Standard Units

Along with microphones, mixing desks and recording devices, studios use a host of other equipment for processing sound. This equipment is often termed "outboard", that is, not part of the mixing desk but attached to it, usually via a patch bay.

Signal processing units take a sound, called a "dry signal", and change it in some way which results in a "wet signal".

The actual units come in all shapes and sizes, but the most common size is the 19-inch rack mountable unit. 19-inch racks are used in studios because they keep a lot of equipment:

• in one handy place
• secure
• close together so they can be patched together easily if needed.

Signal processing units are often called DSPs - Digital Sound Processors. There are units for almost anything imaginable. For example, there are:

• Instrument processors, such as those used by electric guitarists for adding:

• Reverb
• Distortion
• Echo

• Vocal processors – used by vocalists for:

• Adding reverb, echo etc.
• Automatic harmonisation
• Pitch correction

The most common units found in studios are discussed briefly in the following sections. It should be noted that these units are used more for rock and pop music recordings, and much less so for classical recordings, if at all.

A 19-inch rack containing DSPs and other equipment

The Reverb Unit

It used to be that studios were often equipped with dedicated echo and reverb units. These units could add, as their names suggest, echo or reverb (reverberation) to dry signals. These days it is far more common to find studios equipped with single units that do both of these jobs plus a lot more.

These units are capable of adding virtually any sort of reverb or echo effects via their built-in digital processors.

Many modern mixing desks have reverb units built in to them. However, external, i.e. outboard, units are still often used. Different models of reverb unit produce slightly different effects. For example, some produce a warmer sound than others. For this reason producers and engineers still use outboard units as well as those built into desks.

As with all outboard equipment, a dry signal is "sent" to a reverb unit from the mixing desk where it is processed and sent back to the desk. This is achieved using a patch bay to form a loop between the DSP and the desk.

The Alesis Midiverb 4 - a Popular Studio DSP

The Compressor

The function of a compressor is to smooth out fluctuations in the volume (dynamics) of a voice or instrument. It is generally used for rock and pop music, and only very rarely for classical music.

A typical situation when a compressor would be used is for a rock vocal recording. It is likely that during the vocalist's performance there will be undesirable fluctuations in dynamics as the singer adds or removes emotional expression. A compressor can be used to smooth out these fluctuations, while never letting the volume fall below a preset value. This is shown graphically below. Note that the dashed line shows the minimum volume preset:

Compressors often come equipped with another related function built into them called "gate". A gate setting allows through only those signals that are higher in volume than a preset value. This is useful for removing unwanted background signals. For example, due to "overspill" it may be possible to hear a weak drum sound during a vocal track. The gate could be set in such a way as to remove the drum sound while allowing the (louder) vocal sound through.

The Alesis 3630 Compressor Unit with Gate Function