Feedback

Feedback as a term is brought in discussion in most of the cases indicating that ringing noise (a screeching noise, a squealing noise, etc etc) that appears sometimes in sound systems. It occurs when a loop is produced between an input (for example: a microphone, a guitar, etc etc) and an audio output (for example: the PA System, the loudspeakers).

The scheme of a feedback is simple: the microphone captures the sound from the loudspeakers, this sound is amplified further and then it is pushed again in the PA / loudspeakers.

So, feedback, in the context of audio and music production, is a phenomenon where a sound loop exists between an audio input and an audio output. This loop is created when an amplified sound from a speaker is picked up by a microphone (or another input device), re-amplified, and then played back through the speaker, creating a loop that can result in a high-pitched squeal, hum, or ring. This unique phenomenon often manifests as a characteristic howling or screeching noise that amplifies until it reaches the equipment’s maximum output level.

It’s important to clarify that the term ‘feedback’ is also used in other disciplines, such as systems theory and communication theory, to describe a mechanism where the output of a system is fed back into the system as input. While this concept is somewhat similar to audio feedback, our focus here will primarily be on the audio and music production context.

The Importance of Understanding Feedback

Understanding feedback is crucial for anyone involved in the field of audio production and music. This is because feedback, if not properly managed, can be a disruptive presence. It can lead to undesirable noise, equipment damage, and even potential hearing loss. Furthermore, it can disrupt live performances, recording sessions, broadcasts, and any situation where audio quality and clarity are paramount.

On the other hand, when feedback is used creatively, it can add a unique dimension to the music being produced. Some of the greatest musicians and producers have used feedback as an artistic tool to create distinctive sounds and memorable musical moments.

Therefore, a solid understanding of feedback not only helps in effectively managing and preventing it but also opens up new creative avenues for the adventurous musician or producer. From a practical standpoint, understanding feedback helps professionals troubleshoot and problem-solve during live shows, studio recordings, and broadcasting. It also forms the basis for advanced audio engineering techniques and digital sound manipulation in music production software.

The Science Behind Audio Feedback

At its most basic level, audio feedback is a loop between an audio output and an audio input. To comprehend this, one must understand the three primary components involved in creating a feedback loop: a microphone, an amplifier, and a speaker.

The process starts when the microphone picks up sound and converts it into an electrical signal. This signal is sent to an amplifier, which increases the signal’s strength before sending it to a speaker. The speaker then transforms the electrical signal back into sound waves that are broadcast into the environment.

Feedback happens when these sound waves from the speaker are picked up by the microphone again, creating a loop. As this cycle continues, the same sound is repeatedly amplified and broadcasted, which can lead to an ever-increasing and potentially damaging volume level.

The pitch of the feedback is determined by the resonant frequencies of the room or environment and the equipment used. Every room has certain frequencies at which sound naturally resonates more than others, often called room modes or standing waves. Similarly, each piece of audio equipment has specific frequencies at which it resonates. When the feedback frequency aligns with these resonant frequencies, it results in a characteristic howling or screeching sound.

Types of Audio Feedback

There are primarily two types of audio feedback: positive feedback and negative feedback.

  • Positive Feedback: This is the type of feedback most people are familiar with when they think of audio feedback. It’s characterized by a sound that grows in volume until it reaches a maximum level or until something is done to disrupt the feedback loop. This typically happens when the microphone is too close to the speaker, causing the system to pick up its own output signal and re-amplify it.
  • Negative Feedback: This type is less well-known but is a valuable tool in audio engineering. Negative feedback involves taking a portion of the output signal, inverting it, and then feeding it back into the system. This can help stabilize the system, reduce distortion and increase the bandwidth. The key benefit of negative feedback is that it helps to control the overall gain of the system, preventing it from spiraling out of control as can happen with positive feedback.

It’s worth noting that there are other more complex forms of feedback, like controlled or intentional feedback, used as a creative tool in music. We will delve deeper into these as we explore the creative and innovative applications of feedback in later sections.

Causes of Feedback

Acoustic Factors Contributing to Feedback

Understanding the causes of feedback requires examining some of the acoustic principles at play. These principles revolve around sound waves and how they interact with various objects and environments.

  • Resonant Frequencies: As mentioned before, every environment and object has its own resonant frequencies. These are the frequencies at which an object or space naturally oscillates. When the sound produced aligns with these frequencies, it can amplify the sound, increasing the likelihood of feedback.
  • Sound Reflection: Sound waves can bounce off surfaces such as walls, ceilings, and floors, just like light reflecting off a mirror. These reflected waves can re-enter the audio input device, creating a loop that leads to feedback.
  • Directionality and Distance: The direction in which the microphones and speakers are facing, as well as their distance from each other, can affect the likelihood of feedback. Microphones that are too close to speakers or facing them directly are more prone to creating a feedback loop.

The type, quality, and configuration of audio equipment used can also significantly impact feedback occurrence.

