The Mudcat Café TM
Thread #98244   Message #1945531
Posted By: Bernard
23-Jan-07 - 11:04 AM
Thread Name: Omnidirection microphone for session
Subject: RE: Omnidirection microphone for session
It's a complex issue. I'll try to make it simple... -ish!

The Master Volume should not be set too high, to avoid 'pre-amp noise'. This is often a compromise, depending on the quality of the equipment.

Let's start at the beginning (cue for a song?!)...

A 'serious' mixer or mixer-amp will have separate controls on each input channel for EQ and Input Gain.

Input Gain is not to be confused with 'Volume' - this is the control which sets how much signal is accepted into the channel, and it set too high will cause signal distortion even at low levels.

Usually the Input Gain has a 'clipping' LED nearby - this ought not to illuminate except for the occasional flash if someone shouts down the microphone. If it is constantly lit, turn the input gain down gradually. Setting it too low, however, is nearly as bad, as you will amplify the pre-amp noise!

Okay, assuming each channel gain is now set, open the Master Volume to around -15dB as a rough guide. If you haven't got 'negative dB markers', between halfway and threequarters is near enough.

Now open one vocal mic channel gradually until you hear it start to 'ring'. A small ajdustment of the EQ at the frequency of the feedback should enable you to find a little more level from that microphone before it squeals. You should be wary of doing too much to the EQ of a mic, or it will sound unnatural - again, 'compromise' is the keyword.

'Squeak out' each microphone in the same way independently, and then gradually open them all together.

You will find the feedback occurs at a lower level, now... nothing is actually wrong, it's a function of having more microphones 'open'. If you have one microphone open to 'ringing point', you may find you have to back it off by about -3dB when you open another. It's done by feel - listen for the 'ringing', and move the controls very gently by small amounts.

I haven't mentioned any amplified instruments yet. The mistake most people make is to balance out the instruments and try to make the microphones shout above them. WRONG! Get your microphones right, then gradually balance the instruments underneath! This is because there is a limit on how much level a microphone will deliver before it feeds back; such a limit isn't always imposed by instruments... unless they use microphones, of course (Instruments with microphones need to be dealt with in a similar way to vocal mics).

Another useful hint... add your effects (reverb, chorus, etc) after you've got the balance right - then you will know what is causing the unexpected feedback!

This isn't something that works too well on paper, so you will have to experiment based upon the hints to find a good balance.

The Master Volume can now be used to slightly raise or lower the overall balanced signal if need be.

Vocal microphones such as the Shure SM58 are designed specifically for close vocal work - your lips should be virtually touching the gauze ball. If you back off a little, it will 'pop' quite seriously on explosive consonants (p and b). Working around 2" (50cm) away as many people seem to do is precisely why they pop!

Again, on paper it's not easy - experiment!

Microphone technique is just as important as correct setup. I usually tell people to imagine they have their tongue glued to the end of the microphone... keep your mouth pointing at the mic even though you are turning your head, say, to look at the guitar neck.

Does this help?