I need help understaing how to use a professional stage mic/line mixer.

July 13, 2012 11:06 AM

I know next to nothing about professional audio and need expert advice on how to use an intimidating-looking portable mic/line mixer for my office's webcast. What are all those knobs for?!?

My office is planning a live webcast and I have to get the presenters wired for audio. I've been handed two Shure PGX wireless kits, a Mackie ProFX8 mixer and all the necessary mic cables. I just need to mix the microphones down to a single, mono signal that I can send to my laptop.

Which input on the mixer should I use? Which, if any, should I avoid? How much of the EQ, AUX, PAN or other knobs do I need to worry about? Can I just leave them in their default positions? What do they do, anyway? And which output should I use? The unbalanced RCAs or the balanced XLR? If I use the balanced output, which one (let or right) will have my mono signal? Both? The mixer's manual offers some help but it assumes that the reader knows something about professional audio. Sadly, I don't know much.

Finally, for future reference is there an on-line resource that would help me understand how this mixer works?

Thanks in advance.

posted by Jamesonian to media & arts (11 answers total)

At the risk of asking a stupid question that might insult your intelligence, have you looked at the owners manual that is linked on the product page? On a quick skim, it seems to explain exactly what every button and knob on the mixer does.
posted by COD at 11:21 AM on July 13, 2012 [2 favorites]

You may get better advice from others, but here's my two cents:

I would use channels 1 and 2 for your sources.

Plug in using the 1/4 "headphone" style jacks.

Is there any specific reason you want the output to be mono? Stereo is likely to be better since: I would pan one channel slightly to the left and one slightly to the right (to simulate two people having a conversation). The vast, vast majority of podcasts I've listened to are stereo.

I wouldn't touch the AUX or the EQ dials unless you think that someone sounds too tinny (i.e. turn down the high EQ) or too "bass-y" (turn down the low EQ). The AUX knobs seem not necessary for your needs.

I don't think it particularly matters if you use the 1/4" or XLR outputs (I don't see RCA outs), so choose whichever works. I suspect that both sides of the XLR will contain some sound (just like both 1/4" outputs will contain some of the sound).

Disclaimer: My qualifications include running sound in high school theater productions a lifetime ago and a basic interest in this stuff. Others are likely to know way more than me.
posted by Betelgeuse at 11:31 AM on July 13, 2012

Pan will locate a mono source in a stereo field. The mixer has stereo outputs, so if you really want to record mono, you'd choose, say, the left output and pan all your mics to the left.

AUX is usually how much of a channel's signal to send to some auxilliary source. In this mixers case it may be like the MON SEND output or something? I'm not sure.

FX is how much of a channels signal to send to the FX SEND output. You'd attach your effects to this output, and then bring the FX back into the mixer on another channel usually I think. You can probably safely ignore this.

Leave the EQ alone, unless someone's mic sounds too... something (bassy, trebly, etc) and then adjust as required.

GAIN is how much amplification to use in the mic input. Generally keep it as low as possible while getting enough sound from the mic. A good starting place might be to put slider in the middle of it's range and then adjust the gain until it's about right. If it sounds distorted, turn the gain down.

Regarding outputs, ignore the balanced outs - these are for sending to something that has a balanced in and your computer isn't that. "Balanced" lines are basically using 2 wires to send 1 signal. The actual way it's done isn't important but the purpose of it is to reduce noise in very long cable runs.

You can choose which output you want, any of the following is probably fine:
* headphone out
* tape send
* monitor send
posted by RustyBrooks at 11:31 AM on July 13, 2012

Oh! And if you're going to use the "unbalanced" outputs, I think the "Main Out" outputs are your best bet (note that there is a left and right channel for those, too).
posted by Betelgeuse at 11:37 AM on July 13, 2012

"At the risk of asking a stupid question that might insult your intelligence, have you looked at the owners manual that is linked on the product page? On a quick skim, it seems to explain exactly what every button and knob on the mixer does."

I have, actually, but you'd be surprised how much of the technical explanation presumes an underlying understanding of audio engineering. "The left flange adjust your floober level". What's a floober level?!? You get the idea.
posted by Jamesonian at 11:53 AM on July 13, 2012

You'll need two mic cables (xlr -> xlr), one for each of the PX4 wireless units. Run them into mic inputs 1 and 2.

Plug some headphones into the mixer and bring up the monitor fader to unity. Put the phones gain knob (right above that fader) up about halfway.

Bring up the faders on 1 and 2 to unity.

Power on the mics and adjust the white "gain" knob while using the mic to set a good level.

Push in the "low cut" button right below the gain knob to remove rumble and desk noise.

You can ignore the EQ, Aux and Pan knobs (unless you want to spread out the two mics in the stereo field a bit, as suggested above). Leave the EQ and Pan knobs straight up and the Auxes all the way left.

