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Audio Compressors basics
  • Vitaliy_KiselevVitaliy_Kiselev

    Compressors and limiters are specialized amplifiers used to reduce dynamic range — the span between the softest and loudest sounds. The use of compressors can make recordings and live mixes sound more polished by controlling maximum levels and maintaining higher average loudness. Additionally, many compressors — both hardware and software — will have a signature sound that can be used to inject wonderful coloration and tone into otherwise lifeless tracks. Compression can also be used to subtly massage a track to make it more natural sounding and intelligible without adding distortion, resulting in a song that's more “comfortable” to listen to. Alternately, over-compressing your music can really squeeze the life out of it. For those who are unfamiliar with compressors, having a good grasp of the basics will go a long way toward understanding how compression works, and confidently using it to your advantage.

    Check full article at http://www.uaudio.com/blog/audio-compression-basics/

  • 17 Replies sorted by
  • DrDaveDrDave

    I've used compression on and off over a period of many years, and one thing that really stands out is the invention and refinement of the technique of parallel compression--which this article does not mention. Whether it is pop or classical, sound effects or dialogue, I find parallel compression superior, particularly in combination with multiband separation.

  • majoraxismajoraxis

    Hi,

    If you would like to try a super high quality compressor for free and works on Window VST and Mac VST and AU, here's a link:

    TDR Feedback Compressor II Free Download

    TDR Feedback Compressor II

    For better sound quality click on the "PRECISE" option rather than leave it in "ECO".

    To literally hear what the compressor is doing, click on the "DELTA" button. It subtracts the compressed signal from the original signal and allows you to hear the difference.

    This compressor imparts a slight coloration and forwardness to the sound even with a very little gain reduction at low compression ratio (2:1). If you like the way it sounds with the gain reduction meter is barely moving (0-2 db) - that's not a bad thing.

    If you like the sound of it compressing more than a few db's, take DrDave's advice and turn the "DRY MIX" knob to add some of the dry signal back with the processed signal for "parallel compression".

    I have no affiliation with TDR, I just tried it, liked it, and wanted to share something I found useful.

    Mark

  • spacewigspacewig

    @majoraxis Thanks for sharing, will try this one out.

    Also agree with DrDave re parallel comp; best way to kill the life in dialogue is to hammer the transients.

  • DrDaveDrDave

    @majoraxis mixing the dry mix back in is not parallel compression. Parallel compression results from taking a track and copying it, then processing the two tracks simultaneously in different ways, preferably using a multiband splitter to focus the compressor in different ways on different parts of the spectrum.

  • tonalttonalt

    @DrDave Any sound examples and tutorial?

  • DrDaveDrDave

    There is a very basic one with examples on the Samplitude site http://www.samplitude.com/en/news/samplitude-academy-parallel-compression-new-york-compression-with-samplitude.html

    And there is a better one, geared towards people who know something about audio, on the SOS site, but it is PPV http://www.soundonsound.com/sos/feb13/articles/latest-squeeze.htm

    Sadly, most of these online articles aren't really written with an understanding of basic audio. If I have time I can write a short guide. Don't underestimate the value of the Gerzon filters--they are used in the L2 limiter. The newer plugins don't have that.

  • majoraxismajoraxis

    @ DrDave - Wikipedia agrees with both of us on what Parallel Compression is:

    "Parallel compression, a form of upward compression, is achieved by mixing an unprocessed 'dry', or lightly compressed signal with a heavily compressed version of the same signal."

    http://en.wikipedia.org/wiki/Parallel_compression

    Using the Dry Mix knob on this plugin can lead to better sounding "compressed" tracks, regardless of whether we agree on what to officially call the technique. ; )

  • soundgh2soundgh2

    ^ That is indeed the traditional description of parallel compression.

  • johnnymjohnnym

    Fabfilter has excellent, very in-depth tutorials, too.

  • Vitaliy_KiselevVitaliy_Kiselev

  • DrDaveDrDave

    @majoraxis please feel free to use wikipedia for a source for audio information. After all, what could be better?

    For those less inclined to trust wikipedia, parallel compression is when you run two tracks in parallel. Mixing is just mixing. If you are clever with aux busses, you can run two tracks in parallel, one through the main bus, one through the aux bus. It isn't the best way, it doesn't sound the best, and it doesn't work as well, but if you don't want to cut and paste one track next to the other one (easiest and best way) you can run it through a bus. You will have to make sure that your latencies tap out exactly if you use the buss, on two tracks you can line them up very easily and set the delay and so on by copying the track settings, plus the latency going into the effects processor will be identical, along with the pan and any automation or track effects.

    NB: You want the two tracks to phase out exactly if one is inverted (before you add the compressor/effects on one track), that's the key. Then you have zero latency issues.

