The Altec 436 was modified by EMI and used to record the Beatles at Abbey Road studios. The Altec 438c is basically the same thing with extra controls for threshold and release time and the big difference is the 438c features a built in mic preamp. This unit is 100% vacuum tube technology.
Vari-Mu compressors/limiters are a certain breed of compressors, which are held in the highest esteem by some of the greatest engineers and producers in the world. Compressors and Limiters are both forms of automatic volume control, which also imparts certain tonal characteristics on the audio. Unlike most other forms of compressors, Vari-Mu compressors adjust volume changes in a very musical/natural way. Aside from Mastering, the most common use for a vari-mu compressor is vocals. Typically a singer can have a lot of dynamic range between their softer parts and full on wailing. If left untouched, this dynamic range can make it difficult for a listener to hear certain lyrics or passages in the vocals. A compressor can solve that problem.
There are a lot of different compressors out there, which all impart their own sonic signature. Optical Compressors, FET compressors, and Vari-mu compressors are the 3 main types, with vari-mu comps generally being the most expensive and sought after. The vari-mu comp has what most consider to be the smoothest compression character of them all, with a sound reminding some engineers of sweet cream.
The Altec 438c has more color than most vari-mu compressors, which makes it more of a specialty piece of gear, rather than general purpose. Many people prefer it over all other options for recording bass. The 438c is a bit different from other vari-mu's because it also has a built in 12AY7 vacuum tube mic preamp. It is possible to bypass the compressor and use the mic preamp standalone. Its a colorful mic preamp as well and is suitable for anything the engineer/producer wants to make stand out in a mix (ie. vocals).
Posted by Gallery Acoustics Recording Studio at 6:02 AM