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Author Topic: dynamic compression, the pros and cons  (Read 473 times)

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Offline nulldogmas

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dynamic compression, the pros and cons
« on: January 05, 2020, 10:21:03 AM »
I've long applied a smidge of dynamic compression on just the loudest bits of my recordings — say, a 4:1 ratio on everything over -4dB, after normalization — to create more headroom to increase the volume of the overall recording without affecting the sound. (In my experience, most of those high peaks are things like stray extra-loud snare hits that don't sound much different if dynamically compressed a bit.) But I've also wanted to find ways to use compression to address another issue: shows where quiet songs are interspersed with loud songs, to the point where when listening back on speakers you're tempted to continually twiddle the volume knob so that you can hear everything at a pleasant level.

The results so far have been ... not great. If I apply a low compression ratio to everything above the peak level of quiet songs (say, -12dB), the levels work nicely on speaker playback: the quiet songs sound quiet, the loud songs sound loud, but both are nicely audible at living-room playback levels. On headphones, however, the loud songs, which got hit by the compression stick, begin to sound faintly unnatural, with less room to breathe than in the uncompressed versions. I'm finding that's the case even with very low compression ratios, by which point I'm not adding much volume to the quiet bits anyway.

Any suggestions from more experienced audio editors for tricks I could try, or is this just an inherent tradeoff I'm going to have to live with? I recently asked a professional audio engineer friend about this issue, and he replied that “the art of knowing how to use compression well is 90% of what I do, and can’t be replaced by a plugin,” which was simultaneously reassuring and not at all helpful…

Offline jerryfreak

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Re: dynamic compression, the pros and cons
« Reply #1 on: January 05, 2020, 10:23:28 AM »
you literally have to normalize them track by track to maintain dynamics
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Offline nulldogmas

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Re: dynamic compression, the pros and cons
« Reply #2 on: January 05, 2020, 12:01:05 PM »
you literally have to normalize them track by track to maintain dynamics

I thought of that, but then I'd end up with obvious seams where the volume levels suddenly drop or rise. Not to mention the question of what to do about loud songs with quiet sections.

Offline opsopcopolis

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Re: dynamic compression, the pros and cons
« Reply #3 on: January 05, 2020, 12:08:17 PM »
In theory you could achieve what you're trying to do solely with compression, but you'll end up with a lot of artifacts because you'll be squashing the louder tracks by 12db (in your example.) In my experience, the best way to handle something like this would be to manually bring up the volume of the quieter tracks to meet the louder ones. You could do that any number of ways, but I can't really think of an automatic way that won't leave you with considerable artifacts.
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Offline nulldogmas

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Re: dynamic compression, the pros and cons
« Reply #4 on: January 05, 2020, 12:36:41 PM »
In theory you could achieve what you're trying to do solely with compression, but you'll end up with a lot of artifacts because you'll be squashing the louder tracks by 12db (in your example.)

Not by quite that much — if the top 12 dB is squashed by a 1.5:1 ratio, then it's only lowering the loudest bits by 4 dB. (I think. logarithmic scales make my head hurt.) But yes, there is squashing going on, and hence artifacts.

I guess my question is whether there's any particular technique of squashing that is less noticeable to the human ear and brain, or if it's always about finding a happy medium between two less-than-ideal results.

(The third option I guess would be to always play back my recordings at real-life volume on a concert-venue PA system, but I suspect the neighbors would complain.)

In my experience, the best way to handle something like this would be to manually bring up the volume of the quieter tracks to meet the louder ones. You could do that any number of ways, but I can't really think of an automatic way that won't leave you with considerable artifacts.

I'd be fine with doing this manually, but any suggestions for making the seams between the loudened quieter tracks and the unenloudened loud tracks less awkward? I'm especially stymied by places where a loud organ wash or guitar squall slowly fades out, for example.

Offline EmRR

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Re: dynamic compression, the pros and cons
« Reply #5 on: January 05, 2020, 12:56:52 PM »
Transients many times sound better in a clipper/brickwall limiter with lookahead versus compression. 

Try parallel compression at a low ratio for the question of bringing up low level detail and averaging out overall volume. 
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Offline jerryfreak

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Re: dynamic compression, the pros and cons
« Reply #6 on: January 05, 2020, 08:10:07 PM »
you literally have to normalize them track by track to maintain dynamics

I thought of that, but then I'd end up with obvious seams where the volume levels suddenly drop or rise. Not to mention the question of what to do about loud songs with quiet sections.

its doable, albeit time intensive

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Offline heathen

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Re: dynamic compression, the pros and cons
« Reply #7 on: January 05, 2020, 11:30:44 PM »
Try parallel compression at a low ratio for the question of bringing up low level detail and averaging out overall volume.

