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LP recordings: Normalization and limiter

Posted by tketcham (A) on November 10, 2021 at 06:24:25

Wanted to post my recent discovery of using the Limiter function in Audacity to bring clipped peaks back below the 0dB threshold after normalization. Constructive criticism and alternatives are welcomed and appreciated.

I use Audacity to normalize (amplify) the LP recording to levels that are closer to CD rips and digital albums so that changing between LP recordings and digital albums I don't have to make drastic changes in volume levels. I'd been using Normalize in Audacity, setting the peaks from -0.5dB to -1.5dB depending on LP mastering, so the average RMS levels are somewhat similar. Audacity has a Measure RMS tool to check sound levels so that's helpful. But in order to get consistent gain levels it involves reducing (de-amplifying) the highest peaks down to the level of the "typical" peaks, especially for LPs with lots of dynamic range contrast. It's a tedious task and takes way too much time.

Recently I discovered another new function in Audacity, Loudness Normalization, that amplifies the waveform using the perceived loudness levels of LUFS (Loudness Units Full Scale) so it's easy to normalize the files to a relatively consistent average RMS value. I found that using a LUFS value of -15 to -16 gets me closer to digital albums, which are often -12 to -14 LUFS, without pushing the gain too much. That's helpful, but albums with wide contrasts in dynamic range cause the Loudness Normalization process to run those high peaks into the clipping zone. I sometimes have to set the LUFS value at -17 to avoid clipping peaks, but even then there can be some clipping. (See below.) So I still ended up editing peaks prior to boosting gain.

LP SIDE - PRE-NORMALIZE (Avg. RMS = 22.9 dB)

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LP SIDE - LOUDNESS NORMALIZATION at LUFS 16 with CLIPPING (Avg. RMS = 18.8 dB)

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LP SIDE - LOUDNESS NORMALIZATION at LUFS 17 with CLIPPING (Avg. RMS = 19.7 dB)

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However, I did some reading and discovered Audacity's Limiter function can bring those peaks back under 0dB using the Soft Limit setting. Now I just normalize to -16 LUFS and use the Limiter function to reduce the clipped peaks. See below.

EXAMPLE TRACK - LOUDNESS NORMALIZATION at LUFS 16 with CLIPPING

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EXAMPLE TRACK - LOUDNESS NORMALIZATION at LUFS 16 after LIMITER

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EXAMPLE PEAK - LOUDNESS NORMALIZATION at LUFS 16 with CLIPPING

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EXAMPLE PEAK - LOUDNESS NORMALIZATION at LUFS 16 after LIMITER

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EXAMPLE PEAK - PRE-NORMALIZATION

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I don't typically try to use the limiter with that many clipped peaks but from what I can see (and hear) the end result is basically what I was doing by manually editing peaks. This saves me a lot of time! I sometimes reduce amplitude of a portion of the waveform (i.e., a single song) before running normalization to avoid having so many clipped peaks to limit. I'm down to just a quick edit to remove needle drops and lifts, a quick Loudness Normalization step, and a final Limiter process if needed. My LP recordings are now fairly consistent in volume levels and closer in amplitude to CD rips or album downloads.

Comments? Questions or clarification?

Thanks,
Tom

PS: I will also mention that I got tired of having to deal with clicks and pops as a separate process so I bought a SweetVinyl SugarCube SC-1 plus, which processes the clicks and pops on the fly at 24-192 and sends a S/PDIF signal to the Tascam DA-3000 for recording. I've been very happy with the resulting sound quality of the recordings. A good balance between noise reduction and ultimate transparency.

Edits: 11/10/21 11/11/21 11/11/21

This post is made possible by the generous support of people like you and our sponsors:

Herbie's Audio Lab

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