basics.md 2.6 KB
title: Audio Basics breadcrumbs:
- title: Media
title: Audio
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Bands:
- Lows (ca. 20Hz-100Hz)
- Low midrange (ca. 100Hz-1kHz)
- High midrange (ca. 1kHz-10kHz)
- Highs (ca. 10kHz-20kHz)
Signal levels:
- (Note) This is the voltage (and somewhat impedance) inside cables/equipment.
- Mic level: Output from a microphone. Very weak, requires a preamp.
- Instrument level: Output from e.g. a guitar. Like mic level but slightly stronger.
- Line level (+4dBu): Professional equipment.
- Line level (-10dBV): Consumer equipment. Lower than +4dBu. Not to be confused with dBv.
- Speaker level: High-power signal going from an amplifier to a (passive) speaker.
- Phono: Old, for turntables etc. Much lower voltage than line level. Typically needs a phono preamp/stage with RIAA equalization.
Balance mode:
- Unbalanced: Ground and signal.
- Balanced: Ground and hot and cold signal with equal impedance. The cold signal is 0V but not (directly) connected to ground.
- Differential: Balanced but the cold signal is the opposite voltage of the hot signal instead of 0V.
- Balanced and unbalanced mono plugs/sockets can generally be connected together (with the loss of the balanced signal), but don't connect e.g. a stereo unbalanced TRS to a mono balanced TRS. It'll sound weird due to the signal mismatch.
Ground loops:
- When there exists physical loop in the ground wires. Typically when devices are connected to different grounded power outlets.
- Different potentials in the loop will cause undesired current flow.
- Can be heard as a 50Hz/60Hz hum in the audio signal.
- Solutions:
- Use balanced signals.
- Connect all equipment to a single grounding point, i.e. a single power outlet.
- Break the shielding on one cable to break the loop. Different boxes, like DI units, may have this as a feature known as a ground lift. However, make sure all shields are connected at one end (don't lift everything). Don't break the shielding/earthing on devices that needs it for safety reasons!
- Use a ground loop isolation transformer.
- Group the ground cables together so no currents get induced into the cables.
- Use a resistor and/or a ferrite bead to limit AC current.
Phantom power: Applies 48V to XLR3 (or similar) inputs, for powering mics and similar. Applying this to devices which aren't made for it can break them.
Impedance: Basically resistance but for AC.
Proximity effect: Increase of low frequency response when a audio source is close to a directional or cardioid microphone.
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