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What is Gain Staging in Digital Audio?
Digital audio represents the audio waveform as a series of numbers, each number indicating a voltage in the electrical signal when it was converted from (or to) an analog signal. More numbers (voltage levels) represents more accuracy in the signal’s representation. Too few numbers introduces “quantization noise”.
For our purposes, the “noise floor” of a signal is the noise level in the quietest part of the recording; this might include noise that was picked up by the microphone, or dither noise that was used to cover up quantization noise inherent to digital maths. If the noise floor is less than the noise in your environment, then you won’t even notice it.
Generally speaking, 16-bits worth of numbers can recreate everything between a typical quiet-room noise and a very loud sound (i.e.“CD quality sound”). A 24 bit number can store signals from an infinitesimally small noise floor (lower than a very quiet studio), all the way up to a roaring jet-engine volume.
Regardless of the number of voltage steps, there will be a value that indicates “maximum volume”, and if you exceed that value, then the system must “clip” the excessive values to the largest possible value.
A very short “clip” is almost always unnoticeable (just at the peak of a snare-drum hit, for example). But sustained clipping, when the signal is significantly outside the bounds of the “real world”, creates lots of ugly distortion that we want to avoid.
So our goal is to prevent signals from clipping, but keep them well clear of and above the noise floor. Luckily with modern 20+ bit converters, this is very easy to do.
With modern A/D converters, we recommend that you record your signals with the peak meter never exceeding -15 dB. This indicates that the signal was far from the clipping level when it was converted to digital. With the increased low-level resolution of modern converters, it is not necessary to record at high levels.
This video discusses some additional thoughts about gain staging:
Floating-point processing
Internally, Mixbus uses a technique called floating-point math. For our purposes, this means that some extra bits are reserved to store numbers outside the range (both louder and quieter) than the range of the analog world. This means that it is essentially impossible to “clip” the math inside Mixbus. In practice, this means that you can boost a signal very loud – even louder than would normally be allowed in the analog realm – and as long as you reduce it by the same amount later, it won’t be clipped when it is heard at the output.
To this end, Mixbus provides many levels of gain adjustment which will allow you a wide range of creative options.
Region Gain and Region Gain Curves
- Region Gain and/or Gain Automation: Increasing a region’s gain in the editor will provide:
- Each region has a volume setting (accessed with the Cut Gain and Boost Gain shortcuts). The gain increase/decrease visibly affects the waveform display
- Region gain curves allow the gain to change through the length of the region
Channel Strip Gain stages
- Channel Input Trim: This stage is used to bring the overall level of the track to a usable level. The trim knob is located near the fader for easy access.
- Fader: Used to achieve an overall balance of all tracks in a session. This is also a good place to make artistic changes such as bringing an instrument forward during a solo.
- Make up gain within the In-line compressor: Make up gain is used to restore perceived level loss during compression. If the compressor meter is hitting -3 dB during transients, a make-up gain of 1 or 2 dB may be useful. It can also be used as a fast and easy way to adjust the level post fader.
Mix bus
- Input Trim: This knob is used to adjust the volume at the input of the master bus.
- Tape saturation: The tape saturation meter does not monitor level, rather it monitors the amount of saturation effect. This effect will add harmonic density which can result in an increase in perceived loudness. Turning the tape saturation knob off will allow signal to pass unaffected.
- Fader Used to achieve an overall balance of all tracks in a session.
- Make up gain within the In-line compressor Make up gain is used to restore perceived level loss during compression. It can also be used as a fast and easy way to adjust the level post fader.
Master bus
- Input trim This knob is used to adjust the volume at the input to the master bus. This is a useful tool if you’ve balanced the mix with the track faders, but the overall level is still too low or high.
- Tape saturation The tape saturation meter does not monitor level, rather it monitors the amount of saturation effect. This effect will add harmonic density which can result in an increase in perceived loudness. Turning the tape saturation knob off will allow signal to pass unaffected.
- Fader Used to achieve an overall volume of all tracks in a session.
- Make up gain within the In-line compressor Make up gain is used to restore perceived level loss during compression. It can also be used as a fast and easy way to adjust the level post fader.
- Final Limiter The final limiter is a brickwall, lookahead limiter with a very fast attack and release. The threshold is preset at -1 dBFS. If a signal peak is going to exceed -1 dBFS, the lookahead limiter will reduce the volume slightly before and after the peak. Yellow indicators show gain reduction in increments of 1 dB.
Monitor Section (if enabled)
- Attenuator provides an output level for the speakers, as well as mute and a configurable “dim” control. Use these controls to reduce the volume in your speakers WITHOUT affecting the level of the master bus output. For more details, visit the Monitoring Section
VCA Faders (if enabled)
- A VCA Fader can be used to adjust the level of multiple faders from one master fader. For more details, visit the VCA Strip section.
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