Signal Flow and the Audio PathInput Sources (microphones, instruments, playback devices)
Monday, January 15, 2024
In live audio engineering, input sources are the origin points of sound that are captured and processed through the sound system. These sources can be broadly categorized into microphones, instruments, and playback devices:
Microphones:
Dynamic Microphones: Robust and capable of handling high sound pressure levels, dynamic microphones are often used for vocals, drums, and guitar amplifiers. They are less sensitive to moisture and temperature changes, making them suitable for live performances.
Condenser Microphones: More sensitive and accurate, condenser microphones require phantom power and are used for capturing more nuanced sounds like acoustic instruments, overheads for drums, and vocals in a controlled stage environment.
Ribbon Microphones: Less common in live sound due to their fragility, ribbon mics are valued for their warm and natural sound, sometimes used for miking guitar cabinets or orchestral instruments in a live concert setting.
Electret Microphones: Electret microphones are a type of condenser microphone that utilizes a permanently charged material called an electret to convert sound waves into electrical signals. They are widely used in various applications, including telecommunication devices, recording studios, and consumer electronics.
The electret material used in these microphones is typically made of a thin, polymer film that is permanently charged. This charge allows the electret to act as a polarizing element, creating a fixed electric field within the microphone.
When sound waves enter the microphone, they cause the electret material to vibrate. This vibration changes the distance between the electret and a metal plate, which in turn alters the capacitance of the microphone. The capacitance changes are then converted into electrical signals by the microphone's circuitry.
One of the advantages of electret microphones is their small size and low cost, making them suitable for use in compact electronic devices such as smartphones, laptops, and digital cameras. They also have a relatively flat frequency response and good sensitivity, allowing them to capture a wide range of frequencies accurately.
In terms of power requirements, electret microphones typically require a bias voltage to maintain the charge on the electret material. This bias voltage can be provided by the microphone's circuitry or an external power source, depending on the microphone design.
Overall, electret microphones offer a convenient and cost-effective solution for capturing audio in various applications, thanks to their small size, sensitivity, and relatively flat frequency response.
Instruments:
Direct Input (DI) Boxes: Electric instruments such as bass guitars or keyboards are often connected to the sound system through DI boxes, which convert unbalanced high-impedance signals to balanced low-impedance signals suitable for long cable runs to the mixer.
Electronic Drum Kits: These can be connected directly to the sound system via multiple outputs or a stereo mix, providing individual control over each drum sound.
Amplifiers and Speaker Cabinets: Electric guitars and basses are often miked with dynamic microphones placed in front of their amplifiers, capturing the sound of the instrument as shaped by the amplifier and speaker cabinet.
Playback Devices:
Media Players: Devices such as CD players, MP3 players, or smartphones are used for playing pre-recorded music, backing tracks, or sound effects. They typically connect to the sound system through line-level inputs using TRS or RCA connectors.
Computers and Digital Audio Workstations (DAWs): Computers running DAW software can serve as playback devices or as sources for virtual instruments and samples. They connect to the sound system via audio interfaces using various types of digital or analog outputs.
Samplers and Sequencers: These devices are used to trigger sound samples or sequences during a performance and are connected similarly to other line-level sources.
Each input source requires appropriate handling to ensure the best sound quality. Microphone placement, DI box usage, and the correct setting of levels and gain structures are all crucial aspects of working with input sources in live audio engineering. Additionally, it's important to consider the acoustics of the performance space and the potential for feedback when placing and selecting microphones and instruments.