Audio signal flow is the path an audio signal takes from source to output.[1] The concept of audio signal flow is closely related to the concept of audio gain staging; each component in the signal flow can be thought of as a gain stage.
In typical home stereo systems, the signal flow is usually short and simple, with only a few components. However, in recording studios and performance venues, the signal flow can often be quite complicated, with a large number of components, each of which may cause the signal to fail to reach its desired output. Knowing each component in the signal flow becomes increasingly difficult and important as system size and complexity increases.
Feedback
Feedback, also called "Howl-Round," occurs when the output of a device is accidentally connected to its input. If the device is amplifying the signal, then the amplified output will be fed back into the input, where it will be amplified again and sent to the output, where it will return to the input, be amplified again, and sent to the output, ad infinitum. An understanding of signal flow is important in preventing feedback.
CD playback example
The following example will trace the signal flow of a typical home stereo system while playing back an audio CD.
The first component in the signal flow is the CD player, which produces the signal. The output of the CD player is connected to an input on a receiver. In a typical home stereo system, this connection will be analog and unbalanced at consumer line-level of -10dBV using RCA connectors. By selecting the proper input on the receiver, the signal is routed internally to an amplifier which boosts the signal voltage from line-level to the voltage required by the speakers. The output of the amplifier is then connected to speakers, which convert the electrical signal into acoustical sound.
Single vocalist recording signal flow example
The exact series of elements in a signal flow will vary from system to system. The following example depicts a typical signal flow for recording a vocalist in a recording studio.
Singer Signal Flow Example
The first element in the signal flow is the vocalist, which produces the signal. This signal propagates acoustically to the microphone according to the Inverse-square law, where it is converted by a transducer into an electrical signal. Other objects may also produce sound in the acoustical environment, such as HVAC systems, computer fans, traffic noise, elevators, plumbing, etc. These noise sources can also be picked up by the microphone. It is therefore important to optimize the acoustical signal/noise ratio at the microphone. This can be accomplished by reducing the amplitude of unwanted noise (for example, turning off the HVAC system while recording), or by taking advantage of the inverse-square law; by moving the microphone closer to the signal source and farther away from any noise sources, the signal/noise ratio is increased.
After the microphone, the signal passes down a cable to the microphone preamplifier, which amplifies the microphone signal to line level. This is important because a line-level signal is necessary to drive the input circuitry of any further processing equipment down the chain, which will generally not be able to accept the extremely low-voltage signal produced by a typical microphone.
For the purposes of this example, the output of the microphone preamplifier is then sent to an EQ, where the timbre of the sound may be manipulated for artistic or technical purposes. Examples of artistic purposes include making the singer sound "brighter," "darker," "more forward," "less nasal," etc. Examples of technical purposes include reducing unwanted low-frequency rumble from HVAC systems, compensating for high-frequency loss caused by distant microphone placement, etc.
The output of the EQ will then be sent to a compressor, which is a device that manipulates the dynamic range of a signal for either artistic or technical reasons.
The output of the compressor is then sent to an analog-to-digital converter, which converts the signal to a digital format, allowing the signal to be sent to a digital recording device, such as a computer.
Vocalist live sound signal flow example
The following example traces the signal flow of a vocalist performing in a church.
The signal flow begins as in the previous example; singer, microphone, microphone preamplifier, EQ, and compressor. For this example, this signal then flows into a mixing board, which allows the signal to be routed to various outputs. The mixing board includes facilities for a main mix bus, which we will send to the house sound system, a monitor mix bus, which we will use to create a monitor mix for the singer, and an auxiliary mix bus, which we will use to create a second mix to be sent to the lobby and nursery.
Band signal flow example
A diagram of a typical signal flow for a band
Broadcast performance signal flow example
In this example, we will explore the signal flow of a hypothetical rock concert. For our example, this concert not only has a live audience, it is also being broadcast on live TV, and it is being recorded, with copies of the recording being sold to the public immediately after the concert is over. The signal from each microphone is therefore being sent to five places; the house sound system, the in-ear monitor system for the performers, the broadcast system, the recording system, and to the lobby, restrooms, and backstage areas so that people can hear the performance while outside the performance area.
Overview diagram of Signal Flow for this example.
The house sound system will be controlled from the "Front of House" position, also called the "Mix position." This position is usually located behind the audience.
The view from the Front of House Position.
The in-ear monitor system will be controlled by a monitor mix engineer located in the wing on one side of the stage. It is necessary that the monitor mix engineer be able to communicate with the performers, so being in close proximity to them is essential. The monitor mix position is often called "monitor world."
