Parallel Compression: Haven't found the answers

[Cubic Spline]

Originally Posted by Greg Reierson

Yep, that's exactly how it works. The main signal is unaffected. When mixed, the parallel channel adds significantly when under threshold (because it's not being compressed) and adds little above threshold (because it is being heavily compressed with a high ratio, fast attack, slow release and 10-2-dB of GR during the loud spots). That is how it lifts low level detail but leaves loud sections mostly as they were.



You are wrong. My guess is that you don't understand how to properly set up a parallel compression path.


GR

If i'm downward compressing a signal, and then applying a constant boost to put the peaks where they were, the peaks are inchanged and low level boosted, but it's still downward compression !

An upward compressor keeps the gain INCHANGED above treeshold, and is raising the gain DYNAMICALLY under :
for a 2:1 ratio, some signal 2db below treeshold will get +1 db of boost, and a signal 20db below treeshold will get +10db of boost.

it is NOT the same has having +6.02db CONSTANT boost for all levels below the treeshold, as will the parallel downward compression (not touching the gain below the treeshold) : it can only give a straight line x=x as a transfert function below the treeshold, and so beeing downward !

It's just basic math.

ps : sorry for my english

[evosilica]

Originally Posted by Greg Reierson

Here's a quick test. Two sound files and two images. Before and after. This is clearly an bottom - up form of gain manipulation where the loud section is mostly untouched and the quiet section is increased in level. The parallel path was about 3:1 with a fast attack, a slow release with a hefty amount of gain reduction during the loud sections and much less during the quiet sections. You can see the recovery in the quiet spots. Obviously, it would have to be tweaked for audio content but this is the general idea of how it works.

GR

Please show the ramp part. The part you show is only relevant for time constants. So your post proves nothing.
I could match your graph with any downward compressor + makeup gain. Doesn't make it upward though.

My guess is that you don't really know the difference between upward and downward compression.

[evosilica]

Originally Posted by Cubic Spline

If i'm downward compressing a signal, and then applying a constant boost to put the peaks where they were, the peaks are inchanged and low level boosted, but it's still downward compression !

An upward compressor keeps the gain INCHANGED above treeshold, and is raising the gain DYNAMICALLY under :
for a 2:1 ratio, some signal 2db below treeshold will get +1 db of boost, and a signal 20db below treeshold will get +10db of boost.

it is NOT the same has having +6.02db CONSTANT boost for all levels below the treeshold, as will the parallel downward compression (not touching the gain below the treeshold) : it can only give a straight line x=x as a transfert function below the treeshold, and so beeing downward !

It's just basic math.

ps : sorry for my english

That's exactly what i'm trying to explain the whole time. Thanks for the support

[evosilica]

Originally Posted by recordinghopkins

evosilica gets points from me for using cool edit pro!

HAHA! thx for making me smile in the morning

[Storyville]

Effects of parallel compression can be replicated using downward compression with impractical ratios (1.0832:1) if you go mathematical.

Functionally this means parallel compression is completely different as the mentality around using it would be a different mindset.

[evosilica]

Originally Posted by MarkRB

From a mixing perspective I'm generally in your camp Evo. Parallel compression is largely overrated.

There are quite obvious reasons why it doesn't sound and isn't the same though. The difference isn't huge in real life applications and that is largely why I don't really care for it but there are differences.

You should try experimenting with impulses rather than simple tones. the differences come from the transient response.

Try some drums and flatten them with an L2 or similar and leave that sitting at -10. Add back in the dry uncompressed drums peaking at 0.

Try and emulate that exact sound with a single compressor. You just cant.

Don't get me wrong, i love parallel compression and use it a lot. I love the fact i can heavily compress a signal, level match it with the dry signal and then blend to taste. This is a great way of dialing in the "strength" of compression while remaining equal loudness and therefore not be fooled by "louder = better"

you can't do this with a normal compressor without tweaking 2 knobs at the same time. (ratio and makeup that would be)

But still, i think it's good to know, eventhough at first it might seem so logical, that it's upward, it is not, if you look closer it's always downward compression.

[rhythminmind]

Make up gain is the missing link. It's not an unmodified mix of compressed signal + dry. It's compressed signal + make up gain + dry. This creates a user set level for unmodified peak transients. & a user set below threshold gain increase.

Sent from my T-Mobile G2 using Gearslutz App

[rhythminmind]

It's the same as a max compression setting. Most compressors don't have this function. It will create curves like this.

Sent from my T-Mobile G2 using Gearslutz App

[evosilica]

Originally Posted by rhythminmind

It's the same as a max compression setting. Most compressors don't have this function. It will create curves like this.

WHAT is the same as a max compression setting? Parallel compression? Not at all.
Just check it with the test tone i've attached.

