Atmos, eARC, codecs, watts: sound terms explained plainly

Soundbar, speakers or headphones: the data sheets are full of terms that confuse more than they explain. Here are the most important ones, sorted by what they mean in everyday life.

Dolby Atmos and DTS:X

Both are sound formats with height: effects are placed as objects in the room, no longer fixed to channels. Atmos is standard on streaming services and soundbars, DTS:X more on Blu-ray. Whether it impresses depends less on the logo than on the speakers that carry the sound upwards.

ARC and eARC

ARC (Audio Return Channel) sends the sound from the television over HDMI to the soundbar – compressed. eARC has the bandwidth for lossless formats such as Dolby TrueHD and Atmos in full quality. Look for eARC when buying a television; when connecting, use the right HDMI socket on the television – it is labelled.

Channels: 2.1, 5.1, 7.1.4

The first number is the speakers at ear height, the second the subwoofer, the third the height speakers. 5.1.2 therefore means five speakers, one subwoofer, two in the ceiling. With soundbars the numbers are counted generously – the drivers all sit in one enclosure.

Watts

The power rating says little about loudness and nothing about sound. What matters is continuous power (RMS), not the peak figure; and whether the speaker produces a lot of sound pressure with little power is stated in the sensitivity in decibels. A good speaker with 50 watts plays louder and cleaner than a bad one with 200.

Impedance and sensitivity

The impedance in ohms (usually 4 or 8) has to suit the amplifier; modern amplifiers cope with both. The sensitivity (decibels at one watt at one metre) says how loud a speaker gets per watt – 90 is good, 85 needs a more powerful amplifier.

Bluetooth codecs: SBC, AAC, aptX, LDAC, LC3

The codec determines how heavily music is compressed for wireless transmission. SBC is the basic form, AAC Apple's choice, aptX and aptX Adaptive that of Android manufacturers, LDAC Sony's with the highest data rate. LC3 is the new standard for Bluetooth LE Audio – more frugal and the basis for Auracast, with which one transmitter serves many listeners at once. Important: both sides must support the codec.

WiFi streaming: AirPlay, Chromecast, Spotify Connect

Over WiFi, music travels uncompressed and without interruption by phone calls. AirPlay 2 is Apple's route, Chromecast Google's; Spotify Connect and Tidal Connect link the services directly to the speaker. Multiroom systems such as Sonos or BluOS bring their own technology and usually support several of these.

Hi-Res and lossless

CD quality is 16 bit and 44.1 kHz; Hi-Res goes beyond that. Lossless (FLAC, ALAC, Apple Lossless) means nothing is discarded. The audible gain over good streaming is small and needs good speakers – placement often brings more.

Room correction

Dirac Live, Audyssey, YPAO, Trueplay: software that measures the room and adapts the sound to it. With subwoofers and in difficult rooms it brings more than any cable.

What counts

eARC on the television, one streaming route that everyone in the household uses, and speakers that suit the room. The rest is data sheet.