those 2 pieces of gear. while it's certainly a lot easier and works in some situations (especially some of the newer software stuff...i've been loving native instruments' guitar rig, for example), you're basically just trying to fake a good ol' speaker and mic through complicated physics models or a long chain of circuitry.

there are a couple of good reasons for compression in a live setting. the first is the obvious asthetic choice, as properly used compression (even set very lightly) helps a mix to sound a lot more exciting and in your face. the second is to protect your speakers, as they're a lot more easily damaged by sudden spikes in power than by a high average power. a properly set compressor can allow a pa to go considerably louder without distorting or damaging equipment. i come from a recording background, but in both worlds compression is equal parts artistic and technical. there are a lot of situations in which compression just sounds good, but even in situations where the sound isn't appropriate a compressor set transparently can have huge technical benefits.
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[User Picture]From: arcsine
2005-12-08 03:35 am (UTC)
Actually that helped a lot, thanks! I always wondered what the big deal was about collector pickups and amps... Now I know. So, in essence, I should leave the decision up to the guitarist unless they don't care, and make my own decision based on their playing style otherwise.

I completely understand the purpose of a compressor now, I just think I'm the kind of guy who would try to engineer them to as little use as possible.
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[User Picture]From: avsquad
2005-12-08 04:45 am (UTC)
excellent. glad to hear i managed to help some. as a general rule, you can get away with a di on a clean pop guitar, but anythign with the tiniest bit of grit is not going to do well without an amp and speaker on the front end.

i agree on compression. it's entirely overused in the recording world and i'm sure the same is true in the live world. i saw some tv show the other day where the singer's voice kicked the hell out of the master compressor and the whole band sounded like they went away any time he sang. it was painful.
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[User Picture]From: avsquad
2005-12-08 12:42 am (UTC)
as for overamping...this one's not my field of expertise at all, but i'll do my best. in studio setups, we usually overamp speakers because most amps don't have the dampening factor needed for really good sound. the dampening on an amp is quite possibly the most important part of the equation when it comes to getting a nice punchy sound out of your speakers, and most amps are way underdampening when they're being pushed. as an example, the guy i often work for designed a paid of tad studio monitors that we've installed in kid rock's studio, eminem's studio, etc. even dr. dre has a pair (with 4 18' subs, mind you). we often amp them with a crown reference II, but in some cases will use the even more powerful reference I (a $6000 2 channel amp, mind you). the reference II can get those suckers up to a good 130-140 db, enough to cause extreme physical pain (and closing in on the ranger where you literally lose conrol of your bowels)...i've only heard them up to about 120 and i had to leave the room. the reference I is total overkill and completely unnecessary...they get installed with the gain set about halfway up and the console monitor pot is still touchy as well and will almost never get above about 1/4 of the way up. the speakers do, however, sound better, because the amp is acting well within its limitations and dampening extremely effectively. again, this is definitely not my area but i've heard a couple setups both ways and you can definitely tell the difference.

if you want to take your initial direct out argument to an extreme, you really shouldn't be putting eqs or crossovers into the chain either. both components add massive phase distortion (especially the low end ones used in most pa setups), and when you're running through an eq on the board, an eq on the stereo out, a crossover, then hitting two non-cocentric drivers in two or more speaker cabs (giving you 4+ sound sources for the same signal), the phase distortion is going to be huge. we keep all those things in there because in the end it all sounds a whole lot better than taking a direct out from the guitar and running with no eq to one driver, which would be the cleanest solution.

sorry to ramble on. hope this helps some...
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[User Picture]From: arcsine
2005-12-08 03:51 am (UTC)
Definitely not rambling on, so far you've had a ton of informative and useful stuff to say.

I am damned impressed that you're connected to an engineer for TAD, they make some serious speakers. I'm more of a Dynaudio man myself, though. As for amps, why not use something more refined, like a Bryston or a Rotel? Sure, Crown amps are durable and put out reliable power, but for real fidelity their designs can be rather spartan. As for overpowering speakers, yeah they may sound slightly better at controlled input levels, but any respectable amp manufacturer that says their amp does 200wpc will perform well with a speaker meant to handle 200w long term. To me, having to overpower speakers is a sign of poor coil design.

