Q: “Why Would I Use Compressor Instead Of A Leveler And Vice Versa?”
A: There are some famous compressors and levelers out there in the audio world whose names seem to come up all the time when producers and engineers let the ‘feline out of the rucksack’ when it comes to their secret sonic weapons. Two of the most famous, the 1176 compressor and the LA-2A Leveling Amplifier are both now manufactured by the same company, Universal Audio, which naturally begs the question; What’s the difference between a compressor and a leveler (leveling amplifier), and why would I use one or the other?
First, let’s determine what distinguishes one from the other, since it’s the job of both to ‘ride gain.’ Or, as gadget-girl would put it: employ a variable gain amplifier to reduce the dynamic range of the program material. (Spare us the techno-babble, gadget-girl) Simply put, in music, ‘dynamic range’ is the difference between the quietest and loudest volume of an instrument, part or piece of music, and it is the job of a compressor or leveler to compress, or limit the dynamic range so that the soft parts are not too soft, and the loud parts don’t pin the meters (distort the music) or make your ears bleed.
First, lets define what limiting is. A limiter is a circuit that allows signals below a set value to pass unaffected, and clips off the peaks of stronger signals that exceed this set value. (Or, as a limiter would put it; “You can only go so loud and no louder, or I will taunt you a second time.”) The basic difference between the two is that a leveler functions more like a limiter and is program dependant, whereas the compressor has the ability to change the value at which a signal is passed or compressed (threshold), as well as the speed at which the compressor responds to a signal (attack), the ratio of input signal to output signal, (e.g. A ratio of 4:1 means if 4db in, 1db comes out. Or, think Mad Max: “Two go in, one comes out, two go in, only one comes out… ladies and gentlemen, limiting time is here!”), finally, a compressor allows you to determine the length of time that the compressor acts on the signal. (Release) When a compressor is set with a very high ratio it begins to act like a limiter. A leveler, or leveling amplifier basically has only two controls, as in the case of the LA-2A: Gain, and Peak reduction. As we said earlier, the leveler is program dependant, meaning that it acts on the totality of the music coming through it, both high and low levels, based on an internally set compression slope. What makes the LA-2A unique is that it uses an electro-optical attenuator system that allows instantaneous gain reduction. The opto-compressor is thought to be more musical since it’s response is non-linear, just like the music passing through it. (For more background on optical compression characteristics see WFTD – Optical Compressor.) Some people feel that the more linear response of a VCA controlled compressor is not as musical, but in reality, both are effective tools based on the musical context you use them in, which is what we are about to discuss.
An opto-controlled leveler like the LA-2A or the Summit TLA-50 are often used on vocals and instruments like acoustic guitar because of their non-linearity in release times (as mentioned earlier). Most engineers think they are not as effective on percussion as an FET (solid state) compressor like the 1176 would be, since the ability to control attack and release times (also mentioned earlier) allows you to bring out the attack of the drums more effectively. (There are compressors that do have an electro-optical circuit, but they also have attack and release controls that do make them useful for percussion.) Perhaps the most prevalent use of a leveling amplifier is for stereo bus compression or for stereo mains output. The idea is that running your stereo mix through LA-2As or a pair of TLA-50′s is the secret sauce that ‘glues’ a mix together, making it sound like a whole, and not just a collage of different parts. (Mastering secret revealed!)
Keep in mind, that when we compress a signal, it’s volume decreases, so usually there is a gain make-up control to bring the level up. With a leveling amplifier, the gain make-up is built in to the circuit, which makes them a little harder to set. That is to say, they require a little more finesse since it’s easy to overuse them, but having only two controls makes them easier to use as well. Also, since they are program dependent, there is no set rule for basic settings. Keep practicing; you’ll get the hang of it.