An example of a monitor mix position
The broadcast mix will be controlled from a broadcast truck, located in the parking lot behind the performance venue.
Arena Television OB8 working for the BBC at Wimbledon Tennis Championships, UK
The recording system will be located in another truck, located next to the broadcast truck.
For this example, the lobby, restroom, and backstage mix will be controlled by an assistant stage manager from backstage.
Stage managers panel
To facilitate this 5-way split, a device called a microphone splitter will be used. The microphone splitter serves several purposes; it will split the signal 5-ways, provide phantom power for condenser microphones and active DI boxes, and it will provide isolation between the 5 outputs, preventing ground loops. Preventing ground loops is an extremely important function, as the severity of ground loops typically increases with distance. In a large network of interconnected sound systems, such as the one in this example, ground loops could become dangerously severe. Isolation to prevent ground loops is therefore vitally important.
An example of a microphone splitter
Let's begin by tracing the signal path from the splitter to the audience. The signal leaves the splitter, typically via an Audio multicore cable, and travels to the Front of House position. Here, the still-mic-level signal enters into a microphone preamplifier, which boosts the signal voltage to line level. For this example, the microphone preamplifier is built into a mixing board. It is typical for a mixing board to include a line trim after the preamplifier. This allows the amplitude of the now line-level signal to be adjusted. This may be done for artistic or technical reasons. A typical application for the line trim is attenuating signals that were intentionally amplified too much by the microphone preamplifier. Over amplifying the signal can cause the preamplifier to distort, which can under certain circumstances produce a desirable sound.
After the line trim, the signal is processed by the mixing board's EQ, filter, compressor, limiter, de-esser, delay, reverb, and any other signal processing features the mixing board has available and that the mix engineer chooses to use. The processed signal is then sent to the mix bus, where it is combined with all the other signals coming from the stage. The balance of signals is controlled by faders.
The mix is then routed to one of the mixing boards outputs, and flows into a loudspeaker controller. This device processes the signal to optimize it for the sound system installed in the performance venue. It then flows into a rack of amplifiers, and then to the speakers.
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal. It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input. An amplifier is defined as a circuit that has a power gain greater than one.
A microphone, colloquially called a mic, is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, live and recorded audio engineering, sound recording, two-way radios, megaphones, and radio and television broadcasting. They are also used in computers for recording voice, speech recognition, VoIP, and for other purposes such as ultrasonic sensors or knock sensors.
An audio power amplifier is an electronic amplifier that amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving loudspeakers or headphones. Audio power amplifiers are found in all manner of sound systems including sound reinforcement, public address, home audio systems and musical instrument amplifiers like guitar amplifiers. It is the final electronic stage in a typical audio playback chain before the signal is sent to the loudspeakers.
A mixing console or mixing desk is an electronic device for mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals from electric or electronic instruments, or recorded sounds. Mixers may control analog or digital signals. The modified signals are summed to produce the combined output signals, which can then be broadcast, amplified through a sound reinforcement system or recorded.
Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the input. The average or peak output signal level is used to dynamically adjust the gain of the amplifiers, enabling the circuit to work satisfactorily with a greater range of input signal levels. It is used in most radio receivers to equalize the average volume (loudness) of different radio stations due to differences in received signal strength, as well as variations in a single station's radio signal due to fading. Without AGC the sound emitted from an AM radio receiver would vary to an extreme extent from a weak to a strong signal; the AGC effectively reduces the volume if the signal is strong and raises it when it is weaker. In a typical receiver the AGC feedback control signal is usually taken from the detector stage and applied to control the gain of the IF or RF amplifier stages.
Balanced audio is a method of interconnecting audio equipment using balanced interfaces. This type of connection is very important in sound recording and production because it allows the use of long cables while reducing susceptibility to external noise caused by electromagnetic interference. The balanced interface guarantees that induced noise appears as common-mode voltages at the receiver which can be rejected by a differential device.
A preamplifier, also known as a preamp, is an electronic amplifier that converts a weak electrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier and a loudspeaker. Without this, the final signal would be noisy or distorted. They are typically used to amplify signals from analog sensors such as microphones and pickups. Because of this, the preamplifier is often placed close to the sensor to reduce the effects of noise and interference.