Now you'll need a cord that goes into your laptop (1/8" mini jack) on one end and is split into two 1/4" jacks on the other. Try Guitar Center. Put the main fader up to unity and you should have signal coming into your laptop ready to be recorded.

(Alternate cable - RCA -> 1/8": use the 'tape out' outputs at the top of the mixer and turn up the 'tape level' knob above the main fader to adjust the output. Also, in this situation there is no reason to use the 'tape in' inputs at all. You can safely ignore them for now.)

There's no way to put "just mono" into your computer (unless you have a digital i/o device, which you didn't indicate) - but if your pan knobs are straight up, both the left and right signal will contain the same information, and will create a "mono" output when used together.
posted by Aquaman at 12:20 PM on July 13, 2012

It might be worth your time and money to hire someone to spend an hour or two with you to show you how to properly use your equipment. There are a million little things that could go wrong, but once you understand the basics in a somewhat comprehensive way, troubleshooting is not too difficult.

For example, if you just clip on the wireless lapel mic to the presenter, and they move around a lot, they may cause a whole lot of noise to be picked up on the recording. There are a few very simple things you can do to prevent this, but if you didn't know that ahead of time, you might find your recording to be unusable. (for example, you can make a very small loop in the cable just below the microphone element, and tape that to the inside of a jacket or shirt. This will help to prevent the mic from picking up as much noise from cable vibrations.)

I teach recording and audio lessons in the Seattle area, and I could probably show you enough in 2 hours for you to have great results with your system. The $60 it would cost you is much much less than the price of your equipment, but would end up giving you a huge improvement in quality.

Put an ad on craigslist, and I'm sure you can get some expert advice for a small sum of money.
posted by markblasco at 12:46 PM on July 13, 2012

Each mic unit plugs into a mixer input, preferably using XLR (which balances the audio to reduce noise.)

Each mixer input, set the EQs to center (and turn off the EQ bank if possible), set the pan to center, turn the auxiliary sends (AUX, FX, whatever) all the way off, and set the fader to 0.

Now, you have only two things to play with: the GAIN on each individual input, and the master sends (L and R) that will go to the machine webcasting this.

To make it easier, set the master sends to 0 just like you did each track fader. Put the mics on some standins in advance, and have them sit/stand (whatever the presenters will do) and talk amongst themselves, ignoring the mics. Adjust each track's GAIN so that the level indicator for that track is neither fully lit (LEDs all lit up to the top) or barely lit (few or no LEDs lit) as they talk. Repeat for all the mics.

That is it, you're done until the show. During the show, lower all the track faders except the people talking; for the people talking, turn the track fader up to 0, then push the fader higher or lower if someone is either really quiet or really loud, to get them back to that neither fully lit nor barely lit state while talking.

Hope that helps!
posted by davejay at 1:04 PM on July 13, 2012

but you'd be surprised how much of the technical explanation presumes an underlying understanding of audio engineering.

If that's the position you're in, then I really really really strongly second markblasco's suggestion that you pay a pro to give you a hands-on lesson, maybe even to work your first webcast.

Because Mackie manuals are seriously about the best in the business for taking somebody from "utter NOOB" to, "Hey! Sound comes out!"

You can also check out their Support page, which has links to a useful FAQ & a Glossary.

I'm pretty sure everybody else here is right - I seriously can't read the replies in detail without My Eyes Glazing Over (nobody's fault but mine; busman's holiday) - but honestly I don't see any answers that are significantly less "technical" than the manual.

You have a whole pile of questions. If I was in the room with you I could explain it in a couple of hours, as mark says. Trying to answer all of them from scratch using only words, no diagrams, no way to demonstrate "turn this knob and this happens - ya stumped me.
posted by soundguy99 at 10:36 PM on July 13, 2012

Also, another way to find a reputable pro to help you out besides Craigslist (Craigslist honestly, IMO, being very much a YMMV situation depending on the city you're in - there are quite a few people advertising their "pro audio" services on my local C'list that I wouldn't trust to mix cake batter, much less a band);

These days just about every single college, university, community college, etc etc has some kind of "music technology/audio engineering" program. My experience has been that the instructors are all active pros, teaching as a second job/moonlighting. Look to see if any college near you has some kind of course in this audio stuff and contact the instructors.
posted by soundguy99 at 8:57 AM on July 14, 2012

I'd like to thank those audio professionals who recommended that I find an audio professional. Unfortunately, if that was a viable option for me I wouldn't be in this predicament. Time does not permit it as the show goes live on Monday.

I'd also like to thank davejay who did what others couldn't and gave me the perfect answer that I need to get started. I can't thank you enough.
posted by Jamesonian at 6:47 PM on July 14, 2012