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Microphone Month 3

Mackie mixer’s extra headroom explained.

Q: “Why do Mackie mixers seem to have more headroom and dynamic range than other mixers?”

A: Well, it depends on which mixers you’re comparing them to, but Mackie has done some pretty smart things to their mixers that make them very quiet when compared to just about any mixer.

One secret is how low noise the circuits are. With a lower noise floor there’s more “room” for signal. In other words, the internal signal levels don’t have to be as high to overcome noise, and this means the nominal signal level is lower, which means levels can be pushed further before major distortion sets in – and this means more headroom. How do they do this? The “VLZ” found in many of their product’s names actually means something – Very Low Impedance. As with mix amp headroom (which we’ll talk about next), “noise” is a cumulative thing. One channel might sound quiet when you’re demoing the mixer at a store, and the published noise spec might seem OK. But how will your overall mix sound when you have 12, 16, or 32 channels going? This is when channel after channel of additive noise can combine to sabotage your sound. Mackie says, “VLZ wouldn’t be necessary if we did all our recording in outer space or other places where it’s extremely cold. At absolute zero (-273 degrees Celsius), circuit components are noise-free because the atoms that comprise them are completely at rest. However, at over three hundred degrees hotter (room temperature), all the atoms in circuit components are agitated and constantly crash into each other. That causes little random voltage spikes that create thermal noise, or white noise (non-electronic types call it hiss). Mackie deals (with) thermal noise by making internal impedances as low as practical, at as many places as possible within the mixer. Very Low Impedance is achieved by scaling down resistor values by a factor of three or four, resulting in a corresponding reduction in thermal noise.”

Another factor is the mix amp. Perhaps the largest bottleneck in any mixer is the mix amplifier, where all signals come together. If it can’t handle the full force of a dozen or so simultaneous inputs plus aux returns, you hear some very gnarly distortion. Basically, as more and more signals are summed together by a console mix amp, its output level invariably rises toward the maximum operating level. Each time the number of input signals is doubled, the output level goes up by as much as 3dB (though usually less than that). It doesn’t take long to overload a conventional mix amp. And backing down the main faders doesn’t get you out of the red, since the bottleneck problem occurs before this point. Mackie says, “All Mackie mixers have main mix amps that use our distinctive negative gain mix amplifier architecture. Instead of mixing channels together at unity gain where headroom is quickly exhausted, our mixers get more headroom by mixing at -6dB. At this negative gain level, they are capable of summing four times the number of hot signals before clipping. That nets out at double the amount of mix amp headroom available with many other compact mixers.”

This doesn’t include their power supply designs or their XDR mic preamps, which we’ll cover in another inSync Tech Tip, but suffice to say that it’s not on accident that Mackie mixers are known for their headroom.

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