Every hobby is full of three-letter acronyms that are entirely incomprehensible to anyone outside of the community. All too often, beginners to personal audio get overwhelmed by the alphabet soup of naming conventions. Even veterans skimming through a review or technical article can sometimes use an easy point of reference.

To help, we present this quick reference guide that includes most of the common headphone acronyms that you are likely to encounter on your audio journey.

Acronym DefinitionDescription
AACAdvanced Audio CodingAn audio coding standard for lossy digital audio compression. Wireless CODEC of choice for Apple.
A/DAnalog to DigitalThe conversion process from analog audio to a digital file.
ADCAnalog to Digital Converter or Audio Device Class (when referring to USB audio.USB peripherals that support the Audio Device Class send or receive audio and additional functionality.
AES3Audio Engineering SocietyA standard created by the Audio Engineering Society for transferring a stereo digital audio signal (2 channels of uncompressed PCM audio) over a single XLR digital cable. S/PDIF is a variant.
AIFFAudio Interchange File FormatAn uncompressed file format developed by Apple in 1988 as a WAV alternative.
ALACApple Lossless Audio CODECAn open-source format created by Apple and competing with FLAC.
aptXAudio Processing TechnologyA family of proprietary audio codec compression algorithms owned by Qualcomm, with a heavy emphasis on wireless audio applications.
ASIOAudio Stream Input/OutputA driver protocol for digital audio, providing a low-latency and a high fidelity interface.
ATRACAdaptive Transform Acoustic CodingA family of proprietary audio compression algorithms developed by Sony. MiniDisc was the first commercial product to incorporate ATRAC in 1992.
BABalanced ArmatureSmall and lightweight driver originally developed for hearing aids, featuring a vibrating reed suspended in a magnetic field within an enclosure. Often combined with multiple variations in an IEM.
BNCBayonet Neill–ConcelmanA miniature quick connect/disconnect connector used for coaxial cable.
CBRConstant Bit RateA method for encoding audio files that keeps the bitrate unchanging.
CDCompact Disc Co-developed by Philips and Sony and released in 1982.
CIEMCustom In-Ear MonitorA type of IEM that is made specifically to fit a single person’s ear canal.
COAXCoaxialA standard electrical connection of the S/PDIF standard, typically through a single 75 ohm coaxial (2-conductor) cable.
CODECCoder-DecoderA device or computer program which encodes or decodes a digital data stream or signal.
D/ADigital to AnalogThe conversion process from a digital file to analog audio.
DACDigital to Analog ConverterA device that decodes digital files to analog. Maybe abbreviated as ‘D/A’, ‘D2A’, or ‘D-to-A’.
DAPDigital Audio PlayerAn electronic device capable of storing and playing high-resolution music or media files.
DATDigital Audio TapeAnalog signal recording and playback medium developed by Sony and introduced in 1987.
DDDynamic DriverTraditional speaker driver type featuring a diaphragm moved by a coil suspended in a magnetic field.
DOPDSD Over PCMAn open standard method for transferring DSD audio over PCM.
DSDDirect Stream DigitalSony and Philips designed a system of digitally recreating audible signals for the Super Audio CD (SACD).
DTSDigital Theater SystemsSurround sound formats for both commercial/theatrical and consumer (home theatre) applications.
EACEnhanced Audio CODECAn audio codec developed and owned by Beijing E-World, to compress the audio signal by utilizing the redundancy as well as the relevancy.
FLACFree Lossless Audio CODECThe (almost) universal standard, open-source format for lossless digital music files.
FPGAField Programmable Gate ArrayA general-use powerful computing chip that can be programmed for any number of purposes. Used by Chord Electronics (amongst others) for their DAC products.
HDHigh-DefinitionTypically applied to video content, but may refer to Hi-Res Audio.
HDMIHigh-Definition Multimedia InterfaceA proprietary audio/video interface for transmitting uncompressed video data and compressed or uncompressed digital audio data.
Hi-FiHigh FidelityThe high-quality reproduction of sound.
Hi-Res AudioHigh-Resolution AudioDigital music files that have a higher sampling frequency and/or bit depth than CD – which is specified at 16bit/44.1kHz.
IEMIn-Ear MonitorOriginally intended for live musicians, now a popular type of headphone that inserts into the ear canal.
IMDIntermodulation DistortionThe ratio (in dB) between the power of fundamental tones and third-order distortion products.
IPXIngress Protection CodeThe level of protection of a device against water ingress (waterproofness or water-resistance). The IPX mark is followed by a number 0-8 (0 – no protection at all, 8 – fully submersible in fresh water of up to 3m/9ft depth). Not rated for saltwater.
