What’s the difference between opto, FET, VCA or tube compressors? Learn this and more in our primer.
"Making the needles stand on end” is how one recording engineer described the heavily compressed sound of ’80s rock bands. What is compression and how can we make the needles stand on end? For starters, we should clarify that we’re talking about dynamic range compression, using devices like compressor pedals, and not digital-data compression, such as MP3 encoding.
Essentially, compressors do what I do when I’m watching a movie after the kids are asleep. I turn up the volume to hear the dialog and quickly turn down the volume when the car chase and explosions kick in. It’s important to note that turning the volume up and down should not introduce distortion, as this volume change is done over many audio cycles. This is opposed to clipping the signal, which compresses the signal but introduces harmonic distortion.
Fig. 1. One of the great studio compressors, the Teletronix LA-2A Leveling Amplifier, first appeared in 1965 and was produced until 1969. This tube-driven electro-optical attenuator system is now available again from Universal Audio, which builds LA-2A repros in California using old-school, point-to-point wiring.
Let’s take a look at a classic studio compressor, the Teletronix LA-2A (Fig. 1). See those two big knobs on the front? One is marked gain and the other is marked peak reduction. If we start by turning up the peak reduction knob, the level of the loud parts of the signal will be reduced and the overall perception is that the program material is quieter. That’s when we can reach for the gain knob and increase the volume so that the overall perception is that we are back to where we started in terms of level, but with a reduction in dynamic range.
Dynamic range is the measurement of the difference between the quietest parts and the loudest parts. Metallica’s “Creeping Death” would have a fairly low dynamic range while Nirvana’s “Smells Like Teen Spirit” would have a larger dynamic range.
What about one-knob compressors? It’s possible to combine the peak reduction and gain knobs into one knob by using a pot that has two elements. These pots are usually used for stereo signals but we can coerce it into turning up the gain and peak reduction at the same time. This is what I’ve done with the Strymon OB.1. Since a compressor is typically near the beginning of the pedal chain, we can adjust the amount of increased gain to match the amount of peak reduction when using a medium-output pickup. This results in an experience where everything gets smoother, but not louder or quieter.
But what about low- or high-output pickups? The low-output pickup is not going to trigger the peak reduction as often and the signal will get louder as the comp knob is turned up. The opposite happens with the high-output pickups as they drive more peak reduction. This is where the level knob can be used to provide a fine adjustment on the amount of overall gain.
What’s the difference between opto, FET, VCA or tube compressors? The peak reduction circuit needs to be able to turn down the volume in response to a control signal—standard audio circuit components like resistors, capacitors, and op-amps can’t do this.
Opto compressors use a light-dependent resistor (LDR) and a fixed resistor to create a voltage divider that reduces the signal level. The resistance of an LDR goes down as it is exposed to light. Incandescent bulbs, LEDs, and electro-luminescent panels have been used to control LDR. One of the properties of an LDR is that it can be turned on (gain reduced) quickly, but turns off relatively slowly. This has a natural musical property and creates some the character of opto compressors.
FET compressors use JFETs or MOSFETs (two types of transistors) to create a voltage-controlled resistor that is used in a voltage divider like the LDR. But FETs are lightning fast and can clamp down or release as fast or as slow as the peak reduction circuit dictates. These compressors are usually associated with the pumping kind of sound you get from many compressor pedals.
VCA (voltage-controlled amplifier) compressors use an integrated circuit multiplier that can be very fast and precise. You are more likely to see a VCA in a rack unit than a pedal.
Many “tube compressors” are really opto compressors with tube gain stages, but there are circuits that use a tube as the variable gain element. The LA-2A we discussed earlier falls in this category.
What about blend knobs? Some compressors will allow you to mix your uncompressed signal with the compressed signal. If the compression circuit has a very aggressive squash, then mixing in some uncompressed signal will get some of the dynamics back while maintaining overall compression.
Do you need a compressor pedal? Before deciding, take some time to explore the various available technologies to discover which devices work best with your music and guitars.
Gregg Stock is Senior Analog Guru and Engineer at Strymon.
Kick off the holiday season by shopping for the guitar player in your life at Guitar Center! Now through December 24th 2022, save on exclusive instruments, accessories, apparel, and more with hundreds of items at their lowest prices of the year.
We’ve compiled this year’s best deals in the 2022 Holiday Gift Guide presented by Guitar Center.
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About Mystery Stocking
Each year, Premier Guitar likes to put out these mystery boxes as a part of bringing some fun to the holiday season. Remember, this is supposed to be a fun holiday treat! If the contents of this box will ruin your holiday, deplete the last of your bank account, or end your ability to see the good in humanity, it may not be for you.
- This year's Mystery Stocking will cost $44.95. ($39.95 + $5 Flat shipping)
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- There has been a huge demand for these in the past. We really did sell out in less than 4 minutes last year. When they are gone, they are gone.
- One per household, one per person.
Q: What's in the Mystery Stocking?
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A. You can't. This year, we're limiting to one per household, so more people can get in on the fun!
Featuring the Adaptive Circuitry recently introduced on their Halcyon Green Overdrive, Origin Effects have brought us a pedal with a character all of its own and a new flavor of drive.
