Calibration and Levels

**Apple** · 06-18-2004

Any input on proper calibration of the meters of mixdown deck with the meters on a mixer?. I read somewhere that you could simulate a fairly good tone generator by hitting a certain note on a synthesizer. I can't remember now. My meters on my Mackie don't exactly match up with my HD-24. I don't think I can do anything to calibrate those.

**Cloneboy Studio** · 06-18-2004

They aren't supposed to be 'the same'. Different gear has different levels before they clip. Decibels as a measurement don't really translate very well as an absolute measurement of sound level.

**DonF** · 06-21-2004

Originally Posted by Apple

My meters on my Mackie don't exactly match up with my HD-24. I don't think I can do anything to calibrate those.

Cloneboy Studio is right. They're not supposed to be the same. A big part of the reason is that they're designed for different purposes.

On analog equipment like the Mackie, "zero" on the meter represents the nominal operating level. You want to keep your levels near zero most of the time, with peaks going above (sometimes well above) zero. As the signal goes above zero, distortion increases gradually until the device's absolute maximum level is reached; this level might be +24dBu. At that point, waveforms are clipped, and the sound becomes rather unpleasant. Between zero and the clipping point is what's called "headroom".

Digital equipment, on the other hand, uses zero to represent its absolute maximum level. The number of bits used in the device's representation of digital audio mathematically determines the highest signal level that can be recorded. The analog electronics in the A-D convertors are calibrated to provide that "full-scale" signal when a certain signal level is present at the analog inputs. Up to that level, the waveform can be accurately represented, and there should be no apparent distortion. But if the level goes above the maximum, the hardware runs out of bits, and simply clamps the signal to the highest level until it drops down again. The sound is way beyond unpleasant.

A-D convertors usually have a nominal operating level, often represented by a color change on the meter (from, say, green to yellow). Generally, though, they don't mark it with a zero. On the HD24, I believe the nominal level is -15dBFS (that's 15 dB below the "full-scale" reading). If you use this as your nominal level, you have 15dB of headroom. This is roughly in the same ballpark as many analog recorders, but remember that the "ceiling" in digital audio is much harder than it is in analog; so it won't hurt to give yourself a little extra headroom.

Then we run into the issue of analog interface levels. Most pro equipment is "+4", which means that zero on the meters gives you +4dBu (1 volt into a 600 ohm load) at the output. A lot of prosumer gear runs at "-10" (-10dBv, or -10dbV, or -10dBu, which are all slightly different). Mackie compromises by saying "zero is zero" -- 0VU is 0dBu (0.775V into 600 ohms), so when you plug the output of the Mackie into the HD24 and run a test tone at 0VU, you should see (*scratching head*) something like -19dBFS on the HD24. If you use that as your nominal level, you'll have 19dB of headroom on the Alesis. When you're hitting the ceiling on the Alesis, the Mackie will still be in its comfort zone, since it supposedly has 26dB of headroom.

Bottom line: I wouldn't worry too much about the different readings on the meters. Just use zero on the Mackie as your nominal level, and all should be well. If you're concerned that your mixes aren't coming out hot enough, don't worry. Getting the mix hot is the job of the mastering engineer.