[echoRausch]

Originally Posted by evosilica

I think this is right. I don't get this parallel compression thing and don't understand why everybody rants about it.

It's the same as using a compressor on an aux in your mixer, not new, not innovative at all.

I did numerous tests, even with 3 or 4 parallel compressors with different timing settings but despite it all sounds interesting it never got used on a real cut.

Another thing is the TC 6000 DXP mode which is an upward style compressor and indeed VERY usefull.

TC's desciption of the parallel mode describes parallel as upward style compression but like evosilica stated above I don't understand why.

Maybe BK can chime in and explain as he's a huge fan of parallel compression.

[dualflip]

Originally Posted by Cubic Spline

If i'm downward compressing a signal, and then applying a constant boost to put the peaks where they were, the peaks are inchanged and low level boosted, but it's still downward compression !

An upward compressor keeps the gain INCHANGED above treeshold, and is raising the gain DYNAMICALLY under :
for a 2:1 ratio, some signal 2db below treeshold will get +1 db of boost, and a signal 20db below treeshold will get +10db of boost.

it is NOT the same has having +6.02db CONSTANT boost for all levels below the treeshold, as will the parallel downward compression (not touching the gain below the treeshold) : it can only give a straight line x=x as a transfert function below the treeshold, and so beeing downward !

It's just basic math.

ps : sorry for my english

Evo and this guy are correct. In order to be called "Upward compressor" the signal needs to be bosted according to a ratio rather than a fixed gain, thats just doubling the signal and having a compressor limiting after it crossed a certain threshold.

Now it is true that when the signal crosses the threshold the sum between both dry and wet signals will vary according to the compressor, but in the case of parallel compression it will vary DOWNWARDS not upwards after it crossed the threshold, plus, like they mentioned earlier, the signal should be boosted proportionally before it reaches a certain threshold not after it crossed it.

Sure parallel compression gives a unique effect, some may say it cannot be replicated, that may be true, still that doesnt make it upward. I understand how it can be percieved as upward since the quiet stuff get raised and the loud stuff stays untouched. However the soft stuff is raised by a fixed ratio between the two signals and this doesnt happen in upward compressor

With parallel compression, the loud stuff may only seem to be unaltered, while in fact it will depend on the compressor settings how much will the loud signal will be altered or not. Parallel compression is upward-like compression, but not equal to upward compression.

P.S. All this stuff can be proven mathematically or graphically. I agree that most stuff in audio can be subjective, this is not, and evosilica is providing scientific data to back up his arguments, and unless you are willing to be in the same ballpark and willing to provide your own data then theres no point trying to discredit his arguments.

[mahler007]

Originally Posted by evosilica

parallel compression is NOT upward compression but downward. I don't know who spread this false information, you can read it even in wikipedia , but it's wrong. Generate a simple ramp and see what it looks like after parallel compressing it.

Bob Katz categorizes parallel compression as an "upward compression" technique on p. 133 of the first edition of "Mastering Audio," FWIW. Maybe he'll chime in on this thread...

Cheers,
Andrew

[Cubic Spline]

Originally Posted by dualflip

With parallel compression, the loud stuff may only seem to be unaltered, while in fact it will depend on the compressor settings how much will the loud signal will be altered or not. Parallel compression is upward-like compression, but not equal to upward compression.

I don't see why. If you call parallel compression "upward-like compression", so downward compression + makeup gain is also "upward-like compression".

[stinkyfingers]

think about the harmonic distortion generated during downward compression vs. upward compression and mayhaps that will clear things up for you who do not understand the difference...

[evosilica]

Originally Posted by mahler007

Bob Katz categorizes parallel compression as an "upward compression" technique on p. 133 of the first edition of "Mastering Audio," FWIW.

Well, then he made a tiny little mistake ... no big deal imo, we all make mistakes.
And no big deal in a mastering book at all, because in the end it's about how you use things and what you achieve with them and not how they are categorized.

[Laurend]

Downward compression modifies the gain above the threshold.
Upward compression modifies the gain below the threshold.

One more video here:
Audio Dynamic Processors by Transfer Curves - YouTube

Parallel compression belongs to the downward genre. The gain below the compressor threshold is linear despite increased by the addition of the direct signal. Only the upper part of the transfer curve in affected.

[evosilica]

Originally Posted by Laurend

Downward compression modifies the gain above the threshold.
Upward compression modifies the gain below the threshold.

One more video here:
Audio Dynamic Processors by Transfer Curves - YouTube

Parallel compression belongs to the downward genre. The gain below the compressor threshold is linear despite increased by the addition of the direct signal. Only the upper part of the transfer curve in affected.

fix'd

[Laurend]

Originally Posted by evosilica

fix'd

too much copy/past...

