Diving Deeper: Styles of Compressors?

[AcousticDreams]

Bob Womack's excellent suggestion: "study the theory, design, and applications of compressors." So that Is exactly what I hope to accomplish in this thread with all of your help.
With a little web research, I found some reasonable explanations. However there are some confusing crossover information that I hope we can further expand upon.

FET: Uses a Field-Effect Transistor for gain reduction.
Characteristics: Fast Action & provide Better Transient Response. Faster Attack & Release times compared to other types. Add harmonic Distortion

"These are the go-to compressor when taming the dynamics for aggressive sources such as drums, heavy electric guitars, percussion and aggressive vocals. FET compressors are commonly the choice for parallel processing because of the aggression and vibe they add."

Vari-Mu (Delta Mu): Use Tubes to control the gain reduction stage.
"The Bias of those tubes is altered by the input voltage which results in a gentle , rich sound signature which is comparable to Optical compressors in terms of musical characteristics"
Characteristics: Soft-knee Compression . Attack & Release times are generally slower (Some Vari-Mu have variable Attack & Release times, but the tube circuits still keep the Attack times slower. )

"Can add a lot of compression without much gain reduction or loss in sound character. Ratio parameter is dependent on program= it increases as input voltage increases. Variable-mu compressors sound great as bus compressors and mastering tools and are perhaps less effective on tracks with fast-acting transients."

Optical : Uses a light element and optical cell to alter the dynamics of an audio signal. As audio signal increases, the light element emits more light and causes the optical cell to attenuate the amplitude of the output signal.

Characteristic: Exhibit Soft Knee compression. Frequency-dependent attack. Transparent. Slow Attach & time Release.

"Opto compressors are often chosen to help smooth out audio with fewer transients, helping to fit tracks into the mix without colouring them too much. They are typically avoided for bus compression and mastering."

VCA ( voltage controlled amplifier) are perhaps compressors with the fastest response of the attack and release parameters.
Character: Less coloration compared to Optical or tube
Known to offer the highest possible amounts of gain reduction often followed by the best transparency.

"This makes their use widely applicable to general duties where transparency is the main goal"
__________________________________________________ ___________

Which compressor style do you like to use & Why? For: Vocals, Acoustic Guitars, Symphonic Virtual instruments.

[DupleMeter]

You left out Diode-Bridge compressors (like the 33609).

Also, I’m not sure you can categorically claim all [insert comp type] has X characteristic. For instance. A lot of old optical compressors have a “dog tail” knee.

I think experience is the best teacher here. You have to play with these compressors & hear & feel what they do to different sources.

That said, to answer your question about compressor choices:

I steer clear of VCAs because I feel they’re very sterile. They don’t bring anything to the party.

FETs are great when you need fast compression or you want to add that bite that the FET circuit has. I could seriously be happy with just a good FET compressor. Like a Purple MC77 or API 525. You’ve heard the 1176 on acoustic guitar on the CSN albums. You could probably get away with 90% of your compression needs with an 1176 in the “Dr. Pepper” setting.

Optical compressors are smooth and too slow to cause any serious harm. They’re typically very gentle compressors, like the LA2A, and considered “do no harm” compressors. They tend to have a “softness“ to their tone that can sometimes be a little problematic with very low frequencies. The one exception I can think of are the JoeMeek optical compressors (like the SC2), which can be quite aggressive for an optical. I like a nice opto on vocals.

Tube/VariMu compressors are also one the slow side, but tend to have lots of color. I think they make great bus compressors doing 1-2 dB of gain reduction. Most people think of the Fairchild, but I always found it a bit too grungy. Manley makes a nice one, and my favorite is the SPL Iron.

Diode-Bridge compressors can be fast, like a FET, but not as “bitey”. The classic Neve compressors fall into this category. Again, great bus compressors.

[dnf777]

Originally Posted by Knives&Guitars

Optical : Uses a light element and optical cell to alter the dynamics of an audio signal. As audio signal increases, the light element emits more light and causes the optical cell to attenuate the amplitude of the output signal.

.

So does an optical compressor only compress the high end of the signal (ie act as a limiter). or does it also boost the lows also? In any case, it seems that optical compressors are rather inefficient, having to convert audio/electronic waves to optical energy (and back again) in order to achieve results.

I bare my ignorance in a genuine attempt to better understand compression...and eventually (hopefully) appreciate what they do with my ears. Of all the pedals on my board, the compressor is the only one that I often can't hear a difference when I press the button. I realize my style of playing can largely influence the compression amount...

[jim1960]

Originally Posted by dnf777

So does an optical compressor only compress the high end of the signal (ie act as a limiter). or does it also boost the lows also? In any case, it seems that optical compressors are rather inefficient, having to convert audio/electronic waves to optical energy (and back again) in order to achieve results.

I bare my ignorance in a genuine attempt to better understand compression...and eventually (hopefully) appreciate what they do with my ears. Of all the pedals on my board, the compressor is the only one that I often can't hear a difference when I press the button. I realize my style of playing can largely influence the compression amount...

A compressor lowers the volume of the loudest parts of a signal in order to reduce the dynamic range (range of loudness) of a track. You control at what point the compressor kicks in with the threshold adjustment. Everything above the threshold is processed by the compressor, everything below remains unprocessed. How much the signal gets compressed is determined by the ratio adjustment. After compression is added, the track will sound quieter so makeup gain is used to bring the overall loudness back up. And since you're raising the volume AFTER the signal is compressed, the dynamic range of the compressed signal will be less and the track will have less variation in loudness.

The difference between a compressor and a limiter essentially comes down to the ratio. On a compressor, you set a ratio for when the compressor kicks in but some sound will still exist above the threshold setting (unless you've maxed out the ratio). On a limiter, the ratio is very high and everything above the threshold setting is turned down.