  • Microphone Sensitivity: Highly sensitive microphones can pick up faint sounds, including their output from speakers. This can create a feedback loop if not correctly managed.
  • Amplifier Gain: If the gain on an amplifier is set too high, it can over-amplify the audio signals, making the system more susceptible to feedback.
  • Speaker Position and Volume: Speakers that are too loud or poorly positioned can cause sound to be picked up by microphones more easily, again leading to potential feedback.
  • Improperly Tuned Systems: Sound systems need to be properly tuned to the specific acoustics of the room they are in. If a system is not correctly tuned, certain frequencies may be overemphasized, leading to feedback.

Environmental Factors

Several environmental factors can also contribute to the creation of feedback loops.

  • Room Acoustics: The size, shape, and materials used in a room can significantly affect its acoustics. Hard, flat surfaces reflect sound waves more than soft, textured surfaces, increasing the risk of feedback.
  • Background Noise: High levels of ambient noise can force a sound engineer to increase the volume or gain of a sound system, increasing the risk of feedback.
  • Obstacles and Sound Barriers: The presence of objects and barriers between the sound source and the microphone can cause sound waves to reflect or diffract, increasing the likelihood of those waves being picked up by the microphone and causing feedback.

The Mechanics of Feedback

An Overview of the Feedback Loop

Feedback, at its most basic, is a cyclical process. It begins with a sound source, which is then picked up by a microphone. This signal is then amplified by the sound system and emitted through the speakers.

  • Initial Sound: The cycle begins with an initial sound that is picked up by a microphone. This could be anything from a vocalist singing into a microphone to an instrument being played.
  • Microphone Reception: The microphone translates this acoustic energy into an electrical signal that can be manipulated by audio equipment.
  • Amplification: This signal then travels to an amplifier (possibly through a mixing console), where it is boosted to a level that can drive the speakers.
  • Output: The amplified signal is then sent to the speakers, which convert the electrical signal back into acoustic energy—sound—that can be heard by the listeners.
  • Loop: If the speakers are too close to the microphone, or if the volume of the sound system is too high, the sound from the speakers can be picked up by the microphone, creating a loop. This is the feedback loop, and it will persist until it is interrupted.

Factors that Influence the Feedback Loop

Several factors can influence the creation and persistence of a feedback loop.

  • Volume and Gain: The louder the sound system, the more likely feedback is to occur. Similarly, higher gain settings on the microphone or amplifier can increase the chance of feedback.
  • Distance and Orientation: The closer the speakers are to the microphone, and the more directly they are facing each other, the more likely feedback is to occur.
  • Frequency Response: Each piece of audio equipment has its own unique frequency response. If a microphone, amplifier, or speaker is particularly sensitive to a certain frequency, it can increase the likelihood of feedback at that frequency.
  • Acoustic Environment: The acoustic properties of the environment can also significantly influence the feedback loop. In a room with many hard, flat surfaces, sound waves can bounce around, increasing the likelihood of feedback. Conversely, in a room with softer, more absorbent surfaces, sound waves will be absorbed rather than reflected, reducing the chance of feedback.

How to Control Feedback

Tips for Reducing Feedback

  • Correct Microphone Technique: One of the easiest ways to reduce feedback is to use correct microphone technique. This includes not pointing the microphone at the speakers and not placing the microphone too close to the sound source.
  • Optimize Speaker Placement: Positioning the speakers properly can have a significant impact on feedback. As much as possible, speakers should be placed in front of the microphones and pointed away from them.
  • Monitor Levels: Keep an eye on your levels. If the sound system is too loud, feedback is more likely. Make sure the gain is set at the right level—not too high, but enough to provide a clear signal.
  • Adjust Room Acoustics: Consider the room’s acoustics. Hard, flat surfaces can cause sound waves to bounce around and lead to feedback. Using absorptive materials can help to reduce this.

Tools and Techniques for Controlling Feedback

  • Equalization (EQ): EQ is a powerful tool for controlling feedback. By identifying the frequencies at which feedback occurs, you can reduce those frequencies using an equalizer.
  • Feedback Suppressors: These are devices or software that detect and eliminate feedback. They work by automatically recognizing the feedback frequencies and cutting them out.
  • Directional Microphones: These microphones pick up sound from a specific direction and can be useful in reducing feedback. They’re most effective when used in an environment where the sound source is consistent and predictable.
  • Sound Check: Before any performance or recording, do a sound check. This will help you identify potential feedback problems and address them before they become a problem during the performance.
  • Acoustic Treatment: Acoustic treatment can dramatically reduce the likelihood of feedback by reducing reflections and reverberations in the environment. This can involve adding absorptive materials, diffusers, or bass traps.

