Talk:Dynamic range compression: Difference between revisions

Side-Chain?

I believe the words "Side-chain" aren't used correctly here. The way it's defined right now is what I would call "Ducking" (there's a quick note about this alternate name). The page goes on to define "Parallel compression" as what I would call a "Side-chain effect." This page backs up my definition of Side-Chain: [1] I would define the three terms like this:

Side-Chain - using two copies of the same signal (only one with an effect applied), and mixing the two together.

Parallel Compression - This is exactly the same as Side-Chain Compression in my book.

Ducking - Using the amplitude of one signal to control the gain of another. The example of having background music fade out while someone is talking and fade back in when they finish talking is perfect.

I hope I'm not being too pro-active, but I'm going to change these right now.

Do you agree / disagree? Blue Dinosaur Jr 21:01, 12 November 2007 (UTC)

• I've just found contradicting links that support the original defined term. As a result, I am not going to edit the original page. What kind of authority can we find on this subject to provide ourselves with a good source? All I've done is confused myself. Blue Dinosaur Jr 21:07, 12 November 2007 (UTC)

I don't see a huge problem with Side Chaining as it stands now. Perhaps it isn't as clear as it can be for the layman, but it isn't wrong. I'll give some thought to how it could be made more clear. Binksternet 21:14, 12 November 2007 (UTC)

'Dogshit' reference

Is it really necessary? I don't think it adds anything to the article and just has the ability to offend, but as a newbie to editing Wikipedia, I'll leave it to this article's regulars. 65.107.212.130 (talk) 22:23, 14 January 2008 (UTC)

I like it as a nice bit of straight-talking, though I won't insist on keeping it.--Father Goose (talk) 03:52, 15 January 2008 (UTC)

poor definition

This article is a good introduction to the topic, but it could use some editing. For example, its definition of a compressor would more-accurately describe a limiter.

Also, the lack of hardware brand names and a description of their products is a major omission. A detailed description need not be advertising.

WilliamSommerwerck (talk) 12:30, 23 March 2008 (UTC)

If you are capable of making those changes, by all means, do.--Father Goose (talk) 02:27, 24 March 2008 (UTC)

"Music production" and "Marketing" sections are reduplicative

The "Music production" and "Marketing" sections seem somewhat reduplicative. They should probably be combined. —Christian Campbell 02:22, 2 April 2008 (UTC)

Compression in Digital Arena

I removed:

"Compression in the digital arena is essential, as digital recording levels are very intolerant to clipping (over-modulation); they much more sensitive than recording tape used previously in analog recordings."

Because:

1. It is confusing. Is it referring to compressing an analogue signal prior to conversion to digital, or digital compression when it is digital audio?
2. It is not correct. That is, compression is not essential for digital recording. 24 bit digital has more than 140dB of dynamic range, so plenty can be spared for headroom to preventing clipping at A/D conversion. For 16bit or lower, it may be useful, but not essential. Proper gain structure may be all that is necessary. Regarding DSP compression for a digital audio signal, proper gain structure should prevent the need for compression to prevent clipping. Clipping is unlikely as bit-depth in modern DAWs is high enough to provide adequate headroom. In other situations it maybe useful, but not essential.

Iain (talk) 08:05, 17 May 2008 (UTC)

Good move. Thanks. Binksternet (talk) 08:09, 17 May 2008 (UTC)

Main Definition change

I changed:

"Dynamic range compression also called DRC (often seen in DVD player settings), audio level compression, volume compression, compression, or limiting, is a process that manipulates the dynamic range of an audio signal. Compression is used during sound recording, live sound reinforcement, and broadcasting to alter the perceived volume of audio. A compressor is the device used to create compression."

to:

"Dynamic range compression also called DRC (often seen in DVD player settings), or simply compression, is a process that reduces the dynamic range of an audio signal. Compression is used during sound recording, live sound reinforcement, and broadcasting to alter the perceived volume of audio. A compressor is the device used to create compression."

Because:

1. I don't know of anyone who speaks about "audio level compression"
2. It has been a common recommendation not to use the term "volume" with relation to professional audio. while "amplitude" is the bi-polar magnitude of signal, "level" is the uni-polar, and "loudness" is the perceived level, "volume" was never properly defined and is only common in domestic applications.
3. Dynamic range compression is not limiting. Limiting is a subset of dynamic range compression, but the two terms are not interchangeable.
4. "manipulates" changes to "reduces" as compression always reduces dynamic range.
5. "perceived volume" change to "level" as the operation of a compressor is actual and not only perceptual.

Izhaki (talk) 13:41, 28 July 2008 (UTC)

Those aren't bad changes. By the way, I moved your Talk entry down to the bottom of the page as is the norm. Your rearranging of the Talk entries to put the most recent on top was not optimal. Binksternet (talk) 15:11, 28 July 2008 (UTC)

Looks good to me.--Father Goose (talk) 18:42, 28 July 2008 (UTC)

Attack / Release Image is misleading

If we want to be 100% correct, then the image above is misleading or possibly even incorrect. Reason is that the attack and release never correspond to the exact time it will take gain reduction to reach full effect or dive back to 0 dB. Instead they are always linked to a set amount of dB. Please see the main article for detailed explanation of this, and feel free to try it out with your compressors to see that 10 dB of gain reduction will take longer to diminish compared to 20 dB.

