calibrating recording chain?

[canadave]

Hi all,

Okay, I'm just an amateur trying to do what really should be a professional's job, so bear with me Use words of one radio syllable please!

I'm trying to calibrate things at our community radio station. We record voice tracks into Adobe Audition. The output from Audition is sent out via the computer's sound card to our radio console, which has an audition bus with left and right VU meters. I'd like to calibrate everything so that the meters in Audition and the VU meters give useful and correct information to anyone recording.

I see there is a way in Audition to generate a 1KHz test tone. I assume that will be what I use to calibrate things, correct? If so, I just need some details on the process:

1. The tone itself should be Base Frequency = 1000Hz, Frequency (under "Frequency Components") = 1000Hz, and both the Volume sliders should = 0db...correct?

2. Once I've generated this test tone, what level should the Adobe Audition meter show when I play back the tone? 0db?

3. When I play back the tone, there are a few things I can set: the fader on the radio console, the fader on the computer sound card output, and the VU meter trim on the radio console. What should I be setting to what? Should the fader on the radio console be full up (0db)? Should the sound card fader be full up?

I'm just not sure what levels I'm aiming for on the VU meter and the Adobe Audition meters, and I'm also not sure where the various faders should ideally be placed in order to achieve whatever it is I'm trying to show on the meters.

Thanks for any help you kind folks can provide!

 

[frankberry]

You really need professional help. 0dB on Audition is the absolute peak digital level before clipping.
You will need 15 or 20dB headroom for your recordings.
I suggest that you record a -15dB 1kHz test signal using Audition. This should be a good starting point for setting levels.
DO NOT adjust the VU meter trimmers.
I strongly urge you to call a local radio station and get some technical help.

 

[Goat Rodeo Cowboy]

Maybe I am your kind of guy. I often use a lot of single syllable words.

Some of the questions you have asked do not have a firm, finite answer. As they say when playing cards, "Dealer's Choice" on some of your puzzles.

On a steady tone, you can get the "meters" in AA to read zero and get your console meters to read zero but then when you record some voice or music and play through the system, you are going to see some difference in what the meters seem to be telling you. Get ready for a big word: That is what the big-boys call ballistics. The on-screen meters in AA are totally electronic and they can very in real-time indicate voltage peaks. I don't know what meters they are putting in consoles these days, but the traditional VU meter as we have known it through the years is a little bit of a slower acting, power averaging indication. Kind of like a graceful young lady skipping down the sidewalk while humming a waltz or something.

You didn't tell us which version of AA you are using, and which version of operating system you are using. Or digitizing hardware (sound card). In Windows 7, for instance, many of us no longer have meters or volume sliders on a screen to set inputs and outputs.

When you are recording something via AA, you set whatever input control you have (knobs on a pre-amp or USB device) so that peaks indicate "X" Here is where you will get 5 opinions if you have 4 people in the room. You want your recording volume set so the very loudest peaks are maybe -3, some people prefer somewhere around -6 and other like -9.... and here I am describing the waveform you see on the screen when the recording is done. The little on-screen horizontal meter(s) of Audition should indicate similar peaks.

Feeding out of the computer and into an analog mixing console.... this is where you will get a lot of opinions. The buys who set up for mixing house-sound for concerts and for house-sound in places of worship, talk about "gain staging" and when you are mixing 32 or 48 channels and you have a lot of in-line processors involved, this gets critical.

If I were doing what you are doing, I would set the console faders where you normally want them to work (70%?) and then simply adjust the output of your AA/computer so that you get the meter readings you want on the console.

// ***** //

This is almost another topic. I walked you through choosing a normal recording level. As an "editing" process you not only want to find the begining and end of your recording and "bob-off" the noise and dead space before and after, but now that you can see the loudest place in your recording, you want to either adjust the entire file until the very highest peak is 0 or -1 or -3 or whatever standard your station had decided upon. (This would be called "normalization" and AA has a process that will do that for you. Better you, you may want to run the recording through a "compression" process to bring down not only that one highest peak, but all peaks that stick up way beyond other typical content levels. Compression is an acquired taste. It is like your wife asking: "What color dress should I wear today?" If you compress, then normalize afterwards.

Have I confused you? Now, do you have a whole new set of questions?

By the way, using 1khz tone has long been a handy steady-state program signal when synchronizing meters in a series of devices. AA will also generate for you WHITE noise or PINK noise. (The newest version of AA also has a new category: BROWN noise!!!) You might also want to look at your levels using a broad spectrum of sound in addition to just using the narrow 1khz tone.

 

[Telosian]

Hi Canadave. You say your console has an audition bus with VU meters. I'm guessing this is an analog console. If you can share the brand/model, it will be easier to help you. As Mr. Berry pointed out, 0dB can mean different things on different gear. 0VU for example is usually +4 dBu in a calibrated system (although not always). What Audition calls 0dB doesn't give us any clue. Since dB is always a relative value, we need to know the reference. If it is near clipping, then it really should say 0dBfs for Full Scale. But let's sort that after we get your console information. Too many variables now. Given the brand of the console, we'll know some things about your system levels and this will give us a starting point to calibrate Audition.

 

[Robert Bass]

I'm not sure about the current version of Adobe Audition, but if the scale it uses is dBfs (like the older versions), then -15 dBfs on Audition's meters = 0 dBvu on a traditional analog meter. Most digital metering systems use dBfs whereby the "fs" stands for full scale.

R

 

[Goat Rodeo Cowboy]

keep in mind that AA does not CONTROL and does not METER (for calibration purposes) what the output from a computer sound card will be. The implied definition of zero level in Audition would be the full scale definition. Audition is only metering the signal that will cause the peak to sneak up and kiss the point at which clipping begins.

The metering mechanism in Audition has no knowledge whether you are simply observing the visiual dynamics of the audio signal (How loud, how consistent) or setting the gain level in the output section of your hardware device. Just for grins (and conformation) I just opened up Audition and loaded an existing file. Audition throws a fit and temper-tantrum that you do not have an audio hardware device attached and tries to brow-beat you into linking to one. But it will open the file, and it will allow me to do some audio processing to the file including normalizing and changing the overall gain a stated amount.... in dB's.

So how would Adobe put a designation as to what 0 dB means... when the software really could care less what the output hardware is. Now, with my external unit plugged back in, I can go to the front panel of the hardware and mechanically change the ACTUAL hardware output level of the signal, and the metering on the Adobe Audition screen does not change while the audio does change.

In discussions like this, we tend to want to make a computer software (Audition or otherwise) behave just like blood-and-guts hardware with tubes, transistors and power plugs do. In a concert hall or in a church or in a high school auditorium, we are concerned that EVERY piece in the audio chain operates at an audio level that keeps peace in the family, and letting one piece of equipment operate outside of its favorite range can totally destroy the output signal. The meter indications of Audition are not an identical twin to what happens in a piece of hardware in a recording or house sound system.