Origin Effects introduce the new M-EQ DRIVER mid booster & drive pedal. Based on a vintage Pultec studio EQ, this unique pedal offers a range of mid-focused tones, from a subtle mid boost to thick, resonant overdrive. Featuring the Adaptive Circuitry recently introduced on their Halcyon Green Overdrive, Origin Effects have brought us a pedal with a character all of its own and a new flavor of drive.
A choice of three mid-range frequencies ensures that you can boost just the right part of your guitar signal and, when pushed harder, can elicit a range of saturation from a classic “mid-hump” overdrive to fierce “cocked wah” distortion. Thanks to the Adaptive Circuitry, the high-end roll-off of the Cut control is reduced as the pedal cleans up. This allows for a smooth transition from warm overdrive to bright clean tones in response to playing dynamics or guitar volume knob changes.
Introducing... M-EQ DRIVER || Mid Booster & Drive
Built-in the UK to the highest standards, the M-EQ DRIVER continues the Origin Effects tradition of vintage, studio-inspired tones in modern guitar pedals. The Origin Effects M-EQ DRIVER is available now from Origin Effects dealers worldwide.
RRP: 259 GBP (Inc VAT) / 319 USD (Ex TAX)
For more information, please visit origineffects.com.
The Badlander 25 is designed to carry the tradition of high performance, high gain forward with tight low end, an aggressive midrange character, and enhanced harmonic content.
Badlander 25 Head
Mesa/Boogie’s Badlander Series of amplifiers draw inspiration from Mesa’s legendary Dual Rectifiers, paying homage to rock and heavy sounds in their own distinctive and percussive way, with a focus on today’s musical genres. Its tight low end, refined top end, and defined mids combine with Mesa gain for huge tones that will appeal to rock leaning guitarists who like a bit of Brit influence with their American-voiced gain. The Badlander 25 Head uses the same straightforward channel format as its 50 and 100 Watt siblings, with 2 identical, footswitchable channels each containing Clean, Crunch, and Crush modes that feed an EL84 power section to deliver an unprecedented fierceness and harmonic complexity. The Badlander 25 Head combines these ingredients in a small package and power range that adds a raw character all its own, offering the essential voice, performance, and features of the Badlander 100 and 50 in a fiery-sounding, ultra-portable low-power format that’ll gratify those not seeking big horsepower.
Badlander 25s employ a pair of EL84 power tubes operating in MESA’s proprietary Dyna-Watt Class A/B Pentode for maximum power, punch, and clarity, producing 25 Watts or switched to its 10 Watt Class A/B Triode setting for lush harmonics and a sweet, liquid feel at lower volumes.
The Badlander 25 Head packs a built in CabClone IR Direct Interface making recording and cab-less live capture consistent and easy. Players can choose from a preloaded collection of eight Rectifier Closed-Back and Boogie Open-Back Cabinets IRs from MESA’s standalone CabClone IR for a wide array of sounds and responses.
A Tube-Driven, Series Effects Loop acts as a circuit bridge, permitting players to patch their favorite outboard effects between the preamp’s end to just before the Driver tube feeding the power section.
For guitarists seeking the tone and feel of an all-tube amplifier with huge sounding gain that is voiced to handle the demands of today’s musical genres, the Badlander 25 Head delivers from a package that fits in an overnight bag.
Badlander 25 1x25 Combo
Mesa/Boogie’s Badlander Series of amplifiers draw inspiration from MESA’s legendary Dual Rectifiers, paying homage to rock and heavy sounds in their own distinctive and percussive way, with a focus on today’s musical genres. Its tight low end, refined top end, and defined mids combine with MESA gain for huge tones that will appeal to rock leaning guitarists who like a bit of Brit influence with their American-voiced gain. The new Badlander 25 1x12 Combo uses the same straightforward channel format as its 50 and 100 Watt siblings, with 2 identical, footswitchable channels each containing Clean, Crunch, and Crush modes that feed an EL84 power section to deliver an unprecedented fierceness and harmonic complexity. The Badlander 25 Combo combines these ingredients in a small package and power range that adds a raw character all its own, offering the essential voice, performance, and features of the Badlander 100 and 50 in a fiery-sounding, ultra-portable low-power format that’ll gratify those not seeking big horsepower.
A UK-made Celestion Creamback 65 Watt speaker is MESA’s driver of choice for this 1x12 Combo amp. G12M-65 Creamback is ideally suited for the Badlander 25 as its power handling permits added low-end grunt complementing the warm and vocal mids, crunchy upper-mids and sweet, refined highs.
The Badlander 25 Combo packs a built in CabClone IR Direct Interface making recording and cab-less live capture consistent and easy. Players can choose from a preloaded collection of eight Rectifier Closed-Back and Boogie Open-Back Cabinets IRs from MESA’s standalone CabClone IR for a wide array of sounds and responses.
For guitarists seeking the tone and feel of an all-tube amplifier with huge sounding gain that is voiced to handle the demands of today’s musical genres while being incredibly portable, the Badlander 25 1x12 Combo delivers.
BADLANDER™ 25 Head & 1x12 Combo | MESA/Boogie
Explore and shop the Badlanders on www.mesaboogie.comand at all authorized Mesa/Boogie dealers.