This image can be made correct if "phase" is used instead of "time"; so "attack phase" and "attack time". Iain - it's your illustration. Izhaki (talk) 13:40, 29 July 2008 (UTC)

Is that image trying to convey such specifics? I think it's more general than that. It doesn't look wrong to me. Binksternet (talk) 15:04, 29 July 2008 (UTC)

One can assume by this illustration that the actual figure you set on the control (say, the attack time 10 ms) is really the time it takes gain reduction to reach full effect. Completely up to you guys. Izhaki (talk) 15:41, 29 July 2008 (UTC)

Rane's Chapter 3 on Dynamics Processors says about the attack control that it can be thought of as specifying "...the time required for gain to settle to a defined percent of final value. Typical are 86% or 95% of the final value." The image above has no specified time of attack, so we aren't looking at whether it has hit within ~90% of its mark by that time. Binksternet (talk) 16:37, 29 July 2008 (UTC)

And then it goes on to say: "It is important to understand the difference between release rate -- as determined by this control -- and release time. There is no industry standard and different manufacturers define this control differently. Rane defines this control, in a compressor for example, as how long it takes for the gain to change by 10 dB, not how long it takes to return to unity gain (no gain reduction). To calculate the actual release time requires a little math: Release Time = (Gain Reduction x Release Setting) / 10 dB"

The main problem is that most compressors use the term "release time" to what is in practice "release rate" (and this is how Rane call it) - This is the core of the issue, wrong terminology. If you ask most people what is "release time" they will say that it is the time they set on the control on the compressor, not many people are aware that what they are setting is the release rate. At the moment the article defines "attack time" as what being set by the control, it does not fit with the current illustration. Either the illustration needs to change to "attack phase" or the article has to change to "attack rate". The latter change, so I believe, would cause confusion. I hope this is clearer now.Izhaki (talk) 18:40, 29 July 2008 (UTC)

I think 'attack phase' is the best term. To avoid any confusion, can we use 'attack phase' in the article text as well. For example: "A compressor does not react instantaneously to changes in the signal. The 'attack phase' is the period when the compressor is increasing gain reduction to reach the amount that is determined by the ratio. The 'release phase' is the period when the compressor is decreasing gain reduction to the level determined by the ratio, or, to zero, once the level has fallen below the threshold." What do you think? Iain (talk) 07:31, 30 July 2008 (UTC)

That's very good (although it does not resolve the original issue with the illustration), but it teaches the reader nothing about the actual attack and release controls. I think that the first thing we need to decide is the terminology to be used. How do we call what is set by the attack and release controls on the compressor? Attack time? attack rate? attack settings? Izhaki (talk) 08:14, 1 August 2008 (UTC)

• The illustration is easily fixed, but I did not want to make changes if there is not general agreement on terms.
• I intended the explanation of the controls to follow my proposal above. For example:

"A compressor does not react instantaneously to changes in the signal. The 'attack phase' is the period when the compressor is increasing gain reduction to reach the output level that is determined by the ratio. This happens when the input level increases (and is above the threshold). The 'release phase' is the period when the compressor is decreasing gain reduction to the level determined by the ratio, or, to zero, once the level has fallen below the threshold. This happens when the input level decreases. The length of each period is determined by the rate of change and the required change gain reduction. For more intuitive operation, a compressor's attack and release controls are labelled as a unit of time (often milliseconds). This is the amount of time it will take for the gain to change a set amount of dB, decided by the manufacturer, very often 10 dB. For example, if the compressor's time constants are referenced to 10 dB, and the attack time is set to 1 ms, it will take 1 ms for the gain reduction to rise from 0 dB to 10 dB, and 2 ms to rise from 0 dB to 20 dB.

• What do you think? Can we agree on the terms 'attack phase' and 'release phase' at least? Iain (talk) 09:42, 1 August 2008 (UTC)

The explanation above and the use of 'phase' in it makes perfect sense to me. I have to non-related reservations though:

• "A compressor does not react instantaneously to changes in the signal." - A digital compressor is perfectly capable of acting instantaneously on input signals. Not only that, but with the standard DAW dual-buffer operation, compressors can use look-ahead that lets them act on signals 'before they happened'. What's more, the attack and release are not acting on the input signal but on the gain reduction amount (and the sentence, as it stands, is more linked to peak/RMS sensing). I would change this opening sentence to: "A compressor might provide a degree of control over how quickly it acts."
• "This happens when the input level decreases." This sentence has to be omitted as it is incorrect: the gain reduction might still increase when the input signal drops in level. Think of compressor with a ratio of 1000:1 and a burst noise that overshoot the threshold by 10 dB and then drops to 5 dB above the threshold; but due to slow attack, the gain reduction was only at 3 dB when the signal dropped by 5 dB - the gain reduction will still rise to 4.99 dB. Again, the link between the attack and release and the input signal is dangerous - compressors, by design, have time stage following the scale stage (ratio) and the time stage will only be linked to the input signal if auto-attack or auto-release is in force.
• If all is good and sound, we can apply the corrected explanation; accordingly, I believe that in the illustration 'time' will have to change to 'phase'. Also, I think it could be improved if you draw values on the level axis and use a ratio of, say, 2:1; If you are in a lazy mood, I can illustrate it myself.Izhaki (talk) 11:43, 1 August 2008 (UTC)