The Art of Using Feedback

Creative Use of Feedback in Music Production

  • Harnessing Feedback as a Sound Effect: Despite its notorious reputation, feedback can be used creatively in music production to produce unique and interesting sounds. This includes using controlled feedback to create sustained tones, complex harmonics, or gritty distortion.
  • Layering Feedback in Tracks: Feedback can be recorded and layered in tracks to add a sense of depth and character. When controlled and utilized properly, feedback can add another dimension to the audio palette.
  • Using Feedback in Sound Design: In sound design, feedback can be manipulated to create a variety of effects. This could include everything from creating ambient noise for a movie scene to crafting unique sounds for a video game.
  • Feedback in Electronic Music: Electronic music often embraces feedback as a creative tool. By running audio signals through a series of processors and back into themselves, electronic musicians can create textures and atmospheres that would be impossible to generate through traditional means.
  • Jimi Hendrix: Known for his experimental approach to the electric guitar, Jimi Hendrix often used feedback to enhance his performances. His rendition of “The Star-Spangled Banner” at Woodstock in 1969 is perhaps one of the most famous examples of controlled feedback use in music history.
  • The Beatles: In their song “I Feel Fine”, The Beatles used guitar feedback intentionally as part of the song’s introduction. This marked one of the first uses of feedback in a pop song.
  • Nirvana: The grunge band, Nirvana, used feedback as a sonic texture in many of their songs. Kurt Cobain’s use of feedback in tracks like “Smells Like Teen Spirit” and “Come As You Are” helped define the grunge sound of the 90s.

These examples show how feedback, often perceived as a technical flaw, can be harnessed and transformed into an artistic tool when approached creatively.

Feedback in Live Performances

Unique Challenges and Solutions

Live performance environments often present a unique set of challenges when it comes to controlling feedback. The complexity arises from the larger number of variables, including the acoustics of the venue, the number and types of microphones being used, and the volume and positioning of speakers.

Every venue has unique acoustic characteristics. Learning to understand these variables and adapt to them is crucial in preventing and managing feedback. Solutions may include adjusting speaker placement, microphone selection and placement, and utilizing sound-absorbing materials.

The proximity of microphones to monitors can significantly influence the likelihood of feedback. By following proper microphone techniques and positioning monitors correctly, performers can greatly reduce the chance of feedback.

A deep understanding of the signal chain in a live sound setup can aid in pinpointing potential feedback issues. This includes knowing the routing of audio from microphones, through the mixing board, out to the amplifiers, and finally to the speakers.

Feedback Management Techniques in Large Venues

  • Using Feedback Suppressors: In large venues, hardware or software feedback suppressors can be particularly useful. These devices work by detecting the frequency of the feedback and applying a notch filter to eliminate the offending frequency.
  • Sound Check and EQ: A thorough sound check and EQ adjustment can help identify and mitigate potential feedback problems before the performance starts.
  • Microphone Choice and Placement: The use of directional microphones can help focus on the sound source and reject unwanted noise from other directions, reducing the chance of feedback.
  • Speaker Placement: Placing speakers properly can significantly reduce the likelihood of feedback. The primary goal is to ensure the loudspeakers are not pointing directly at any microphones on stage.
  • Use of In-Ear Monitors: In-ear monitors (IEMs) are a popular solution in large venues for reducing stage volume and hence the likelihood of feedback.

Managing feedback in live performances, especially in large venues, is both an art and a science. It requires a deep understanding of the technical aspects of sound reinforcement, as well as a keen ear and the ability to make quick adjustments on the fly.

Regulations and Standards on Sound Levels

  • Understanding Legal Frameworks: There exists a variety of national and international laws, regulations, and standards pertaining to the permissible levels of sound in different environments. These include occupational safety standards for noise exposure in workplaces, regulations for sound levels in public spaces, and standards for sound transmission between residences.
  • Adherence to Occupational Safety Standards: In a professional audio environment, like a recording studio or a live performance venue, it’s critical to adhere to occupational safety and health regulations related to noise exposure. These standards often include maximum allowable sound levels and required usage of hearing protection devices.
  • Responsibility of the Audio Professional: As an audio professional, it is your responsibility to ensure sound levels are within legal limits to prevent any legal consequences and to maintain a safe environment for everyone present.
  • Regulation of Audio Equipment: Some jurisdictions have regulations for audio equipment, including limits on the sound output of loudspeakers. Familiarity with these rules is important for compliance and avoiding potential legal issues.

The Impact of Excessive Feedback on Hearing Health

Feedback, particularly when it’s loud and unexpected, can pose serious risks to hearing health. High volume feedback can potentially lead to noise-induced hearing loss, a permanent condition resulting from prolonged exposure to loud noises.

It’s essential to understand what constitutes a safe sound level and duration of exposure. Prolonged exposure to any sound above 85 decibels can cause hearing damage. For every 3 decibels above this threshold, the safe exposure time is halved.

Audio professionals should use appropriate hearing protection, especially when dealing with potential feedback situations. This can include earplugs or over-ear protection, and in some situations, custom-molded in-ear monitors can provide both high-quality audio and significant hearing protection.

As an audio professional, it’s crucial to be an advocate for hearing health. This can involve educating others about the risks of loud feedback, the importance of hearing protection, and the need for regular hearing tests.

Understanding the legal and health aspects of feedback is a crucial part of being a responsible and ethical audio professional. Ensuring that you adhere to regulations and protect your hearing, as well as the hearing of those around you, can help you maintain a long and successful career in the audio industry.