D

dB

See Decibel.

DC

Abbreviation for direct current.

Decibel (dB)

  1. Relative measurement for the volume (loudness) of sound. Also used to measure the difference between two voltages, or two currents. See Zero dB.
  2. A numerical expression of the relative loudness of a sound. The difference in decibels between two sounds is ten times the common logarithm of the ratio of their power levels.

Delay

Outboard sound equipment that can momentarily stores a signal being sent to part of a P.A. system so that delayed reinforced sound reaches the audience at the same time as live sound from the stage.

Delay is an effect used in live audio engineering to intentionally delay the sound coming through a speaker or other output device. Some key things to know about delay:

  • Purpose: Delay is used to control timing between different speakers, fill in gaps, or create special effects like echo or doubling. It helps synchronize and blend sounds from different sources.
  • How it Works: A delay unit records an incoming audio signal and plays it back after a set period of time determined by the “delay time” setting. This creates a duplication of the original sound that is heard later.
  • Delay Time: This setting controls how much latency there is between the original sound and the delayed sound. Short delay times under 100ms create a “doubling” effect. Longer times over 100ms can produce an echo.
  • Feedback: Controls how much of the delayed signal is fed back into the input to create repeating echoes. Higher feedback settings produce more repeats.
  • Uses: Delay is used on vocals to thicken them, on guitar to add depth, and on live sound systems to synchronize speaker stacks or fill in areas with poor coverage. Extensive delays create special effects.

Delay (Digital, Analogue)

  1. Effect used to create echo…echo…echo…echo…echo…
  2. In more advanced systems used in very large venues, delay can be used to time the arrival of the signal to the speakers in the back of the room so that people in the back hear the sound coming from those speakers at the same time that the sound coming from the speakers in the front of the room arrives.

Diaphragm

A thin flexible membrane or cone that vibrates in response to electrical signals to produce sound waves. Distortion is usually referred to in terms of total harmonic distortion (THD) which is the percentage of unwanted harmonics of the drive signal present with the wanted signal. Generally used to mean any unwanted change introduced by the device under question.

Digital Recording

  1. ADAM: (Akai Digital Audio Multitrack). 12 track recording onto Video 8 tape. 16 bit, 44.1 or 48 kHz sampling rate.
  2. DAT (Digital Audio Tape) Cassette-like system which has much higher quality than standard audio cassettes. Widely used in gathering sound effects, for news gathering, and for playback of music.
  3. DCC (Digital Compact Cassette) Rival to DAT which also plays standard audio cassettes.
  4. MiniDisc : Uses computer disk technology, rather than tape. A laser heats an area of magnetic disk which is then written to by a magnetic head. When cooled, the magnetic information is read from the disk by laser. Tracks can be named, and are instant start. Very theatre-friendly system.
  5. Direct to Disk : Uses the hard disk present in most PCs as the recording medium.

Diffraction

The breaking up of a sound wave caused by some type of mechanical interference such as a cabinet edge, grill frame, or other similar object.

Direct box

Used in line to convert a high impedance signal into a low impedance signal.

A direct box, also known as a DI box, is a key device used in live audio engineering and recording situations. Here’s an overview:

  • Purpose: A direct box converts an unbalanced, high-impedance instrument signal to a balanced, low-impedance microphone-level signal. This allows the instrument to be connected to audio equipment like mixing consoles, recording interfaces, etc.
  • Why It’s Needed: Many instruments like electric guitars, basses, keyboards have an unbalanced output that is prone to hum and interference. A DI box converts the signal to balanced to reduce noise. It also matches the impedance and levels between the instrument and other equipment.
  • How it Works: A DI box contains a transformer that converts the impedance and balances the signal. Passive DI boxes don’t require power, active DI boxes also boost the signal strength.
  • Uses: DI boxes are used onstage to connect instruments like guitars, basses, and keyboards to a mixing console. In the studio, they allow instruments to be plugged directly into an audio interface.
  • Types: Passive DI boxes are simpler and don’t require power, while active DI boxes boost the signal. There are also ground lift switches to remove hum and headphone outputs.

Distorted

The way your PA sounds just before it blows up. Fuzzy and scratchy. If you hear this, it either means you have something hooked up wrong, or something in the system is going bad. It could be anything from your super expensive soundboard to a five-dollar patch cord.