    Copy the tracks, with all the settings, apply the multiband splitter, use a limiter (recommend waves L2 but Samplitude has a very good one built in) and you are good to go in a few seconds, and can tweak all the settings perfectly on the second track, The splitter isolates the band you want to work on.

    The L2 uses the Gerzon psychoacoustic shaping for a natural sound.

    If you use the in/out bus of the cheesy plugin and think it sounds the same, by all means do it that way! If you haven't tried it the other way, take a minute to try it and see the endless possibilities.

  • thepalaliasthepalalias

    Update: Another good free compressor is ReaComp in the free ReaPlugs suite (no affiliation). ReaPlugs VST are the same plug-ins normally bundled with Cockos Reaper, but for use with any Windows VST host. If you want to use them on OS X, you have to get Cockos Reaper.

    http://www.reaper.fm/reaplugs/

    Here are some of the features.

    • Compression modes for standard and feedback (as well as internal or external sidechain with filtering)
    • 0 to 64x oversampling
    • Variable knee
    • Separate dry and wet faders.

    Etc.

    Anyway, in terms of using parallel compression, @DrDave is right that avoiding phase artifacts is the key. But as one of my favorite mastering engineers that I ever worked with used to point out to me, multi-band processing can cause potential phase issues at every crossover point. But depending on your personal taste and your goal with the sound you are going for, phase coherence may or may not be the sound you are looking for - I just suggest trying parallel compression without multi-band processing and good phase coherence first, before getting fancy. :)

    On the other hand, if you want to get fancy, Reaper is uncommonly flexible about routing (each bus can be as many channels as you want and you can route any plug-in to almost any channels on the bus for the inputs and outputs, even duplicating) and plug-in delay compensation.

  • oscillianoscillian

    And for those of us more inclined to Instagram presets: http://www.propellerheads.se/products/reason/index.cfm?fuseaction=get_article&article=devices_audiomatic

    I just love the SSL mixer clone in reason, parallel compression works great with it!

  • oscillianoscillian

    Poll: Bob Clearmountain vs Justice style compression?

  • oscillianoscillian

    VMS Multiband compressor: just love the sound and control.

  • majoraxismajoraxis

    @ Dr. Dave,

    I do not disagree that you offer an acceptable approach to parallel compression, but I am certain it is not the only commonly acceptable approach. As you have indicated that Wikipedia is possibly not a credible source for audio information, here's a quote from Sound On Sound's Technical Editor regarding parallel compression (in mastering):

    "In essence, the signal to be processed is split, one path feeding the output directly while the other feeds a compressor. The output of the compressor is mixed into the main output along with the direct signal, and this is why it’s called parallel compression..."

    Here's a link to the article http://www.soundonsound.com/sos/jan10/articles/qa0110_2.htm

    Anyways, can we agree to you disagreeing with me and me agreeing with you? ; )

    BTW - I respect your passion for audio, it's great that you are willing to share your knowledge and experience to everyone's audio benefit here on Personal-view. As an audio guy I want to encourage your valuable contribution, even if there are few rough edges in the process.

    Peace,

    Mark

  • DrDaveDrDave

    @majoraxis, that may be, my recollection is different. It could very well be that the definition has changed since I was a student. Stuff changes all the time.

    Sound on Sound: I don't regard SOS as a reputable source, it is a popular magazine, and you are free to use it. I think the idea that SOS sets itself up as some sort of authority on digital audio is good business, but their articles are often full of all kinds of garbage. I still enjoy the magazine. One of the most hilarious things I have ever seen is their analysis of "correct" microphone positions. Magazine writers have long, extensive resumes that consist of articles they have written for the magazines. They aren't teaching at Detmold.

    The guy who developed sidechain compression from the original 1977 article is Hulse. Strangely, his name is omitted from the Wikipedia and SOS articles. I'm sure it was a complete accident that they left his name out. Get it straight from him, or use any of the several versions floating around. http://homepages.paradise.net.nz/rhulse/Side%20Chain/sidechain.htm

    If you have technical training in audio, here is the math: http://homepages.paradise.net.nz/rhulse/Side%20Chain/sidecmat.htm

    Note that there are other engineers who dispute the math, and even dispute that the effect is real. That's show biz.

    @thepalais excellent point .Too much multiband can tweak out the sound. You only split the bands if you need say, more bass, for example. It is way, way more transparent because you compress only one portion of one of the two tracks. Big difference. If you are just compressing the one track, you don't need the splitter, but in practice most material will benefit from this.

    Phase issue with the multi splitter: if you are using say 20 percent of the compressed track with the 100 percent of the noncompressed track, the splitter will not have a significant effect on the overall phase. There is a threshold for these phase effects, so factor that in.

    Anyone who hasn't tried the Gerzon shaping with parallel compression, I recommend trying it. Old but good. There is no point in using a cheap plugin for this particular effect.

    Just have fun, try it every way people suggest, or invent your own.

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