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diff --git a/normalization.md b/normalization.md new file mode 100644 index 00000000..31e73aa5 --- /dev/null +++ b/normalization.md @@ -0,0 +1,107 @@ +[[!meta title="Normalizing audio"]] +[[!meta copyright="Copyright © 2026 Dhruv Kadam"]] + +## Classifying Audio + +Before getting started normalizing, you should quickly check what kind +of audio you have. I find that it can be broken into four basic types. + +### Ideal Audio + +This is the kind you want. This audio has a consistent volume (Low +distance between peaks and valleys), and little to no background noise. + +### Semi-Ideal Audio A + +Audio with consistent background noise, yet consistent volume. This will +look like Ideal Audio for the most part, but the areas without speech +won't be silent. Consistent background noise means something like a fan +going in the background, or the noise of a highway audible in the +recording. + +### Semi-Ideal Audio B + +Audio with no background noise, but not consistent volume. This can be +identified by large distances between peaks and valleys. + +### Sub-Ideal Audio + +Audio with background noise and no consistent volume. Combines the worst +traits of Semi-Ideal A and B. + +### Note + +All of the above assume that the speaker is audible throughout. If the +audio includes noises that overpower the speaker, or the speaker cutting +out, then you should attempt to get a re-recording if possible. I +suppose you can use an AI tts solution as well, but that depends on if +you have the original script. + +## Audio Normalization + +### Ideal Audio + +For basic normalization of Ideal Audio (recorded at a mostly consistent +volume and good quality), you can use FFMPEG. + +``` example +ffmpeg -i input.opus -af "loudnorm=I=-14:TP=-2.5:LRA=10" output.opus +``` + +::: center +Apply loudness normalization filter and target for -14 LUFTS, -2.5 true +peak, with the distance between the quietest and loudest points being at +most 10 decibles +::: + +I find that this is the optimal range, with lower LRAs sounding tinny. +Keep in mind the true peak means that anything above it will be cut off +abruptly. Better than clipping, but not by much. + +You can also use the loudness normalization filter in [Audacity. Linked +is a short +guide](https://www.youtube.com/watch?v=RR7fCquUDAM&pp=ygUfYXVkYWNpdHkgbG91ZG5lc3Mgbm9ybWFsaXphdGlvbg%3D%3D). +If you do this, make sure to use the legacy limiter filter to set a true +peak. + +### Semi-Ideal Audio A + +- First, normalize the audio to something high, such as **-6** or **-5** + LUFTS. This makes the background noise profile much more obvious. +- Secondly, open Audacity and use the [Noise reduction + filter.](https://www.youtube.com/watch?v=bMefnFkCanE&pp=ygUYYXVkYWNpdHkgbm9pc2UgcmVkdWN0aW9u) +- Then, follow the steps for Ideal Audio. + +### Semi-Ideal Audio B + +- Open Audacity and determine the peaks and valleys. +- Use the **Normalize** tool (Not *Loudness* normalize!) to bring the + valleys down to the median. You don't have to target your desired + LUFTS level. In fact, I would recommend targeting about 6 DB above it. +- Utilize the Compressor tool, I find that the Podcast/Radio preset + works well. +- Now follow the steps for Ideal Audio. + +### Sub-Ideal Audio + +- First, normalize the audio to something high, such as **-6** or **-5** + LUFTS. This step can optionally be skipped if the noise is loud + enough. This makes the background noise profile much more obvious. +- Secondly, open Audacity and use the [Noise reduction filter.](https://www.youtube.com/watch?v=bMefnFkCanE&pp=ygUYYXVkYWNpdHkgbm9pc2UgcmVkdWN0aW9u) +- Follow the steps for Semi-Ideal Audio B. + +# Additional Notes + +- The filter curve EQ, as well as Bass and Treble boost or any other + volume-based Audio "Touch ups" should be used after normalization. + Using them before would defeat their purpose. +- The point where noise reduction is used is the best time to use other + distraction reducing tools, such as click reduction. +- Do not use the legacy compressor in Audacity, as I find it lowers + audio quality. Legacy limiter is okay though. +- You can use the "Fix Clipping" tool under the analyze section to, + you guessed it, find clipping. +- I've had mixed results with the clip fix tool, but it's worth a shot + if there's no other options. +- If you use an AI "voice cloning" tts solution, remember that any + noise that shows up in the sample clip will be added in the tts. |