A DI unit is an electronic device typically used in recording studios and in sound reinforcement systems to connect a high output impedance unbalanced output signal to a low-impedance, microphone level, balanced input, usually via an XLR connector and XLR cable. DIs are frequently used to connect an electric guitar or electric bass to a mixing console's microphone input jack. The DI performs level matching, balancing, and either active buffering or passive impedance matching/impedance bridging. DI units are typically metal boxes with input and output jacks and, for more expensive units, “ground lift” and attenuator switches.
In audio engineering and sound recording, a high impedance bridging, voltage bridging, or simply bridging connection is one in which the load impedance is much larger than the source impedance. The load measures the source's voltage while minimally drawing current or affecting it.
A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers in enclosures all controlled by a mixing console that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience. In many situations, a sound reinforcement system is also used to enhance or alter the sound of the sources on the stage, typically by using electronic effects, such as reverb, as opposed to simply amplifying the sources unaltered.
Line level is the specified strength of an audio signal used to transmit analog audio between components such as CD and DVD players, television sets, audio amplifiers, and mixing consoles.
In an electrical system, a ground loop or earth loop occurs when two points of a circuit are intended to have the same ground reference potential but instead have a different potential between them. This is typically caused when enough current is flowing in the connection between the two ground points to produce a voltage drop and cause two points to be at different potentials. Current may be produced in a circular ground connection by electromagnetic induction.
A pickup is a transducer that captures or senses mechanical vibrations produced by musical instruments, particularly stringed instruments such as the electric guitar, and converts these to an electrical signal that is amplified using an instrument amplifier to produce musical sounds through a loudspeaker in a speaker enclosure. The signal from a pickup can also be recorded directly.
In audio processing and sound reinforcement, an insert is an access point built into the mixing console, allowing the audio engineer to add external line level devices into the signal flow between the microphone preamplifier and the mix bus.
A bass amplifier is a musical instrument electronic device that uses electrical power to make lower-pitched instruments such as the bass guitar or double bass loud enough to be heard by the performers and audience. Bass amps typically consist of a preamplifier, tone controls, a power amplifier and one or more loudspeakers ("drivers") in a cabinet.
A channel strip is a device that allows the output of an audio device to be amplified to a line level and integrated into some other system. An audio channel strip may be a stand-alone unit or one of many units built into a mixing desk. It usually includes a microphone preamp with a switchable phantom power voltage to power condenser microphones and some form of audio equalization. Some designs also offer other facilities including audio compression, de-essing, noise-gating and limiting.
Re-amping is a process often used in multitrack recording in which a recorded signal is routed back out of the editing environment and run through external processing using effects units and then into a guitar amplifier and a guitar speaker cabinet or a reverb chamber. Originally, the technique was used mostly for electric guitars: it facilitates a separation of guitar playing from guitar amplifier processing—a previously recorded audio program is played back and re-recorded at a later time for the purpose of adding effects, ambiance such as reverb or echo, and the tone shaping imbued by certain amps and cabinets. The technique has since evolved over the 2000s to include many other applications. Re-amping can also be applied to other instruments and program, such as recorded drums, synthesizers, and virtual instruments.
The term microphone preamplifier can either refer to the electronic circuitry within a microphone, or to a separate device or circuit that the microphone is connected to. In either instance, the purpose of the microphone preamplifier is the same.
In audio engineering, a gain stage is a point during an audio signal flow that the engineer can make adjustments to the level, such as a fader on a mixing console or in a DAW. Gain staging is the process of managing the relative levels in each step of an audio signal flow to prevent introduction of noise and distortion, feeding the inserts, such as equalizers and compressors with the right amount of signal, particularly in the analogue realm. Ideal gain staging occurs when each component in an audio signal flow is receiving and transmitting signal in the optimum region of its dynamic range.
A keyboard amplifier is a powered electronic amplifier and loudspeaker in a wooden speaker cabinet used for the amplification of electronic keyboard instruments. Keyboard amplifiers are distinct from other types of amplification systems such as guitar amplifiers due to the particular challenges associated with making keyboards sound louder on stage; namely, to provide solid low-frequency sound reproduction for the deep basslines that keyboards can play and crisp high-frequency sound for the high-register notes. Another difference between keyboard amplifiers and guitar/bass amplifiers is that keyboard amps are usually designed with a relatively flat frequency response and low distortion. In contrast, many guitar and bass amp designers purposely make their amplifiers modify the frequency response, typically to "roll-off" very high frequencies, and most rock and blues guitar amps, and since the 1980s and 1990s, even many bass amps are designed to add distortion or overdrive to the instrument tone.
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