Gain structure

One of the most common mistakes that I see are being made with something simple as gain structuring. But is it really that simple?

Well, to understand how to correctly structurize all the levels in your production we first need to understand a little bit more about how sound levels are measured.

dB’s relative to scales

Sound is measured in dB’s, which stand for Decibels. The dB is logarithmic, which means that the represented power doubles every 3dB increase. The decibel is also relative to a scale, of which there are a lot, for instance: dBSPL (Sound Pressure Level), dBv (referenced to 1 Volt) and dBu (unloaded, no output impedance). Where the first scale is used to measure acoustic sound, the second and last scales are meant to measure electronic sound levels.

Measuring

Measuring electronic sound levels has its roots in the analog domain, where a certain voltage represents a certain decibel level. For 0 dBu this is 0.775Volts. The standard world wide studio calibration level is +4 dBu, (1.225Volts). For every piece of equipment, there is a maximum amount of dB’s which it can handle before “clipping” occurs. The standard for our Neumann N20 console is +22dBu (which is more than 9 Volts!!!). The room between the nominal +4 and +22 dBu is called headroom, in other words, to leave room for dynamics and transients.

Clipping

BBgwPSo, what exactly happens when a signal clips? Well, the small amplifiers and signal generators can’t handle the amount of level anymore, and they will cut off before the peak of the waveform is reached, as you can clearly see in this image.

Digital levels

Okay, that is cool, but what if I would work in the box? Well, digital levels are measured differently again, they are measured on the dBFS scale, which stands for Decibels on Full-Scale. 0dBFS represents the maximum level your converter can produce. Because this level depends on the type of equipment you use (which can scale from your laptop’s output to a professional Apogee converter), there is no conversion formula. In White Sea Studio, the calibration is set to -18 dBfs = +4dBu, this means that at 0dBFS we will have a +22dBu output level at the converter.

Why should I care?

Well, where analog clipping is a little bit forgiving, (since it can’t make a pure DC straight line), digital clipping isn’t. Where analog clipping can actually bring a sort of warm feeling to the sound, digital clipping will sound harsh and not nice to listen to. Studies have even shown that the human body responds in a negative way to digital clipped sound.

My advice: Keep your levels low, at say: -20 dBFS, most certainly when working in the box, since there are few chances of noise production. Also, keep a good eye on your levels in between different pieces of outboard or plugins!

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