Gain Staging using True Peak Meters
Using True Peak Meters (PPM) for Mixing and Calibrating Levels in your DAW.
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When it comes to gain staging our mixes we are afforded all manner of metering options. From the DAW specific Peak Programme Meter to the wonderful LUFS Meter we are spoilt for choice. Each meter has its uses but if I had to be honest you could replace every single one of your meters for a half decent LUFS meter. But to effectively gain stage using True Peak Meters (LUFS) we need to understand a few basic concepts.
Headroom is the difference between an audio tracks peak level (when the meter is displaying its highest value) and 0 level (ceiling) on the output meter. Let me give you a simple analogy I always use to explain headroom to my students. You are 6 feet tall and you enter a room that is 10 feet high. You have 4 feet of headroom. I know it’s simplistic but it works for me.
In digital audio we are concerned with two values: the noise floor which is the lowest or quietest value, and the ceiling which is 0. This difference between the noise floor and ceiling is what we refer to as dynamic range. In layman’s terms think of this as being the difference between the quietest and loudest part of an audio signal.
Peak Transients are simply the loudest (highest) peaks that you see when you view an audio waveform magnified.
Inter Sample Peaks can also be grouped with this fine set of problematic transients but we have ways to catch and manage ISPs. A simple yet effective solution is to set your limiter’s output ceiling to -0.3. That usually ensures that all ISPS are caught in time.
Inter-sample peaks (ISPs) occur during the D/A conversion process when the audio waveform is being reconstructed, during sample rate conversion and a multitude of other processes. Detecting and managing them are critical when it comes to gain staging and this is one of the areas that true peak meters, or LUFS meters, excel in.
Gain staging involves optimising the audio signal through each and every process whilst maintaining ample headroom and a healthy signal to noise ratio, all the way from external hardware to the final stereo mixbus. We achieve this by managing the relative gains of every process and sound and making sure not to exceed the ceiling.
Now that we understand what gain staging is let us look at an example that involves gain staging using the LUFS meter.
LUFS meter – Loudness Units Full Scale
Loudness meters are the rage nowadays and rightly so. They measure perceived loudness which is a huge step forward from measuring average or peak levels. Loudness Units (LU) are denoted in decibels, so 1 LU is equivalent to 1 dB. We also have a variant of LUFS called LKFS which adopts weighting to account for differences in frequency response. Additionally loudness measurement requires integration over time, whether that be in the long term — the entire duration of the programme — or over just a few seconds.
LUFS meters give us all manner of information and over specific times. These include the following:
Momentary – which measures loudness over 400 ms (milliseconds). This is extremely useful as we can gauge what is happening to the programme material over the last 400 ms. This allows us to view transients as they move by in the meter’s display.
Short Term – measures loudness over 1-3 seconds. This is very useful in that you can visually see what is happening to transients over this time period.
Long Term – also known as Integrated Loudness – measures the whole programme material. This is the most important value as we can see what the perceived loudness of our music is. This allows us to make mix critical edits.
True Peak – this measures inter-sample peaks (ISP) and is everything that the PPM wasn’t.
Premium Video Tutorial
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Topics covered in this video are:
- What are True Peak Meters
- What is PPM
- What is LUFS
- How do True Peak Meters work
- Learn how to manage the dynamic range of your mixes
- Understanding how meters display values using the various industry standards