Also, more about crossovers. To me, it makes much more sense to use a high-quality DBX crossover and EQ to properly distribute to a bi/triamped setup, especially if you're not going to use the crossovers in the speaker cabinets. I'd never dream of putting an extra crossover in a system that only ran one speaker input. I'd rather dig the crossover board out of a cabinet and rewire it with new connectors per driver.
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[User Picture]From: avsquad
2005-12-08 04:49 am (UTC)
whew.

yeah...the engineer i work for is a great guy and has designed some great sounding rooms (54 sound, fbt east and west, rustbelt, etc). i work for him in the studio most of the time, but i tag along on speaker installs whenever i can. according to glenn, the reference series are the only crown amps worth anything, and they actually stopped making them a couple of months ago. i'm not sure what he'll be switching to, but i'd guess bryston. we've been putting in bryston crossovers and white eqs on pretty much every setup, which sound great.

once we start getting into specifics of speaker design, i'm in over my head. i've spent a little of time looking at glenn's work and get the basic physics of it, but i haven't had time to get into anything real specific. i do my best to stick to recording music as much as possible.
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[User Picture]From: pfrank
2005-12-06 07:58 pm (UTC)
crap, I have a textbook at home that explains exactly why micing a speaker is a good idea in some situations. I'll look it up later if no one else knows...
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[User Picture]From: ego_likeness
2005-12-06 08:12 pm (UTC)
Miking guitars.
1. (The short answer) Because that was how it was done up until a few years ago with the exception of the users of Sans Amps, but there were only a few of them.

2. (The long answer) Because sound is generally created by a vibrating object moving air, that sound is then coloured by the air it passes through. For instance a bass wave can be up to 12 feet from tip to tip, meaning that if you are any closer than 12 feet, you wont hear it properly, you might feel it, but thats different. Miking a guitar or any other instrument adds a sense of presence that is not innate to the signal. There is a very noticable difference between close miking a guitar and miking it from a foot away.

Plugging directly in to the PA is the equivelent of having the audiences head next to the amp. It *can* sound flat or thin. If you are using good amp modeling gear, thats not so much a problem. You can also compensate with reverb, however its important to remember that reverb is a *simulation* of space, not the space itself.

Its a trade off between the ease of using a DI and the sound of the air moving.

I personaly use a pod live, and not an amp. And for that matter when I did use an amp, it was only to monitor my guitar and was pointed at me not the audience, the guitar was still run direct.

-

The compression and limiting on a PA is in place to protect the system from bands and sound people who dont know what they are doing. Tho more often than not it is only neccicary to limit the signal going to the house system as you correctly point out compression can modify the signal. However that modification of the signal is usually only an issue with bands that pre-mix their sound from stage, as the house sound man will intheory compensate for the compression on the system in the mix.

Your pa signal path looks correct, except that the limiting should be introduced as the last device in the chain before the amplifier.

Its also harder to blow a system with the traditional miking amps because there is a physical limit to the sound from stage, where as if I go in with a compleatly direct rig (like we use) and the gainstaging is set wrong, and there is no limiter in place, if I have a massive volume jump on my end I will blow his system.
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[User Picture]From: arcsine
2005-12-06 08:27 pm (UTC)
OMG I LOVE YOU. Thanks for this heaping helping of useful info!

The way I understand the longer explanation of micing vs DI is that you get off-axis reflections in from a mic along with the signal, thus artificially multiplying your soundstage and in effect creating an exponentially bigger room. More air equals more repetions of the waveform which equal more harmonics, which you mentioned can also be achieved by using reverb. This sounds attractive at first, but gets _really ugly_ mathematically. Am I right?

Also, now that I have a known-good reference, how worth my money would it be to buy a handheld audio analyser? My experience in home theater is that if you have a handle on THD and aplitude over frequency, phase, and constructive over destructive harmonics, you're in the bag. If it's worth it at all, am I better off with a self-contained unit or a PC software-based analyser and a good mic?
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[User Picture]From: ego_likeness
2005-12-06 08:48 pm (UTC)
In answer to your first question, reverb is like anything else, if you know how to use it, then your fine, overuse of it is always a problem. Live, its best to be conservitive with the reverb, *especially* if it is added from stage, because the sound guy would have no way of fixing any harmonics or other issues (muddyness etc) caused by it.

As to your second question, if your looking into recording at home, then your have to go down a checklist before you worry about and audio analizer.
1. Get good monitors
2. Get a good amp
3. Acousticly treat your room

Once you have done that, and you have a nice even spread of sound, then you can worry about other issues.

