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How does Match Loudness actually work?

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How does Match Loudness actually work?

Postby HastieBeatz » Thu Apr 19, 2018 9:02 am

Hello!

I'm looking to set up a process for normalising my audio files, but in a pretty manual way. Basically, I want to know all the steps that are taking place throughout, rather than letting Adobe Audition use an automated process. The Match loudness process is close to what I'm looking for, but I'm thinking of the following basic steps:

1. Hard Limit - figure out what level to hard at based on a particular stat of the file.

2. Normalise to -2db

3. More? let me know if I should be adding.

It's step 1 I need some help on. What stats would you use to figure out a starting point for the hard limit? I know you're going to say 'it depends, needs to be done by eye' but the trouble is I need to write a script around this to allow it to be done automatically.

So, the Amplitude statistics give me a lot - do one of the RMS measures give me a decent starting point? Eyeballing it, the Maximum RMS Amplitude looks like it's in the right ballpark, for example.

Any help would be appreciated!
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Re: How does Match Loudness actually work?

Postby Dave B » Thu Apr 19, 2018 11:35 am

Have a google / search this forum for references to the LUFS scaling. These are 'loudness units' and are designed to indicate a perceived loudness to a track. Hard limiting these days is frowned upon as an old 'loudness war' technique and is now only used to (as it should do) catch the high peaks in dynamic audio. RMS is no longer an indication - it's been superceded by checking your LUFS metering.
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Re: How does Match Loudness actually work?

Postby Hugh Robjohns » Fri Apr 20, 2018 10:44 am

HastieBeatz wrote:1. Hard Limit - figure out what level to hard at based on a particular stat of the file.

2. Normalise to -2db

3. More? let me know if I should be adding.

Just be aware that this processing isn't matching loudness -- it's matching peak level, which is a very different thing!

There are plenty of third-party algorithms around based on the ITU-R BS1770-4 standard that genuinely match loudness between files in both manual and automated batch processes. The Nugen Audio AMB is one such which works very well:

https://www.nugenaudio.com/amb-audio-ma ... correct_59

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Re: How does Match Loudness actually work?

Postby CS70 » Fri Apr 20, 2018 5:21 pm

HastieBeatz wrote:Hello!

I'm looking to set up a process for normalising my audio files, but in a pretty manual way. Basically, I want to know all the steps that are taking place throughout, rather than letting Adobe Audition use an automated process. The Match loudness process is close to what I'm looking for, but I'm thinking of the following basic steps:

1. Hard Limit - figure out what level to hard at based on a particular stat of the file.

2. Normalise to -2db

3. More? let me know if I should be adding.

It's step 1 I need some help on. What stats would you use to figure out a starting point for the hard limit? I know you're going to say 'it depends, needs to be done by eye' but the trouble is I need to write a script around this to allow it to be done automatically.

So, the Amplitude statistics give me a lot - do one of the RMS measures give me a decent starting point? Eyeballing it, the Maximum RMS Amplitude looks like it's in the right ballpark, for example.

Any help would be appreciated!

What Hugh says. The loudness factor is a function of the integration of the peak curve over the most relevant portion of the song. A way to lower it is to have as less as possible between peaks - if your waveform looks like a double comb, for example.
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Re: How does Match Loudness actually work?

Postby HastieBeatz » Mon Apr 23, 2018 9:53 am

This is really useful - thanks so much for the help folks.

Out of interest, then, if I use loudness, is that not still going to be affected quite negatively if I have a file with some nasty peaks, or would you expect a loudness adjustment process to include a touch of compression to bring down those peaks first?

Or... would doing a hard limit to get rid of the worst peaks, then a loudness process to bring it to 19 or 16 lufs, for example, be a good approach?
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Re: How does Match Loudness actually work?

Postby job » Mon Apr 23, 2018 8:38 pm

HastieBeatz wrote:Out of interest, then, if I use loudness, is that not still going to be affected quite negatively if I have a file with some nasty peaks, or would you expect a loudness adjustment process to include a touch of compression to bring down those peaks first?

Depends on the window that's used for the leveling/matching. The shorter the window the more the peaks are brought inline with each other.
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Re: How does Match Loudness actually work?

Postby CS70 » Mon Apr 23, 2018 9:38 pm

HastieBeatz wrote:This is really useful - thanks so much for the help folks.

Out of interest, then, if I use loudness, is that not still going to be affected quite negatively if I have a file with some nasty peaks, or would you expect a loudness adjustment process to include a touch of compression to bring down those peaks first?

Or... would doing a hard limit to get rid of the worst peaks, then a loudness process to bring it to 19 or 16 lufs, for example, be a good approach?

Actually the reverse is true. The less you limit (so long you don't exceed the max headroom of course) the better off you are, because you will retain more of your dynamic range.

There is no "loudness process" to apply, other than good mixing of course :-) Loudness is a number quite directly correlated to the shape of your waveform (in a little more detail, for ITU-R BS.1770-3, the shape of your waveform when seen in overlapping 400ms samples and after applying a mid-highs shelf boost and a hi-pass filter whose corner freqs depend on the sample rate... but shape nonetheless).

What happens is that on playback, the source will apply a volume gain or de-gain until that number equals a target number. Then - and that's the critical bit - the user will use their own volume control to increase or decrease the level as they like. Assuming the user sets his volume so he can hear the quieter bits, the louder bits will *really* pop out, making things far more exciting.

So, so long your song is well balanced (i.e. the relationship between the loud bits and softer bits is as you like, and as suits your music), and your master output is set to be in the ballpark of the target number used by the source, you're all set. The source won't change the level much and it'll be only the user to have control on the volume, and able to use the full range of his playback system. The "loudness process" is only about moving the master slider, perhaps.
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Re: How does Match Loudness actually work?

Postby job » Tue Apr 24, 2018 2:04 pm

job wrote:
HastieBeatz wrote:...if I use loudness...
Depends on the window...

My bad, for some reason i was thinking that you wanted to control those peaks and was therefore thinking of some kind of leveling process... even though i quoted you asking about loudness :headbang:
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