LANLocal Area NetworkA computer network that interconnects devices within a limited area.
LDACLow latency Digital Audio CodecDeveloped by Sony, lossy but supports up to 24-bit/96kHz and is the first wireless codec with the ‘Hi-Res Audio Wireless’ certification.
LHDCLow latency High-Definition CODECHigher quality CODEC that allows almost 3 times the data transmitted wirelessly compared to SBC.
LEDLight Emitting DiodeTypically used as an indicator for power etc.
MP3MPEG-1 Audio Layer III or MPEG-2 Audio Layer IIIAudio coding standard for lossy digital audio compression.
M4AMPEG-4A format encoded with either AAC or ALAC (and as such can be lossy or lossless.
MMCXMicro-Miniature CoaxialVery small coaxial connectors, with a lock-snap mechanism allowing 360-degree rotation often used on IEMs in place of a 2-pin connector.
MQAMaster Quality AuthenticatedLaunched in 2014 by Meridian Audio and is a hybrid of lossy and lossless compression.
NFCNear Field CommunicationAn automatic method of wireless data transfer used to quickly pair Bluetooth devices and for tap and go payments from devices.
NRRNoise Reduction RatingThe standard for hearing protection attenuation across North America. Single Number Rating (SNR) is the EU’s standard.
OCCOhno Continuous CastA casting process for copper or silver wire that draws a single crystal up to 125 meters in length, providing the least possible oxides and other impurities.
OFCOxygen-Free CopperCopper alloys that have been refined to reduce the level of oxygen contained to .001% or below.
OGGOgg VorbisSomewhat uncommon free lossy digital audio file format.
OpampOperational AmplifierA DC-coupled, high-gain electronic voltage amplifier chip with a differential input and (usually) a single-ended output.
OTAOver The AirA synonym for wireless, typically referring for a method of updating software, such as firmware, achieved without connecting a device with cables.
OTGUSB On The GoAllows USB devices (such as tablets or smartphones) to act as a host, allowing other USB devices, such as DACs, to be attached to them.
OTLOutput TransformerlessA type of vacuum tube audio power amplifier which omits an output transformer for greater linearity and fidelity. Common examples are the Bottlehead Crack and the Darkvoice 336SE.
PCMPulse-Code ModulationA method used to digitally represent sampled analog signals.
R2RReel to Reel tape player or Resistor to Resistor type DAC.A DAC based on an electrical circuit made from repeating units of resistors. Often referred to as a ladder DAC.
RCARadio Corporation of AmericaThe ubiquitous RCA analog audio connector.
RMSRoot Mean SquareThe continuous (or music) power that the amplifier can deliver.
SACDSuper Audio CDHigh-resolution disc format created by Sony and Philips.
SBCLow-complexity Subband CODECA medium quality Bluetooth digital audio CODEC for devices like headphones or loudspeakers.
SPCSilver Plated CopperWire composed of a copper core covered by a silver plating.
SINADSignal-to-Noise and Distortion RatioThe ratio of the total signal power level (Signal + Noise + Distortion) to unwanted signal power (Noise + Distortion). Higher is better. More often used in DAC measurements than SNR.
SNRSignal-to-Noise RatioA measure that compares the level of a signal to the level of background noise.
S/PDIFSony/Philips Digital InterfaceCoaxial or optical digital audio connection.
THD+NTotal Harmonic Distortion + NoiseTotal Harmonic Distortion is the sum of all the harmonic distortion products in a measurement. THD+N adds noise to this figure.
TOSLINKToshiba LinkA common digital optical connector system.
TRSTip Ring Sleeve3-pole unbalanced stereo connector - 6.35 (¼”) or 3.5mm (⅛”).
TRRSTip Ring Ring Sleeve4-pole connector - unbalanced 3.5mm (⅛”) or balanced 2.5mm.
TWSTrue Wireless StereoBluetooth device function allowing for stereo sound in devices without any external or connecting wires. Typically associated with small IEMs like the Apple Airpods.
UACUSB Audio ClassStandards for USB device compliance, including classes 1, 2, and 3.
USBUniversal Serial BusA data transfer protocol where the USB-host, initiates a transfer and the devices respond to the host.
WAVWaveform Audio File FormatDeveloped by Microsoft and IBM, and is the standard CD format encoding method.
WMAWindows Media AudioA series of proprietary audio codecs developed by Microsoft.
VBRVariable Bit RateA method of encoding lossy audio files where the bit-rate fluctuates depending on the requirements or complexity of the audio.