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Re: dynamic compression, the pros and cons
« Reply #8 on: January 06, 2020, 08:26:58 AM »
Envelope tool, increase volume of quiet parts, decrease loud ones. I use this a LOT for quiet acoustic concerts with enthusiastic applause.

Offline nulldogmas

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Re: dynamic compression, the pros and cons
« Reply #9 on: January 06, 2020, 09:49:00 AM »
Try parallel compression at a low ratio for the question of bringing up low level detail and averaging out overall volume.

https://taperssection.com/index.php?topic=137594.0

Thanks — I've been struggling to understand the benefits of parallel compression vs. just adjusting the regular compression curve, and as usual Gutbucket explains it in a phrase ("At high level portions the uncompressed track drowns out the compressed copy completely").

Offline Gutbucket

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Re: dynamic compression, the pros and cons
« Reply #10 on: January 06, 2020, 11:59:17 AM »
Parallel compression is sometimes referred to as "bottom up" compression, which is helpful in differentiating what it does in comparison to standard compression which brings the "top down".  Parallel comp is especially useful for this type of application because when set correctly it automatically brings up the level of the quieter portions without negatively impacting the loud parts.

It's usually best to use a combination of both approaches, or even extend it further in a 3-way approach.. each doing little bit such that the combination of all three provides the desired reduction in overall dynamic range in a more transparent sounding way:

Narrow fast-acting limiting/comp to control errant high peaks (bringing the "top down")
Wider slow-acting compression (general program "leveling")
Parallel compression to raise the low-level material (bringing the "bottom up")

I recently asked a professional audio engineer friend about this issue, and he replied that “the art of knowing how to use compression well is 90% of what I do, and can’t be replaced by a plugin,” which was simultaneously reassuring and not at all helpful…

True on both accounts. It's artfully applied EQ and Dynamics for the most part.
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Offline nulldogmas

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Re: dynamic compression, the pros and cons
« Reply #11 on: January 06, 2020, 05:59:51 PM »

It's usually best to use a combination of both approaches, or even extend it further in a 3-way approach.. each doing little bit such that the combination of all three provides the desired reduction in overall dynamic range in a more transparent sounding way:

Narrow fast-acting limiting/comp to control errant high peaks (bringing the "top down")
Wider slow-acting compression (general program "leveling")
Parallel compression to raise the low-level material (bringing the "bottom up")

Thanks, very helpful, as were all your posts in that long-ago parallel compression thread.

So when doing parallel compression, do you generally keep your attack and release settings fairly low? (There's a mention in that thread of Bob Katz recommending a near-zero attack time and 0.25s release time.) In my initial trials, that's very effective at changing the relative volume ratios of loud and quiet sections, but it also has the effect of raising the quiet bits of loud sections (in between drum hits, say), which is something I'm hoping to minimize.

Offline Gutbucket

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Re: dynamic compression, the pros and cons
« Reply #12 on: January 06, 2020, 07:20:19 PM »
You want relatively aggressive attack and release times on the parallel comp, generally.. but whatever works.   You don't want to hear low level "breathing" from a slow release, and transients through the non-compressed parallel channel generally cover the fast attack distortions.

Make-up-gain certainly brings up the noise-floor along with the lower level material you want increased, and is one thing to listen for which limits (no pun intended) how far you can go with it.  If you do the parallel comp as separate compressed and uncompressed tracks in mixer view, you can play with how much squashing you do on the comp'ed channel pair in combination with the channel fader level of that pair verses that of the uncomped channel pair in search of the best balance.  For instance, you might play with a somewhat lower compression ratio (but still a very low activation threshold) along with a level adjustment to the comp'ed pair.

You want the threshold low so that the comp is working pretty much all of the time, but you can also play around with where that low threshold is set in an attempt to reduce the increase of noise-floor while still keeping the compression high, but you'll want to carefully listen for it working audibly in the quiet parts.  A very low threshold avoids that.
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Offline nulldogmas

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Re: dynamic compression, the pros and cons
« Reply #13 on: January 06, 2020, 10:18:35 PM »
Thanks, Gutbucket, and all — this has been extremely helpful.

For anyone interested, the optimal (at least out of all the iterations I tried) settings I landed on were: -15dB threshold, 4:1 compression ratio, no gain, 0s attack time, 0.25s release time. Then I mix-pasted the two files together at a ratio of -3dB (uncompressed) to -1dB (compressed). (Keep in mind that I hadn't added any gain to the compressed version, so it was a fair bit lower peak volume than the uncompressed at this point.) The result brings up the quiet parts a fair bit, and the small amount of noticeable compression on the loud songs — which manifests mostly as a smidge more oomph and a smidge less dynamic range — is something I can live with in exchange.

I'm sure I'll have to reinvent this wheel for the next recording I want to do this for, but it's a start, anyway.

 

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