Signal Processors

Microphone PreAmplifiers or just PreAmp or MicPre
This is one of the pieces in the audio signal chain which can make a lot of difference on how the entire system sounds. All microphones connect into this preamp and it usually has a line level output which goes into the line level input on the mixers. This way you can bypass the preamps on the mixer which are of inferior quality. You can read about them in the Recording section. Example: Great River Preamps.

Effects Processor / Reverb Unit
The reverb unit usually comes into place after the equalizer and compressor and used to make the Masjid SOUND BIG by giving it some space. Reverberation (reverb) is the continuous presence of reflected sound after the original source of sound has stopped. 

The longer this reflected sound is present the lesser the speech clarity. Longer reverb means less clarity and shorter reverb means more clarity. Tajweed will be completely destroyed if this is not set correctly. Please remember reverb is different from echo. A touch of reverb can make speech very clear and intelligent whereas any form of echo will make speech and Tajweed very difficult to understand. Every room / mosque has natural reverb unless you kill it with treatment. Be sure to take this into account when using any form of artificial reverb effect.  

We almost always do not use any reverb unit in large mosques as they have natural reverberation. Many times we have to cut down natural reverb using sound absorption panels with heavy curtains to bring the RT (reverberation time or decay time) to less than a second. A RT between 0.25 and 0.50 second is best for Masjid setup. Also please set pre-delay wisely. Shorter the better - between 10 and 35 millisecond is the best. 

Our choice of reverb unit when used is made by Lexicon (MX200, MX300 and MX400 models). You do not need to have this unit if your mixer has built in DSP processor / reverb effect. Soundcraft mixers have lexicon reverb chip as they are both from the Harman group. Other effects units include TC-Helicon MX-350, carvin FX2 etc.

Compressor / Equalizer
We almost always do not use any compressor and have rarely used an equalizer in any Masjid. Our approach is to get a flat sound with minimum equipment. This saves time, money and leaves fewer parts to break. Rupert Neve once said that it is ideal to have a microphone and a wire with gain. This is the best and only combination needed. A compressor raises the volume of quiter parts and lowers the volume of louder parts making the entire audio volume / level fall within a desired range. Using an equalizer you can boost or lower certain frequencies in the audio frequency range. For example if the sound is very boxy / muddy, then we cut down 500Hz by 3 to 6 db. Some good equalizers are from dbx series.

Feedback Eliminator / Destroyer / Suppressor
It is very common to see feedback issues in a Masjid whenever the PA system has some decent output level. An easy solution to this is to throw a automatic feedback eliminator between the mixer and the amplifier. There are a few models out there but two of the best ones are dbx AFS224 and Shure DFR22.

Sonic Maximizer
This is a piece of equipment which acts like a glorified Equalizer. It makes the mid and high frequencies very clear and you can hear a clear sonic separation. This gear goes right before the amplifiers. Example: BBE Sonic Maximizers.

This is a piece of equipment which cuts down sibilance - The ESS (S / SH / Z / ZH) sound. This sound when exaggerated, is very annoying and hurts your ear too much. For example Was-Sammaaee will generate sibilance. Most sibilance related to tilawat is around 8 KHz. 
Since de-esser's cut down frequencies 
related to the ess sound, they also have adverse and undesirable effect on other sounds which happen to be in the same frequency band. So be careful how much to de-ess and also choose a transparent de-esser. The good ones are expensive. The best option is to avoid it by reciting into the mic at an angle rather than straight into it. Another option is when about to recite the ESS letters, move away a bit from the mic. If your voice is too sibilant then try the Shure SM58 mic and see if it works for you.

Lexicon MX-300

Rolls Equalizer 

Universal Audio Compressor