If your thinking about using an audio analyser live, im not sure what the point would be. Your live sound will *never* sound exactly the way you want it. The main reason being you are onstage and not in the room, and are not hearing it from the audience point of view. Even if you bounce back and forth between stage and the floor during soundcheck, you are still only able to get yoursound part of the way there, because there are no bodies to absorb the sound, nore is there no crowd noise. The trick is finding a balance between being a control freak (as I am with our sound) and recognizing that there is a point where you must give the soundguy *some* control.

Currently we use 6 channels, 1 Kick 2 Other drums 3 guitar/kbds/piano 4 bass 5 both vocals 100% dry 6 both vocal effects 100%wet which allows us to set up quickly maintain control and let the soundguy mix for the room.

We are considering modifying that setup as there are issues with it from time to time, but for the most part its very from flexable room to room.

As a side note, its also important to remember that each show will sound very different not just because of the sound system, but more than anything else due to the shape of the room and what its built out of.
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[User Picture]From: arcsine
2005-12-06 10:08 pm (UTC)
Just to make sure we're on the same page, I'm the sound guy for Labyrinth now. I haven't been in a band in 8 years, I mostly DJ. Don't record at all. Anyway:

Good point about the reverb, I don't imagine a lot of live racks have effects processors in them. I'm guessing that's why the DBX DriveRack series has a bunch of sub-harmonic synthesizers, amp modelling, and that kind of stuff in it. Just another way of saying "small stack of carefully-tuned effects" in words that mixer techs understand.

As for the analyser, I'd be using it on a tripod. Setting it up in the middle of the house, setting it to take a sample, doing a sound check, then making any adjustments based on the results. In that respect, a laptop-based analyser would be helpful as I could just run a long-ass mic cord instead of running around a lot. You're right though, bodies = baffling. Doing sound check is one of those catch-22s.

The purpose I had in mind for using an analyser for sound check is to have a neutral reference to avoid contouring the sound towards my listening preferences. I have weird tastesIt's better to have the sound calibrated than to try to please a bunch of different people with different levels of hearing loss.

That's a damn smart set of outputs, I wish I did your sound last time you were here. Giving the soung guy both wet and dry vocals essentially puts the effects loop mix knob in the booth, which is _awesome_. Being able to use the final sound out of the PA to build the total effects instead of trying to pare down vocal effects pedal reverb + house reflections is beautiful.

As for construction materials and room geometry, I think that's a pipe dream of anyone who cares about audio theory. Club owners know looks are more important to the customer than acoustic properties.
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[User Picture]From: ego_likeness
2005-12-06 10:24 pm (UTC)
Labyrinth...Detroit right?
We had pretty solid sound when we played there a few months ago.

I think your idea of using the analyser is a good one, particularly if its more for pre-recorded audio. Sadly I dont think most bands have a consistant enough sound for it to be much use with them. However from a clubby dancy situation, its always a good idea to tune the pa to compensate for the geometry of the space. From a band perspective that can backfire if the band premixes and prefers to eq their own stuff, so its good to be able to compleatly bypass the house eq if neccicary. Particularly if your dealing with electronic bands.

Bands with all live gear, amps/drums and such is much more about keeping the vocals above the sound coming off of the stage, because most bands with amps dont understand they are only for stage sound. But thats a whole other pile of stupid.
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[User Picture]From: arcsine
2005-12-06 11:39 pm (UTC)
You got it! Remember the hot girl DJ? That's my wife, meta_x, and I was the guy in the booth with her, grilling the sound guy for similar info. I've done a _lot_ to get that place to sound half-decent, but it keeps getting ripped back apart by some of the kiddie punk bands that play there.

Yeah, it's partially to get the system to sound right for DJs as well. Tuning a system for spatial acoustics takes moving the cabinets, which the owners probably wouldn't want me to do, and most other places I've worked hang their speakers. Sucks, because a lot of them are placed all wrong and firing right in to eachothers' paths.

I think it's because they're so used to practicing with the same setup that they don't realize the room is much bigger and the audience isn't listening from the same position/direction. They just want to do whatever it was they did at practice when it sounded the way they want.
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[User Picture]From: witchchild
2005-12-07 06:06 pm (UTC)
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[User Picture]From: witchchild
2005-12-07 06:20 pm (UTC)
nevermind. Muricated wasn't accepting my login, but it is now.
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