Audio signal flow
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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.
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 are 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
In this example, we will trace 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 buss, which we will send to the house sound system, a monitor mix buss, which we will use to create a monitor mix for the singer, and an auxiliary mix buss, which we will use to create a second mix to be sent to the lobby and nursery.
Band Signal Flow Example
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.
The house sound system will be controlled from the "Front of House" position, also called the "Mix position." This position is usually located towards the back of the audience.
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 broadcast mix will be controlled from a broadcast truck, located in the parking lot behind the performance venue.
The recording system will be located in another truck, located next to the broadcast truck. The lobby, restroom, and backstage mix will be controlled from the Front of House position.
To facilitate this, 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.
See also
Notes
- ^ Steven Roback (2004). Pro Tools 6 for Macintosh and Windows (2nd ed.). Peachpit Press. p. 303. ISBN 978-0-321-21315-0.