What follows is an article I have put together based on research I have conducted, personal practice and experience, and some enormously valuable technical help from John Scrip, A.K.A. MASSIVE Mastering. Although I’ll talk about analog systems here, the majority of this article is written to help the digital home studio.
Eliminating unwanted noise is a fundamental task in any studio, be it a digital in-the-box set up, or a purely analog rig. But perhaps the most important point of understanding your gain structure, is its impact on headroom in your mixes. As John has pointed out to me, everything starts with having and protecting the right amount of headroom at every stage in the audio production process.
Building in the right amount of head room begins with having the right gain structure in your signal chain when you begin tracking. It’s widely understood that mastering too hot is not a good thing. Mixing too hot is even worse, as it will leave less headroom for the mastering stage. But tracking too hot is the worst thing you can do to a mix. Since it’s the first stage, it drives a domino effect of hot and hotter signals throughout the rest of the audio production process.
Digital recording systems that operate at 24 bit resolution are designed to capture a high quality sound while assuring the best signal to noise ratio and dynamic range possible. Having said this, dealing with noise and distortion are a frequent challenge for the home studio operator. In the majority of cases, your equipment is not the problem, but the gain structure of your signal chain may be.
Using the correct gain structure in either digital or analog studio scenarios assures that the final result utilizes all of the dynamic range available while minimizing background noise and without any undesired signal distortion. This may seem like an obvious and generic statement, but it’s very relevant when discussing gain structure as any added distortion to your signal in an early stage of your signal chain, cannot be later removed in subsequent stage. Independent of the function of any of the pieces of gear (hardware or software) in your signal chain, it’s important to guarantee that the level of the line out of each piece of gear is adequate for feeding into the input line of the next piece of gear in the chain. Every piece of your signal chain (hardware or software) should be adjusted so that each receives the appropriate input signal. As a consequence, all pieces of your signal chain are optimized within their dynamic range.
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A good gain structure is based on having every piece of your signal chain operating within the appropriate range even though unwanted distortion in your signal can occur at any point in your signal chain. Preamps are especially susceptible to internal distortion, especially those that are built into lower end mixers. It is also possible that you microphone adds distortion, but it is more likely still that your preamp is creating the distortion. In this case, an accurate measurement can serve as a guide to solving the problem. Once distortion has been introduced into the signal, it cannot be resolved by lowering the volume of the channel. You first have to correctly adjust the gain of the preamp. Just make sure you do so without an EQ, as EQ can influence the signal being measured.
ANALOG VERSUS DIGITAL
The most critical moment to guarantee an optimal gain structure is during the tracking process. If you are working with analog equipment there will always be a certain dynamic margin (the amount of space available between a processor’s line level signal and the point in which distortion begins to occur) available before any distortion becomes evident. But keep in mind that depending on the converter and how its calibrated, analog signals can become distorted well before they will actually clip the digital converter, again assuming the converter is calibrated low enough.
But moving from the analog world to the digital world we eventually reach a point of no return wherein all of the bits are 1s and anything beyond that point corrupts the signal. Twenty four bit recording allows for much more dynamic range than we can ever achieve with analog gear, and it is important to not run an analog signal too hot (+12cBVU for example), so as to leave enough headroom. Smaller analog distortions can add up during a mix. For this reason, the importance of headroom (assuming a converter calibrated to -18dBFS = 0dBVU) is to allow healthy recording signals with lots of room for the occasional errant peak.
A possible solution is to adjust the sensitivity of the line in on your sound card. Instead of adjusting the line out of the mixing console to match the line in of the sound card, it’s possible to configure your sound card to a sensitivity of -10dBV. If the level of the signal of the line outs of the mixing console are +4dBu, you can achieve 0dBFS for the digital line in with a level of +4dB VU on the analog mixer. One tip is to insert a VU meter into your signal chain, wherein you can monitor that input levels are within reason. A -10dB signal at 0dBVU sent unbalanced is going to read 0dBVU. Just as a +4dBU signal at 0dBVU is going to read 0dBVU.
To obtain the maximum signal-to-noise ratio for a digital line in, it’s not always easy. With a 16 bit system for example, leaving 6dB of margin reduces the level of signal to noise to 90dB. Some argue to very lightly apply an analog compressor before going into the line in of the sound card. This can smoothen out the transitory peaks and raise the level of the weaker signals. However, others including John Scrip, (A.K.A. MassiveMastering), say a 90dB dynamic range is much better than nearly any input chain. A 6dB margin, even at 16 bits, is hotter than the desired input. Even if your input levels as low as -30dBFS in 24 bit (or around -15 to -12dBFS in 16 bit) that wouldn’t be leaving too much headroom.
In the digital world, a poor gain structure can have a much more catastrophic effect than in the analog world. If you saturate a virtual channel beyond 0dBFS you can damage the audio signal. The advantage of those virtual mixers is that the measurement can help you detect and resolve problems easily. All of your channels, busses or aux channels, groups or main outs, have a peak meter that gives you additional visual information about your audio signal. But if they are approaching Full Scale (0dB) the mix is too loud and all of the headroom required for mastering is being used up. Keep in mind, that in the digital world the signal is always controllable. If it’s too hot, you simply turn it down. However, in the analog world, any damage done to the signal on the way in is permanent.
And so I end this article where we began. Everything starts with having and protecting the right amount of headroom at ever stage in the audio production process. Building in the right amount of head room begins with having the right gain structure in your signal chain.
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