Thanks evosilica

[dualflip]

Originally Posted by Cubic Spline

I don't see why. If you call parallel compression "upward-like compression", so downward compression + makeup gain is also "upward-like compression".

You are not considering that compression + makeup gain will not leave the loud parts untouched, while parallel compression has a similar effect to upward compression because at first glance (depending on the compressor settings) it will leave the loud parts untouched while raising the softer parts (even at a fixed ratio). So you see, what i meant is that parallel compression is similar to upward compression, but its not because it is downard, thats why i call it upward-like, because its not upward but it produces a similar effect.

[William Bowden]

Originally Posted by mahler007

Bob Katz categorizes parallel compression as an "upward compression" technique on p. 133 of the first edition of "Mastering Audio," FWIW. Maybe he'll chime in on this thread...

Cheers,
Andrew

Bob doesn't hang around these parts anymore... Though some airborne pigs were sighted off Dover recently - so I could be mistaken...

The King

[stupid_question]

It's not upward compression (or is it? )...it's downward compression mixed with a dry signal, hence the name 'parallel compression'. The transients above the threshold can't remain intact like they would in upward compression because they are being combined with the sound of a compressed signal whose transients have most likely been changed in some way, creating a new sound entirely and not leaving anything untouched. If you had a slow attack some of the transients might stay the same, but the same thing could be said for normal downward compression. You are still going to get a different sound to regular compression though because of the artefacts created by the parallel compressor, which would be working much harder than a compressor with a very low ratio, and also the way you approach it as you would have much more control than fiddling around with tiny ratios...but it's definitely downward, whatever that means!

[VCrane]

Best thread ever!

[Joelistics]

Call it whatever you want, parallel compression is a great way to increase low level detail while keeping transients intact (when set up appropriately). In my book that is upward compression, but I'm not going to lose any sleep arguing about semantics.

Fact is that the OP asked about when parallel compression should be considered.

I might consider using it in a number of scenarios (but I'll stick to the ones relevant to mastering):

1. Raising quieter passages without influencing transient perception of loud ones.

2. Pulling out detail (reverb, quietly mixed instruments etc) during loud passages.

3. Getting drums that have been mixed too loud to blend with the the rest of the arrangement without changing their transient information (or only subtly, whatever does least harm...)

4. Beefing up thin sounding mixes that don't need too much dynamic control overall but some more meet on the bones.


I will use very different settings in all of those scenarios also dependent on the music of course..




Also, yes parallel compression could be followed by a regular downward compressor, although I wouldn't ever use parallel compression together with more upward compression. There's only so much low level boosting before the music will sound unnatural/pumpy/processed..

[dualflip]

Originally Posted by stupid_question

It's not upward compression (or is it? )...it's downward compression mixed with a dry signal, hence the name 'parallel compression'. The transients above the threshold can't remain intact like they would in upward compression because they are being combined with the sound of a compressed signal whose transients have most likely been changed in some way, creating a new sound entirely and not leaving anything untouched. If you had a slow attack some of the transients might stay the same, but the same thing could be said for normal downward compression. You are still going to get a different sound to regular compression though because of the artefacts created by the parallel compressor, which would be working much harder than a compressor with a very low ratio, and also the way you approach it as you would have much more control than fiddling around with tiny ratios...but it's definitely downward, whatever that means!

Actually its the other way around, you would need a very fast attack and high ratio, so the transients do not sneak through and sum with the original dry audio creating distortion and uneven peaks, thus leaving it untouched. Thats why i said that the loud parts may APPARENTLY be untouched, depending a lot on the compressor settings and the audio being feed into the compressor. And yes, it is downward

[ThomasE]

Originally Posted by evosilica

i agree on fake upward, because it sound quite similar as subtle upward, but then you could also call "low threshold - low ratio (1.1-1.2:1)"-downward-compression "fake upward", as it has the exact same transfer function.

No, the transfer functions are different. Attached is a quick spreadsheet simulation of an ideal downwards compressor, showing transfer curves for ratios of 1:1 and 10:1, as well as the 50/50 summing (parallel compression). There is also a dotted 1:1-line shifted down in gain. Think about it -- when the signal rises in level, the contribution to the summing from the compressed signal will eventually be much smaller than the clean signal, making the clean (1:1 ratio) signal dominate.

Since the 50/50 curve approaches 1:1 when input level increases, it is IMO possible to view the whole thing as some sort of upwards compressor. When seen as an upwards compressor, it has a very wide-knee and a (very abrupt) return to 1:1 for signals below the original threshold. The threshold for the upwards compression isn't easily defined due to the wide knee. It is NOT the same as the set threshold on the downwards compressor, but rather somewhere above. I do agree that it's still very much a downwards compressor, but the upwards-idea isn't all wrong IMO.