Distortion

Distortion is an effect that occurs when an audio signal is altered, resulting in clipping, crunching, or other types of signal degradation. Here’s an overview of distortion in live audio:

  • Causes: Distortion happens when a signal exceeds the dynamic range that equipment can handle. This can be from pushing levels too high or from equipment flaws.
  • Types: Common types are clipping (hard distortion), overdrive (smooth/warm), fuzz (thick/fuzzy), and bitcrushing (digital/aliasing). Each has a characteristic sound.
  • Uses: Musicians intentionally use distortion to get “gritty” or “dirty” tones, especially with electric guitars. It adds harmonics and sustain.
  • Problems: Unintended distortion results in unpleasant jagged, crunchy sounds. It can damage equipment and listeners’ ears at extreme levels.
  • Avoiding: Keep levels below maximum to avoid clipping. Use proper gain staging through each piece of equipment. Use quality cables/speakers.
  • Fixes: Reduce overall gain at instruments, preamps, and the mixer. Use correct input sensitivity settings. Patch around faulty cables/equipment. Use limiters.
  • Creative Uses: Some engineered distortion adds warmth on vocals, power to drums, and ambience on keys. Use subtly and with caution.

Dolby

Trade name for a series of noise reduction systems that have become standard on many tape playback machines. Many film soundtracks are produced using this process. Different varieties are found from Dolby B on most personal cassette players, to Dolby SR and Digital, the current state of the art for cinema.

Dolby is an audio noise reduction and encoding technology originally developed for consumer formats like tapes and movies, but also used in professional live sound. Here’s an overview:

  • Noise Reduction: Dolby systems reduce hiss and static in recordings and audio signals by boosting quieter sounds during recording, then reversing the process during playback. This minimises noise without affecting louder sounds.
  • Encoding: Dolby Digital, Dolby Pro Logic and other encoding methods allow multi-channel surround sound to be stored and transmitted efficiently. This maintains quality while conserving bandwidth.
  • Use in Live Sound: Dolby noise reduction units are used with analog tape and broadcast signal chains to minimise hiss. Dolby encoders encode surround mixes and matrix stereo signals for concert recording and broadcasts.
  • Dolby Atmos: A newer object-based 3D surround sound format that positions and moves audio elements in 3D space. It’s used in cinemas and increasingly in live sound for very immersive experiences.
  • Limitations: Dolby technologies require compatible encoding/decoding hardware end-to-end. This can limit applications and introduce latency into surround sound monitoring.

In summary, Dolby technologies optimise audio signals to minimize noise and enable advanced surround sound capabilities for both recorded and live applications. Audio engineers utilise Dolby tools appropriate to their workflows.

Driver

See transducer.

Drum Frequencies

Drum frequencies typically vary between 20Hz (kick drum) and 8kHz (cymbals). >>> List of drum frequencies and how to mic them.

Dynamic Range

Dynamic range refers to the difference between the loudest and softest sounds in an audio signal, which is an important consideration in live sound. Here’s an overview:

  • Definition: Dynamic range is the ratio between the highest peak level and the lowest noise floor that equipment or audio can reproduce. It’s measured in decibels (dB).
  • Wider is better: More dynamic range allows quieter sounds to still be heard despite loud transients. This provides greater nuance and realism.
  • Limitations: Audio equipment has limited dynamic range due to noise floors and headroom limitations. Trying to exceed this causes clipping and distortion.
  • Compression: Processing like compressors and limiters can intentionally reduce dynamic range by attenuating louder signals. This helps prevent peaking when signals get too loud.
  • Problems with insufficient range: Signals that lack dynamic range sound flat and lifeless. Exceeding system dynamic range causes clipping and distortion.
  • Gain staging: Careful gain structuring through the signal chain preserves as much dynamic range as possible by optimising levels at each stage.
  • Finding the right balance: When mixing live sound, engineers aim for an optimal blend of dynamics and loudness for the venue and genre.

In summary, understanding and optimising dynamic range is crucial for live audio engineers to deliver clean, impactful sound.

Dry

Describes a sound coming from the PA with no effects on it.

Dynamic Mic

Robust type of microphone which picks up the sound on a diaphragm connected to a coil of wire which moves within a magnet. An alternating current is induced into the wire which provides the electrical output. Most dynamic mics have low output impedance of 200 Ohms. See Condenser Mic.