Other hardware

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Bluetooth (A2DP)

Advanced Audio Distribution Profile (A2DP)

Standard baseline codecs:

Sub Band Codec (SBC) – not great
LC3 – the new baseline of Bleutooth 5.1. About Opus level, allegedly

Standard optional codecs:

MPEG-1,2 Audio: = MP3, almost never used
AAC: relatively good decode support, transparency possible at bluetooth bitrates, but latency can be an issue
ATRAC: never used

Vendor extension codecs:

AptX, LDAC, LLDC: in general lower complexity but higher bitrate (still within BT limits) than AAC, transparency possible; AptX and LDAC has wide support

Bitrate is limited by bluetooth link. A maximum of 2 channels is enforced for all codecs: this is a headphone protocol, not a speaker protocol. No back-channel is defined.

Sub Band Codec

Sampling Frequency - 16000, 32000, 44100, 48000 (some are optional, see references)
Channel Mode - mono, dual channel, stereo, joint stereo

The bitrate used for CD-quality () audio is 229 kbps and 328 kbps for middle and high quality, respectively.

Reference: BLUETOOTH Advanced Audio Distribution Profile 1.0

Headphones

Some Styles (smallest to largest)

In the ear - outputs directly into the ear canal
Earbuds - sits in the outer ear
Supra-aural - sits on the ear
circumaural - completely cover the ear

Terminology used for comparing headphones

Noise Cancelling
- active
- passive

Frequency response - The range of frequencies the headphones can reproduce

Impedance - Doesn't mean much by itself, but in general, impedence should be matched across a system.

SPL@1kHz, 1V rms - Sound Pressure Level. How efficient the unit converts electrical energy to sound energy.

Neodymium - The magnet of choice for high end headphones.

Popular Headphones

Sub $30
Sub $100
$100 - $300
$300+