Feedback / Microphone: Difference between revisions

    <div><h2>Introduction</h2>

If you have questions about this article, please see this

<big> {{Community|link=https://twitter.com/ST_Muso/status/1391466144138100736|text=Microphone Feedback discussion}}</big>

== What is feedback and how does it occur? ==

Feedback occurs when the sound from the loudspeaker (or loudspeakers if a microphone is connected to more than one) is louder at the microphone than the sound of the voice.

This fundamental fact is shown in the figure below. Note that in the diagram an L1 system is shown but the same fundamental fact is true for ANY loudspeaker.

[[Image:Feedback fig 1.jpg|400px|Microphone Feedback]]

If you understand this diagram, it is relatively easy to understand how changes in an amplification system and the room can contribute to either increasing or decreasing the likelihood of feedback.  

 

 

 

 

Use a directional microphone. [[Microphone Directionality#Supercardioid_/_Hypercardioid|Hypercardioid]] is better than [[Microphone Directionality#Cardioid|cardioid]], which is better than [[Microphone Directionality#Omnidirectional Microphone|omnidirectional]]. All sound waves impinging on the microphone from a direction other than the intended signal is "noise" and will lower the threshold of feedback.

 

 

In addition, most directional microphones have a strong behavior called [[Proximity Effect|proximity effect]]. This is the strong buildup of bass and low-mid response as the source (say the voice) to microphone distance decreases. For microphones intended to sound natural when the voice is very close -- say one of a number of popular stage vocal microphones -- what this means is that low-to-middle frequencies from sources at a distance, including loudspeakers being used to amplify the voice, are largely rejected by the microphone. This is a real plus in terms of avoiding microphone feedback.

 

Conversely, an omnidirectional microphone (equal sensitivity to sound coming from any direction) has no proximity effect. This is an advantage often in the studio where the engineer wants consistent tone regardless of distance. But it's a disadvantage on stage in terms of feedback. An omnidirectional mic collects more sound that's not the target, and because it has no proximity effect is more susceptible to feedback at low-to-mid frequencies than a directional mic.

 

;There are two basic types of microphone — omnidirectional and unidirectional.  

 

If you are using vocal effects like reverb, chorus, or delay, turn them off until you can get sufficient [[Gain Before Feedback|gain before feedback]] to get performance level volume. Then add the effects back into the signal chain (one at a time) so you can be aware of the individual impacts that each effect is having on feedback.

If you are using a TC-Helicon vocal processor and you have the '''Tone''' processing on, you should not use a T1® Microphone Preset. Using both at the same time can reduce your gain before feedback. For more detail see [[:Category:TC-Helicon|TC-Helicon]].

=== Open Microphones ===

Use as few open microphones as possible.  

:Note that each time the number of open mics in a sound system is doubled (1 to 2, 2 to 4, 4 to 8, etc.), the overall gain [before feedback] of the sound system drops by 3 dB. This means that more open mics equals less gain in the PA system.<ref>[https://www.shure.com/en-US/performance-production/louder/feedback-fact-and-fiction Shure - Feedback Facts and Fiction]</ref>

=== EQ and Tone Controls ===

Wherever possible, acoustic instruments should use pickups instead of microphones. Pickup systems provide much higher [[Gain Before Feedback|gain before feedback]] than microphones.

=== The Benefit of ToneMatch Presets ===

A microphone that is not tonally balanced requires expertise and sophisticated equipment to equalize optimally. ToneMatch takes the guesswork out of getting studio-quality sound from a microphone connected to an L1 system. Equalization attempted by those not necessarily skilled in the art, or with tone controls that are not sophisticated enough, can leave peaks in the tonal response of the microphone -- peaks that are more likely to invite feedback.

When you sing or play at the loudest you will perform, the channel light should be solid green. Occasional flickers of red are okay. But if you see solid red, turn down the volume. Important: Use [[#Close Microphone Technique|close-microphone technique]]. The farther you are from the microphone, the greater the likelihood of feedback.

==== T4S/T8S Gain Staging ====

{{:T1 ToneMatch® Audio Engine / Gain Staging a Microphone}}

Your first adjustment for any input to your {{T1}} is the Trim setting. The exact position of the Trim will vary depending on signal strength of your input source. The correct setting for any particular source may be different from your other sources.  

[[Image:T1TrimPots.png|T1® Trim Pots]]  

=== Noise Gate ===

Use the Comp Gate ({{T1}}, {{T4S}}/{{T8S}}) to mute the microphone

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{{:Feedback / T1 ToneMatch® Audio Engine / Comp Gate}}

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Sometimes the geometry and configuration of the mic(s) will cause one particular frequency to be reinforced more than all the others, relatively independent of the positioning of the microphone. By identifying that particular frequency, one can use the T1® to reduce ("notch out") just that one particular "problem" frequency.

{{:Feedback / T1 ToneMatch® Audio Engine}}

{{:Microphone Sensitivity and Feedback}}

* A [[{{PAGENAME}}##Supercardioid_.2F_Hypercardioid|supercardioid or hypercardioid microphone]]

* A microphone that has a [[ToneMatch]] preset

* For any L1 model or any ToneMatch mixer, you can use a condenser or dynamic microphone.  

* For an [[S1 Pro+]] / [[S1 Pro]] use a [[Dynamic Microphones|Dynamic Microphone]]. The S1 Pro family to not support condenser microphones

* For more insights, please see [[Review / Microphone / Various|Microphone Reviews]].

{{:Feedback Destroyer}}

Here's a quick link to other articles about <categorytree mode="pages" hideroot="off" namespaces="Main">Feedback</categorytree>

* [http://www.shure.com/stellent/groups/public/@gms_gmi_web_ug/documents/web_resource/us_pro_mics_for_music_sound_ea.pdf Microphone Techniques for Live Sound Reinforcement] Shure Educational Publication 2006 39 pages - pdf format

*[[Media:us_pro_mics_for_music_sound_ea.pdf|Microphone Techniques for Live Sound Reinforcement]] pdf format

* [http://www.shure.com/ProAudio/Resources/HowToUse/us_how_to_use_vocalmiking Vocal Miking Problems and How To Solve Them]

* [http://www.shurenotes.com/issue27/article.html Debunking Common Audio Myths] (related to microphones)

[[category:Feedback]]

[[category:Performance]]