[rick-slo]

Knives&Guitars,
What are you recording (solo guitar, guitar and voice, other instruments)?
Have you ever posted one of your recordings on the forum? What is it about your recordings that you believe using compression would improve?

[AcousticDreams]

Originally Posted by dnf777

I bare my ignorance in a genuine attempt to better understand compression...and eventually (hopefully) appreciate what they do with my ears. Of all the pedals on my board, the compressor is the only one that I often can't hear a difference when I press the button. I realize my style of playing can largely influence the compression amount...

I am also a novice, eager to learn & discover.

A Recording Compressor most likely has many more controls than a Guitar Compressor pedal. Plus as you can see above there are so many different types of compressors, each offering a slightly different take on compression duties.

Originally Posted by rick-slo

Knives&Guitars,
What are you recording (solo guitar, guitar and voice, other instruments)?
Have you ever posted one of your recordings on the forum? What is it about your recordings that you believe using compression would improve?

I am recording Acoustic guitar, Voice and Symphonic Virtual instruments. To my way of thinking, compression is important in most every area if your are a dynamic player or signer. Of which I am. I even find it useful with my VI's when Chords are played.

For myself and my style of playing and singing...I find compression paramount. This probably will not make sense to you...but I find that compression gives me more of the natural sound that I hear from my guitar and or voice. This would not be true for everyone though. And many would find the opposite effect. It all depends upon your playing style & listening perspective.

A lot of my love for compression comes from my understanding of the Inverse Square law. When I was a Pro Photographer for the music industry, the Inverse square law ruled every photo shoot. Now, many people accept that the Inverse Square law also applies to sound. While this is not a difficult theory to explain it still would take a while to explain it thoroughly. Just think of those party Flash Pictures where the the people are lit, but the background is dark.

It could most certainly said that not everyone needs compression. However I feel in the Digital World it is especially important. In the old days just recording into tape gave you some compression. Others claim that transformers can give a mild compression factor.

I have not yet posted any recordings as I am still learning. I am not ready. The bulk of my time is not spent recording...it is spent learning. I hardly ever record...But I do experiment. Someday...soon!

I see that you live in San Luis Obispo. One of my very favorite areas in California. I have probably been to Montana de Oro... at least 30 times during my lifetime. It has everything. Beautiful overlooking cliffs on the ocean. Where you can see Whales at the right time of the year. On the way in you Pass Sand Dunes and then through a grove of Eucalyptus trees. And if you are there at the right time...the migration of Butterflies. You live in a truly magical Place. What a great place to play acoustic guitar.

[rick-slo]

Thanks for the detailed reply. Regarding where I live I feel blessed. Actually I live in Los Osos (right near Montana de Oro) about ten miles west of San Luis Obispo.

[Bob Womack]

A little-known characteristic of the Neve 32264 diode bridge types is that the threshold is frequency dependent. Chain a pair together and they are indeed nice bus compressors. I loved 'em.



The later SSL per-channel VCA dynamics section and Bus Compressor were much more transparent. Horses for courses, thou knowest...

Bob

[kellyb]

FWIW, my experience (or lack thereof) is that many compressors have a tonality, first and foremost that transcend their technical designs. Yes, there are optical and FET and VCA and vari-mu knee/envelope characteristics, but when people are talking about that "classic FET sound" sound, they're often talking about an 1176, which engineers use without compressing just for sound of its line amp. 1176's also brighten things IMO. Fairchild emulations darken them. Long story short, learning to hear different compressors is a lot more than hearing different compressor types - at least it seems to me. And, in my case, if I don't like the sound, I couldn't care less what it's doing. The Distressor is a good contemporary flexible compressor that will cover a LOT of compression tasks when they're necessary without branding the sound too much IMO. On it's faceplate, it actually says 'Opto' near the slowest attack setting I think, but I don't think there's any optical element in the hardware.

The difference between La2a and La3a compressors kinda highlights what I'm talking about. Both optical and ultimately, pretty similar compressors, but many have strong preferences about their sounds and using one of the other for specific things.

If you have any tape machines (or tape plug ins) that have a bias adjustment, these can be cool sources of "compression" (overbiasing a little). You mentioned transformers; a/d converters like Burl have them, as well as an attenuator on the front end so that you can run hot signals into them and saturate the transformers, and there's a sort of compression thing that happens there, too.

[b1j]

Would you say that compressor plug-ins (emulators) native to a DAW like Studio One also color the sound the way its hardware model does? Should I try to train my ears to hear that in the in-the-box compressor, or would it be a waste of time?

[DupleMeter]

Originally Posted by b1j

Would you say that compressor plug-ins (emulators) native to a DAW like Studio One also color the sound the way its hardware model does? Should I try to train my ears to hear that in the in-the-box compressor, or would it be a waste of time?

Some do, some don't. I'm not familiar with what comes with Studio One, but if they're emulating old hardware, they should also be emulating the nonlinearities of the analogue circuit.

One of the easiest ones to test is any 1176 emulation. If you don't hear it add a sparkle to the signal, it's NOT an 1176 ;-)

[kellyb]

I'm not acquainted with the Studio One comp, as I use Logic. Re: plugins 'coloring' the signals in potentially educational/informative ways, my experience is that UAD, Plug-in Alliance stuff, Soundtoys, current Waves, etc...do an admirable job trying to model color. The Logic compressor plug-in attempts to do that, but I wouldn't give it a passing grade. The Logic comp does, however, do a good job of modeling the different attacks/releases/envelope/knee characteristics is a useful and educational way for sure. You can get good results from it in practice. I'd guess the Studio One comp does that, too!