Simple Mixing questions....

[Cleffer]

I am an engineer at an NBC affiliate and have a couple of questions that you folks are more than qualified to answer. In fact, they are downright basic and stupid, but it's one of those things that hardly ever comes up until something like this happens.

We used to have an engineer here that was a major audiophile, in fact he owns his own recording studio and is extremely successful in our area. Before he left, he calibrated all of our audio equiptment, including our main audio board used for newscasts. Jump to present....

We have a new audio operator whi knows very little about audio and proper mix levels. I taught him the way I knew how, but other people have told him "Their way" and now he is extremely confused. We use Sony WRT lavs and MDR's for canned music, and that's about it....Questions..

1. I told him to set the anchor mics so the peak rides at 0db. Other people have been telling him the average should be at 0db. Who is right? It is my understanding that levels above 0db usually indicate one form or another of distortion (depending on your meter calibration)

2. Submaster A is used for mics and is much hotter than the Master output. He has been using Submaster A to set his mic level, however, the Master out suffers greatly since it is set considerably lower than the Submaster Vu. How should this situation be treated?? What about when you add another submaster for instance, a music bed?

Thanks for your time and answers. I greatly appreciate it.

Cleff....

 

[jvasey]

Cleff
If your signal stays in the anaolog realm, the peaks over 0db will be fine, but I still wouldn't keep the average as high as 0db.
More likely, your signal gets converted to digital, in which case peaks over 0db will cause distortion to be produced by the a>d converter. The people advising your guy otherwise, probably are used to the pre-digital way of doing things.

Secondly, why is your subA hotter than mains?
It should be set to match. Are you compressing the mics as a group? Is the subgroup being returned through other channels?

[Edited by jvasey on 09-10-2000 at 22:27]

 

[sonusman]

Hire me for that job!

If it pays like $50k a year that is....

Okay, about metering. There is Peak Metering, and RMS metering. More then likely, the console is showing RMS, which means that there are Peaks in the audio that CAN (notice I didn't say ARE) much higher then this. Just a clarification here.

The most important thing you don't want to do is clip the output of the mixer. It is not important to know why, just don't...

Now, many mixers are capable of up to +20db of gain before they start to distort, or clip. This effectively gives you a +20db of "headroom" (the added volume, or signal above 0db that you have to take into account transient peaks in the audio). 0db really means nothing more then a calibrated level that the equipment is set to. The inputs and outputs of the equipment can handle and create more then the 0db volume. 0db means unity gain, and is used as a way to reflect average volume. I am being redundant and vague. Anyway....

0db is the average you should have for the talking head mic. Of course the volume will go up and down a bit while they are talking, but it should stay within the parameters of the equipment without distortion.

In broadcast, the output of the mixer is ALWAYS ran into a Peak Limiter so that the input of the transmitter is never clipped. It would be a good idea to take a look at the Peak Limiter unit and see how much limiting it is doing with the RMS level of the talking head averaging 0db. If you are getting around 6-10db gain reduction, you are doing pretty good. Anything more then that, you may want to back off the volume a bit. More then around 10db of gain reduction starts making the audio sound fuzzy from the distortion caused by the compression of the levels.

Now remember, when you start adding more audio sources that will be going at the same time as the talking head, you have to take into account the added volume at the output of the mixer. Playing a bed track in the background may only increase the overall volume by a couple of db, but if you are already close to the maximum volume at the output with just the talking head mic, you really can't be adding more volume with a bed track right? So what to do......hmmmmm...

Well, you just need to bring the talking head mic down a little bit. Not much, just enough to allow for the extra volume of the bed track in the background.

Gain structures can be simple, but hard to explain. Here is my best shot (well, not my best shot, but the shot I can explain in a very short amount of time here....

The preamp for the mic should be Soloed and set so that the average level of the mic is around 0db. Remember too that the Solo function is usually POST EQ, so, make sure that you check your Solo level after applying eq to the channel.

All input sources should be set up this way initially.

Now, the output of the mixer should be set to what ever the Unity level marking is. On some console, like my Soundcraft Ghost, that is the Master Fader all the way up. On other mixers, Unity level will be marked with a 0. Put the Master Fader here and leave it alone!

Now, if you are going to run your individual channels to subgroup masters, then set the loudest channel in that subgroup to 0db on the channels fader. Mix together all the others to whatever mix you want to have.

At this point, your Subgroup Master can be set so that Subgroup is averaging 0db on the Master Fader meter.

If you are running channels straight to the Master Fader, then of course you should just set the channels faders to the level you want.

Now, just like the Master fader output of the console, the Subgroup levels can only go so high before distortion, or clipping. If you clip them, the resulting distortion will be evident at the master fader. Remember, it may be the combined volumes of the channels feeding the subgroup that are causing it to clip. If this is the case, you will need to lower the channel volumes that feed that subgroup.

Also, if you have several subgroups that are all feeding the master fader, the combined volume of the subgroups may cause the master fader to clip. In this case, you need to bring down volume of the individual subgroup master faders to prevent this.

Starting to get he point?

It is good to set up the conole so that every thing, the individual channels preamp volumes, the subgroup master volumes, the master fader volume, all are set at unity gain. If the performace is performed well, and mixed well, ou will never exceed to maximum output potential of the console, and shouldn't be hitting the limiter very much.

This is the kind of stuff that is easier to show people then to explain in print. Just remember these few things.

Set preamp levels so that the average level is around 0db.

Keep the Master Fader level set to 0db.

Adjust individual channel volumes, and subgroup master volumes appropriate to how you need the mix to sound, with the priority of the subgroup master faders being what you turn down is the output on the console is starting to get too high.

Really though, it sure sounds like you station needs a competant sound board operator. There are many issues to consider here, and someone experienced and familiar with signal path will keep your stations output sounding really good, and the levels hot (which is what the big wigs want, a station that is louder then the rest! )

I would slut my services to the man for, oh, $50 an hour, and promise of all the beaufiful anchor women to go have drinks with me....

Good luck.

Ed

 

[dobro]

All the anchors there are gay, dudeman, but the job's yours if you want it.