Effects and Signal Processors are important tools in the recording studio as well as part of a versatile and professional live sound setup. In fact, it's very difficult to see a professional setup that doesn't include some sort of effects and signal processing such as Compressors & Limiters, EQ, Crossovers and Reverb, for instance. PMT Online stocks a huge selection of all the best FX, which you can order online or in-store.
Compression / Limiting is one of the most widely used effects in music. It affects the dynamic range of the audio signal and is able to reduce the volume of a loud sound after it reaches a certain threshold, or to amplify a quiet sound. It's commonly used in public spaces playing quiet music, to make sure quiet bits can be heard. In mixing & recording it can make sounds seem louder and fuller.
Equalisers are an essential tool in the studio and in a live music venue, too. They can help to make things sound better by boosting certain frequencies or by cutting others, and, for instance, help combat feedback in live situations. Most Mixers will have basic EQ controls, but for a professional setup, you'll want a dedicated EQ rack unit, which can help you tailor your sound much better, by targeting much more specific frequencies.
Crossovers are recommended for bigger, professional sound system setups, where multiple speakers are used. They allow you to split the frequency range of the audio signal to different speakers - which means each speaker can sound better than if they were handling all the frequencies at the same time. For this reason, using crossover is a must for any respectable professional setup.
Reverb is another commonly used effect that no recording studio can be without. Most recordings will benefit from some sort of Spring, Plate or Hall reverb somewhere. A well-equipped recording studio and live venue will also have some sort of FX units at their disposal. Rack multi-FX units can provide everything you'll need... then some!