I don't think it's of any importance at all if parallel compression is considered to be upwards compression or not, but I do think that the resulting transfer curve is interesting. I have always pictured this as the reason to why parallel compression sounds different (to my ears) than just lowering the ratio.

Originally Posted by evosilica

LOL, it's easy to say you are wrong, but not to prove me wrong. show me the setting, that results in an upward-style graph. i have attached my test tone. just feed it through your settings and see it never behaves like upwardcompression!

The test tone has a linear amplitude ramp, making the resulting waveform sort of show the transfer function with linear X and Y axes (when viewed with the normal linear-amplitude view that most DAWs use). This makes it difficult to make a direct comparison with the compressor transfer curves usually seen, since they normally have logarithmic X and Y axes.

[Laurend]

Here are some transfer curves obtained using an infinite ratio on the compressor. The direct gain is adjusted for a global unity gain.
The global (direct + compressed) ratio is determined by the threshold of the compressor.



The maximum action is focused just above the threshold point. Then the curve relaxes until reaching the unity gain. This point makes the parallel compression so special.

[Red Mastering]

I have a headache looking at those screens...
I am happy I deal with a sound not with diagrams
does parallel sound good to your ears ?
well, if yes, then go for it!

[evosilica]

Originally Posted by ThomasE

No, the transfer functions are different. Attached is a quick spreadsheet simulation of an ideal downwards compressor, showing transfer curves for ratios of 1:1 and 10:1, as well as the 50/50 summing (parallel compression). There is also a dotted 1:1-line shifted down in gain. Think about it -- when the signal rises in level, the contribution to the summing from the compressed signal will eventually be much smaller than the clean signal, making the clean (1:1 ratio) signal dominate.

Since the 50/50 curve approaches 1:1 when input level increases, it is IMO possible to view the whole thing as some sort of upwards compressor. When seen as an upwards compressor, it has a very wide-knee and a (very abrupt) return to 1:1 for signals below the original threshold. The threshold for the upwards compression isn't easily defined due to the wide knee. It is NOT the same as the set threshold on the downwards compressor, but rather somewhere above. I do agree that it's still very much a downwards compressor, but the upwards-idea isn't all wrong IMO.

I don't think it's of any importance at all if parallel compression is considered to be upwards compression or not, but I do think that the resulting transfer curve is interesting. I have always pictured this as the reason to why parallel compression sounds different (to my ears) than just lowering the ratio.



The test tone has a linear amplitude ramp, making the resulting waveform sort of show the transfer function with linear X and Y axes (when viewed with the normal linear-amplitude view that most DAWs use). This makes it difficult to make a direct comparison with the compressor transfer curves usually seen, since they normally have logarithmic X and Y axes.

Thanks for this great post. This looks interesting. How did you create the graph?
So i got fooled by the linear scales? ... i will check that later. but your post makes sense

[jonathan jetter]

[deleted]

[Cubic Spline]

Originally Posted by ThomasE

No, the transfer functions are different. Attached is a quick spreadsheet simulation of an ideal downwards compressor, showing transfer curves for ratios of 1:1 and 10:1, as well as the 50/50 summing (parallel compression). There is also a dotted 1:1-line shifted down in gain. Think about it -- when the signal rises in level, the contribution to the summing from the compressed signal will eventually be much smaller than the clean signal, making the clean (1:1 ratio) signal dominate.

Since the 50/50 curve approaches 1:1 when input level increases, it is IMO possible to view the whole thing as some sort of upwards compressor. When seen as an upwards compressor, it has a very wide-knee and a (very abrupt) return to 1:1 for signals below the original threshold. The threshold for the upwards compression isn't easily defined due to the wide knee. It is NOT the same as the set threshold on the downwards compressor, but rather somewhere above. I do agree that it's still very much a downwards compressor, but the upwards-idea isn't all wrong IMO.

I don't think it's of any importance at all if parallel compression is considered to be upwards compression or not, but I do think that the resulting transfer curve is interesting. I have always pictured this as the reason to why parallel compression sounds different (to my ears) than just lowering the ratio.



The test tone has a linear amplitude ramp, making the resulting waveform sort of show the transfer function with linear X and Y axes (when viewed with the normal linear-amplitude view that most DAWs use). This makes it difficult to make a direct comparison with the compressor transfer curves usually seen, since they normally have logarithmic X and Y axes.

Yeah with parrallel, the compressed part is not a straight line as it is with classic downward compression.

But for the low levels, logarithmic axis or not, linear is a straight line in both cases.

But with the knee of the curves above treeshold, i agree that we can see it as an "upward like" compressor with a max gain, so under a certain level, boost is constant. If the treeshold is high, it will not sound like upward, and the lower the treeshold, the closed to upward it can sound.

A downward compressor with a max gain reduction will also have a similar curve.